Adaptation Flashcards
define “An Adaptation”
a trait or integrated set of traits that has evolved by natural selection.
define “Adaptation”
a process in which the traits of a population evolve over generations resulting in individuals with increased fitness than before.
define “An Adaptation for X”
an trait that evolves involving X as the selective pressure
why do we need to be cautious when interpreting traits as adaptations?
- the trait might be an adaptation, but not for the function stated
- the trait might not be an adaptation at all
what is “active selection”
when a trait is currently being maintained by selection for a certain factor X.
how can you tell there is ongoing selection for a trait?
- variation in traits in the population
- the variation is heritable
3a. the traits affect function
3b. there are measurable effects of the trait on fitness
define Ancestral Constraints
these are traits that are inherited from an ancestor that are difficult to change that do not optimize function and limit further adaptation.
ex. human pelvic bone for birthing babies
how does natural selection affect adaptation?
natural selection moves species toward adaptive “peaks” or to adaptations that result in highest fitness. This process takes many generations to get to a point of properly increased fitness.
define Maladaptive Intermediates
the intermediate adaptations and mutations a species goes through before it can reach a high adaptive peak that has overall increased fitness for the species.
how does natural selection work if it has no foresight?
Natural selection works by selecting for traits that already exist in a population that may be alternates to the wild type. These alternates are randomly created due to mutation, recombination, drift and sexual reproduction.
what is Mutation Accumulation Theory?
theory that deleterious mutations are accumulated over time, acting on you in old age, because there was little selection against them.
I.e. as organisms age, they senesce and die.
what is the Antagonistic Pleiotropy Theory?
theory that deleterious mutations are selected for because they have beneficial effects in early age to ensure healthy reproduction, and detrimental effects in old age by decreasing health.
- spend a lot of energy early in life to ensure reproduction, exhaust resources that damage health later in life.
define Pleiotropy
when a gene has more than one effect
types of interactions between species?
- competition
- mutualism
- predation
- commensalism
- parasitism
what determines the success of an invasive species?
when a species, in its original environment, is held to a modest population size, but then when it enters a new ecosystem it becomes very successful.
define Coevolution
this is the evolution of two of more species that are influenced by each other through their interactions.
- also called reciprocal adaptation, species adapt traits as a response to living with another species.
what is “Entangled Fates”?
a mutualism mechanism where if the descendants of interacting lineages have their fates tied together, that promotes cooperation between the species regardless of whether there is an initial mutual benefit.
“If the success of my babies depends on the success of your babies, I will cooperate with you”
what is “Co-Speciation”?
when two species are mutualists (have entangled fates), the divergence of one species results in the divergence of the other.
- creates parallel phylogenies of the two species
define Vertical Transmission
when the offspring of interacting species also interact, resulting in Co-speciation and/or evolution of cooperation (entangled fates).
define Sexual Cooperation
males and females share reproductive interest in combining gametes
define Antagonistic Coevolution (sexual conflict)
in sexual selection, it’s when the evolution of one sex (eg. males) results in the evolution of the other sex (eg. females).
males have adaptations to take control over reproduction, therefore female evolve adaptations to take control over reproduction
define Isogamy
means same sized gametes
define Cryptic Female Choice
- occurs after mating
- not easily visible choice, since it is internal choice she makes of whether or not to use a mate’s sperm and if she would want to support his offspring
- decision can be made after copulation occurs
define Anisogamy
when certain gametes are really big (eggs) and some are really small (sperm)
- animals and land plants are anisogamous
what does the difference in egg sizes mean for the organism?
- eggs are large and have high energy/resource cost to make, so few tend to be produced
- sperm are cheap and require minimal energy/resources, so many are produced
define Operational Sex Ratio
this is the ratio of available males to females for mating.
there are more males, looking for another mating, and fewer females, because others are tied up growing eggs and tending babies, so they aren’t in the pool of available mates.
MORE males competing for FEWER females
what is risk of bad choice? (with respect to sexual selection)
females have much more at stake in each mating. In general for animals, consequences for male choosing “wrong” female
- 5 minutes and a bit of sperm
consequences for female choosing “wrong” male
- days, weeks or years of investment in bad babies
what is variance in reproductive success?
the VARIANCE in male reproductive success is greater than the variance in female reproductive success. Females tend to be more assured to have some offspring whereas males aren’t as guaranteed to have offspring (some have a lot, some have none)
define Intrasexual selection
when males compete amongst each other and the females mate with the winner
male-male competition
when intrasexual selection happens, males send to fight, usually over territory, and the female mates with the one that wins the territory.
define Intersexual selection (female choice)
females choose among available males according to their qualities
define Direct benefits hypothesis
females choose males that give them resources or protection which help the female survive and reproduce.
