Biofluorescence Is Phylogenetically Widespread and Highly Variable in the Skin of Plethodontid Salamanders

Biofluorescence is the absorption and reemission of light by living organisms. Several studies have shown biofluorescence to be widespread in a variety of animal groups, though few of these studies have taken a comparative approach within a specific taxonomic group. Plethodontidae is the most speciose family of salamanders and one such group in which biofluorescence has recently been discovered. However, the distribution and sources of biofluorescence have been assessed in only a few species. We used a combination of microscopy and histology to characterize biofluorescence in eight genera and 12 species representing most of the major branches of the plethodontid phylogeny. We found biofluorescent skin in all 12 species, though the distribution, sources, and intraspecific patterns in biofluorescence varied greatly between species. Biofluorescence was more abundant in ventral skin than in dorsal skin in most species. All species possessed glandular and/or non-glandular (chromatophore-based) sources of biofluorescence. Biofluorescent glands also displayed impressive variety both between and within species, with several distinct morphologies that were typically carbohydrate-rich. We also documented male, female, adult, and juvenile biases in biofluorescence in various species. With so much variation in the sources and patterns of biofluorescence, it seems likely that this phenotype may serve unique functions in different species. Our results provide the first family wide assessment of biofluorescence in Plethodontidae while laying the groundwork for future studies of the functions of biofluorescence in each species.