Cutaneous water loss and covalently bound lipids of the stratum corneum in nestling house sparrows (Passer domesticus L.) from desert and mesic habitats.

Lipids of the stratum corneum (SC), the outer layer of the epidermis of birds and mammals, provide a barrier to water vapor diffusion through the skin. The SC of birds consists of flat dead cells, called corneocytes, and two lipid compartments: an intercellular matrix and a monolayer of covalently bound lipids (CBLs) attached to the outer surface of the corneocytes. We previously found two classes of sphingolipids, ceramides and cerebrosides, covalently bound to corneocytes in the SC of house sparrows (Passer domesticus L.); these lipids were associated with cutaneous water loss (CWL). In this study, we collected adult and nestling house sparrows from Ohio and nestlings from Saudi Arabia, acclimated them to either high or low humidity, and measured their rates of CWL. We also measured CWL for natural populations of nestlings from Ohio and Saudi Arabia, beginning when chicks were 2 days old until they fledged. We then evaluated the composition of the CBLs of the SC of sparrows using thin layer chromatography. We found that adult house sparrows had a greater diversity of CBLs in their SC than previously described. During ontogeny, nestling sparrows increased the amount of CBLs and developed their CBLs differently, depending on their habitat. Acclimating nestlings to different humidity regimes did not alter the ontogeny of the CBLs, suggesting that these lipids represent a fundamental component of SC organization that does not respond to short-term environmental change.