- males that offer more resources are given a better chance to mate.
define Good genes, honest signals
females choose males with good genes or traits that are correlated with his having alleles good for survival and reproduction because it helps her offspring do better.
indirect benefit to her - it helps her offspring do better.
what is an honest indicator?
If ANY male can make a trait, it’s not an honest indicator of quality.
Females should be selected to pay attention to only honest indicators, i.e. traits that are COSTLY to make (not all males have them)
define Sensory bias
sensory attraction of females to males (physical attractiveness or showiness).
- Does not necessarily help choose a quality male
define Runaway sexual selection
Once a population has alleles for a male trait and a female preference for it, this results in a positive feedback loop that drives these traits to fixation regardless of how useful/indicative the male trait actually is.
- as this occurs, linkage disequilibrium between the choosey female trait and the attractive male trait gets stronger
- may have no survival or fecundity benefit
define frequency-dependent selection
when the strength of selection on an allele depends on the frequency of the allele
are the mechanisms for sexual selection mutually exclusive?
No, there can be males that offer direct benefits AND have good genes AND/or have sensory bias, etc.
define hermaphroditism
when an organism has both male and female reproductive parts
define dioecy
when male and female reproductive parts are found in separate individuals
opposite of hermaphroditism
what is the evolutionary enigma of sex?
sexual reproduction evolved early and has been maintained across most eukaryotes despite substantial costs of sex
such as the cost of finding mates, destruction of favourable gene combinations, risk of not finding a mate, risk of disease transmission during mating
what advantages pay the costs of sex?
sex can generate variation needed by selection through recombination and segregation… variation that is missing due to the limitations of selection in finite populations
negative epistasis hypothesis for sex
epistatic selection in the past led to negative genetic associations, resulting in
- extreme genotypes being less fit compared to intermediate genotypes, causing extreme genotypes would become less frequent, decreasing genetic variance in fitness through disequilibrium
- Sex and recombination work to break up these associations and introduce new variation
define Selective Inference hypothesis for sex
essentially says that all forms of selection can interfere and result in changes in recombination frequencies, bringing favourable alleles forward and to higher frequency in the population and reducing unfavourable alleles.
define Quantitative Traits
for many traits, the interaction of many genes and the environment produce a pattern of continuous phenotypic trait variation
- “nature vs nuture” describes the interaction of genetics (nature) and the environment (nurture) in determining our traits
what frequency pattern do we see in quantitative traits?
when there are multiple loci contributing additively to a trait AND/OR the trait is influenced by the environment, a continuous normal distribution is seen.
3 forms of selection on quantitative traits
- directional selection - trait values on one side of the distribution are favoured by selection
- stabilizing selection - trait values around the mean are favoured even more by selection
- disruptive selection - trait values on either side of the mean are favoured by selection
what are sources of more extreme traits in organisms that tend to be found in domestication?
- new environments increase selection on certain traits revealing different phenotypes
- new allele combinations are favoured
- new ‘beneficial’ mutations arise and are favoured by selective breeding
define Breeding Value
the breeding value (of a genotype) tells you how much that individual contributes to the trait mean of its offspring
- it is not a direct measure of the phenotype of the individual
- it measures the degree to which an individuals phenotype can be expected to be transmitted to their offspring
define epistasis
a circumstance where the expression of one gene is modified (e.g., masked, inhibited or suppressed) by the expression of one or more other genes.
what determines the phenotypic value of complex traits?
Phenotype is a function of Genetics and Environment and its value is determined by how these interact to influence the trait(s)
how can we determine additive effects of alleles?
- for quantitative traits, alleles at many loci contribute to the trait values OR could have few loci but large environmental effects
- usually the identity of all loci involved is unknown
- So, must use the transmission of the trait values across generations to understand how the quantitative traits respond to selection
define Phenotypic Variance (Vp)
Vp describes the variability among a set of individuals for a particular trait (both genetically and environmentally influenced)
define Additive Genetic Variance (Va)
genetic variance due to additive effects of alleles is equivalent to the variance in breeding values
it describes the AVERAGE degree to which offspring are expected to resemble their parents
define Narrow Sense Heritability (h^2)
*Typically what’s meant by “heritability”
describes the proportion of phenotypic variance due to additive genetic variance among individuals
- equivalent to the variance in breeding values of individuals in the population
h^2 = Va/Vp
- also the extent to which we expect trait variation to be passed from parents to offspring
define Broad-Sense Heritability (H^2)
describes the proportion of phenotypic variance due to total genetic variance among individuals
H^2 = Va/Vp
important points about heritability relevance and meaning?
