Gene‐flow between niches facilitates local adaptation in sexual populations

Abstract

In sexual populations, gene-flow between niches is predicted to have differential consequences on local adaptation contingent upon the nature of trade-offs underlying local adaptation. Sex retards local adaptation if antagonistic pleiotropy underlies trade-offs, but facilitates adaptation if mutation accumulation underlies trade-offs. We evaluate the effect of sex in heterogeneous environments by manipulating gene-flow between two niches in sexual and asexual populations using steady-state microcosm experiments with yeast. We find that only sex in the presence of gene-flow promotes simultaneous local adaptation to different niches, presumably as this exposes mutations neutrally accrued in alternate niches to selection. This finding aligns with work showing mutation accumulation underlies trade-offs to local adaptation in asexual microbes, and with inferences of divergence in the presence of gene-flow in natural sexual populations. This experiment shows that sex may be of benefit in heterogeneous environments, and thus helps explain why sex has been maintained more generally.

Turnover in local parasite populations temporarily favors host outcrossing over self‐fertilization during experimental evolution

“…Further, theory predicts that outcrossing may be favored in the context of frequent migration because sex can break down unfavorable genetic associations that are introduced from outside populations (Agrawal, 2009; Lenormand & Otto, 2000). An experimental evolution study in which sexual and asexual yeast populations were subjected to varying levels of migration between two different selective environments showed that only the sexual populations that experienced migration adapted to both environments (Gray & Goddard, 2012). Therefore, frequent host migration coupled with frequent environmental change may provide the most likely context for the maintenance of outcrossing, apart from host–parasite coevolution.…”

“…Recent experimental evolution studies have demonstrated that sex can be favored when populations migrate between heterogeneous environments or adapt to new environments. Gray and Goddard (2012) passaged sexual and asexual yeast populations in two different selective environments with varying levels of migration between the environments. Only the sexual populations that experienced migration exhibited simultaneous adaptation to both environments.…”

A parasitic selfish gene that affects host promiscuity

“…The data reported here suggest a VDE carrier would enjoy increased survival under these conditions. Finally, while we now have a good handle on the reasons that sex is maintained [36][37][38][39], we have less evidence for why sex evolved [18]. Selfish elements may spread through sex, and some ideas suggest that selfish elements drove the initial evolution of sex [17].…”

ObStruct: A Method to Objectively Analyse Factors Driving Population Structure Using Bayesian Ancestry Profiles

“…When individuals sampled from discrete points (such as similar geographic locations or niches) tend to be more closely related to one another than between points, this supplies evidence of population structure. Subgroups isolated by barriers to gene flow will become increasingly differentiated by the processes of mutation, selection and drift but sufficient gene flow between subgroups will serve to homogenise groups into a single population [5]–[7]. Classic population genetics methods estimate the combined effect of these processes to infer the extent of population subdivision by analysing allele frequencies within and between sampled populations, that may or may not be differentiated [8].…”