Data from: Variation in opsin genes correlates with signaling ecology in North American fireflies

Genes underlying signal reception should evolve to maximize signal
detection in a particular environment. In animals, opsins, the protein
component of visual pigments, are predicted to evolve according to this
expectation. Fireflies are known for their bioluminescent mating signals.
The eyes of nocturnal species are expected to maximize the detection of
conspecific signal colours emitted in the typical low-light environment.
This is not expected for species that have transitioned to diurnal
activity in bright daytime environments. Here, we test the hypothesis that
opsin gene sequence plays a role in modifying firefly eye spectral
sensitivity. We use genome and transcriptome sequencing in four firefly
species, transcriptome sequencing in six additional species and targeted
gene sequencing in 28 other species to identify all opsin genes present in
North American fireflies and to elucidate amino acid sites under positive
selection. We also determine whether amino acid substitutions in opsins
are linked to evolutionary changes in signal mode, signal colour and light
environment. We find only two opsins, one long wavelength and one
ultraviolet, in all firefly species and identify 25 candidate sites that
may be involved in determining spectral sensitivity. In addition, we find
elevated rates of evolution at transitions to diurnal activity, and
changes in selective constraint on long wavelength opsin associated with
changes in light environment. Our results suggest that changes in eye
spectral sensitivity are at least partially due to opsin sequence.
Fireflies continue to be a promising system in which to investigate the
evolution of signals, receptors and signalling environments.