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Evolution of interacting phenotypes Interacting phenotypes occur whenever „[...] interactions among individuals help determine the phenotype“ (Moore et al. 1997) Interacting phenotypes: theory Social environment Focal individual ψ IGE IEE Ψ: interaction coefficient IGE: indirect genetic effect IEE: indirect environmental effect 1 Interacting phenotypes: theory Derivation of variance components a) Traditional phenotype Random (stochastic) environmental deviation zi = ai + ei „Take the covariance“ for trait i zi = ai + ei Cov(ai,zi)=cov(breeding value, phenotype) cov(ai , zi )= cov(ai , ai + ei ) = ai + ai ei 2 0 e Additive genetic variance Genotype X environment covariance Interacting phenotypes: theory Derivation of variance components a) Traditional phenotype VP ,i = Gii + cov(a, e) Positive genotype x environment covariance (breeding value and environmental value for the trait point in same direction) → More than the additive genetic component in the phenotypic variance is exposed to selection. Heritability estimates inflated Negative genotype x environment covariance → Less than the additive genetic component in the phenotypic variance is exposed to selection. Heritability estimates deflated 2 Interacting phenotypes: theory Derivation of variance components a) Interacting phenotype (exemplified by maternal effect) Non-random maternal environmental deviation zi = ai + ei generation „Adaptations involving maternal effects are different from „normal“ traits in that the genes underlying their expression are contained within the maternal generation while the phenotypic variation on which natrual selection may act is expressed by the offspring“ (Mousseau and Fox, 1998) t-1 eo(t)=mzp(t-1) P r t O ao,t m: maternal effect coefficient zo (t ) = ao (t ) + eo ( t ) → eo ( t ) = mz p ( t −1) z p ( t −1) = a p ( t −1) + e p ( t −1) zo ( t ) = ao ( t ) + m(a p ( t −1) + e p (t −1) ) = e 0 = ao + rma p + me p Interacting phenotypes: theory Derivation of variance components a) Interacting phenotype (exemplified by maternal effect) „Take the covariance“ for trait i Cov(ai,zi)=cov(breeding value, phenotype) Let‘s assume no genotype X environment covariance cov(ao + rma p , ao + ma p ) = = ao + (1 + r )ao ma p + rm 2 a p 2 2 = Goo + (1 + r )mGop + rm 2G pp Direct Genetic Effect (DGE) Variance Direct-indirect covariance Indirect Genetic Effect (IGE) Variance Kirkpatrick and Lande 1989; Cheverud and Moore (1994) 3 Interacting phenotypes: theory Effects of maternal effects on expressed genetic variance and evolutionary change 1. Increased (or decreased) expressed total genetic variance (depending on sign of m) 2. After selection, the environment provided by the parent still reflects the selection in previous generation → environmental effect on phenotype of offspring of current generation (timelag) [ ] Δzo = Goo + (1 + r )mGop + rm 2G pp β o m is the „maternal effect coefficient“ determining the sign and strength of effect of a maternal phenotype on the offspring phenotype (independent of genetically inherited influences). In general interacting phenotype theory, ψ is the „interaction coefficient“ determining the strength of effects of the social environment of phenotypic expression of a focal individual. Evolutionary consequence of maternal effects (directional selection on offspring body size with a positive effect of maternal environment on growth) β=0.2 β=0.0 Maternal effect Traditional trait (R=h2S) Kirkpatrick and Lande, 1989 4 Interacting phenotypes: experiments Adaptive maternal effect Gryllus pennsylvanicus Hogna helluo Storm & Lima, 2010 If induced by the environment, maternal effects constitute a form of transgenerational phenotypic plasticity. If the phenotypic effect on the induced maternal effect in the offspring enhances offspring fitness, it is an adaptive maternal effect. The effect of female cricket (Gryllus pennsylvanicus) exposure to odours of a predator (wolf spider; Hognal helluo) on offspring antipredator behaviour and survival under threat of predation is a recent example. However, the maternal effect itself can be heritable, generating IGE‘s Interacting phenotypes: experiments Adaptive maternal effect Passer domestiduc (Haussperling) In many bird species, females deposit androgens into the eggs. Studies on different species showed that the quantity of transferred hormones is partly induced by social and environmental factors during egg production (e.g., coloniality, food availability) Partecke & Schwabl, 2008 5 Interacting phenotypes: experiments Adaptive maternal