post midterm Flashcards
Two definitions of adaptation
- characteristics that enhance the survival or reproductive success of organisms that bear it relative to other stages
- process of genetic change in a population whereby as a result of nat sec the average state of the character is altered (the population becomes better adapted to their environment
What is the adaptationist fallacy?
evolutionary biologists had a habit of proposing adaptive explanations for any trait by default without considering non-adaptive alternatives, and often by conflating products of adaptation with the process of natural selection
changes in organisms are not always adaptations - neutral theory
For it to be considered an adaptation it must increase _____
fitness
Adaptations produce more ____ individuals
complex
selection ____ towards complexity, genetic drift ____
does, does not
3 ways to recognize adaptations
By the complexity and design
By an experiment
By the comparative method which requires lots of evidence and to be phylogenetically informed
Define Exaptation
- the evolution of a function of a gene, tissue or structure other than the one it was originally adapted for. Can also refer to the adaptive use of a previously nonadaptive trait
Define directional selection
- selection for a value that is higher or lower than its current mean value
- often produced by sexual selection
Define stabilizing selection
selection that maintains the mean of a character at or near a constant intermediate value in a population
Define disruptive selection
Selection in favour of two or more phenotypes against the intermediate - diversifying selection
Mean fitness ___ with successive generations of selection (as the allele with lower fitness is purged from the population
increases
What is the cost of adaptation?
Cost penalty of adapted individuals in a changing environment
- rats resistance to pesticides decreasing fitness after pesticides no longer present
What is the common trend among pesticide resistance?
generally based on single mutations of large effect and gene for resistance is at least partially dominant
Antagonistic selection can lead to ___ ___ ___
antagonistic niche polymorphism
Antagonistic selection can be due to ___ or ___, define these terms
Temporal fluctuation - environments favor different genotypes across generation
Spatial fluctuation - different genotypes are best adapted to different microhabitats or resources
Heterozygote advantage is _____ selection
stabilizing
Heterozygote disadvantage can lead to:
fixation of one of the alleles - can lead to a population with fitness slightly less than theoretically possible
Define antagonistic selection - provide an example
When one selection force opposes a different selection force
- Sickle cell anemia - anemic with A2A2, at risk for malaria with A1A1 - Heterozygote is a middle phenotype
- this is actually a bad example - diversifying selection is better - big males v small females - selecting for opposite traits
Negative frequency dependent selection means it is beneficial to be the _____ geno/phenotype
rare
- parasitic fish favoring a side - favor the side that less fish pick = more food 4 u
Define positive frequency dependent selection
the fitness of a genotype is greater the more frequent it is in a population
What is Mullerian mimicry?
two or more unpalatable species mimic eachothers warning colorations
Define Cline
a gradual change or gradient in an allele frequency or in the mean character trait over a geographic transect.
What is the breeders equation - define the variables
R = h^2S
R = response to selection
h^2 = heritability estimate of trait
S = selection on the trait
Define correlated selection
selection favours certain combinations of traits over others
- ex) spotted vs striped coloration and escape behaviour in garter snacks
(either is easier to see and flees or harder to see and stays put)
Define and provide the equation for broad scale heritability
an estimate of the proportion of phenotypic variance with a genetic basis BUT does not give an accurate reflection of the AMOUNT that wil be transmitted across generation
H^2 = Vg/ Vp
Define narrow scale heritability
an estimate of the proportion of phenotypic variance with an ADDITIVE genetic basis
WILL give an accurate reflection of the amount that will be transmitted between generations
What are the six causes of linkage disequilibrium?
Non random mating
New mutations
Union of two populations
Low/ negligible recombination
Genetic drift
Natural selection
Define life history
Age specific probabilities of survival and reproduction in a population
Define semelparity?
Reproductive strategy in which an organism produces all of its offspring in a single event
Define iteroparity?
reproductive strategy in which an organism produces offspring across multiple events
Age specific patterns of survival and reproduction in a population are depicted in a ____
life table
define senescence
declining reproduction/ physiological condition with age
Two leading theories on why we age?q
- mutation accumulation with age
- antagonistic pleiotropy
Explain the idea of mutation accumulation with age?
selection will more effectively purge deleterious mutations affecting early life traits than those affecting late life traits. - Therefore mutations affecting late life traits accumulate
Explain antagonistic pleiotropy
an allele that has a beneficial effect on one trait ( early life reproduction ) has a detrimental affect on another trait ( late life reproduction)
What are life history trade offs?
