Evolutionary Ecology

What are challenges for studying senescence?

1. Data can be hard to get, sample sizes are smaller in older age classes 2. Natural selection acts on a cohort of individuals as they age (poor quality individuals will be removed from the cohort as they age)

What is selection?

A statistical association between variation among individuals in a trait and variation in fitness Selection is a quality of the population (an ecological process that acts on a population)

Examples of differences in which natural selection can act on

Body size, coloration, metabolic rates, body proportions, maturation schedules

Aphasia

Deficit in language comprehension and/or production Damage to the left Broca's area

QLT analysis of coat color in mice

Genetic architecture of pigmentation in a cross between beach and mainland species QLT mapping within full-sibling crosses identifies 2 major regions of the genome associated with phenotypic variation 1) agouti 2) melanocyte-stimulating hormone receptor Some beach populations had non-functional Mc1r receptor Agouti gene expression variation explains light fur colors at all locations mRNA isoform from Exon 1C associated with light coat colour in two different mice species

Mechanisms of reproductive isolation

Genetic drift in small populations Ecological differences among habitats Assortative mating in habitat Female preference for particular value of male trait

Is non-linear selection always stabilizing?

No, stabilizing selection implies an optimal intermediate phenotype

Disposable soma hypothesis

The evolution of separate germ line and soma is occasional somatic death Trade-off between reproduction and somatic maintenance Selection favours the evolution of separate germ line and soma cells Aging results from unrepaired damage to cellular machinery

Target of selection

The trait that is specifically responsible for fitness differences (i.e. survival or not)

Genetic variance

Vg = Va + Vd + Vi (genetic variance is made up of additive + dominance variance + interaction variance)

Father-offspring regression and mother-offspring regression

When father's contribute only sperm (i.e. sperm) and nothing else, we can perform a father-offspring regression of phenotypes Comparing the F-O regression to the mother-offspring regression can reveal maternal effect contributions on offspring phenotype This works for most plants, arthropods, and reptiles where fathers contribute little beyond sperm Will not work if father contributes more than genes

Complete analysis involves three different causal relationships

1. A selection analysis 2 and 3. A performance analysis 1 and 2 are often performed as separate analyses, usually involving different individuals because 1 often involves data from individuals in the field and 2 involves data from different individuals under control conditions Step 3 is often not possible because we rarely have performance information about individuals that we then can relate to fitness under natural conditions, making this kind of quantitative analysis impossible

Female prezygotic isolation hypothesis

1. Established populations: elaborate male courtship displays and choosy females 2. Founder effect when colonizes: low population density --> selection for floozy females --> male courtship dance loses elements, diverges from ancestral 3. Choosy females (ancestral population) refuse males from derived population. But floozy females mate with ancestral males

Two ways to estimate linear selection

1. Estimate S as the slope of a linear regression 2. Compare mean phenotypes between samples taken before and after (S= mean(after) - mean(before))

Two evolutionary hypotheses for why we lose physiological capacity with age

1. Mutation accumulation: mutations occur in soma cells at a steady rate over our lives. A non-lethal mutation may still limit our physiological capacity making us susceptible to being selected against. So, early life mutations are more likely to be removed than late life mutations from a population as selection weakens with age. 2. Antagonistic pleiotropy: pleiotropy is when a single gene has multiple phenotypic effects. Perhaps there are some genes that have good effects early in life and so selection (which is stronger early in life) favors them. But these early in life 'good' genes have 'bad' effects latter in life. Those latter bad effects aren't removed because selection weakens with age. For both hypotheses, age-dependent selection is the ultimate cause of 'aging' by allowing mutations with bad somatic effects to persist in a population. These two hypotheses are not mutually exclusive - both can contribute to aging in a population

How to distinguish direct vs indirect selection

1. Use the statistical method of multiple linear regression to isolate the effect of each variable while holding other variables constant (the selection gradient analysis) 2. Perform manipulative experiments where you keep other traits constant

Criteria of a trait being an adaptation (4) and a 5th that is disagreed about

1. evolving/recently evolved under natural selection 2. has a function that influences performance at some ecological task 3. performance affects fitness 4. heritable variation exists for the trait in the population 5. current vs. original function and selection

What is a population?

