all Flashcards
define adaptation
a characteristic that enhances the survival or reproduction of organisms relative to alternative character states
are all traits adaptations?
no
what happens at hardy Weinberg equilibrium?
gene frequencies don’t change and there is no evolution
what are the 4 evolutionary forces needed to disrupt HWE and give a few points on each
- mutation- random, new variation, heritable change in genetic material
- genetic drift- random changes In unselected allele frequency, can lower heterozygosity, can cause isolated pop to diverge
- migration- counteracts divergence and is due to drift
- natural selection- drive changes in gene frequencies, fitness and adaptation focused
define natural selection
differential survival and/or reproduction of classes of entities that differ in one or more characteristics
what are entities?
genotype, pop, species
define fitness
probability of survival X average number of offspring for a class of individuals
define gene pool
total aggregate of genes in a pop at any one time
define evolution
any change in gene frequencies, developing from earlier forms
for what 3 reasons do we know natural selection exists?
- correlations between trait and environment
- responses to experimental change in the environment
- correlations between trait and fitness component
what is an example study of correlations between trait and environment and a justification for natural selection existing?
Endler 1980 study of Guppies- poecilia reticulata
- predicted that colouration and pattern differs between rivers due to predation rate
what is an example study of responses to experimental change in environment?
Endler 1980 guppies
- tested with 10 ponds (high predation-4, low predation-4, control-2)
- guppies moved between ponds so no isolation
- no difference in spots per fish for black, yellow, red but was for blue and iridescent as under different selection pressures
- less spots when higher predation
- smaller spots on coarse gravel but when predation switch to large spots to match background
what is the guppy example study of correlations between trait and fitness
endler 1980 guppies
- is an effect in fitness
- but when no predators number of spots kept rising and did opposite to background so must be +ve to being visible such as for sexual selection
- rarer pattern more attractive to females as more carotenoids= faster more viable sperm
what is the locatello study example study of correlations between trait and fitness
2006
+ve to mating with orange males as those with more carotenoids had faster, more viable sperm
what is the Hughes study example study of correlations between trait and fitness
2013
more of an effect is male is rare, making him more attractive
- negative frequency dependent selection
what does the Kottler study suggest?
2018
suggests involvement of sexually antagonistic coevolution for correlation between trait and fitness
what are 6 problems with detecting selection?
- consequences of physics/chemistry so the trait may not be adaptive (red blood cells red as consequence of iron in haemoglobin- not adaptation)
- genetic drift can spread traits
- ancestral state (selection pressure change quickly so adaptation may not longer be relevant)
- selection might not cause change even if acting
- selection may not be working at individual level
- linkage
what is linkage?
- recombination during reproduction causing a genetic mashup
- 2 or more non-allelic genes inherited together as are located closely on same chromosome
what is gene flow?
the transfer of genetic variation from 1 pop to another
what is linkage disequilibrium?
alleles appearing together more often than you would expect by chance
what is a chromosomal inversion?
DNA gets a loop/flip so recombination can’t affect these sequence of genes so alleles are locked in and passed on through generations
what are hitchhiking alleles ?
If allele next to beneficial one selection will act on entire chunk of DNA so both alleles are passed on through
- selective sweep
- one allele appears beneficial but it isn’t and its frequency changes even though itself isn’t under selection
give 3 reasons for linkage disequilibrium
- beneficial alleles group together
- structural changes such as chromosomal inversion
- hitch hiking alleles
what is an example of hitchhiking alleles?
Atwoods experiment on E.coli in 1951
His+ allele: cell can make histidine
His- allele no histidine
- his allele hitchhiking due to association with advantageous mutation
- ‘His’ alleles respond to selection but aren’t under selection
what did chan et al discover and when?
2012- evidence for selective sweeps in mice for body size genes
what 5 things will natural selection NOT do?
- not always lead to adaptation
- not always produce perfection
- no always progress
- not produce balances harmonies world
- not consider ethics
what is directional selection?
shifts overall population by favouring an extreme phenotypes (most common when environmental change and migration)
give an example of directional selection
drug resistance in plasmodium falciparum
- over time increase in malaria resistance to antibiotics due to increased use
- 2014 study Nwakanma found high peak with use of antibiotic antifolate which was introduced 2005
- now resistance kept down by using ACT which is plant material combined with antibiotics
what is divergent selection?
favouring variants of opposite extremes but not the intermediates
- normally when 2 different environments between populations
- if in same pop is disruptive selection
what is the great tit example of divergent selection?
- females black stripe fades away
- males black stripe reaches between feet
- stripe made from melanin which is costly to produce
- thicker stripe means better quality male as can provide more parents care and offspring
what was Senar’s study and when and what type of selection?
2010 using recapture technique
- forest tits with a bigger stripe had survival increase
- city tits found after a certain point no longer beneficial to have thick stripe and lower quality males may be forced here as less nutrients
- urban tits smaller stripe may make them fitter
- divergent selection between urban and rural great tits
how does stabilising selection act + 2 example?
against extreme phenotypes and in favour of intermediates, narrowing genetic variation
- human birth rate
- Rundle 2012 drosophila serrata genici variation higher among low fitness individuals compared to higher
what is heterosis?
hybrid vigour which improves the function or increased characteristics in hybrid offspring
what is fluctuating asymmetry in fish?
phenotypic measure of how different the two sides of the fish are
what is the inbreeding vs outbreeding in bluegill sunfish?
individuals with intermediate genetic variance had higher breeding success and lower fluctuating asymmetry
- more asymmetry = higher fitness
- more inbred and diverse fish had lower breeding success
what is a combination of all 3 selection types example? (4 points and evidence for each type)
spade foot toads (spea multiplcata)
- 2 morphs studies in infancy
- omnivore: longer intestine, more teeth, bottom of water
- carnivore: feed on shrimp, hover in water column
- mark recapture technique by Martin and pfennig 2009
- DIVERGENT: intermediates less likely to survive with smaller body size, extremes more efficient feeders
- DIRECTIONAL: carnivores favoured over omnivores by this selection as greater prop recaptured
- STABILISING: intermediate form not lost when co-occuring with more dominant spea bombiforns and intermediate is favoured
variation is necessary for selection but what can selection often reduce?
variation
in what 4 ways are genetic variation and polymorphism maintained?
- diploidy
- gene flow
- mutation
- balancing selection (heterozygous advantage, frequency dependent selection)
how does diploidy maintain genetic variation and polymorphism?
- 2 sets of chromosomes
- hides genetic variation in recessive alleles of eukaryotes
- 2 individuals with recessive alleles must mate for expression to be seen
- detrimental or beneficial alleles may be hidden without being expressed
- if environment changes and has beneficial phenotype selection favours so may have advantage over pop
what can happen when moving between pops and what is an example?
can increase genetic variance
spade foot toads- when adults become toads enter new environment bringing genetic background
what are the 2 main types of mutation and what does one of these branch off into?
somatic and germline
germline: block or point mutations
what are block mutations?
affect entire chunks of chromosome (insertion, deletion, inversion, translocation, duplication)
what are point mutations ?
occurs at 1 base (insertion, deletion, inversion, substitution)
what does it mean if a point mutation is synonymous?
silent with no effect
what does it mean if a point mutation is nonsynonymous?
missense: changes amino acid
nonsense: stop codon produced
frame shift: disrupts codon pattern
what do all types of mutations add?
variation
what does balancing selection do to the allele proportions?
keeps it them at the same level
what are 2 examples of heterozygote advantage?
- sickle cell anaemia in Africa: 1 copy= malaria resistance, 2 or 0 copies= sickle cell anaemia
- connexion 26: builds up and thickens skin epidermis: 1 copy= more immune due to thickness and aids cell repair, 2 copies= deafness
what are 4 critiques to answer: is heterozygote advantage likely to be common for balancing selection?
- good adaptation should be fixed at 100% in pop asap but its not
- what seems to be heterozygote advantage mightn’t be
- heterozygote advantage imposes ‘load’ on pop (may decrease overall fitness)
- heterozygote advantage unstable due to duplication
what did Sellis in 2011 argue?
that heterozygote advantage does make sense as need to be fit in heterozygous form first as is how it arises through mutation
what is the selection coefficient?
(how much below fitness of pop- amount mutation affects fitness)
- difference between mean relative fitness of individuals of genotype and of reference of genotype
what allele types are generally less fit?
homozygote recessive
what is associative overdominance?
increase in fitness of heterozygotes at neutral locus as is in linkage disequilibrium at locus under selection
what is genetic load?
difference between maximum (1) and mean fitness
what does a genetic load of 0.3 mean?
pop is working at mean fitness 3% below total fitness
what is the genetic load of sickle cell anaemia?
