Evolution After Midterm 1 Flashcards
What are qualitative traits?
Discrete phenotypes ; can assign individuals to categories with ease
What are quantitative traits?
- indiscrete, measurable phenotypes; cannot using with ease, varying intensities
Is most biological variation quantitative or qualitative? Can we use HW models?
- most variation is quantitative, must be measured
- most traits are also multi locus (>2) - so we cannot use HW / Mendelian ratios
What are mendelian ratios initially for? Can they be used to explain range of phenotypes in organisms?
measure qualitative and discrete traits passed on in mendelian ratios -
- but Mendel’s model of inheritance can also be used to explain range of phenotypes observed (still sorts independently)
Why do we need quantitative genetics?
- we need it to study multi locus traits
- most ecological relevant traits are multi locus, too complicated for HW models
provides tools for: predicting response to selection, measuring differences in survival/reproduction, measuring heritable variation
What traits must phenotypic variation have that allows populations to evolve?
- must be heritable allowing for differential reproductive success
What are the traits we observe in determining heritable variation?
- determine how much of a trait is due to environmental and genetic variation
- determine genetic contribution
What is heritability?
the fraction of total variation in a trait that is due to variation in genes
What is broad sense heritability (H^2)?
- for population
- ratio of the total genetic variance to total phenotypic variance
- includes all genetic contributions to a population’s phenotypic variation
for an individual : P = G + E
total variation: Vp = Vg + Ve
What is the equation for broad sense heritability?
H^2 = VG/VE = VG/(VE+VG)
What is narrow sense heritability?
ratio of additive genetic variance to total phenotypic variance : in individuals (how much parent passes on to offspring)
- describes extent to which offspring resembles parent
What does h^2 allow us to predict?
- allows us to predict how a population will respond to selection because it describes the extent to which offspring resemble their parents
What does an h^2 value of 0, 0.5, 1 indicate?
0 means that all variation is due to the environment, 0.5 means there is some genetic and environmental component, 1 means variation is entirely due to variation in genes
What is the equation for narrow sense heritability?
H^2 = Va / Vp = Va / VA + VD + VE
What is additive vs dominant genetic variance?
- VG = VA + VD
- additive is the variation due to additive effects of alleles/loci (co-dominance ; how much it ‘adds’ since they are combined and express new combined traits)
- Dominant is the variation due to gene interactions like dominant alleles
- if some dominance, VA reduced
What does it mean when all genes act additively?
VG = VA
will narrow sense heritability change if we switch environments?
yes!
- look at eq- it will change as environment or allele frequencies change
What are the 3 methods of determining whether traits are determined by genes or the environment?
- GWAS (Genome wide association studies)
- QTL (quantitative trait loci)
- Common garden experiments
What are GWAS?
- genome wide association studies looks for association between loci and phenotypes
- sequence many individuals, find SNPs (Single nucleotide polymotphisms) - look for association of SNPs with phenotype of interest
- confirm with other populations
What is QTL mapping?
- quantitative trait loci - portions of the genome that influences quantitative traits
- QTLs are mapped by identifying which molecular markers correlate with an observed trait
- do not actually identity which genome but just stresses of DNA linked to the causal gene
What are common garden experiments?
- test for environmental effects by growing species outside of their usual environment
- don’t usually know the genes just that they differ - can detmeurine H or h ^2
What does variation within a common garden experiment indicate?
No VE< only VG
Can heritability within populations describe the causes of the differences?
heritability within populations tells us nothing about the causes of differences between population means in different environments - changes in environments causes changes not genes
Why is heritability often misinterpreted?
- assumes that differences between populations are due to differences in genes
- not the case, must consider environment
Describe the example of IQ in humans
IQ in humans, h^2 = 0.6 indicates some heritability
- so we can assume that there is a genetic component in differences in populations
BUT this does not imply that IQ differences between populations are due to genetics, the groups have different environments
- phenotypic differences but no genetic differences
to test this we would need to compare both values in different environments:if genetic, should show difference, if environmental should show same curve (not ethical / confounding factors in people)
Can genotypes respond differently to different environments?
YES species may be locally adapted, gentoypes can respond differently to different environments
What are adaptations?
Inherited traits that make an individual better suited to their environment: increases their fitness
- must evolve via natural selection and serve the same trait as it did when it was developed
How can we prove that a trait is an adaptation?