A group of organisms of the same species occupying a particular space at a particular time

Haldanes

A measure of the change in mean value of a trait in a population per generation Higher values indicate more rapid change in the trait per generation

Maternal effects

A particular type of phenotypic plasticity Parents (mothers in particular) can have a large influence on the early environment experienced by their offspring Defined as maternal contributions to offspring phenotypes beyond their direct genetic contribution This is a cross-generational form of phenotypic plasticity Contributes to non-genetic resemblance between parents and offspring

What determines how quickly we age?

A trait that affects whether you live or die before you reproduce has a huge effect on life time fitness Any trait that enhances survival to maturation and reproduction will be strongly favoured by selection

Examples of consequences of variation to individual performance

Acquiring energy or finding food, finding mates, avoiding predators, refuging, migrating, social skills

Allopatric speciation Parapatric speciation Sympatric speciation

Allopatric Different places Could be due to geological barrier (vicariance), or the founder effect (m=0) Parapatric Connected (0 < m < 0.5) Sympatric Same place (m=0.5)

Parent-offspring regression

Allows parents to breed Mean of the two parents' phenotypes is the midparent value Mean of all offspring is the offspring value Regress offspring values on midparent values The slope estimates heritability

What do positive maternal effects do in terms of evolution?

Amplify evolutionary responses per generation The rate of trait evolution increases Works in two ways: changes the parent-offspring resemblance - for positive maternal effects, increases rate of selection The effect of increasing or decreasing the resemblance of parents and offspring is to sharpen or soften respectively the ability of selection to distinguish phenotypic differences among individuals in the population

What is performance analysis?

An approach that tests the functional utility of traits in the context of the presumed source of selection Measure aspect ratio (the target trait) on many of the population Then evaluating whether variation in the trait affects function

Sodium amytal test

Barbiturate anesthetic (depressant) on GABA receptors Injected into either left or right carotid Try to silence one whole hemisphere If the left hemisphere is frozen: entirely mute for a few minutes, when they do start to talk they show really big speech impairment, and will not remember common series of words When you freeze right hemisphere there is little effect on the speech

Broad sense and narrow sense heritability

Broad sense = proportion of total phenotypic variation that is due to all sources of genetic variation H2 = Vg / Vp Narrow sense - proportion of total phenotypic variation that is due to all sources of genetic variation h2 = Va / Vp

Gene flow

Can bring alleles to new locations -may increase or decrease fitness Gene flow means immigration and successful breeding with other fur colour ecotype

What is a fitness landscape?

Combinations of traits to visualize a fitness Its appearance depends on the functional relationships between the traits and the effects of that relationship on fitness

Two classes of traits that can be targets of selection

Continuous - spectrum of intermediate values between its limits) Discrete - an absence of intermediate values Continuous traits are thought to be affected by many gene loci: polygenic Discrete are affected by only a few or even a single loci

Apraxia

Difficulty with the motor planning to perform tasks and movements when asked -the inability to correctly carry out learned purposeful movements Due to left brain dain damage Speech apraxia: children think they are talking but it is mostly gibberish

Phenotypic variance

Dispersion of measurable trait resulting from an interaction between its genotype and its environment i.e. what selection acts on Vp = Vg+ Ve

Reaction norms

Each line on the graph represents a different genotype Genetic correlation between each trait assuming a high heritability If reaction norms do not cross then genetic correlation is positive Can be linear, curvilinear, or even discontinuous Can measure individuals, genotypes, families, members of whole populations

Two ways to measure non-linear selection, C on a trait

Estimate a non-linear fitness function Using a before vs. after comparison of variance in phenotype to estimate a difference values

What is correlational selection?