0.1
what is gene duplication?
event in which one gene gives rise to 2 genes that can’t be operationally distinguished from one another
what can make heterozygote advantage vulnerable?
gene moving from one locus to another further up so every individual has the gene in heterozygote form
where is there evidence of duplication in genes?
genes controlling colour vision in humans
what is frequency dependent selection and what would it be for -ve freq dep selection ?
the survival and reproduction of any one morph changes (declines=NFDS) if that phenotypic form becomes more common in environment
what are 2 examples of positive frequency dependent selection?
- survival/reproduction increases in form more common
MULLERIAN MIMICRY - poisonous individuals copy one another, more common the trait, more survive and come fitter
CYTOTYPE EXCLUSION - plants can gain new chromosomes
- need another plant of same ploidy level to mate
- if more in environment, fitter individual
does PFDS or NFDS maintain polymorphism?
NFDS
what are 2 examples of NFDS?
- advantage of the rare
BATESIAN MIMICRY - cheat mimics poisonous one, better to be rare so undiscovered by predator
HOST PARASITE CYCLES - parasite evolves attack mechanism, host evolves defence
what is the lake tanganyika cichlid example of NFDS? (Hori 1993)
- P.microplepsis
- predatory with mouths facing different sides and eat chunks of flesh from prey fish
- if one side more common with cichlids prey fish will become more defensive on that side
- maintain max fitness when equal prop of each morph in pop
- if 1 increases the other doesn’t do as well
- what % women and men are left handed
- what are 3 results of it
- what was suggested about it
- 10% W 12% M
- lower height, reduced longevity, fighting/sports advantage
- Raymon 1996 suggested NFDS
what is the environmental tolerance of tropical species like?
- restricted in range
- stable environment
- more under threat if environment changes
what are the 2 climatic variability hypothesis?
- species with greater physiological tolerance to climatic variable can extend their distributions higher latitudes
- species with low genetic variance are unlikely to have great physiological tolerance
what is heritability and what can increase it?
prop of phenotypic variation in pop due to genetic differences
- increasing genetic variance increases heritability
what was the study on environmental tolerance in drosophila? (6)
kellermann 2009
- 2 subsets studied (global and tropical)
- measured additive genetic variance
- found more varied the genome the more tolerable
- tropical less varies
- genetic variance increases when more adapted to desiccation or cold
- not due to inbreeding depression as all species have the same wing size so traits aren’t showing the same pattern
in what 3 main ways do species get around the issue of lack of genetic variation?
- mutation
- phenotypic plasticity
- transposable elements
in terms of mutation how may adaptations arise?
single base pair mutation and spread rapidly
how did mosquito culex pipiens become resistant to insecticide?
gene flow
single base pair mutation -> change in amino acid -> target site changed shape -> insecticide no longer works
a) what did Zuk study in 2006 to do with mutations on O.orchracea and T.oceanicus? (6)
b) what suggests where the mutation is ?
c) where was the density of silent males found to be higher?
d) where did the flat wings get closer to and why?
a)
- parasitic fly buries its eggs in cricket
- crickets usually give out call to attract females
- 1991: 30% male crickets parasitised
- 2001: one calling, not many around
- 2003: many crickets but none calling
- 2004: 121/133 males had flat wing which is silent so wing morph completely changed
b) female can mate with flat wing male and produce normal male so suggests on X chromosome
c) Kauai island of Hawaii
d) closer to speaker with call emitted as believed females will gravitate to the sound so can intercept other males going here
what did Mukai discover in 1972 on an experiment of drosophila?
as mutations accumulate mean variability decreases and variance among chromosome increased
what was Kassen and Bataillon’s study and when?
2006
- on P.fluorescens bacteria
- total 655 mutations
- 28 had +ve effect
- on average -ve effect so selection has to work continuously against mutations to maintain fitness
what is phenotypic plasticity and what can it allow for?
same genotype produced different phenotypes due to environmental conditions
- allows for flexibility and variance
- may allow persistence in new environment for long enough that selection can act
what are 2 very brief examples of phenotypic plasticity?
hydrangeas- different colours due to different soil ph
drosophila- inverse relationship where the hotter the temp the smaller the body size
explain Wijngaarden’s study for phenotypic plasticity
Bicyclus anynana- squinting brown bush butterfly 2002
- temp affects morph: brighter in summer as mating season at this time
- temp increases eye spot increases
- tried to change reaction norm of species through artificial selection pressure
- but mechanisms controlling plasticity not changed under artificial selection
- plasticity buffers genotype from selection working on it
what may be a constraint to adaptation?
plasticity can buffer genotypes from section acting upon it and if environment changes the genotypes may not longer be able to cope
give 9 points about transposable elements
- may mean more of fitness landscape available
- likely involved in genome evolution
- group of genetic structures varied in response
- hop around genome
- previously thought to be detrimental
- some jump to preferred spots linking to adaptability, causing new phenotypes to occur
- can preadapt populations by generating genetic variation or phenotypic plasticity in source pop
- stress during introduction of individuals into pop alters epigenetic control of TEs so gene regulation altered
- new TE inserts can create genetic and phenotypic variation which can aid adaptation
what are transposable elements like in mammals?
- no evidence of increased adaptability
- significant amount of genome made up of them
- may allow pops to explore fitness landscape in a shorted amount of time
a) what is a fitness landscape in general and what does selection drive?
b) what is dynamic fitness landscape
c) static?
a) map of adaptive landscape where a bigger peak= higher fitness, selection only drives populations up a peak
b) as fitness landscape changes populations evolve to track the peaks
c) population evolves to only 1 peak
what are the 3 evolutionary forces of a fitness landscape?
- selection: head to nearest area of peak fitness
- drift: less power to drive species up a peak
- mutation: species taken from 1 point to another on landscape
who proposed the original fitness landscape and when?
Wright 1932
what is the T.oceanicus cricket example of a fitness landscape?
- singing males on 1 peak- song is adaptive
- success of fly reduces fitness peak which constrains that adaptive path
- mutation offers a jump to another peak
most traits don’t work in unison- what can correlated traits do?
hinder pathway of evolution
what is pleiotropy?
where one gene affects more than one character/phenotypic trait
what does the direction of evolution depend on?
genetic correlation
what can genetically correlated traits be and what do they take longer to do?
constraint
longer to reach peak of landscape
what Is the Galapagos finch example of correlated traits from 1977?
- drought caused decline in smaller seeds but larger seeds survived so was increase in seed size and hardness
- beak size and bird weight increased after drought to utilise larger seeds
- but bill length increased even though selection acting to make it smaller, because selection was so strong for bill depth
- if the environment changes is it more beneficial to be positively or negatively correlated?
- which has a narrower range of where species can sit within environment?
- what happens if working against each other?
- do they have the same mean and trait levels?
- positively
- negatively
- contains fitness of individual
- same mean but at same environmental gradient different trait levels
why is it important to figure out how traits influence each other?
how species evolve
what are hybrid zones and give 6 points about them
where genetically distinct populations meet, mate, reproduce
- challenges view of species and confuses taxonomists
- can be asymmetric
- congregate in areas of low density
- can be barriers to gene exchange
- show historical patterns
- covers cline between 2 distinct pop of alleles
for what 2 reasons are hybrid zones good to study?
- involved in nearly all speciation events (except polyploidy selection)
- range of genotypes show genetic differences and selection pressures that separate taxa
what is the distribution of the European hedgehog like and what are the 2 main species?
Erinaceus europaeus
Erinaceus concolor
- based on mtDNA 4 subgroups found in Europe (northward migration)
what was the post glacial recolonisation? (6)
- most of Europe covered in glacier so species were in southern warmer refugia
- facilitate persistence of components of biodiversity over millennia and under changing climates
- after ice age glacier retreated and species followed it back up Europe
- populations previously isolated met so many hybrid zones created
- plants followed similar pattern
- locating hybrid zones can infer a lot of species history
list the 4 consequences of hybridisation
- indefinite
- merge
- reproductive isolation
- third species
what is the indefinite consequence of hybridisation? (5)
- some interaction between 2 pops in hybrid zone
- selection maintains steep clines at some loci
- could be tension zone
- could move to area of low density
- only if character differences favoured by different environments
what is the merge consequence of hybrid zones? (4)
- pops and alleles merge becoming 1 pop
- fitness of hybrids not lower than original pop
- introgression and post zygotic barriers broken down
- variation and distinction between 2 pops lost
what is the reproductive isolation consequence of hybrid zones? (3)
- selection acts to keep pops apart
- strengthening of barriers to gene exchange
- large areas of genome protected from introgression
what is the third species consequence of hybrid zones? (2)
- hybrids become reproductively isolated from original pop
- new species forms
what is a cline?
a change in allele frequency over a geographical transect/hybrid zone
what can we use cline characteristics to tell us? how does the cline differ if no gene flow or lots of gene flow?
about the mixing of populations such as shape, co-occurance and movement of cline
NO gene flow: g=0 steep stepped cline
LOTS: g=1 shallower cline
what is the equation for cline shape?