effect Ficedula albicollis (Halsbandschnäpper) But it has recently also been shown that the amount of androgens females deposit in the eggs has a heritable components. Thus, the offspring phenotype affected by the maternal androgens are partly determined by IGE‘s. Tschirren et al., 2010 Conservation Genetics 6 Conservation Genetics Central Questions 1. What is the unit of group to be conserved (what is an ESU (an „evolutionarily significant unit“)? The population, subspecies, or species? When are two groups genetically distinct enough to warant protection of each? 2. How do genetic factors, especially random genetic drift, inbreeding depression, and mutation, directly affect current population viability and extinction risk? 3. How much genetic variation is available in endangered and threatened species for adaptation to future environmental change? 4. What are the targets of selection humans (as agents of selection) affect most? How strong is selection exerted by humans? An what are the prospects that the target of selection can adapt to the human-induced selection? Conservation Genetics Defining ESU‘s Although controversial, the following criteria are central to defining ESU‘s: 1. Current geographic separation 2. Neutral genetic differentiation among ESU‘s caused by past restriction of gene flow 3. Locally adapted phenotypic traits caused by differences in selection 7 Conservation Genetics Extinction Risk Local Adaptation Judgement of Extinction risk versus local adaptation of ESU‘s is critical to regulate human intervention. There are genetic and ecological factors affecting both extinction risk and the scope for local adaptation. From previous chapters we know that adaptation is more likely in large populations with large additive genetic variance. Small populations tend to harbour less genetic variance due to inbreeding and drift. Genetic factors affecting extinction risk Inbreeding and small effective population size Inbreeding 8 Genetic factors affecting extinction risk Inbreeding and small effective population size Effective population size N=12, Ne=12: 16 Populations constructed from unrelated individuals N=12, Ne=3: 16 Populations constructed from three fullsibling families Conservation Genetics Va, Ne, Na, S Va, Ne, Na, S Va, Ne, Na, S Va, Ne, Na, S Va, Ne, Na, S Gene flow 9 Genetic factors affecting extinction risk Inbreeding and small effective population size Genetic rescue in adders (Vipera berus) To protect isolated populations on the verge of extinction, gene-flow may be artificially managed by introducing individuals from large populations with substantial genetic variation. However, if populations differ not only due to drift, but due to local adaptation, such introduction may be counterproductive leading to outbreeding depression. If local adaptation is important, introduction represents gene-flow of less fit genotypes for the local ecological conditions. Resistance to Pesticides and Antibiotics 10 Conservation genetics Concluding remarks • Humans alter evolutionary dynamics of many species by affecting gene flow, acting as selective agent and by subdividing populations • Conservation biology has the difficult task of maximizing the „longevity“ of ESU‘s given these impacts • For feasibility, past research mostly relied on neutral genetic markers in an attempt to estimate extinction risk, heritability, population differentiation (Fst) and gene-flow. But the correlations with the corresponding direct estimates are weak (not surprisingly) • Evolutionary change depends on an interaction between strength of selection and the amount of additive variance in a population. The stronger the selection from human activity, the larger the variance required to allow a population to adapt. Often, there is little knowledge of heritable variation in populations at risk of extinction General conclusions • Most phenotypes are continuous, and have a multigenetic basis • Mendelian inheritance translates quite easily to continuous variation • Two covariances are in the center of the theory of phenotypic evolution: the covariance of phenotype and genotype (inheritance), and the covariance of fitness and phenotype (selection) • Both covariances need to be studied experimentally to understand the evolution of a system • The covariances can have a complex biological basis, including direct genetic, plastic, environmental and indirect genetic effects • Because in conservation biology, we try to „manage“ evolutionary processes, quantitative genetics is required when attempting to predict likelihood of adaptation versus extinction 11