Evolution of Phenotypic Plasticity and Gene Expression during Character Displacement

Abstract

Abstract Character displacement – trait evolution that arises as an adaptive response to competition between species – is central to the origins, abundance and distribution of biodiversity. Yet, until recently, little was known of character displacement's underlying mechanisms. Although character displacement is assumed to arise solely through changes in deoxyribonucleic acid (DNA) sequence, many species can also respond adaptively to competition by facultatively altering traits via phenotypic plasticity, which frequently entails changes in gene expression. New research has revealed that these two mechanisms might often act together during character displacement. In particular, character displacement might proceed through an initial phase in which trait (and gene expression) differences are environmentally induced to a latter phase in which such differences become fixed via changes in DNA sequence. This plasticity‐first hypothesis has increasing support, suggesting that it may be a common pathway to character displacement. Key Concepts Competition is a key driver of phenotypic divergence between species. Character displacement is an evolutionary process in which natural selection causes a shift in phenotype production to reduce competition. This shift often causes competing lineages to differ more where they occur together (sympatry) than where each occurs in the other's absence (allopatry). Both DNA sequence changes and phenotypic plasticity can play a role in mediating character displacement. Competitively mediated phenotypic plasticity involves environmentally induced changes in gene expression. Character displacement might undergo plasticity‐first evolution, whereby it transitions from an environmentally induced phase to a genetically fixed one. An example of plasticity‐mediated character displacement comes from spadefoot toad (genus Spea ) tadpoles. As a consequence of character displacement, sympatric populations of one species ( Spea bombifrons ) have lost diet‐dependent plasticity in gene expression. Thus, character displacement has facilitated genetic assimilation at both the phenotypic and molecular levels in this species. Further exploration of character displacement's underlying mechanisms might provide some of the most compelling cases of plasticity‐first evolution and genetic assimilation in nature.