W (directly proportional to) square root of d2/s
W=width of cline
d= dispersal/gene flow
s= selection
why was it believed that romans created a high dispersal and wide cline?
frequency of B allele in blood group declines in E to W gradient which reflects the invasions into Europe from Mongolia after roman empire collapse
what is heterozygote disadvantage?
lower intrinsic fitness than either parent
- homozygotes are acting with each other and heterozygotes are unfit and so selection against them
explain the Hoekstra example of a sharp cline
2004- rock pocket mice (C.intermedius)
- 2 morphs with melanin causing black coloration
- sampled at different locations of each substrate type
- 4 amino acid variations cause the colour differences
- some interbreeding
- selection acts to keep coloured alleles in their areas
- gene flow/dispersal smooths out changes in phenotype frequency at boundary
- selection pressures strong from predation
what type of hybrid zone do each of these show?
- hedgehogs
- rock pocket mice
- secondary
- primary
what are the 2 types of hybrid zones?
PRIMARY: natural selection alters alleles in a continuous population
- environment affects different loci in different places
- likely a sharp cline
- alleles change depending on environment
- neutral alleles maintain similar level
SECONDARY: formally allopatric species expand to meet again
- clines expected to be in same place
- even neutral alleles will change
what is the mytilus edulis example of primary hybrid zones?
blue mussels
- Ap94 allele increases amino peptidase 1 activity so higher amino acid conc in cell as are cleaved off of end of proteins
- cline maintained by selection against Ap94 in environment and against gene flow from oceanic populations
- the environment change causes the allele change
- freq of allele increases as salinity increases
what is the house mouse example for a secondary hybrid zone?
mus musculus
macholan 2007
- 1800 mice at 105 sites on Germany border hybrid zone
- change in morphology down centre of Europe of 2 morphs M.musculus and M.domesticus
- 2 loci sampled
- allozyme loci: different forms of enzyme do the same job- neutral
- x-linked loci: under strong selection
- neutral allele only affected by selection if hitchhiking alleles or under linkage disequilibrium
- neutral allele has a larger cline width
what is the European toads example for a secondary hybrid zone?
- western yellow bellied toad bombina variegate
- eastern fire bellied toad bombina bombina
- strong barrier to gene flow so even neutral genes influenced by selection
- allozymes and morphological characteristics coincided
what do clines move in response to and what does this influence?
strength of dispersal
influences shape and location of cline
how may different alleles follow different pattens?
- B allele could be linked to A allele so a similar pattern seen
- if B selectively neutral can move on its own, dissociating from original population
- backcrossing can occur
what is back crossing
hybrid crossed with parent so offspring can move across hybrid zone in different way to to A allele
what is introgression and when may it occur?
movement of genes from 1 species or pop into another by hybridisation and backcrossing
- can occur if selectively neutral where alleles merge into population
what is pre zygotic isolation?
factors keeping individuals apart before egg and sperm meet (habitat, temporal, morphological, behavioural)
what is post zygotic isolation and what are 3 types?
reproductive barrier after fertilisation
- hybrid inviability
- hybrid infertility
- hybrid breakdown
what is the genetic basis of a barrier?
dobzhanksy-muller model 1934
- genes interact with everything on genome
- if allele evolves in 1 pop that has never mixed with another and is introduced to it there is potential conflict between alleles, disrupting each others function
- incompatibilities can arise from background mutations
- over time they can build up
what does mating preference have to be linked to to lead to reproductive isolation and speciation?
adaptive trait
what is the direct system of mating preference link to adaptive trait and an example?
- same gene as mating preference is adaptive and affects the preference
- referred to as magic traits or multiple effect traits
- male Panama butterflies spend more time courting those with the same wing type
what is the lake Victoria cichlid example fo direct system of mating preference link to adaptive trait?
- shallow water: blue colour
- deeper water: red colour
- at different depths males evolve different colours due to eye adaptations
- easier to see red females in deeper water
- female preference for males based on same trait
what is the indirect system of mating preference link to adaptive trait ?
adaptive gene linked to one affecting mate preference so adaptive and mate choice are on 2 linked loci
- selection against recombination
- females only mate with males with adaptive trait
- example of linkage disequilibrium
what is the reproductive character displacement from reinforcement hypothesis and who suggested it?
Alfred Russell Wallace
- selection for pre-zygotic isolation barrier is due to selection against mating, creating unfit hybrids
- theoretically completes speciation when post zygotic barriers are incomplete
- can only happen in sympatry
- often more obvious in selected traits
- if barrier not there individuals may mate with others from a different population
- selection acts to put a barrier there to stop groups breeding when living in the same region
what is the allopatry and sympatry between the pied flycatcher and collared flycatcher?
- females are brown
- males of the 2 species look similar so in sympatry pied flycatcher changes his plumage to become brown like female in order to stand out from other flycatcher to be reproductively successful
- indirect system
- mate preference allele needs to change as well as the adaptive trait changing (theory of reinforcement)
what did price and bouvier discover about birds in 2002? (7)
- collected data from literature about recorded matings
- individuals less closely related and more diverged fail to produce fertile offspring and often sexes are inviable
- only 62% of same species produced fully fertile offspring
- standard cytochrome b clock estimated time of divergence as 2% per million years
- species with infertile hybrids last shared common ancestor 7mya
- 5mya for passerines , 17mya for non passerines
- strong support for haldane’s rule
what is haldanes rule?
when a cross produces inviable or sterile offspring the heterogametic sex is more strongly affected
why may female birds suffer more from inviability?
they are the heterogametic sex ZW rather than ZZ
what did the coyne study of drosophila find?
- different combinations of chromosomes leads to different effects
- X chromosome has major effect on sperm motility
- clear difference in isolation for sympatric and allopatric taxa
- sympatric more likely to have diverged from each other
where does pre zygotic isolation evolve faster and what can speed it up?
sympatric pairs
reinforcement
what are speciation genes?
genes which cause reproductive isolation on their own
what is the current speciation hypothesis?
- small adaptive divergence
- divergent areas grow via linkage
- genomes diverge so much that interbreeding very reduced
- isolation
in drosophila mauritiana and drosophila simulans:
a) what differs between them
b) how may it have evolved
c) what is it similar in structure to
d) what does asymmetry in sequence evolution suggest
e) where is the biggest ratio of change and whats it acting for
a) OdsH which causes sterile males to appear in D.simulans when allele moved to them
b) gene duplication
c) ancestral gene unc-4
d) differential functional roles
e) in non synonymous substitutions- selection acting for mutations changing function of protein
what is likely to contribute to species differentiation where the divergence is likely due to selection?
duplicated genes that are in the process of evolving into new functions at the time of species separation
give 6 points about what speciation is?
- speciation is a multi level process unfolding through time and space
- populations subjected to demographic processes and redistributed in space
- periods of physical separation will alter with periods of gene flow
- different mechanisms acting at different phases of divergence process
- barrier loci contributing to reduction in gene flow can accumulate gradually until diverging genomes eventually won’t mix any further
- introgression can favour divergence or hybridisation may generate new isolated populations
what are 4 contributors to speciation?
chance, ecology, reinforcement, sexual selection
what are 3 examples of chance mutations?
- spontaneous polyploidy speciation
- long term drift can lead dobzhanksy muller incompatibilities
- mutation order speciation
- founder effect speciation
what is mutation order speciation?
- different populations find different genetic solutions to the same selective problem
- different alleles due to different selection pressures
- ecology evolved but doesn’t favour divergence
- divergence is random
what is founder effect speciation and what is it also known as?
peripatric speciation
- small satellite population diverges from large ancestral population usually by isolation and inbreeding forms a new population
what is the paradise kingfisher example for founder effect?
- each island of papa New Guinea has their own species that are morphologically different to each other
- some left the ancestral pop to other islands
- dependent on chance as to which birds left the mainland
give 9 points about polyploid speciation
- more than 2n
- important in plant species more so than sexually reproducing taxa
- often associated with reproductive isolation and morphological differences
- instant new species (salutational )
- usually formed by failure of division in meiosis
- some fish polyploid
- plains viscacha rat the only mammal
- 15% angiosperms show polyploid speciation
- 31.37% ferns
what are 4 advantages of polyploid speciation?
- heterozygote advantage
- extreme phenotypic traits
- reproductive isolation
- duplication on big scale
what can polyploid hybrids have in terms of the fitness landscape?
more of it opened up to them and can jump between peaks on the adaptive landscape
whats the difference in genetic variation between homoploid and polyploid hybrids?
polyploid have less genetic variation as are fewer of them
what can divergent selection between environments cause?
barriers to gene flow
what 3 things are ecology mechanisms related to?
- environmental differences (habitat structure, climate, resources)
- ecological interactions (disease, competition, behavioural interference)
- sexual selection
what was found for the ecological differences for Timema cristinae
- 1 resembles pine needle and the other is on open flat leaves so is fatter and flatter
- show reproductive isolation even though the same species
- Nosil investigated which aspect of ecology influencing the most
- different host pairs show more isolation than same host pairs
what are pea aphids dependent on?