Form of selection that results in two traits changing in a functional way with each other E.g. in snakes, they have patterns relating their skin colouration to their escape behaviors when they flee a predator The simple multiple regression model that we have used to study selection can be extended to include a test for correlational selection (done by including an interaction term that estimates how much of the effect of one trait on fitness (colour) depends on the phenotype of the second trait (behavior))

Male mollies and tail swords

Functional sword tail hypothesis: preference is based on male sword length itself and not on some other characteristic of the male that is related to sword length Female preference hypothesis: prefer males with longer tail swords (regardless of the absolute length of the tail sword, given a choice between males of different lengths, female will prefer a longer male) We can evaluate both of these issues with a single manipulation: artificially increasing or decreasing the sword length in a sample of males, and then measure female preference The functional sword hypothesis was supported, as was the female preference hypothesis Not yet complete evidence to allow us to claim one hypothesis or another

Antagonistic pleiotropy

Genes with beneficial effects early on have deleterious effects later E.g. an allele that favors calcium build up in the bones of juveniles could be strongly favoured for its affect on juvenile performance and survival even should that same allele cause calcium to build up in arteries over a life time and so reduce performance in adults

Sources of trait variation in a population

Genetic Va = additive (summed effects of all loci) Vd = dominance (interactions between alleles within a locus) Vi = epistatic (interactions among loci) Environmental Ve = environment of individual Vm = among families Vp = phenotypic Vp = Va + Vd + Vi + Vm + Ve

Additive genetic variance

Genetic variance associated with the average effects of substituting one allele for another

Quantitative traits

Height, weight, bill depth Traditionally thought of as being made up of an infinite number of loci all having a small effect Genetic variance associated with the average effects of substituting one allele for another

How are heritability and inheritance different?

Heritability is not the process that passes DNA from a parent to an offspring; that process reflects inheritance, which is a property of individuals (across generations) Heritability is not the relationship between an individual genotype and its phenotype; that relationship is an individual is genetic determinism through development Individuals of different genotypes cause variation in genotypes in a population Heritability is a statistic about the average correspondence between parents and offspring in that population (it is a population statistic)

What limits selection?

If there is not much variation among individuals, then there is not much opportunity for selection As the variance (range) in fitness w gets smaller, this causes the slope of the line (B1) to tend to 0

Polygenic trait

Influenced by many genetic loci Interaction between alleles is epistasis Interaction with environment is phenotypic plasticity

Model of sympatric speciation by sexual selection only

Initial ecological divergence is unnecessary Sensory bias or genetic drift variation in preference Fisher runaway processes

Conclusions: Guppy adaptation

Introduction experiment more powerful way to test hypotheses about natural selection than correlation approach Experimental response to selection had to be assessed in a common garden experiment in the lab Differences persist in the lab for two generations therefore genetic basis not plastic response in response to detection of a predator Conclusions are that environmental transplant experiments can be valuable in estimating the speed at which local adaptation can take place Multiple generation culturing of different populations of guppies in common lab environment especially helpful

How strong is natural selection?

It appears that selection on most traits in natural populations is relatively weak (and often not even statistically significant) Most traits are relatively weakly selected or are only rarely under strong selection

Factors that will cause the evolution of slow aging rate

Low adult mortality (high survival) Increased fecundity with age (many species have better eggs and more eggs as they get older, which increases lifetime reproductive success) Delayed reproduction (favours genotypes that live long enough to mature)

Qst

Measures degree of genetic divergence among populations for quantitative traits predicted to be under selection (requires data from common garden experiment)

Fst

Measures the degree of diverge among populations for neutral loci (effects due to drift and migration)

Character displacement hypothesis

Morphologically similar species have evolved to become more different Two species should be more different where they occur sympatrically than when they occur allopatrically If the mean value for the character for each species differs more in sympatry than allopatry then there is evidence that coevolution has made those populations more different

What mechanisms drive phenotypic change in a population over generations?

