Molecular Population Genetics: Introduction

Ewens, Warren J.

doi:10.1007/978-0-387-21822-9_9

Cited by 369 publications

(713 citation statements)

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“…Neutral variation in realized life histories affects the progress of natural selection. In a finite population selection has to be balanced against random drift that is measured by 1/n, where n is the observed population size (46). When there are neutral differences in lifetime reproduction, the effective population size is reduced by a factor approximately equal to the annual variance in lifetime reproduction, V/T, where V is variance in lifetime reproduction and T is generation time (22).…”

Section: Ymentioning

confidence: 99%

Neutral theory for life histories and individual variability in fitness components

Steiner

Tuljapurkar

2012

Proc. Natl. Acad. Sci. U.S.A.

104

168

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Individuals within populations can differ substantially in their life span and their lifetime reproductive success but such realized individual variation in fitness components need not reflect underlying heritable fitness differences visible to natural selection. Even so, biologists commonly argue that large differences in fitness components are likely adaptive, resulting from and driving evolution by natural selection. To examine this argument we use unique formulas to compute exactly the variance in life span and in lifetime reproductive success among individuals with identical (genotypic) vital rates (assuming a common genotype for all individuals). Such individuals have identical fitness but vary substantially in their realized individual fitness components. We show by example that our computed variances and corresponding simulated distribution of fitness components match those observed in real populations. Of course, (genotypic) vital rates in real populations are expected to differ by small but evolutionarily important amounts among genotypes, but we show that such differences only modestly increase variances in fitness components. We conclude that observed differences in fitness components may likely be evolutionarily neutral, at least to the extent that they are indistinguishable from distributions generated by neutral processes. Important consequences of large neutral variation are the following: Heritabilities for fitness components are likely to be small (which is in fact the case), small selective differences in life histories will be hard to measure, and the effects of random drift will be amplified in natural populations by the large variances among individuals.L ongitudinal studies of humans and other species show that individuals within a population often differ greatly in age at death and lifetime reproduction (1-4). For example, the SD of human age at death was ∼40% of life expectancy (∼35 y) in the early 1800s and ∼20% in the late 1900s even with a much higher life expectancy (∼70 y) (3). Lifetime reproduction of human females in high-fertility societies had a SD-to-mean ratio [coefficient of variation (CV)] of ∼0.5-1, and there was much greater variability in male lifetime reproduction (5, 6). Such variation obviously leads us to ask, Do the longest-lived individuals (or the most prolific reproducers) differ from other individuals because of heritable genetic differences? Many researchers assume the answer is "yes" (7-10), because both age at death and lifetime reproduction should be related to fitness (although they are not fitness, which is a property of genotypes as we discuss below) (Box 1). However, the desired genetic variation need not exist. For example, populations of genetically identical nematodes in the laboratory display substantial variation in age at death with CV ∼ 0.2. This variation is clearly not due to genetic differences, but is generated by stochastic variation during development (11). In this and other examples, individual fates are shaped by a sequence of stochastic ev...

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Section: Ymentioning

confidence: 99%

Neutral theory for life histories and individual variability in fitness components

Steiner

Tuljapurkar

2012

Proc. Natl. Acad. Sci. U.S.A.

104

168

View full text Add to dashboard Cite

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“…The other extreme w → 0 is called the weak selection limit; in this case, all strategies have almost the same effective payoff and the dynamics is dominated by neutral drift. We study the Moran process (46,47), where in each generation an individual is randomly picked to change strategy (die), and another individual is picked proportional to effective payoff to be imitated (reproduce). With probability u, a mutation occurs and instead a random strategy is chosen.…”

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confidence: 99%

Evolution of fairness in the one-shot anonymous Ultimatum Game

Rand

Tarnita

Ohtsuki

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

195

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Classical economic models assume that people are fully rational and selfish, while experiments often point to different conclusions. A canonical example is the Ultimatum Game: one player proposes a division of a sum of money between herself and a second player, who either accepts or rejects. Based on rational self-interest, responders should accept any nonzero offer and proposers should offer the smallest possible amount. Traditional, deterministic models of evolutionary game theory agree: in the one-shot anonymous Ultimatum Game, natural selection favors low offers and demands. Experiments instead show a preference for fairness: often responders reject low offers and proposers make higher offers than needed to avoid rejection. Here we show that using stochastic evolutionary game theory, where agents make mistakes when judging the payoffs and strategies of others, natural selection favors fairness. Across a range of parameters, the average strategy matches the observed behavior: proposers offer between 30% and 50%, and responders demand between 25% and 40%. Rejecting low offers increases relative payoff in pairwise competition between two strategies and is favored when selection is sufficiently weak. Offering more than you demand increases payoff when many strategies are present simultaneously and is favored when mutation is sufficiently high. We also perform a behavioral experiment and find empirical support for these theoretical findings: uncertainty about the success of others is associated with higher demands and offers; and inconsistency in the behavior of others is associated with higher offers but not predictive of demands. In an uncertain world, fairness finishes first.cooperation | prosociality | stochastic dynamics

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“…The fixation probability, Φ A ðyÞ of strategy A with initial frequency p A j t ¼ 0 ¼ y, satisfies the following backward Kolmogorov equation (Ewens, 2004): 2.6. The condition b=c 4 k=AðA ¼ 1 þ kp=ð1 À pÞÞ Consider a two-strategy game between cooperator C and defector D, with the following payoff matrix:…”

Section: Updating An a Playermentioning

confidence: 99%