Molecular evolution of luciferase diversified bioluminescent signals in sea fireflies (Crustacea:Ostracoda:Cypridinidae)

Integrative studies of courtship signals provide rich opportunities to understand how biological diversity originates, but understanding the underlying genetics is challenging. Here we show molecular evolution of a single gene - luciferase - influenced diversification of bioluminescent signals in cypridinid ostracods, including their radiation into dozens of Caribbean species with distinctive courtship displays. We report emission spectra from twenty-one species, thirteen luciferases from transcriptomes, and in vitro assays that confirm function from four exemplar species. We found most sites in luciferase evolved neutrally or under purifying selection, including multiple sites that affect the color of bioluminescence in mutagenesis studies. Twelve sites in cypridinid luciferase evolved under episodic diversifying selection, including five that correlate with changes in kinetics and/or color of bioluminescence, phenotypes that manifest at the organismal level. These results demonstrate how neutral, pleiotropic, and/or selective forces may act on even a single gene and contribute to diversification of phenotypes.