Natural and section selection (genetic change in a population over generations) Drift (chance effects on fitness: genetic change in populations over generations) Non genetic changes: cultural evolution, multi-generational maternal effects, plastic phenotypic responses to changing local environment

What would a slope of B1=0 indicate?

No selection on the trait A large value would be stronger selection for larger Z A small value would be stronger selection for smaller Z

Is every trait evolving under natural selection?

No! Selection thinking only provides a basis for asking questions If the data doesn't support the selection hypothesis, maybe the feature is not an adaption Then it's a new hypothesis, maybe the trait is a by-product of previous evolution or selection on another correlated trait, or maybe it's a maladaptation

Is selection always linear?

No! Selection may favour intermediate values (stabilizing selection) or extreme values (disruptive selection) These are both non-linear fitness functions, with more complex versions of selection differentials

What is selection thinking?

Observing a trait, could be anything: a molecule, an aspect of physiology, behavior, morphology, history, any of these is a trait Then hypothesize that the trait may have evolved in the population due to natural selection acting on it for some function that could have enhanced fitness There are three things here, each causally affecting the next: Trait X --> affects ecological performance Y --> individual fitness Z

Qst and Fst

On average, drift and migration will act on all neutral loci in a population (Fst), but selection will only act on specific quantitative loci that influence fitness (Qst) When traits are genetically diverging likely due to drift: Qst have roughly same value as Fst When traits are adaptively diverging likely due to selection: Qst larger than Fst When traits are adaptively converging due to the same pattern of selection: Smaller Qst than Fst

Selection occurs when...

Only some individuals are likely to survive or reproduce

What causes varied traits in individuals within a population

Ontogeny (development), rearing environment (good vs poor conditions), and genetic differences

Infintesimal model

Phenotypic traits are made up of many genes, each with a small effect All under relatively weak but continuous selection, so that not too much genetic variation is lost due to selection Whatever variation is lost is replaced by new mutations

Environmental variance

Phenotypic variation caused by the environment

Fisher runaway hypothesis

Positive feedback Trait preferred is arbitrary Females choose males with trait Females with preference have offspring carrying male trait allele and preference allele Selection for increased male trait, favours stronger female preference

Examples of isolating mechanisms

Premating: temporal or habitat selection, behavioural isolation, copulation mechanically impossible Prezygotic but post mating: gametes incompatible, no egg released by female Postzygotic: zygote dies, F1 hybrid inviable or sterile, F2 generation inviable or sterile

Senescence

Process of aging Senescence is the decline in physiological capacity with age Has high evolutionary potential because it may affect individual fitness As we age, our reproductive success declines and also our ability to survive likely declines because of reduced physical ability, mental ability, etc. For most organisms, reproductive potential and survival tend to increase with time early in life, after a certain age individual reproduction and survival begin to decline with age Senescence is not a target of selection, it evolves as a by-product of selection acting on energy allocation between germ line and soma Selection on all traits (including energy allocation) declines with age

Darwins

Proportional rate of change in trait per unit time Measured as the difference in log mean trait value at the beginning and end of a time interval measured in million years

Response to selection

R = Sh2 S= selection imposed on the population H2 = heritability of trait

Laboratory common environment experiment for guppies

Randomly sampled wild guppies (females store sperm from multiple males) from high and low predation sites Offspring from each wild female reared in a constant environment in the laboratory Second generation lab offspring are produced by mating these lab offspring to those from the first generation litters of other mothers Females in high predation environments have smaller offspring but produce litters more often than females in low predation environments Second and third litters of female descendants from north slope continued to show a difference between high and low predation sites but females descendents from South slope did not Suggests that the difference seen in first litter had been due to an environmental effect on mothers

Dichotic listening test for lateralization of language

Recall as many as possible of 6 digits simultaneously spoken to the two ears, 3 in each ears Greater recall of digits spoken to dominant hemisphere (depends on if you are right or left hemisphere dominant)

Adaptation

Results when selection that operates in a generation causes the frequencies of alleles that influence phenotypic variation in a population to change between generations

What is the selection differential?