2 morphs: some live on Alfalfa and some on clover
if you switch them over their fitness decreases
what are monkey flowers dependent on?
habitat type with a coastal form and inland form but if you switch not all will survive to flowering stage
what is the howea plants example for environmental differences? (6)
- lord howe island off coast of Australia
- 2 forms, thatch palm and curly plam covering island live close together coming from 1 ancestral population
- only 6 adult hybrids ever found on island
- only 4 loci found to differ on genome more than expected by chance
- isolated by different habitats such as different soil types even though are close together and have different flowering times (pre zygotic barrier)
- sympatric speciation most likely caused by ecology
what are examples of ecological interactions and 3 points about it?
- disease, competition, behavioural performance
- normally in sympatry
- can be ghost of competition past
- can cause ecological character displacement
what is the ecological interaction for interspecific competition in sticklebacks?
- 2 morphs: brook stickleback and ninepin stickleback
- brook show characteristics of benthic living rather than pelagic when in sympatry with ninepin and develop stronger jaws and wider bodies
- brook in sympatry and allopatry with nine spine exhibit different growth forms
- will separate 2 species but also cause divergence of 2 population of brook sticklebacks
what is the ecological interaction for intraspecific competition in anolis sagrei lizard?
- dulap involved in sexual selection to attract mates
- inhabit many islands and like to sit on different perches
- like to be on perches visible to females
- largest and smallest favoured in the population
- disruptive selection and ecological interactions
give 4 points about reinforcement
- change in mating trait which in sympatry acts to make a distinction
- some argue could also be a starting point: cascade reinforcement
- mechanism to finish speciation process
- for reinforcement to act there must be enough gene flow for hybrids to exist and be selected against
what are 2 points about cascade reinforcement?
- selection favouring prezygotic mechanisms which keeps populations from breeding together (decreased gene flow= less unfit hybrids)
- species 1 and 2 now have area where different mating mechanisms favoured which can cause isolation within species
spade foot toads can hybridise what are 3 alternative hypotheses other than reinforcement acting to prevent hybridisation? and what are the 2 species?
- opportunities for hybridisation declined- no evidence
- hybridisation initially common when 1 species rare- not true
- habitat changes reduce hybridisation- no
- spea bombifrons: plains spade foot toad
- spea multiplicata: New Mexico spade foot toad
how may hybridisation be prevented in spade foot toads?
- females of both species usually prefer a fast call rate
- s.multiplicata females when in sympatry with s.bombifrons will prefer a lower call rate, changing their mating preference
- this is because s.m females suffer more of a decrease in fitness from hybridisation
what does evidence of reproductive character displacement on a study in 2014 on spadefoot toads suggest and what else was found?
- reduced gene flow between populations of s.m
- suggests reinforcement present
- helps to separate populations and reduce gene flow
- could kick start speciation within s.m
what does reinforcement act to prevent but what does it need?
to prevent gene flow but initially needs some
what is the point of maximum reinforcement?
reinforcement can keep pops apart but after a certain point of gene flow- no longer strong enough to keep them apart
what is sexual selection and what does it sometimes involve or work in opposition to?
result of differential reproductive success that arises from competition for mates and access to fertilisation
- can involve (direct female benefits, good genes hypothesis) or work in opposition to natural selection (fisherman runaway, chaseaway selection)
for what 5 reasons is distinction needed for sexual selection and natural selection?
- SS favours mate acquisition and fertilisation, NS favours survival and fecundity
- can act in opposition on one trait
- have differences in rate, strength, direction with SS stronger and faster and focused on 1 gen
- SS may build linkage disequilibrium more effectively
- one type may contribute to divergence whilst the other may inhibit it
sexual selection can generate prezygotic isolation but what is needed and why?
ecological divergence needed for coexistence
what are the 4 ecological interactions with SS?
- food resources
- predation
- parasitism
- sensory bias
in terms of food resources what is an example of NS and SS working in the same direction? (7)
North American red crossbills
- 10 ecotypes coevolved with conifer species
- low gene flow
- overlapping ranges
- unique call types that differentiate between ecotypes
- assortative mating by call type in the wild
- experiment: females consistently chose the efficient male feeders by observation
- sexual selection is related to feeding efficacy
in terms of food resources what is an example of NS and SS working in opposition? (7)
North American swamp sparrow
- females prefer high performance songs (those with smaller beak)
- bigger frequency bandwidth means more attractive males
- trade off between trill rate and frequency bandwidth
- recent colonisation of coastal areas has led to larger beaks
- different food types in coastal areas so larger beaks develop which produce different songs
- not cultural drift, adapting to changing food type
- NS moves species to feed and survive but SS aims to increase freq bandwidth
what is polygamy dependent on and when is it more likely?
environment
- if clumped more likely
whats the difference between the cape penduline tit and the eurasian penduline tit?
cape: monogamous with biparental care and lives in harsh environment
eurasian: sexual conflict over investment and no biparental care, each sex tries to escape having to care for nest and often 20% nests abandoned
what is an example of how predation interacts with sexual selection and what costs are there on the sexual ornaments?
mortality costs
guppy: poecilia reticulata
- when high predation adults and babies eaten
- low predation just babies eaten
- even when no predator still increase in number of spots
- increased predation = female preference for less spots
- decreased predation = female preference for more spots
- no speciation despite rapid co-adaptation of male and female reproductive strategies
what are 3 points of how parasitism interacts with sexual selection and give an example
- can exploit host sexual signals
- parasite load has effect on host condition (increased load means signal not produced well)
- might lead to co-evolutionary cycles that help maintain honesty in sexual signalling
- E.g. common yellowthroat: black mask size related to MHC class 2 allele relating to adaptive immunity, allowing females to use this to choose males with better immunity and juvenile males have decreased mask size
in terms if the interaction between sensory environment and SS:
a) what 3 signals have to navigate an environment?
b) in what 3 ways does sound travel and an example of each?
a) visual, acoustic, olfactory
b) - absorption: air, vegetation, ground
- reflection: trees, buildings
- diffraction: temperature gradient
how does sound differ between dense foliage and open grassland?
dense foliage:
- lower freq
- pure tone where 1 note at a time
- slower rate of syllable repetition
- different frequencies in succession
open grassland
- higher freq
- broadband where several notes at the same time
what is the dialect of the madagascan paradise flycatcher?
- different song types favoured in different environments
- lower and longer songs in denser foliage
- female pref follows what native pop are doing
what is the dialect of the brown headed cowbird like?
when females shown different playbacks of male song they would perform for longer during home dialect playback as prefer familiar songs
why is speciation and level of SS hard to measure and what pixies can be used?
lack of knowledge
- SS: genial size, mating system, dichromatism/dimorphism
- Speciation: number of extant species in a clade
it is unclear if SS leads to speciation- what may be a reason for yes/example?
birds of paradise
- SS more prominent in clades with more species
- more clades show asymmetry in diversity in the direction predicted by SS
it is unclear if SS leads to speciation- what may be a reason for no/example?
dimorphism and dichromatism and testes size studied and found no difference between clades for high levels of 1 and low of another
- no signal of SS in birds explains the variation in species richness
even though there are huge imbalances in studies what is the overall effect size as to whether SS contributes to speciation?
postive- does
why may the signature of selection fade with time?
likely many speciation and extinction events may have happened that we don’t know about
why dont we often know which signal to use for working out SS?
some components of SS may have a stronger influence on speciation rate than others (dichromatism has 10X stronger effect)
what is ‘time for speciation’?
time for reproductive isolation to evolve once process has started
what is ‘biological speciation interval’?
average time between origin of new species and when that species branches again
for each of these what are the TFS estimates?
- horses
- bivalves
- some drosophila
- frogs
- 3my
- 6-11my
- <1my
- 1.5my
the TFS is unknown for songbirds what has been the deliberation about this?
- hypothesised after glacier retreat birds populated rapidly so a lot of speciation
- when looking at sister taxa in 1997 found few speciation events after glacier retreat
- 2004 phylogenetic analyses found the opposite with most speciation after
what is the TFS example of the African cichlid fish?
- 500 species lake Victoria
- lake presumed 750,000 years old
- phylogenetic studies predict cichlids 200,000 years old
- geological data suggests lake Victoria dried out 14,700 years ago
- Verheyen 2003 estimates 98,000-132,700 years ago they moved to rivers and other lakes for refuge
what is the area size effect?
the bigger the area the more chance of speciation occurring?
what pattern don’t ferns follow and so what do they do?
polyploidy common so speciate at random
what do high gene flow and high dispersal area need to speciate?
larger minimum area
what is the slowest and fastest form of speciation?
mutation or drift
polyploid speciation
what is life history and how does it vary and give 7 points as to what it includes
schedule of an organisms life that varies between individuals and species and contributes to overall fitness
- age and size at maturity
- number and size of offspring
- energy allocation to reproduction
- timing of growth
- dispersal patterns
- number of reproductive events
- lifespan and ageing
what does selection act to maximise?
why can’t all traits be maximised?
what is every trait?
