The roles of plasticity versus dominance in maintaining polymorphism in mating strategies

Sylvain Moulherat,Fabien Aubret,Alexis Chaine,Barry Sinervo,Jean Clobert,Alain Mangin

doi:10.1038/s41598-017-15078-1

Abstract

Although natural selection is expected to reduce variability, polymorphism is common in nature even under strong selective regimes. Discrete polymorphisms in mating strategies are widespread and offer a good opportunity to understand the genetic processes that allow the maintenance of polymorphism in relatively simple systems. Here we explored the genetic mechanism underlying the expression of discrete mating strategies in the rock-paper-scissors (RPS) game. Heterozygotes carry the genetic information for two different strategies, yet little attention has been devoted to the mechanisms underpinning heterozygote phenotype and its consequences for allele frequency dynamics. We explored the maintenance of polymorphism under 1) genetic dominance or 2) plasticity, as mechanisms driving the expression of alternative strategies in males. We developed an alternative mating strategy model and analysed allele frequency dynamics using time series analyses. Our results show that both genetic mechanisms can maintain polymorphism depending on population demographic characteristics but that plasticity can enhance the likelihood that polymorphism is maintained relative to dominance. Time series analysis on simulation outcomes show that the RPS game is mostly driven by a single strategy, but the importance of this strategy on long term dynamics is stronger when gene expression shows dominance rather than plasticity.

Highlights

Evolutionary mechanisms such as natural selection and genetic drift are expected to reduce genetic variation within populations
The first goal of this study is to explore how different genetic mechanisms leading to the expression of alternative reproductive strategies and demographic stochasticity could influence the maintenance of trimorphism in RPS games under a range of initial conditions concerning species lifespan and allele frequencies
Simulations with populations initially composed by individuals presenting only two of the three alleles leads to the fixation of the strongest strategy in the RPS game (i.e. P wins against M, M wins against S, and S wins against P)

Summary

Introduction

Evolutionary mechanisms such as natural selection and genetic drift are expected to reduce genetic variation within populations. This genetic information could be antagonistic and reduce a heterozygote’s performance compared to homozygotes Such a cost would have an important impact the stability of the RPS game[7] especially since a low cost to heterozygotes could induce a strong allele frequency disequilibrium which could explain why plasticity in alternative mating strategies has rarely been documented in nature to date. The individual-based-model allows us to simulate the effects of individual genetic information (i.e. are individuals homozygotes or heterozygotes for the gene coding reproductive strategy?), social environment and demographic stochasticity on the maintenance of alternative reproductive strategies In this framework, we explore the maintenance of polymorphism under two hypotheses on the mechanisms leading to individual phenotype:. Past diploid models explicitly ignored over-dominance and only considered co-dominance or dominance[8,24,34]

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Conclusion