Adaptive changes in the epidermal structure of the heat‐acclimated rock pigeon (Columba livia): A comparative electron microscopy study

Abstract

The purpose of this study was to find out whether the microstructure of the highly permeable skin of heat-acclimated pigeons allowing increased evaporative cooling differs from the skin of pigeons in the non-acclimated or cold-acclimated state. In addition, the correlation between epidermal morphology and cutaneous water evaporation in heat-acclimated pigeons was elucidated. The epidermis of heat-acclimated pigeons differs in several respects from the epidermis of non-acclimated or cold-acclimated birds. Both the dorsal and the abdominal skin include modified areas, characterized by increased vascularization, epidermis with greater thickness, and changes in intracellular structures. Greater thickness results from hypertrophy of epidermal cells possibly due to greater fluid content of the sebokeratinocytes in the germinative layers. The stratum corneum includes corneocytes with thickened cornified envelopes and contains greater mass of keratin-complex material compared to non-acclimated and cold-acclimated pigeons. The extracellular space between the compactly piled corneocytes contains amorphous lipoid material. The multigranular bodies lack compact organization of lipid bilayers. The transitional layer in the heat-acclimated pigeon displays atypical keratohyalin granules, which are multilateral and dendritic in shape. It is concluded that the dorsal and abdominal skin of heat-acclimated pigeons contains areas that differ in structure from their counterparts in non-acclimated and cold-acclimated pigeons. The structural characteristics of these modified patches suggest a high rate of cutaneous evaporation and decreased skin resistance to transepidermal diffusion of water vapor. Thus, the skin of a heat-acclimated pigeon responds to the thermoregulatory requirements for increased cutaneous water evaporation by structural changes. J. Morphol. 235:17–29, 1998. © 1998 Wiley-Liss, Inc.