1) determine the function of the trait
2) prove that individuals without that trait have a decreased fitness compared to those with the trait
Explain the ox and red billed oxpecker example
- initially thought to be mutualistic
- experimentation revealed that ox tried to shoo them away, they collected earwax, harvested dead skin and ate blood
- parasite load (ticks) did not change, but earwax decreased and open wounds increased
- conclusion: birds are a blood parasite
(does not define all interactions between oxpeckers and large mammals - eg; birds on the rhino help them =mutualist) - nature is complicated
- oxpecker adapted for blood collection not parasite removal
What are some key points on adaptive studies proven by the ox and oxpecker?
- adaptations are not as obvious as they appear
- plausible hypotheses are the beginning of experimentation not the end
- all hypotheses must be tested!
What are the main approaches for studying adaptation?
- controlled experimentation
- observational research
- comparative method
Describe controlled experiments. what factors make for a good experiment?
- this is where one trait is changed, ideally all other traits are identical and the one independent trait is altered to see how it impacts other dependant factors - differences in survival and reproduction should be due to that trait!
factors:
- question phrases as precisely as possible
- all alternative hypothesis and predictions defined (really good ones will test these as well)
- a way to manipulate the independent variable
- a way to measure the dependant variable changes
- randomization, replication, adequate controls
eg; Oldfield mice
Define observational research?
- when a trait is not easily experimented on: careful observation could provide answers instead
- ## eg; Darwin and huxley proposed that humans related to great apes: used comparative anatomy + molecular genetics supports hypotheses (1.3% difference, differences may be due to different gene expression)
Define comparative methods
- observing traits among multiple taxa of populations
- looking for trends in evolutionary history - look for similar traits/functions and if they are very common in multiple species may be an adaptive function
What is the problem with comparative methods?
- some species may have evolutionary history: similarities may be due to relationship and not evolution
- correlations may not be statistically significant
What are the phylogenetic comparative methods?
- 1) PICs : phylogenetic independant correlation
2) phylogenetic generalized least squares
3) logistic regression
Describe the steps to PICs?
1) obtain phylogenic tree of interest
2) find ancestral trait values (averaging descendants)
3) identity sister pairs (taxa-use branch once)
4) calculate contrasts for each pair!
5 ) calculate regression / correlation and determine if relationships are significant
What is required to determine if x and y are co evolving?
- phylogeny
- measurements of 2 traits
Describe PICs?
- to determine if there are correlations between traits we need to evaluate the taxa but ancestral history may make correlation statistically significant
- PICs evaluates the correlations while taking into account evolutionary history
- looks at patterns of divergence as sister species evolve independently from common ancestor: looks at divergence from ancestor
- if contrasts are significant we can conclude that traits are related : because they are related cross all taxa, so as they diverge they change together meaning they are related
- we would expect to see correlation between traits of all taxa because they are correlated
What are some challenges with studying adaptations?
- phenotypic plasticity: genes can undergo evolution: may change in response to environment
- tradeoffs/constraints: trait could reflect a compromise between conception environmental or physiological demands or reflect physical constraints
- selection can act at multiple levels
What does it mean that selection can act at multiple levels?
- selection is the differential survivial/reproductive success of some entity (entities range form nucleotides to genes to cells to individuals to population etc)
Define selection acting at multiple levels:
- at the individual level in a population: variation: different colours
- differential erprodutive success: selective agents remove certain less fit ones
- inheritance: only those remaining (brown beetles) breed and have more brown beetles
- at the cellular level within an individual:
variation: mutations in cells produce more
differential birth and death: mutated cells have more offspring
inheritance: mutation offspring inherited mutated DNA, normal inherit normal DNA
At the species level:
- variation: certain species experience patchy disruption, others don’t
- selection/ differential birth and death: patchy distribution more likely to undergo speciation
- inheritance: patchy species give rise to species with patchy distribution, normal distribution give rise to species with normal distribution
Which levels have the most power for defining whether a trait is adaptive or not?
which have the least?
most: genes and individuals
- Traits directly affect an individual’s fitness, providing clear evidence of adaptiveness. (compare one individual to another can see which is better)
- genes provide direct evidence of evolutionary changes under selection.
