Ecological mechanisms by which phenotypic plasticity promotes and hinders ecological speciation

Background/Question/Methods

It has been argued that adaptive phenotypic plasticity can promote and hinder ecological speciation through its effects on selection and gene flow. Several conceptual models emphasizing the roles of plasticity in promoting diversification and speciation mediated by resource use have been developed. In these models, the speciation process is instigated by intense intraspecific competition inducing negative-frequency dependence, resulting in disruptive selection. When disruptive selection ensues, plasticity may allow the population to phenotypically diversify and specialize on alternative resources to alleviate competition. These models stress that it is in these early stages of speciation prior to genetic divergence that plasticity may play a critical role by facilitating fast phenotypic divergence. However, the ability to express alternative phenotypes through plasticity may, however, interfere with the early phase of the formation of reproductive barriers, especially when geographic barriers are not present. Here, we mechanistically investigate how and under what conditions plasticity can promote and hinder ecological speciation. We extended an existing stochastic individual-based model of predator-prey interactions to incorporate sexual reproduction and mate choice by assortative mating. We varied the strength of female choosiness and habitat sensitivity and assessed their effects on the occurrence of speciation events.

Results/Conclusions

At intermediate female choosiness and intermediate to high habitat sensitivity, speciation occurred frequently in the presence of plasticity, while it was rarely observed in its absence. In contrast, speciation was hindered by phenotypic plasticity at high female choosiness and no habitat sensitivity. Plasticity promoted speciation by accentuating phenotypes, resulting in higher phenotypic differentiation early on between individuals feeding in different habitats. Plasticity could also hinder speciation by providing an alternative strategy for adaptation to habitat heterogeneity. We conclude that the major role of plasticity contributing to speciation is to facilitate the evolution of a reproductive barrier through enhanced phenotypic differentiation between emerging locally adapted phenotypes.