S = Xs - Xp Where Xp is the trait mean in the population before selection and Xs is the trait mean after selection i = s/square root of vp Where square route of vp is the standard deviation of the phenotypic variance in the trait

Breeders equation

S= xs - Xp1 Can use breeder's equation to predict response if you know 1) heritability 2) selection differential How much the population changes depends on 1) heritability 2) selection differential

What is a selection gradient

Selection acting on many possible correlated traits

Guppies in the Aripo River

Sexually dimorphic: male is smaller than female and more brightly coloured Males try to mate before they are eaten which is in itself an indirect consequence of risk Pools above waterfalls had few predators except killifish which only prey on juvenile guppies In low-risk sites there are more sneaker males, as a result, females in low risk sites may experience one unsolicited mating attempt per minute which may prevent them foraging This means there should be strong selection to begin reproducing at a small size

Snail umbilicus

Some snails carry their eggs in their umbilicus Selection hypothesis: coiling the shell to develop an umbilicus is an adaptation to provide a brooding chamber to protect eggs Spandrel hypothesis: the gap is a byproduct of part of the coiling which which evolved for some other reason Selection hypothesis predicts that coiling and brood chambering should evolve simultaneously Spandrel hypothesis predicts that coiling should evolve before brood chambering Phylogenetic data indicates that coiling evolved before brood chambers, suggesting that the umbilicus initially evolved as a spandrel

Spandrels example

Spandrels are triangular feature between arches, so they are a trait of every building made with arches, but are they functional? Do they exist because they are provide functional performance? No, pairs of arches simply cannot be created without spandrels between them Spandrels are a metaphor for traits in organisms that did not evolve directly under natural selection for some performance function Many traits start out as byproducts of other traits (spandrels), may by chance later become functional or useful to an organism

Incidence of right-hemisphere language dominance

Strong right handers: 4% Ambidextrous individuals: 15% Strong left-handers: 27% Handedness and language dominance show a weak association

Quantitative genetics

Study of the genetic mechanisms of continuous phenotypic traits Influenced by many loci each with a small effect Experience both genetic and environmental variation Continuously varying traits in a population

Fitness

Survival and reproduction Measurable and influences how many offspring each individual contributes to the next generation Number of individuals is a good way to estimate fitness, but its hard to measure sometimes

Phenotypic Plasticity

The capacity of a single genotype to produce different phenotypes depending on local environment Plasticity in a population may depend on the environments over which plasticity is tested Not all phenotypic changes over time in a population represent evolutionary responses - could reflect plastic responses by individuals to a change in the environment Heritability of traits that are plastic can change between environments Genetic variation in plasticity of any trait means that plasticity of the trait could also evolve, so is subject to all the same kinds of evolutionary ecological questions that we may ask

Source of selection

The ecological or environmental factor that affects some individuals more than others and so could cause natural selection

What are agents of selection?

The ecological or environmental factor that causes selection E.g. predators, seed hardness We can test the hypothetical cause of selection by testing the prediction that variation in the agent of selection should differentially affect survival and reproduction of individuals in the population Can do this through observational or experimental studies

Oligogenic model

The genetic architecture of quantitative traits involves many loci of small effects and a few loci or large genetic effect (on phenotype) A more dynamically changing form of selection (that replaces mutation as the way that genetic variation is maintained in a population)

Heritability

The proportion of phenotypic variation in a quantitative trait (e.g. height, weight) that is inherited 0<h2<1 Importance of differences in 'genetic effects' to differences among individuals in a population

Selection differentials

The slope of the relationship is an estimate of the selection differential acting on the time the data was taken in the population A linear relationship between a trait and fitness in a population The slope of the fitness function is the selection differential Selection acts through differences in fitness among the individuals within a specific population Note: thought of as the total selection acting on a trait (direct selection on Z and indirect selection on Z)

What is an adaptation?

