Phenotypic plasticity can promote sympatric speciation

Background/Question/Methods

Allopatric speciation has traditionally been viewed as the most likely mechanism for the development of reproductive isolation, hence speciation. Recent studies advocate that ecological speciation (speciation by ecologically based divergent selection) in sympatry is also a plausible mechanism contributing to speciation. Phenotypic plasticity has been suggested as a factor that can facilitate ecological speciation, but the efficacy of plasticity in promoting speciation is debated in literature; it can theoretically either increase or decrease the likelihood of speciation. One possibility is that plasticity can increase phenotypic variation in the population, which in turn may facilitate assortative mating. The objective of this paper is to examine the conditions under which phenotypic plasticity could promote or hinder sympatric speciation and the underlying mechanisms. We developed a stochastic individual based simulation model of a sexually reproducing predator population and asexual prey populations. In the model, the ecological (foraging) trait and phenotypic plasticity of the predator can evolve in response to food availability. Individuals can exploit two prey types, and attack rate and handling time depend on predator phenotypes. Mating can occur in a common or separate mating ground.

Results/Conclusions

We show that sympatric speciation occurs more quickly when phenotypic plasticity is allowed to evolve. This happens under relatively strong assortative mating and moderate habitat sensitivity. Elevated phenotypic variation increases the efficacy of assortative mating and consistency in habitat choice over time. When the population has enough time to evolve sufficient plasticity before it reaches an evolutionary branching point (where selection switches from directional to disruptive), the population is more likely to stay monomorphic. These are, therefore, two alternative evolutionarily stable states in this system. We conclude that the presence of relatively low plasticity can speed up sympatric speciation when assortative mating is sufficiently high. Phenotypic plasticity can also hinder sympatric speciation if individuals possess high plasticity when the population experiences disruptive selection.