Fluorescence and UV–visible reflectance in the fur of several Rodentia genera

Abstract

Mammals are generally brown in colour, but recent publications are showing that they may not be as uniform as once assumed. Monotremes, marsupials, and a handful of eutherians reflect various colours when lit with UV light, mostly purple. Because of these still scarce records, we aimed to explore UV reflectance among rodent genera, the most diverse mammalian group, and the group of eutherians with the most common records of biofluorescence. Here we report structures like nails and quills reflected green, but for most genera, it was faded. However, Hystrix, Erethizon, and Ctenomys showed intense and contrasting green glow, while Chaetomys presented a vivid orange anogenital. The main available explanation of fluorescence in mammals relies on porphyrin. This explanation applies to the cases like Chaetomys, where specimens showed anogenital orange biofluorescence, but does not apply to the green biofluorescence we observed. In our sample, because the structures that reflected green were all keratinized, we have reasons to believe that biofluorescence results from keratinization and is a structurally-based colouration. However, not all spines/quills equally biofluoresced, so we cannot rule out other explanations. Since Rodentia is the most common mammalian group with reports on biofluorescence, this trait likely serves various functions that match the species diversity of this group.

All-a-glow: spectral characteristics confirm widespread fluorescence for mammals

“…We observed red fluorescence in one quenda specimen (figure 2 h ), but not the other quenda examined. This corroborates the suggestion of Sobral and Souza-Gudinho [26] and Toussaint et al . [18] that red fluorescence was a result of a by-product of physiological processes unless it was faded out, but this requires further analysis.…”

“…10: 230325 quenda specimen (figure 2h), but not the other quenda examined. This corroborates the suggestion of Sobral and Souza-Gudinho [26] and Toussaint et al [18] that red fluorescence was a result of a by-product of physiological processes unless it was faded out, but this requires further analysis. Fluorescence of mammalian skin has not been widely reported, although Nummert et al [25] observed florescence of dormouse skin.…”

“…The second phase of our study aimed to (a) identify how widespread fluorescence is in mammals and (b) identify if there are correlations between (i) which part of the animals fluoresce and (ii) their ecology as there have been suggestions that fluorescence may be related to ecological traits such as microhabitat use and activity patterns [18,26].…”

“…Among mammals, the first published reports of fluorescence were in leporids (e.g. rabbits) and hominids (humans) by Stübel [21] with more recent published observations of fluorescence for New World flying squirrels [22], springhares [23], platypus [24], dormice [25] and a variety of other rodents [26], as well as an array of other mammalian species [2,18,27]. There is also a plethora of anecdotal reports of mammals glowing under UV light [e.g.…”

“…To date, the majority of mammals with reported fluorescence are nocturnal, and fluorescence was not observed among some diurnal sciurids [2,22], leading to the hypothesis that fluorescence might be useful at night [22][23][24] or that fluorescent pigments of diurnal species might photodegrade [18]. There may be other functions for this trait yet to be explored for mammals, as has been proposed for other organisms, or fluorescence may have no specific biological function, being simply a consequence of pigment or other surface structural characteristics [1,26]. The reddish UV photoluminescence (= fluorescence) found in nocturnal mammals is thought to be caused by the presence of free-base porphyrins, which are photodegradable and are unlikely to have a specific function, but rather a by-product of physiological processes [18].…”