The genetics of mating song evolution underlying rapid speciation: Linking quantitative variation to candidate genes for behavioral isolation

Differences in mating behaviors evolve early during speciation, eventually contributing to reproductive barriers between species. Knowledge of the genetic and genomic basis of these behaviors is therefore integral to a causal understanding of speciation. Acoustic behaviors are often part of the mating ritual in animal species. The temporal rhythms of mating songs are notably speciesspecific in many vertebrates and arthropods and often underlie assortative mating. Despite discoveries of mutations that disrupt the temporal rhythm of these songs, we know surprisingly little about genes affecting naturally occurring variation in the temporal pattern of singing behavior. In the rapidly speciating Hawaiian cricket genus Laupala, the striking species variation in song rhythms constitutes a behavioral barrier to reproduction between species. Here, we mapped the largest-effect locus underlying interspecific variation in song rhythm between two Laupala species to a narrow genomic region, wherein we find no known candidate genes affecting song temporal rhythm in Drosophila. Whole-genome sequencing, gene prediction, and functional annotation of this region reveal an exciting and promising candidate gene, the putative cyclic nucleotide-gated ion channel-like gene, for natural variation in mating behavior. Identification and molecular characterization of the candidate gene reveals a nonsynonymous mutation in a conserved binding domain, suggesting that ion channels are important targets of selection on rhythmic signaling during establishment of behavioral isolation and rapid speciation.