Can identify specific mutations or alleles responsible for adaptive traits.
least: species and populations
- Comparative analyses across species can suggest adaptiveness but often rely on correlations rather than direct tests of fitness. - harder to determine if it is a result of adaptation or historical relatedness
-Patterns of trait variation across populations might reflect genetic drift, neutral evolution, or historical constraints rather than adaptation
can selection act simultaneously?
yes at multiple levels
What is sexual selection?
- natural selection works on not just traits that improve survival but also those that improve their ability to convince the opposite sex to mate
- differential reproductive success due to individual variation in mating success
- ie: selection for traits and behaviour that improves mating success
How does evolution via sexual selection occur?
–> organisms with heritable traits favouring mating success have more mating opportunities –> increase in frequency in future
Does NS always support sexual selection?
- no sexual selection can be opposed by NS (may not increase fitness or survival but increases reproduction!)
does sexual selection work in different sexes?
- sexual selection works differently in males and females- leads to sexual dimorphism
What is sexual dimorphism? How may it have arose?
- sexual selection acts on males and females differently ; males and females differ morphologically inducing traits not directly involved in reproduction
–> different parts of selecitondue large in part to anisogamy: greater than 2 different kinds and sizes of gametes produced
What is anisogamy?
- reproductive system in which greater than 2 types and sizes of gametes are produced eg; sperm v egg
how did anisogamy come to be?
- where smaller sperm are more mobile, and larger sperm are fewer but larger
- zygote survival increases with size which depends on gamete size
so - selection should favour fusion of protosperm (smaller) and protoeggs (more biomass) (fusion of protoeggs but larger gamete rate)
- disruptive selection = small sperm, large eggs!
What are the two predictions regarding sexual reproduction leading to sexual selection? (gamete size) What do these lead to?
- males should compete for mating opportunities
- females should be choosey
since eggs are large and scare, highly valuable compared to sperm so
- leads to different behaviour, morphology, physiology between sexes
why might males be expected to compete for more mating opportunities?
- lots of variation in male reproductive success: some low some high due to large mass of sperm , females more intermediate reproductive success
Why should females be choosey ?
- eggs are costly and rare, females stand to lose more if they choose the wrong mate:
- especially true for internal gestation: must put energy before offspring are born so must be good investment
Why does selection act differently on males and females?
because of anisogamy!
(more sperm; compete, more variation; fewer large eggs, get to be choosey of males for payoff with rare egg) = under different selective pressures
What are the two forms of sexual selection ?
Intrasexual selection : completion between members of the same sex competing for opposite sex Imore common in males)
- intersexual selection: one sex selects opposite member (typically female chooses male)
what are the 4 mechanisms of intersexual selection?
- 4 evolutionary models:
- direct benefit
- good genes (and costly traits)
- fisher sexual selection
- sensory bias
Describe the direct benefit
- females prefer males who can bring more resources that benefit fecundity or growth ; fly selects male that brings more benefit, and male gets to mate with female
- 2) protection from predators
- mate guarding: males who stay with female before and after copulation benefit: males can prevent other males from mating and protect from predators
- female gets protection from predators
- eg; amphipods; larger ones get more success because of higher survival
Describe the context for the good gene hypothesis
- not all sperm will be equally good last producing offspring - selection fairs females who will choose males with good genes; genes that code for favourable traits
How do females select for the good genes if males can lie?
- expect only traits that are honestly indicative fo quality are selected upon by the female
What is the purpose of ornaments in the good gene hypothesis?
- ornaments can serve as honest indicators of genetic quality based on the handicap principle: only healthiest males can afford to produce and maintain ornaments, less costly for healthier males to produce therefore a good honest indicator
What is the propose of the handicap ornament?
When a trait is a handicap it can serve as an honest single of genetic quality
Describe the fisherian sexual hypothesis?
- some females express a preference for a males trait - if trait and preference are genetic can become linked and increase in frequency - offspring carry both traits
- sexy son mechanism: female mating with who she prefers is reinforcing; leads to offspring having higher reproductive success
How does fisherian sexual selection and NS work together?
- generally there is a balance between the two
What occurs when the association between preference and trait is very high?
- can lead to runaway sexual selection: produces increasingly exaggerated traits in a feedback loop if there is no associated cost
How can we determine the difference between fisher sexual selection and good gene hypothesis?
- good gene hypothesis is an ornament associated with quality
- FSS is preference on top of good genes - ornaments indicate sulky and preference - good genes mechanism strengthens selection
What is the sensory bias model?
