Snake oil in action: Geographic and seasonal variability in epidermal lipids shape evaporative water loss in snakes

Abstract

Many reptiles inhabit deserts where extreme heat and aridity make it imperative to minimize evaporative water loss (EWL) in order to maintain a water balance. We compared the EWL of desert versus Mediterranean snakes and the content and composition of their epidermal lipids, which form the primary barrier against evaporation. We obtained shed skins from two farm-grown species (a desert specialist viper Echis coloratus and its Mediterranean relative Daboia palaestinae), and from 17 captive snake species of both Mediterranean and desert origins, kept under identical conditions. Total EWL was measured in live snakes using flow-through respirometry. Cutaneous EWL was approximated in vitro through the shed skin, and epidermal lipids were quantified following extraction in n-hexane and identified using ultraperformance liquid chromatography–mass spectrometry (UPLC-MS). Total EWL in vivo was 50% higher in Mediterranean than in desert species. In winter, in vitro EWL was 67% higher in Mediterranean than in desert species, and this difference rose to 178% in summer. EWL in vitro was negatively correlated with skin lipid content, and accordingly, desert species had twice the skin lipid content, but only in the summer. Seasonal differences were significant in the multi-species comparison, and not between the farm-grown Echis and Daboia. UPLC-MS confirmed equal quantities of total lipids between the two viper species. However, the abundance of fatty acids was 84% higher in the desert specialist Echis, and these were, on average, ~1 double bond more saturated. There was no difference in ceramide abundance, but ceramide carbon chains were ~1 carbon atom longer in Echis. This lipid profile favours a more compact and stable lipid barrier structure, which improves the skin's resistance to evaporation. Our results show that snake epidermal lipid content and composition vary between biomes and seasons, enabling desert species to maintain water balance under the harsh heat and dryness conditions by limiting water loss. More broadly, this work highlights how fundamental biochemical traits can underlie major ecological differences, and how animals can benefit from these differences and adapt to thrive in extreme conditions. Read the free Plain Language Summary for this article on the Journal blog.