Detecting selection on signaling loci in a North American firefly

Fireflies are known for their charismatic light signals that function in mating. Firefly light signals vary in color, both within and between species, and this variation is correlated with differences in signaling environment (e.g. open field, closed forest) among populations. One hypothesis for the genetic basis of these color differences is variation in the sequence of luciferase, the enzyme that catalyzes the light reaction. In addition, visual sensitivity is expected to evolve to match signal color and is hypothesized to be due to variation in the sequence of opsins, the protein component of visual pigments. Here, we examined the relationship of sequence variation in luciferase and opsins with differences in light color and signaling environment across 12 populations of a widespread North American firefly species, Photinus pyralis. Further, we tested whether natural selection has acted on these loci by examining their population-level sequence differentiation relative to the distribution of differentiation derived from a genome-wide sample of loci generated by double-digest RADseq. These data suggest selection on non-coding variation in luciferase, while opsins evolve neutrally. They also provide the first evidence for substantial population structure in a North American firefly species.