- lifetime reproductive success
- reproduction is costly and requires resources and time
- continuum with all intermediate states possible
what are the 5 life history strategies for a brown rat?
- fast development
- rapid maturity
- high reproductive rate
- low parental investment
- short life
what are the 6 life history strategies for an elephant?
- slow development
- delayed mortality
- low reproductive rate
- high parental investment
- longer pregnancy and high survival of offspring
a life history trait involves intrinsic and extrinsic factors, give
a) 5 intrinsic
b) 2 extrinsic
a) - energy/resource constraints - genetic constraints - phylogenetic constraints - mechanical contraints - physiological contraints b) - ecological factors (predation) - climatic constraints
what is senescence?
age related deterioration of an organism leading to decline in reproduction and probability of survival
what kind of life stages is selection most effective for? and list the 3 evolutionary theories as to why
high reproductive rate
- mutation accumulation
- antagonistic pleiotropy
- disposable soma
what is the mutation accumulation theory for why selection is most effective for life stages with high reproductive rate ? (5 + example)
- mutations that are deleterious later in life are more likely to be maintained in a population
- selection will act against mutations when a high reproductive age
- selection doesn’t act as strongly later on in life so often more mutations
- selection against 1 gene may be more efficient at the reproducing age
- genes active later in life can accumulate in the pop
- Huntingdon’s disease results in death of brain cells and is caused by dominant allele expressed at 30-40 years
what is the antagonistic pleiotropy theory for why selection is most effective for life stages with high reproductive rate ? 2+ example
- 1 gene affects more than 1 phenotypic trait
- +ve for 1 trait but bad for another (trade off where it may be good now but bad later)
- gene may be favoured by selection such as for the gene causing overproduction of sex hormones which is good for reproduction but causes cancer later on in life
what is the disposable soma theory for why selection is most effective for life stages with high reproductive rate ?
- resources finite and energy put towards one function is unavailable for others
- limits towards maintenance cause somatic damage
- if more energy invested into maintenance and growth and less for reproduction the lifespan will be longer
why is the mutation accumulation theory not mutually exclusive?
- heritability increases with parent life span (increased mutation, genetic variance and heritability)
- age dependent increase in inbreeding (more deleterious alleles, more inbreeding depression)
why is the antagonistic pleiotropy theory not mutually exclusive?
- negative correlations between early and late life fitness
in the guppies what is the low and high predation situations on the southern side of the mountains?
interbreed with high gene flow but distinct differences in life history HIGH: crenicichla - female maturation at smaller size - more smaller offspring - male maturation at smaller size LOW: rivulus - female maturation at larger size - fewer larger offspring - male maturation at larger size
in the guppies what is the different high predation situation on the northern side of the mountains?
less vicious Gobie and mullet fish
- no difference in females
- more smaller offspring
- males smaller
in the guppies what are the high and low predation factors due to?
HIGH: addition of predator- evolutionary changes in guppies in accordance with theory
LOW: ecological factors such as predation affecting life history traits
when determine how many babies what are the intrinsic factors/trade offs?
- trade off between number and size of offspring
- offspring have better chance of surviving if larger and more attention from parent
- parents may want more offspring but of smaller size
when determine how many babies what are the extrinsic factors example?
songbirds
- tropical: smaller clutches, fewer chicks, slower growth rate
- temperate: larger clutches, more chicks, faster growth rate
explain in detail Thomas Martin’s findings from songbirds in 2015 ()
- 3 populations studied: Venezuela and Malaysia for tropical species, Arizona for temperate
- peak growth slower in tropical species with same risk of predation as temperate
- nesting period shorter in tropics for same growth rate
- tropical species have initially slower growth rate but catch up to temperate later in life
- mass same at fledging from nest
- higher growth rate for wings in tropics (more resources into growing this)
- tropical species fledge with longer wings as more predation outside nest so need to get away
- wing size can only increase with parental provisioning
- total provisioning decreases with nest predation
- smaller clutches with fewer chicks to increase provisioning rate
- tropical clutch size limited by need to provision for wing growth
what did Martin 2015 discover in songbirds for the difference between bigger and smaller clutches?
bigger: adult mortality rates higher but don’t develop long wings in nest
smaller: increased provisioning in shorter nesting period due to high nest predation
do all organisms reproduce and have sex and are there costs?
all reproduce but not all have sex
costs but lack of explanation for existence
what is asexual reproduction?
a copying process
- some single celled organisms reproduce by mitotic division into 2 daughter cells
- some multicellular algae/fungi bud off single cells/spores
- easy, error free, simple
give 4 points about sexual reproduction
- 2 haploid gametes fuse to form diploid zygote
- involves meiosis and recombination and segregation
- in many unicellular organisms zygote undergoes meiosis
- only half as related to offspring as asexual female
what is the paradox of sex?
- inefficient
- complicated
- time consuming
- difficult
- dangerous
- costly
- SS may lead to evolution of costly traits
- twofold cost of sex
who noticed twofold cost and sex and what is it?
John Maynard smith
- production of males costly
what are parthenogenetic females and points about them and a comparison to sexual females
asexual females producing only daughters
- 2 fold fitness advantage as sexual females waste half their reproductive potential on sons
- multiplying and growing
- sexual females have 50/50 chance of daughter and only half as related to offspring as asexual
in an ancestral female asexual population what happens when the male mutant arrives?
can’t invade pop
- males need females to reproduce but females don’t need males
- if no other benefits to sex then male production should never spread
what are 2 assumptions of the twofold cost of sex? and for sex to evolve at least once what is required?
- every female produced equal no.of offspring
- no differential survival
at least one of the needs to be violated
the twofold cost of sex assumes males contribute only genes and so what can help increase the reproductive output of males?
male parental care
when can natural selection lead to differential survival?
if there is variation in traits sexual population have genetic variation due recombination, segregation, mutation
what can sexual recombination create and destroy?
existing gene combinations whether they are good or bad
what do fitness. consequences depend on?
population composition
if 2 alleles in the initial pop are favourable what % of unfavourable maladapted offspring will be produced? what would the difference be if these recombinant pairs were more common in the initial pop?
50%
recombinant may have a positive effect
what does natural selection favouring or not favouring recombination depend on?
the distribution of genotypes in a population
how is it likely that sex can speed up evolution?
as it is unlikely that the same genotype would be created
also recombination can bring together beneficial mutations that arose independently in different organisms
what can recombination reveal and what does this improve?
hidden variation
improves response to selection
what would happen to a beneficial trait at low level after selection and how may it remain hidden?
can increase in pop but if no sexual variation will remain hidden
what are the 2 main models for determining if the short term cost of sex that affects the next gen can be overcome to generate long term benefits?
- genetic drift (mullers ratchet)
2. selection in a changing environment (red queen)
what can potentially solve problems that mutation and genetic drift create?
sex
what is the genetic drift/mullers ratchet model? (7)
- asexual females will pass deleterious mutations to all offspring
- the number of deleterious mutations in an asexual lineage can only increase her time
- recombination means sexual females may not transfer the deleterious mutation
- can recreate mutation free individuals from mutated individuals
- optimal genotype lost by drift can be reconstructed by recombination
- recombination reduces chances of mutation being passed on
- pointed out by Muller 1964
what is a piece of evidence for muller ratchet model? (5)
Chao 1990
- generated 20 lines of RNA virus and added drift to speed it up
- cultured with single bacterium and incubated and repeated for 40 generations
- froze after each generation and placed in competition with next
- fitness/growth rate declined after subsequent generations
- increased fitness in some hybrid crosses
what is an overview of the red queen model/selection in a changing environment?
- sex evolved because recombination brings together novel genotypes with potentially higher fitness which promotes evolutionary adaptation
- in unpredictable environments any single genotype may not be universally successful
- asexual repeats the same genotypes
- sexual creates variation in offspring fitness
- different environments have different pressures which creates new gene combinations
state the 2 assumptions of the red queen model
- recombination increases rate of adaptation/efficacy of sex
- some novel genotypes have high fitness
what was Goddards 2005 experiment demonstrating efficacy of sex? (9)
- demonstrated sexual pops evolve faster than asexual using yeast
- yeast usually reproduce asexually if sufficient nutrients but if starved reproduce by meiosis producing 4 spores
- 2 genes needed for meiosis melted so reproduction sexual
- tested if sex increased variation and promotes evolutionary adaptation
- compared growth In harsh and benign conditions
- benign: little selection pressure, limited by glucose conc, no fitness increase between the 2 strains
- harsh: both strains affected, 94% growth rate increase for sexual strain and 80% for asex
- recombination provides advantage in harsh but fitness didn’t increase in either strain
- shows efficacy of sec not mechanism
does the twofold cost of sex apply to yeast?
no as no male female distinction
what is the host/parasite example for novel genotypes having high fitness? (4)
- parasites under strong selection to infect
- hosts under strong selection to resist infection
- continuous shifting of selection as infection and resistance is directed to common genotypes (NFDS)
- biotic interactions lead to constant changes in direction of selection
what is the lively study on snails example? (4)
- evidence for novel genotypes having high fitness
- studied small pops of snails of both sexual and asexual females
- +ve correlation between no. of males and level of trematode infection
- don’t support view that sex is maintained by variable environment but does support that sex is favoured by selection from host parasite interactions
what is the morran and lively study on C.elegans? (4)
- evidence for red queen hypothesis where selection from co-evolving pathogens allows the persistence of outcrossing despite costs
- experimental coevolution of c.elegans with bacterial pathogen s.marcescens
- high levels outcrossing suggests selection of sex
- co-evolution could drive asexual populations to extinction or can select for bi-parental care
what are 4 brief examples of where investment in traits is costly?
