An exploration of autofluorescence in tardigrades (phylum Tardigrada)

Abstract

Abstract Recently it was purported that autofluorescence (AF) in Paramacrobiotus n. sp. provided protection from UV radiation. If true, this would be the first documentation of an adaptive function for AF in any microscopic animal. We review what is currently known about AF in tardigrades, and we provide the first true colour images of tardigrade fluorescence. To assess the hypothesis of AF as UV protection we measured interspecific variation and intraspecific variation. We found that interspecific variation was much greater than intraspecific variation. We compared the fluorescence emission spectra for nine species of tardigrades, and together with the true colour fluorescence images, we noticed different patterns of fluorescence suggesting a rich diversity of fluorophores. We examined epidermal pigments of a new species of Milnesium and Ramazzottius kretschmanii and found that they are not the source of fluorescence in these species. We suggest further research is necessary to test the hypothesis that AF is UV protective in tardigrades, and we demonstrate and assess four different research tools for examining autofluorescence in microscopic animals.