A general condition for adaptive genetic polymorphism in temporally and spatially heterogeneous environments

TL;DR

This paper derives a comprehensive analytical condition for when environmental fluctuations in space and time promote the evolution and maintenance of genetic diversity in populations, unifying previous theories.

Contribution

It provides a general, explicit condition linking environmental variability and selection to genetic diversification, applicable across various ecological scenarios and genetic architectures.

Findings

Environmental fluctuations can promote genetic diversity under specific conditions.

The derived condition is robust across different genetic architectures and reproductive modes.

Simulations confirm the analytical predictions even in small populations with stochastic effects.

Abstract

Both evolution and ecology have long been concerned with the impact of variable environmental conditions on observed levels of genetic diversity within and between species. We model the evolution of a quantitative trait under selection that fluctuates in space and time, and derive an analytical condition for when these fluctuations promote genetic diversification. As ecological scenario we use a generalized island model with soft selection within patches in which we incorporate generation overlap. We allow for arbitrary fluctuations in the environment including spatio-temporal correlations and any functional form of selection on the trait. Using the concepts of invasion fitness and evolutionary branching, we derive a simple and transparent condition for the adaptive evolution and maintenance of genetic diversity. This condition relates the strength of selection within patches to expectations and variances in the environmental conditions across space and time. Our results unify, clarify, and extend a number of previous results on the evolution and maintenance of genetic variation under fluctuating selection. Individual-based simulations show that our results are independent of the details of the genetic architecture and on whether reproduction is clonal or sexual. The onset of increased genetic variance is predicted accurately also in small populations in which alleles can go extinct due to environmental stochasticity.