- western grieves: rise out of water and splash which has energetic costs
- guppies: bright tails mean more likely to be predated as more visual
- red deer: antlers grow new each year which has energetic costs and risk of injury
- caw: graduated tail with aerodynamic costs
sexual selection can explain traits that go against natural selection and what is an example of this? (8)
body size variation of Galapagos iguanas
- snout vent length used as measured of body size to work out selection pressures on this
- Santa Fe and genovesa populations
- males grew bigger in both
- body size not under NS as adult survival doesn’t increase with size: survival advantage with body size only until a certain point
- larger ones can’t obtain sufficient resources to maintain body weight in harsh conditions
- males exceeded optimal size for survival but females below
- males and females have different body sizes but eat the same resources
- male selection pressure is to grow larger if can produce more offspring
what is isogamy?
same size gametes- ancestral sexual state
what was the first step in the differentiation of sexes ?
origin of mating types as can only mate with those not your mating type
what 2 things can evolution of mating types lead to and which is necessary for sexual selection?
- ever increasing number of types (ciliates have 48 different types)
- reduction to just 2 types (needed for SS and led to anisogamy)
what is anisogamy?
individuals producing different gametes
there are many hypotheses proposed for the evolution of anisogamy but which is the one with the most support?
Geoff parkers which is based on disruptive selection
what is Geoff parkers theory for the evolution of anisogamy? (4)
- begin with primitive isogamous sexual species with no distinct mating or gamete types
- can either produce 1 large or lots of small games if fixed budget
- smaller and larger games have reproductive advantage and selection for these is disruptive, giving rise to unequal game sizes
- anisogamy results from disruptive selection
- what is zygote size?
- when does zygote viability increase?
- what’s the difference between small and larger gametes?
- sum of games that fuse to form it
- increases with size
- small: produce more and more chance of encountering and fusing with other gametes
large: higher resulting fitness of zygote
how do males essentially parasitise parental investment of females?
- to increase their reproductive output
- male mating success increase linearly with no. of mates
- females don’t benefit as much from more mates
- male mating success more variable than females (Batemans principle)
what did Trivers state in 1972?
variance leads to competition between males and choosiness among females
what is the male variance in mating success for rough skinned newts? (5)
- clear difference in reproductive success of males and females
- most males have few mates and end up with few offspring
- reproductive skew with the small number of males having the most matings
- females more normal distribution of mates and offspring
- males benefit more than females from having multiple partners and gain more offspring for more mates
what is the male variance in mating success for broad nosed pipefish?
- sex role reversal
- males provide majority of offspring care
- females show reproductive skew
- females benefit more from increasing number of different mates
which investing sex competes for which and which is the most choosy?
sex investing least (often males) competes for sex investing most and the one most is more choosy
in what 2 ways has anisogamy resulted in conflict of interest between the sexes?
- competition between males (intersexual)
- female choice of preferred male (inter)
state what 2 theories there are for how sexually selected traits initially evolve and what each is
- good genes theory: traits reflect quality of male, trait evolved first followed by preference, high quality males produce high quality traits
- sensory exploitation: trait evolves because of female preference, females have pre-existing sensory bias for an ornament and chance mutation in a male produced ornament to match bias
what is the auklet example for good genes theory ? (4)
- variation in the genetic quality of males in pop
- high quality males produce high quality males with brighter plumage
- if females choose. brighter male will produce more fit offspring
- ornament and preference will spread through pop
what is the auklet example for sensory exploitation? (5)
- introduced least auklet which is the closest related sister species
- similar ecology and displays same sexual displays but without crest
- stuffed least auklet used to compare attractiveness by putting a crest on the model
- significant effect found: more sexual displays performed to models with crests and most displays to longer rather than shorter crest
- shows preference evolved before trait so trait originated through sensory exploitation
what is the sexually selected trait in the auklet?
feathered ornaments- sexually selected signals with more courtship displays to males with crest and longer crested males more likely to win fight
what are direct benefits to choosing?
material benefits that increase for reproductive success of chooser
what are indirect benefits to choosing?
good genes that will produce high quality offspring for chooser
what is fertility?
ability to produce offspring
what is fecundity?
potential number of offspring that could be produced
give 3 direct benefits of mate choice?
- fertile or fecund mates
- good parenting ability
- resources such as food and nest sites
what is the female choice of fertile males in lemon tetras? (7)
- both sexes have multiple partners in breeding season
- external fertilisation
- no parental care
- spawns roughly 23 times per day with 7 eggs in each spawn
- male fertility declined drastically with successive spawnings
- females prefer males that haven’t spawned recently
- 11/12 tests test females spent more time near non-spawning pair
what is male choice of fecund females in pipefish? (4)
- glue eggs to ventral surface of males who care for eggs
- females larger and more competitive and develop a skin fold
- males prefer females with large bodies and large ventral folds
- females with large bodies and large folds produce more eggs
what is female choice of male parenting ability in mottled sculpin? ()
- females lay eggs in territories of males
- males provide parental care by wafting o2 rich water over them
- all male spawning same quality and size
- females prefer large males
- large males hatch more eggs as can waft more o2 to the eggs
explain each example for female choice of resources:
- female scorpionflies
- male grevys zebra
- swap copulations for nuptial gifts
- males defend waterholes at which females come to drink so mate with the females that come there
what is the fallow deer example for female choice of resources? (8)
- rut peaks with acorn fall
- females feed on acorns and males protect trees
- number of does under tree relates to number of acorns
- food was added to the base of some trees and disturbed
- control: disturbed but no food added
- greater number of females under experimental trees
- females fed preferentially in territories with high quality resources
- evidence for mate choice resulting in direct benefits but lekking males provide no direct benefits as females only get his genes
list 4 models for how sexual selection for indirect benefits is maintained
- fisherman runaway model
- chase away model
- good genes model
- compatibility model
what is the fisherman runaway selection model and who came up with it and when?
females that produce males with attractive traits gain indirect benefits as they’ll produce attractive sons that will in turn be preferred by choosy females (RA Fisher 1915)
what is the bird tail length example for fisherman runaway selection? (4)
- female arbitrarily chooses long tailed male
- male offspring have long tail and unexpressed preference for long tail
- female offspring have preference for long tail and unexpressed long tail
- tail keeps getting longer until some natural selection cost such as predation limits the trait
under fisherman selection what can we predict?
that male traits and female preference should be genetically linked
what is the stalk eyed flies example for fisherman runaway selection?
- evidence of linked trait and preference
- dramatic sexual dimorphism in eye span, largely as a result of female choice for short eye span
- females from long eyespan choose males with long eye spans
what is chase away sexual selection, who suggested it and the 2 assumptions of it?
exaggerated male traits evolve through antagonistic coevolution between the sexes (Holland and rice 1998)
1. males producing larger than average ornament which stimulates females through sensory exploitation
2. traits are disadvantageous to female so evolve a resistance to trait
3. male then evolve a more exaggerated trait and females are then attracted to the male again so the trait escalates
assumptions:
- males seduce females into suboptimal matings
- females evolve resistance to such males
what is the drosophila example of chaseaway sexual selection?
sperm chemicals inhibit other males sperm and causes female to produce more eggs
- harmful to females and can reduce their lifespan
- if coevolve male evolves more toxic sperm and females develop resistance
what is the good genes model?
- males that could survive despite handicaps must be of high quality
- females will mate with high quality males gaining genes that would enable high survival for offspring
- under good genes selection wed predict that male traits should reflect the viability of offspring
what is the peacock example of good genes model?
- evidence of association between male trait and offspring viability
- peahens prefer males with larger eyespots
- better offspring that grew faster and survived longer produced when females mated with males with larger eyespots
why is it not the case with the good genes model that the population only has males with good genes?
would expect poor genes to be selected out but if only good genes variation would decrease and selection would come to a halt
what is the compatibility model?(5)
- individuals choose partners with complementary MHCs (major histocompatibility complex) to them
- predicts organisms will prefer partners with dissimilar MHCs
- signals are scents/odours
- humans both sexes prefer odour of partner with dissimilar MHC
- scents that reminded them of relatives found the MHCs closer
what is the difference between if an MHCX individual mates with another MHCX rather than MHCZ?