- a preexisitn bias in the sensory system of one sex favours member son the opposite sex who display the same trait
- triggered by excitement in element of nervous system or preference due to benefit outside of mate selection
eg; female likes red berries, males develop red wings randomly, female prefers red wing male due to pre exiting trait
In the sensory bias model, does the female inherit the trait preference after the male does?
No! The preference is likely pre-existing
Are intersexual selection models exclusive?
NO! many mechanisms can occur at once
- evolution of. asexual trait could be explained by more than one of these models
What are the forms of combat in intersexual selection?
- cuckoldry, combat, sperm competition,
Cuckoldry?
- male unknowingly cares for young that are not his own
eg; bluegills; sneakers and satellite may get sperm in female that parental then takes care of because he thinks they are his
Sperm competition in bluegills?
Snakers producer low quality short living lots of spemr, while parental produce fewer high quality sperm
What is sperm selection?
- sexual selection acts not only on male behaviour and external morphology but also on sperm’s ability to reach and fertilize eggs
What is postcopulatory sexual selection?
- sexual selection occurring after mating has taken place ( sperm completion)
What is sexual conflict? What can it lead to ?
- because selection can act differently on males and females in terms of mating, they may have traits that are detrimental to the other sex
- can lead to antagonistic coevolution
What is antagonistic coevolution?
- an arms race between males and females
eg; in drosophila seminal fluid- seminal fluid actually decreases longevity of females- it develops a sperm plug and makes her less receptive to other males, and triggers egg production and laying BUT that is costly, reduces survival chances and chances of mating again = antagonistic , the want to mate harms female
What is extinction?
all individuals of a species have died out and left no living descendants
What is a fossil?
- remains or traces of a once living organism
What is fossilization? How does it occur?
- organic material being preserved over time
- very gradual process
- more time = more rock like
- calcium and phosphate are replaced over time by iron and silicate
- sometimes can be preserved in amber
- carbonization also occurs
What is carbonization?
- thin layer of carbon preserved on sandstone or shale
What is the best place to find fossils?
fossil tend to form in sedimentary rock: sand, chalk, shale, sandstone,
What is dissolution?
- when water breaks down fossil and only the outline remains
What is the fossil record?
history of life on earth based on fossil remains: reveals what the earth was like at the time of their existence
What is the law of superposition?
- a way to date fossils based on depth in the soil: ie: deeper= older
- relative age
how do you measure relative and absolute age of fossils?
relative age: law of superposition
Absolute age: radiometric dating (measuring half life, check ratios and / or surrounding sediment)
What is the signor lipps effect?
the gap between the last discovered fossil and the actual date one extinction
- backwards smearing: dating extinction earlier than it occurred
- forward smearing: dating extinction later than it occurred (happens from burrowing animals, can offset risk of error by checking for evidence of burrowing around fossil)
What is a mass extinction?
- series of events that uses large scale loss over broad geographic range - in a relatively short amount of time
- no clear definition but argued that> 75% species loss
How many mass extinction events have occurred? What are they called?
- 5 mass extinctions known to occur within the last 600 million years
- end of ordocivian, late Devonian, late permian, end of triassic, KPg (cretaceous paleogenic boundary)
How do we study ongoing and past extinctions?
ongoing: look for last living representatives
past: search for fossils
Are all extinctions equal?
- no! Loss of larger branch is worse- loses all of the evolutionary history
What are background extinctions?
Extinctions occurring between mass extinctions: 95% of species extinction have been background extinctions
What are some causes of background extinctions?
- predation: predators adapted to become more efficient (prey too) - eg; clams have larger dents before they go extinct indicates that predators became better adapted and wiped the population out
- introduction of new species, overhunting, indirect effects (human intervention)
- disease: can wipe out populations quickly: global decline in amphibians 7/14 gone extinct since 70s = disease takes them out within a few months
- competition: certain species can become better adapted and out compete others with the same niche
Is each method of background extinction exclusive?
- no! They are not mutually exclusive - can occur together eg; extinction of endemic Hawaiian birds caused by two waves of human colonization - introduced disease, predation (hunting for food/feathers), introduced non-native species and habitat destruction
What is an endemic species?
- a species native to the area- many examples of extinctions are from endemic species because local extinction = global extinction
What is a dead clade walking?
A species that survive the extinction event but die in the years following (due to ecological changes associated with the loss of so many species and environmental changes)
