Predator Perspective Drives Geographic Variation in Frequency-Dependent Polymorphism

Abstract

Color polymorphism in natural populations can manifest as a striking patchwork of phenotypes in space, with neighboring populations characterized by dramatic differences in morph composition. These geographic mosaics can be challenging to explain in the absence of localized selection because they are unlikely to result from simple isolation-by-distance or clinal variation in selective regimes. To identify processes that can lead to the formation of geographic mosaics, we developed a simulation-based model to explore the influence of predator perspective, selection, migration, and genetic linkage of color loci on allele frequencies in polymorphic populations over space and time. Using simulated populations inspired by the biology of Heliconius longwing butterflies, Cepaea land snails, Oophaga poison frogs, and Sonora ground snakes, we found that the relative sizes of predator and prey home ranges can produce large differences in morph composition between neighboring populations under both positive and negative frequency-dependent selection. We also demonstrated the importance of the interaction of predator perspective with the type of frequency dependence and localized directional selection across migration and selection intensities. Our results show that regional-scale predation can promote the formation of phenotypic mosaics in prey species, without the need to invoke spatial variation in selective regimes. We suggest that predator behavior can play an important and underappreciated role in the formation and maintenance of geographic mosaics in polymorphic species.

Climate suggests environment‐dependent selection on lizard colour morphs

“…Instead, our results suggest that climatic constraints act with a different intensity (or even direction) on different morphs, which is consistent with our hypothesis that the Y and YO morphs are the most constrained environmentally. Consequently, these rare morphs may persist wherever an ecological window of opportunity appears, resulting in the reported heterogeneous (but not stochastic) geographical mosaic of morph distribution (Holmes et al., ; Thompson, ).…”

“…Bishop et al., ). Hence, comparative studies on morph variation across a heterogeneous geographical range may identify the selective pressures driving polymorphisms (Cox & Rabosky, ; Holmes, Grundler, & Rabosky, ). This is of special interest for identifying relationships between morph composition and environment (e.g.…”

Discrete or indiscrete? Redefining the colour polymorphism of the land snailCepaea nemoralis

“…In another more recent study, a simulation was used to explore the influence of predator perspective, selection, migration, and genetic linkage on colour allele frequencies. The relative sizes of predator and prey home ranges can result in large differences in morph composition between neighbouring populations (Holmes et al 2017). Finally, in an empirical study blue jays Cyanocitta cristata searched for digital moths on mixtures of dark and light patches at different scales of heterogeneity.…”

Shell morphology, growth pattern and population dynamics of the land snail Xerolenta obvia (Menke, 1828) in two areas of different climatic conditions within a temperate climate region

“…Shell polymorphisms in snails are known to be affected by factors other than climate. Selection for crypsis and the tendency for different morphs to select appropriate microhabitats may all have effects (Jones et al 1974, Allen & Weale 2005, Holmes et al 2017, Rosin et al 2018. With only two populations available, we cannot comment further other than to note that X. obvia and other species of open, lime-rich sites such as Granaria frumentum may be subject to heavy predation (Němec & Horsák 2019), and that genetic drift and founder effects may be significant in small, isolated populations (Jones et al 1977, Cook 1998, Ożgo 2008.…”