MHCX: would be MHCX offspring so homozygous offspring which has limited disease fighting capability
MHCZ: heterozygous offspring with greater disease resistance
what did the evolutionary ecologist bill Hamilton state? and also what did he recognise?
one that an organism/himself doesn’t stand united in striving to adaptation, the genome doesn’t share the same evolutionary optimum as individuals
- recognised selection could occur at different levels, between and within individuals
what kind go units does a multicellular organism have?
a hierarchy of replicating units - the units satisfy conditions for natural selection and adaptive evolution (variation, reproduction, heredity)
give points about the genes on the Y chromosome
- only present in half of male sperm but not in female offspring produced
- egg carrels x chromosome so are the homogametic sex
- for Y chromosome optima sex allocation is 100% males
- selection at chromosome level has a bias sex allocation to males
what can genes that drive towards their own optima do?
spread in a pop even if negative effects on carriers fitness
- how many types of mitochondria are there
- is the cell level or mitochondria level higher
- what do the mitochondria do after replication
- 2 types
- cell is higher
- distributed by segregation at cell division into daughter cells
what are the 3 possibilities of two level selection with genomic conflict?
- if both mitochondria types replicate at the same rate and evenly distributed then there is no natural selection at lower mitochondrial level
- if the mt types replicate at different rates then the ratio changes from 1 generation to the next and natural selection acts (no conflict if A type benefits more but if a benefits more is conflict)
- if mt types replicate at same rate but distributed unequally to daughter cells then there is biased segregation favours A at lower level and ratio changes between generations (conflict if mt type favoured at segregation selected against at cell level)
what are mitochondrial petite mutations in yeast?(9)
- in bakers yeast small petite colonies can develop on a culture medium
- colonies have defective mitochondria, severe metabolic problems and poor growth
- yeast cells have many mitochondria with genomes
- petite mutations are often large deletions that allow for a faster mutation of mt genome which outcompetes other mt pithing cell
- clear case of genomic conflict as mutation is selected for at mt level but against at cell level
- successful mutation in short term as mt fixation only at a few cell generations
- asexual is the norm for yeast and genomic conflict arises less easily in this system
- cells with petite mitochondrial mutation will be selected against as mutation lowers fitness of yeast cells
- most suppressive petite mutations show biased segregation when crossed with normal strains
what does sex combine and what can it allow for a greater scope of?
- sex combines genomes from different lineages through recombination
- allows for greater scope for genomic conflict so more likely a mutation causing genomic conflict will spread
what is a petite suppressive mutant example that is transmitted at a higher rate than the rest of the genome?
selfish genetic elements
give 4 points about selfish genes
- selfish genetic elements are transmitted at higher rate than rest of genome
- detrimental/not advantageous to organism
- some genes break rules of mendelian inheritance and overrepresented in offspring (segregation distortion)
- they bias bias segregation and drive meiosis away from equality producing <50% gametes with particular allele (meiotic drive)
what is sex ratio meiotic drive?
occurs when sex chromosome manipulates sperm production to ensure all functional sperm carry selfish genetic element
give 4 points on the sex ratio meiotic drive in drosophila
- drosophila naturally have X chromosome meiotic driver: SR which kills Y bearing sperm of male carriers so only produce x bearing sperm
- female biased broods have transmission advantage so SR passed on to all subsequent offspring if mate with carrier male
- results in heavily female biased population and eventual pop extinction
- SR males only produce half as many sperm so poor sperm competitors
what was N.wedell study on D.pseudoobscura?
- study if polyandry can protect against SR in drosophila
- hypothesised that polyandry female multiple mating may protect from SR by increasing sperm competition and undermining transmission of frequency driving chromosomes
- polyandrous pops had higher prop of males
- 5/12 monogamous lines extinct
- monogamous line showed higher frequencies of SR than the 3 polyandrous lines
- female multiple mating can reduce freq of sex linked meiotic driver
what level can selection theoretically act at? but what does it infer?
levels higher than individual organism such as populations and species
- but infers group selection which is unpopular with ecologists as groups succumb to selfish individuals
did the jurassic forest have pollinators?
no as no pollinators
what is the coevolution of insects and flowering plants?
- insects and angiosperms make up large prop of terrestrial species
- most arose around early cretaceous
what is coevolution? what can it involve? and what 3 things can lead to it ?
- reciprocal genetic change in interacting species owing to natural selection imposed by each other
- involves interactions between groups of individuals or genetic elements within species
- antagonism, competition, mutualism
what is an example of antagonism?
red queen dynamics
what is an aspect of evolutionary biology that has a large impact on our daily lives?
parasitism and disease
what is the equation for parasite evolution and what does each part stand for?
R0= bN/ v + d + r R0: parasite fitness/ no. of new infections bN: rate of new infections b: prob. infecting host N: no. of hosts available v + d + r: rate at which hosts lost v: death by parasite/virulence d: incidental death r: recovery
what are 2 predictions of the parasite evolution equation?
- correlations between virulence and transmission will increase virulence
- vertically transmitted parasites will be less virulent
what are 2 examples of what is vertically transmitted?
- mitochondria
- aphids and their symbiotic bacteria (can provide them with nutrients)
herbivory is an example of antagonism how is it costly to the plant and what are 3 examples of evolved defences?
- have to regenerate lost parts or will have lost leaf area
- thorns/spines
- toxins
- visual cues such as mimicry
what do anti predator defences facilitate?
adaptive radiation by enabling escape from constraints
where are the Passion flowers found, how many species and what speeds up and how?
tropics
40
multiple interactions- speeds up rate of speciation
what is the escape and radiate defence in amphibians?
chemical defence : temperate regions allow for increased speciation rates
- anti-predator defences facilitate adaptive radiation by enabling escape from constraints
what are 4 passiflora adaptations and 2 heliconius butterfly adaptations
PASSIFLORA:
- vines have toxins/cyanogenic compounds in leaves
- egg mimicry
- secrete nectar from leaves to attract ants and wasps which feed on caterpillars
- leaf shape variation to escape detection
HELICONIUS:
- caterpillars can detoxify and disable these and use them for their own defence against predators
- can learn leaf shapes
how was it shown that heliconius can perceive and use leaf shape
- artificial leaves with normal biflora leaf shape and another leaf shape
- if trained with biflora would prefer to fly to that leaf shape but if trained on the other would prefer that one
for what 3 reasons do plants have egg mimicry?
- female heliconius are picky about where eggs laid
- caterpillars of most species are healthiest when fed young shoots which are of limited supply
- competition between individuals and species for host plants
what 2 things can sometimes happen with competition?
- one species can outcompete another and drive them to extinction
- can result in adaptation, reducing competition, helping species co-exist
give 3 points about resource partitioning and niche specialisation
- initially 2 species overlap along dimension of niches with a common resource they compete for
- over time competing individuals experience less success
- natural selection drives species to specialisation and partitioning of resource
what kind of competition can you see in heliconius butterflies, why and what are 3 points on the study?
interspecific due to region of sympatry overlap
- how species fed on plant when separate and reared together
- if species kept together development time is longer
- when alone or together display different feeding behaviours
what is a plant vs pollinator example of mutualism ?
heliconius
- feed on pollen which is unusual as well as nectar so are nutritionally richer so live longer
- prefer flowers that are present for the duration of their lifespan
what is the psiguria example of mutualism?
- small flowers so flower over a long period
- heliconius can learn where flower is and return to it daily over several months
does mutualism mean no conflict? and what is the coffee and citrus plant example?
does not
- have caffeine in nectar
- alters behaviour of bees to improve their learning and memory and increases re-visitation rate of pollinators
- bees will react higher concentrations of caffeine as is slightly toxic to them
- flowers keep caffeine levels at right level so bees don’t reject the caffeine
what are nectar robbers?
bees which can manipulate a flower and drink their nectar directly without pollinating
give 3 points about mullerian mimicry
- heliconius species have evolved bright colour patterns to advertise their toxicity to predates
- predator will learn the warning colours sooner so individual less likely to be eaten
- if several species have same pattern they all benefit by sharing cost of educating predators
what has mimetic coevolution been assisted by?
tool kit of major effect genes
what has genetic mapping shown in terms of colour pattern variation?
that the same 3 genes produce most of the colour pattern variation even in distantly related species
can different traits in the same species co-evolve?
yes in different directions
what are 2 major important factors about coevolution?
- abiotic influences produce adaptation
- biotic interactions probably more important for diversity such as speciation (competition and co-speciation) and maintenance of diversity (antagonism leading to NFDS)
what is fitness an interaction between? and what can selection favour?
genotype and environment with the biotic environment constantly evolving
- selection can favour evolvability (evolution of sex and recombination)
what are the 3 main ways to study coevolution?
- models- parasitism
- observations (phylogenetic coevolution/co-speciation and evolutionary rates, e.g psigura flowers)
- experiments (e.g. competition between caterpillars, learning of leaf shape)
what are 3 examples coevolution below the species level?
