Selection on visual opsin genes in diurnal Neotropical frogs and loss of theSWS2opsin in poison frogs

Abstract

Amphibians are an ideal model for studying visual system evolution because their biphasic (aquatic and terrestrial) life history and ecological diversity expose them to a broad range of visual conditions. Here we evaluate signatures of selection on visual opsin genes of five Neotropical diurnal frog groups, with a focus on three conspicuously colored and chemically defended (i.e., aposematic) clades: poison frogs (Dendrobatidae), Harlequin toads (Bufonidae:Atelopus), and pumpkin toadlets (Brachycephalidae:Brachycephalus). We found evidence of positive selection on 15 amino acid sites inLWS, SWS1, SWS2, andRH1opsin genes, of which one inLWShas been previously identified as important for spectral tuning in other vertebrates. Patterns of selection reveal that the evolution of diurnality was important in shaping the vision of focal frog groups; whether conspicuous coloration has played a role remains unclear, as no support was found but inferences may have been statistically limited by sample size. Furthermore, we provide evidence that theSWS2gene, normally expressed in rod cells in amphibians, has likely been lost in the ancestor of Dendrobatidae, suggesting that under low light levels, dendrobatids have inferior wavelength discrimination compared to other frogs. This might coincide with the diurnal activity of dendrobatids and could have implications for opsin evolution in this clade. Our analyses show that studies of opsin diversification could expand our understanding of how adaptations for diel habits evolve and how visual tuning alters the sensory landscape of animals.

Evidence for ecological tuning of novel anuran biofluorescent signals

“…Future work should compare the maximum biofluorescent emission wavelength to species specific spectral sensitivities as that data becomes available. Recent evidence suggests that ecology and diurnality shape the visual sensitivities of frog vision (44)(45). Hence, examining how biofluorescence may differ in these groups could reveal great insights into the function of anuran fluorescent traits.…”