The effects of sexual selection on trait divergence in a peripheral population with gene flow

Abstract

The unique aspects of speciation and divergence in peripheral populations have long sparked much research. Unidirectional migration, received by some peripheral populations, can hinder the evolution of distinct differences from their founding populations. Here, we explore the effects that sexual selection, long hypothesized to drive the divergence of distinct traits used in mate choice, can play in the evolution of such traits in a partially isolated peripheral population. Using population genetic continent-island models, we show that with phenotype matching, sexual selection increases the frequency of an island-specific mating trait only when female preferences are of intermediate strength. We identify regions of preference strength for which sexual selection can instead cause an island-specific trait to be lost, even when it would have otherwise been maintained at migration-selection balance. When there are instead separate preference and trait loci, we find that sexual selection can lead to low trait frequencies or trait loss when female preferences are weak to intermediate, but that sexual selection can increase trait frequencies when preferences are strong. We also show that novel preference strengths almost universally cannot increase, under either mating mechanism, precluding the evolution of premating isolation in peripheral populations at the early stages of species divergence.

Song evolution, speciation, and vocal learning in passerine birds

“…; Seddon et al. ; Servedio and Bürger ), and variation in developmental processes (Lovette et al. ; Pfennig et al.…”

“…Rates of behavioral evolution may vary among lineages due to numerous factors, including differences in the strength and mode of sexual selection (Ritchie 2007;Kraaijeveld et al 2011;Seddon et al 2013;Servedio and Bürger 2015), and variation in developmental processes (Lovette et al 2002;Pfennig et al 2010;Moczek et al 2011), such as the prevalence of phenotypic plasticity and the degree to which behaviors are learned or innate. Learned traits are socially transmitted and are therefore subject to imprecise copying with reduced effective generation times, which can quickly generate novel phenotypes, accelerate rates of phenotypic evolution, and promote population divergence (Mundinger 1980;Cavalli-Sforza and Feldman 1981;Baldwin 1986;Paenke et al 2007;Pfennig et al 2010).…”

Linking intra- and interspecific assortative mating: Consequences for asymmetric sexual isolation

“…). Although Fisherian sexual selection on single traits promotes sexual isolation and speciation in some theoretical models (Lande ; Kirkpatrick ; Prum ), Fisherian processes can under some ecological conditions instead weaken species boundaries (Servedio and Burger , ). For instance, when sexual selection is a result of open‐ended or directional mate preferences, (Ritchie ; Price ; Boughman et al.…”

“…). Thus, both some theory and empirical work suggest that sexual selection and sexual conflict can oppose sexual isolation and weaken species boundaries (Norvaisas and Kisdi ; Servedio and Burger ). The present study provides an empirical example of how male mate preferences for heterospecific females can weaken sexual isolation when two species that differ in size interact during mating and reproduction (Table ; Fig.…”

“…Moreover, some theoretical models have shown an antagonistic relationship between sexual selection and assortative mating, thereby challenging the common assumption that these processes jointly facilitate speciation (Kirkpatrick and Nuismer ; Otto et al. ; Servedio and Burger , ). For instance, strong assortative mating can generate positive frequency‐dependent selection through a mating disadvantage of rare phenotypes at the tail ends of phenotypic distributions, thereby constraining speciation (Kirkpatrick and Nuismer ; Otto et al.…”