- sexually antagonistic co-evolution (SAC) : chase away sexual selection and an arms race between the sexes
- co-evolution between genes in the genome (mutualistic being coevolved gene networks which can be seen when hybrid is less fit/inviable)
- antagonistic (genome conflict )
how is sexually antagonistic co-evolution genomic conflict?
- most differences between the sexes/sexual dimorphism are produced by difference in expression of autosomal genes (sex biased gene expression)
- genes that show sex biased expression can have different evolutionary rates likely due to sexually antagonistic coevolution/runaway SS
what does group living lead to and what is unlikely?
social interactions
unlikely an interaction mutually beneficial
what is the interaction in each case:
- actor and recipient benefit
- actor does but recipient harmed
- actor -ve, recipient +ve
- actor -ve, recipient -ve
- cooperative
- selfish
- altruistic
- spiteful
what does altruism go against and how can it evolve? theoretically what should happen?
against expected selfish behaviour
- if recipient of altruistic act benefits will leave more offspring
- the actor/giver is not going to leave more offspring
- theoretically should be fewer altruists in next generation and if altruistic behaviours heritable they should ultimately die out
what did Williams state and when about group selection?
1966
adaptation benefiting a group rathe than individual don’t exist- either is not an adaptation or can be explained by benefit to individual
should individual or group selection outdo the other and explain this
individual is the lower level so should out do group
- individual organisms more numerous and turnover quicker than populations they’re in
- potential for replacement of less fit by more fit individuals is greater than that of populations
what is kin selection?
altruistic behaviours can evolve by kin selection
- allele can increase in pop if recipient related to individual performing altruistic behaviour
what is the alarm calling in belding ground squirrel example for kin selection?
- forage in large groups
- females call to alert relatives of danger
- only females remain on natal territory so are highly related to other squirrels in population
what is the bird helpers at the nest example for kin selection?
- helpers tend to be related to parents and are often offspring from previous broods
- parents with more helpers have more chicks
- helpers failed at their own breeding attempts
- usually males, as operational sex ratios skewed to males s they have more resources to use for helping
- males can stay and help for up to 6 years
who selected kin selection and why and what is the rule?
Hamilton - to explain problem of altruism, incorporating the idea of inclusive fitness
rB - C >0
rB > C
r= degree of relatedness/how many identical genes by dense you have
B= benefit to recipient
C= cost to actor
a) what what Hamiltons equation for inclusive fitness?
b) what does amount of indirect fitness depend on?
c) what happens when you increase the amount of indirect fitness?
a) inclusive fitness = direct fitness/personal fitness gains + indirect fitness (additional fitness from relatives)
b) how related individuals are to each other
c) increases inclusive fitness
in hamiltons rule what happens when C increases and when B or r increases?
C: direct fitness increases
B or r: indirect fitness increases
what is the probability of a daughter who has a brother, sharing alleles through…
- mum
- dad
- mum and dad
- 0.5 X 0.5 = 0.25 (mother X brother)
- same as above
- 0.5
what is the probability of sharing alleles with a nephew through…
- mum
- dad
- joint
- 0.5 X 0.5 X 0.5 =0.125 (mum X brother X dad)
- same as above
- 0.125 + 0.125 = 0.25
what are 3 characteristics of eusociality as the ultimate in reproductive altruism and an example?
- overlap in generations between parents and offspring
- cooperative brood care
- specialises castes of non reproductive individuals
e. g.: insects such as termites, Hymenoptera: ants, wasps, bees, also naked mole rats
what is the haplodiploid in Hymenoptera?
- males haploid
- females diploid
- haplodiploidy changes r
- sisters share 100% fathers genes and 50% mothers genes so: (0.5 + 1)/2 = 0.75
- females more closely related to each other (0.75) than to brothers (r=0.25) and their own offspring (r=0.5)
how can females increase inclusive fitness?
by being sterile workers, helping to produce reproductive sisters
is haplodiploidy the explanation of eusociality in Hymenoptera?
- 0.5 relatedness assumes only 1 male fertilises a queen but not true in honeybees where the queen has multiple mates but may reduce r
- in some species colonies are founded by more than 1 queen
- many eusocial non-hymenoptera are diploid such as termites
- many Hymenoptera aren’t eusocial
- haplodiploidy may facilitate eusociality evolution but more important factor may be need of help rearing young
eusociality may have 3 independent origins what are these associated with and give examples of eusociality in groups
nest building and need to supply larvae with food
- spheroid wasp, honeybees, ants, paper wasps
what kind of species does eusociality only occur in?
those with complex nests and extensive larval care
why did eusociality likely evolve?
due to ecological selection pressures rather than underlying genetic system
what is kin selected discrimination in cannabalistic spade foot toad tadpoles
- tadpoles develop into typical morphs eating mostly decaying plant matter
- when conditions change develop into carnivores that eat other tadpoles
- if given choice to eat sibling cannibal morphs will eat non siblings which is consistent wit the kin selection theory
what is sperm heteromorphism?
in some species males produce different distinct morphologies of sperm with 1 morph fertile and the other sterile
is the infertile morph being altruistic to the fertile morph in drosophila pseudoobuscura?
- female reproductive tract spermicidal
- non fertile parasperm protects brother fertile eusperm from female spermicide which is harmful
- the effect is increase with ratio of parasperm to eusperm
- proves sperm to be altruistic
what is the intraspecific conflict in mouse sperm
- have hooks to latch onto female reproductive tract and to each other
- if sperm competition sperm avoid joining with sperm conspecifics and only join to sperm from the same male rather than a brother
- evidence of sperm cooperation where sperm can discriminate based on genetic relatedness
what is the kamikaze sperm hypothesis?
sperm type that sacrificed its own chances of fertilisation to neutralise the sperm of competing ejaculates
- block, incapacitate and kill rival sperm
active kin directed behaviour requires kin recognition how is this achieved?
- smell (mammals and insects)
- song (some birds)
- learned familiarity (raised together)
- visual similarity (chimps, humans)
is kin recognition required for kin selection to operate?
no- kin selection will operate as long as altruists are biased towards kin so selection will favour this behaviour
how many species does the open tree of life aim to represent?
2.3 million species
what did J.B.S Haldane notice ?
inordinate fondness for beetles
how much does species richness vary across clades of tree of life?
a great deal
animals most species rich kingdom
arthropods most species rich animals
- pattern of diversity unevenness common throughout tree of life
what is phylogenetic tree imbalance?
relative numbers of descendent tips on branches that originate at focal node
- if unequal numbers each side of node is imbalance
what are 3 points on the equal rate Markov model?
- species arise from other species
- probability of speciation and extinction per unit time is constant across lineages
what can trees be unbalanced by?
chance
- more likely than balanced and more common than expected under null model
is there variation in clade age for species richness variation?
clade age and species richness are uncorrelated across 1,397 clades of multicellular eukaryotes
- no relationship
what is net diversification rate?
net rate of lineage splitting
= lineage birth rate/speciation - lineage death rate/extinction
when measuring using a lineage through time plot LTT- when is clade growth exponential and what does this look like if logged
if speciation rate constant and extinction zero
- straight line if logged
in Hawaiian silverswords roughly how many species are produced per lineage per million years
0.6
what is the relationship like in kingdoms and other levels between diversification and species richness
strong
how many clades account for what % of vertebrate diversity?
5 clades- 85%
what is a strong predator of species richness at any taxonomic level across tree of life?
net diversification rate
what are 3 factors that may influence diversification rate
species traits and environmental factors
in terms of diversification rates how can speciation and extinction be separated
- if probability of extinction and speciation constant through time then as we approach the present number of extinctions will decline
- extinction can be calculated by comparing the recent slope with the past slope
give points about the trait dependent diversification in nightshades
- large family of flowering plants
- important commercial crops (potato, tomato, pepper, capsicum medicine, petunias, tobacco)
- 2700 species
- 98% hermaphrodites
- 57% self compatible
- 41% self incompatible
what is self incompatibility and what does a loss of it allow?
ability of hermaphrodites to enforce outcrossing and avoids inbreeding depression
- loss enables self fertilisation
- in what kind of lineages are speciation and extinction rates higher
- in which is net diversification higher
- in which is net diversification negative
- Self compatible
- SI
- SC
diversification rates differ among SI and SC lineages how is this distribution maintained?
balancing short term advantages of SC with long term advantages of SI
for what 2 main reasons is heterozygote advantage not common?
- imposes load on the pop (difference between max and mean fitness)
- unstable due to duplication/mutation where disadvantageous allele may be duplicated and fixed at different location so passed onto next generation after recombination (such as globin family of genes)
why is it harder for hitchhiking alleles to occur in mammals?
sexually reproducing so recombination more frequent
what is jones et al 2013 example for hitchhiking alleles in mammals
humans for lactose digestive allele
what is balancing selection?
when selection acts to maintain different morphs in a population