The existence of both a fitness advantage and a concurrent fitness cost
- survival/ reproduction trade offs
- early reproduction/ late reproduction trade offs
- offspring quality/ quantity trade offs
What causes life history trade offs?
physiological constraints and negative genetic correlations
Due to physiological constraints, selection should favor ____ in a given environment>
optimal life history traits
Are physiological constraints and negative genetic correlations mutually exclusive??
nope
Define outcrossing?
mating with another, genetically distinct individuals
define self fertilization?
union of female and male gametes produced by the same genetic individual
Define anisogamy
distinct male and female sexes, defined by gamete size
Define isogamy
uniting cells are the same size - unicellular or colonial organisms
Define dioecious
distinct male and female individuals within a species
Define hermaphroditic?
male and female sexual functions are performed by a single individual - worms, trees etc
Define sequential hermaphroditism?
organisms that change sex over the course of their lifespan like annelid worms
Define vegetative propagation
production of offspring from somatic tissue
Define parthenogenesis
development from an egg to which there has been no paternal contribution of genes - virgin birth
- apomixis - meiosis suppression - individual develops from mitotic cells
- offspring is genetically identical to its mother
What are the pros and cons of sexual and asexual reproduction?
Asexual reproduction is fast, energetically efficient, no partner needed and every individual in the population can reproduce however there is a stark lack of genetic diversity as offspring are identical to the mother - effectively the reverse is true for sexual reproduction
Three hypothesis for the evolution of sexual reproductive systems
- sexual reproduction combines new mutations or rare alleles to create new potentially advantageous phenotypes
- adaptation to varying environments (including parasite pressure) - recombination breaks down linkage disequilibrium and can result in rare genotypes
- separating beneficial vs harmful mutations
What is a mutational meltdown?
mutations in an asexual population will accumulate through generations and ultimately lead to a mutational meltdown or an accelerated loss of fitness
What is Mullers ratchet?
- In an asexual population there is a range of genotypes carrying x mutations
- more fit genotypes can be lost by chance due to genetic drift
- offspring always carry a greater number of mutations than their ancestors
- mutations will accumulate leading to a mutation meltdown
(remember, generally mutations are bad)
What is the Hill-Robertson effect
if
a mutates to A and A has higher fitness
b mutates to B and B has higher fitness
then without recombination A is in linkage disequilibrium with b and B is in linkage disequilibrium with a
Without recombination beneficial alleles can be lost due to linkage disequilibrium with deleterious alleles
Two ideas of the reality of species?
Nominalism - idea that species are artificial divisions of a natural continuum
Realism - idea that nature is, in fact, divided into discrete species.
define species from an evolutionary perspective
real units in nature that represent an independently evolving lineage
Two categories of species concepts
Horizontal - aim to define species at an instant in time and specify which individuals belong to which species at one time
Vertical - aims to define species through time and specify which individuals belong to which species through all time - ex dinosaurs - measuring and recording from a diff time
Two versions of the phenetic species concept?
classic - typological species concept - individuals belong to a species if they share characteristics with the type specimen
modern - statistical techniques for describing phenetic similarity
What is the biological definition of species?
species are groups of actually or potentially interbreeding populations which are reproductively isolated from other groups
- lack of gene exchange between two species due to biological not geographic factors
Define reproductive isolation
lack of gene exchange between two sepceis due to biological not geographic factors
Three stages of speciation?
- Population Isolation
- reduction in gene flow between populations
- commonly due to geographic separation
- could be due to other factors - Divergence
- in morphology, habitat use, mating habits, niche - Reproductive Isolation
- following secondary contact (when populations come back together)
Four general kinds of speciation?
Allopatric speciation by vicariance (barrier/ split in population) - most common
Peripatric speciation - founder effects - strong genetic drift
Parapatric speciation - large range with different habitats but not isolated - slow acting
Sympatric speciation - genetic differences resulting in reproductive isolation - slowest acting