- estimates of heritability are only relevant to the population in which they were estimated for
- heritability estimates are for populations, not individuals
- heritability does not indicate the degree to which a trait is genetically based – it measures the proportion of phenotypic variance that is the result of additive genetic factors
estimating heritability with graphs
make a graph of parent vs offspring trait values, the best-of-fit slope is the narrow sense heritability.
- slope closer to 1 means stronger prediction of trait passed from parent to offspring
what is the Breeder’s Equation
R = h^2 S
it describes how much we expect a trait to change/respond over generations given the heritability and strength of selection on the trait.
h^2 = heritability
R = response to selection (change in trait mean from one generation to the next)
S = selection differential (strength of selection acting within 1 generation)
define Neutral locus
an locus that has no detectable effect on fitness
define Polymorphic locus
a locus that has at least two distinct alleles in a given population
with 3 isolated populations at time t with identical allele frequencies at neutral polymorphic locus, can you predict the outcome of one by knowing the outcome of another? (how the frequencies will change)
No, because each population will experience drift differently.
what are the longterm effects of drift on isolated populations?
- genetic diversity lost due to restricted gene flow in/out of the population –alleles rise to fixation while others are lost
- can expose deleterious recessive alleles as homozygotes by carrying away favoured variation.
define Gene Flow
movement of individuals from one population to another resulting in incorporation of genetic material from one place into another (i.e. migration)
how does migration change with large/small
and nearby/far populations?
- more migration occurs between nearby populations
- more migration occurs OUT of large populations into small populations
define Fst
Fst is a measure of genetic differences between populations, measured by using their heterozygosity at one or more loci.
Fst = (HT - HS)/HT
HT = expected heterozygosity of the total species population (as if at hardy-weinberg)
HS = expected heterozygosity in subpopulation w/ unique allele frequencies
if Fst = 0
there is identical allele frequencies between these populations
if Fst = 1
the two populations are fixed for different alleles.
what is the expected relationship between geographic distance and Fst values for separate populations?
genetic distance (Fst) is expected to increase as geographic distance increases between two populations
define Isolation by Distance
the pattern of increasing genetic with geographic distance.
- represents the outcome of gene flow moving and mixing alleles while genetic drift produces random divergences between the populations
- NOT expected when gene flow is very high between said populations
positive effects of gene flow
- reduces the effects of drift
- allows new alleles to arise by mutation and spread
- populations connected by gene flow may be better at responding to changing conditions
negative effects of gene flow
- when different alleles are favoured in different locations, gene flow will counteract selection contributing to lower mean fitness
- populations well suited to their environments may be negatively impacted by gene flow from populations that are adapted to different conditions
where do adaptive traits come from?
- new mutations that arise in the species or populations as they adapt
- existing variation (alleles already present) that become favoured by selection in some context
what happens to neutral novel mutations when drift occurs?
neutral mutations tend to be lost to drift because they have no selective pressure to be maintained in the population. Unless they are in linkage disequilibrium with a polymorphic allele that is being selected for.
why does context matter when it comes to adaptation and mutations?
because if the novel environment is so harsh that it requires truly novel traits, and individuals can’t escape the conditions, relevant mutations are unlikely to just appear at the right moment.
- timing and type of mutation matters. it’s best if the mutation has an immediate fitness advantage.
define Parallel Speciation and Evolution
when two independent populations of one species diverge into two separate species due to living in ecologically similar habitats, resulting in similar speciation and adaptation events to occur independently in each population
define Standing Variation
Standing genetic variation is the presence of alternative forms of an allele at a given locus in a population. While an allele may be mildly deleterious or confer no fitness advantage over other forms under one set of environmental conditions, that allele may become beneficial if the environment changes.
do adaptive traits tend to be controlled by few loci of large effect, or many of small effect?
- loci with small effects tend to have lower potential to yield large, rapid changes in a trait in response to selection
- large effect mutations, if disadvantageous, tend to be removed from the population by selection very rapidly, whereas if beneficial, will rise in frequency and have larger benefit to fitness–having the most effect on adaptive traits in the population
what are the most common type of mutations (loci)?
mutations of modest/moderate effect are the most common, since they have the most efficient impact on organismal fitness compared to very large or very small effect mutations.
what does it mean if h^2 = 0?
if h^2 = 0, it means that a trait can change within a generation but not across generations (the change isn’t heritable)
the expected mean trait value is equal to that of the original population
