Wings of change: Interspecifically conserved epidermal thickness and seasonally variable pigmentation in bat wing membranes

Abstract

Bats are the only mammals capable of active flight, with wing membranes that function in both locomotion and environmental interaction, reflecting physiological and ecological pressures. Here, we investigated seasonal, species-specific, sex-related, and condition-dependent variation in epidermal thickness and pigmentation in the wing membranes of four bat species (Miniopterus schreibersii, Myotis capaccinii, Rhinolophus ferrumequinum, and Rhinolophus euryale). Using light microscopy and image analysis of wing membrane biopsies, we found that epidermal pigmentation varied significantly with season and marginally by species, with the highest pigmentation observed in spring across taxa. Notably, R. euryale exhibited higher pigmentation levels than M. capaccinii and R. ferrumequinum, and female R. ferrumequinum had more pigmentation than males. Epidermal thickness in R. euryale was greater in summer than in autumn, with a similar trend seen in females relative to males. The body condition index (BCI) was negatively related to epidermal thickness only in R. ferrumequinum. These results indicate that epidermal thickness appears to be interspecifically conserved, whereas pigmentation appears more responsive to seasonal variation. These findings provide a foundation for future research on these epidermal traits in the broader context of mammalian integumentary biology.