Intercellular and covalently bound
lipids within the stratum corneum (SC), the outermost layer of the epidermis, are the primary barrier to cutaneous water loss (CWL) in birds. We compared CWL and intercellular SC
lipid composition in 20 species of birds from desert and mesic environments. Furthermore, we compared covalently bound
lipids with CWL and intercellular
lipids in the lark family (Alaudidae). We found that CWL increases in birds from more mesic environments, and this increase was related to changes in intercellular SC
lipid composition. The most consistent pattern that emerged was a decrease in the relative amount of
cerebrosides as CWL increased, a pattern that is counterintuitive based on studies of mammals with
Gaucher disease. Although covalently bound
lipids in larks did not correlate with CWL, we found that covalently bound
cerebrosides correlated positively with intercellular
cerebrosides and intercellular
cholesterol ester, and intercellular
cerebrosides correlated positively with covalently bound
free fatty acids. Our results led us to propose a new model for the organization of
lipids in the avian SC, in which the
sugar moieties of
cerebrosides lie outside of intercellular
lipid layers, where they may interdigitate with adjacent intercellular
cerebrosides or with covalently bound
cerebrosides.