There are many versions of adaptation 1. Physiological adaptation - individual organisms frequently physiologically adapt to their local environmental conditions (e.g. by sweating to cool down) 2. Adaptation - natural selection causes genetic change over generations in a population in some trait that functionally influences the fitness of individuals (acts on populations 3. The outcome of process in 2, resulting in all individuals in a population having some sort of adaptive feature for their particular local environment First one is physiological, last two are evolutionary

Correlated response to selection

Trait is selected and trait y is not selected Direct response by x Rx = ix H2x Vpx Correlated response by y: Rcy = Ix Hx Hy Rg Vpy (where Hx is SQRT of H2x)

Linkage disequalibirum

Two genetic loci: one locus controls nuptial colour in males and the other controls female preference for male colour When a male with (RR--) mates with a female that stronger prefers red males (--PP) then their offspring will have genotype RRPP

Parasitoids

Typically only parasitize a single species Their baby larva must overcome the immune system of its host Typically the larva eats host's organs in order as the must be kept alive until the parasitoid pupates

Direct vs indirect selection

Under direct selection, selection acts on a trait because variation in the trait directly affects fitness through some effect on organismal function and performance E.g. of indirect selection: individuals with long arms often have longer legs as well, if selection favours longer legs, then it will also indirectly favour longer arms in the population

Cross fostering

Used when fathers contribute more than just genes Eggs are switched among nests soon after laying, so that some/all eggs are reared by animals that are not the true genetic parents The offspring phenotypes will be measured and then regressed two different ways: against the fostered parents vs. against their genetic parents This would only eliminate post-hatch parental effects on young, it does not eliminate what the mom provided to her egg

Variance

Useful tool because it represents the sum total of all effects: genetic, environmental, etc. on phenotypic variance in a population

Natural selection

Variation in some trait occurs in all individuals Variation in the trait among different individuals influences fitness through an effect on the ability to perform some ecological relevant task Trait --> performance --> survival or reproduction Evolution by natural selection: trait values tend to be passed from parent to offspring (note, this is not natural selection, but evolutionary response to natural selection)

Common Garden studies

Vp = Vg + Ve If we eliminate environmental variation by raising everything in the same environment, then Ve = 0 Then differences among individuals only reflect genetic variation Vp = Vg Often the 1st generation is affected by maternal effects, upwards to 3-4 generations (i.e. great-great grandmother may be able to manipulate great-great granddaughter's phenotype in some organisms)

Natural selection for coloration in oldfield deer mice

Why is blond fur adaptive in beach mice? Why is dark fur adaptive in mainland mice? The majority of predators are sight and sound hunters. Therefore, if a mouse blends into its environment it may have a better chance of survival. Brown mice were attacked more on light coloured substrate, white mice were attacked more in the old field habitat

How do mothers appear to help daughters have higher fecundity?

Women whose own mother was alive had greater fecundity and life time reproductive success compared to woman whose own mother was dead Women whose own mother was alive had their first child earlier than women whose own mother had died Women whose own mother was geographically near had more children than women whose own mother had moved away

Can sexual selection lead to speciation?

Yes E.g. female cichlid typically have two absorption peaks in the red-yellow and in the blue regions of the visible light spectrum Females show less discrimination in cloudy water Interbreeding between two species is reduced over time as degree of assortive mating increases

Narrow sense heritability

h2 = Va/Vp or h2 = Va/Va + Vd + Vi + Ve

Multivariate selection analysis

w = B0 + B1z1 + B2z2 These B's evaluate the direct effect of the trait on fitness while accounting for the effects of other traits

Fitness function

w= B0 + B1z

Lande's breeders equation for multiple traits

z= G S/P z= GB