Redefining the study of sexual dimorphism in bats: following the odour trail

Climate is changing, are European bats too? A multispecies analysis of trends in body size

Animal size, a trait sensitive to spatial and temporal variables, is a key element in ecological and evolutionary dynamics. In the context of climate change, there is evidence that some bat species are increasing their body size via phenotypic responses to higher temperatures at maternity roosts. To test the generality of this response, we conducted a >20-year study examining body size changes in 15 bat species in Italy, analysing data from 4393 individual bats captured since 1995. In addition to examining the temporal effect, we considered the potential influence of sexual dimorphism and, where relevant, included latitude and altitude as potential drivers of body size change. Contrary to initial predictions of a widespread increase in size, our findings challenge this assumption, revealing a nuanced interplay of factors contributing to the complexity of bat body size dynamics. Specifically, only three species (Myotis daubentonii, Nyctalus leisleri, and Pipistrellus pygmaeus) out of the 15 exhibited a discernible increase in body size over the studied period, prompting a reassessment of bats as reliable indicators of climate change based on alterations in body size. Our investigation into influencing factors highlighted the significance of temperature-related variables, with latitude and altitude emerging as crucial drivers. In some cases, this mirrored patterns consistent with Bergmann's rule, revealing larger bats recorded at progressively higher latitudes (Plecotus auritus, Myotis mystacinus, and Miniopterus schreibersii) or altitudes (Pipistrellus kuhlii). We also observed a clear sexual dimorphism effect in most species, with females consistently larger than males. The observed increase in size over time in three species suggests the occurrence of phenotypic plasticity, raising questions about potential long-term selective pressures on larger individuals. The unresolved question of whether temperature-related changes in body size reflect microevolutionary processes or phenotypic plastic responses adds further complexity to our understanding of body size patterns in bats over time and space.

Microstructural characterization of the skin in the African straw-coloured fruit bat, Eidolon helvum (Pteropodidae)

The African straw-coloured fruit Bat, Eidolon helvum, is a Yinpterochiroptera bat that is of public health and ecological importance. This study investigated the light microscopic morphology, morphometry and histochemistry of the skin and its glands across the cheek, withers, croup, ventral abdomen, perianal region, wing membrane, intercrural membrane and foot pad of the species. Sweat glands were absent and hypodermis was observed only in the withers, croup and ventral abdomen. The croup had the highest density of hair follicles while the perianal region had the highest density of sebaceous gland acini. The thicknesses of the dermis and epidermis were significantly high in the withers and foot pad respectively. Hair follicles and sebaceous glands were absent in the wing membrane. The sebaceous glands had melanin pigmentation at the periphery and stained positive to Alcian Blue-periodic acid Schiff at the withers and ventral abdomen. Epidermal and dermal thicknesses reported in this study were generally higher than those of Yangochiroptera bats and the presence of sebaceous glands and hair follicles in the wing membrane were variable in different bat species. This study has provided baseline information on the light microscopic morphology and morphometry of the skin and its glands across the various body regions in the African straw-coloured fruit bat. This information would be helpful in the understanding, handling, skin disease treatment and management of the bat in captivity for biomedical research purposes.

Comparative study of the gular gland of three species of Molossidae bats (Mammalia: Chiroptera) from South America

The gular gland is a skin gland located in the suprasternal region of adult males of some bat families. Knowledge of the morphology and functional aspects of these gland types is often limited. This study aimed to describe the structure and composition of the gular glands of three molossid species (Eumops patagonicus, Molossus fluminensis and Molossus molossus) with respect to their reproductive activity and to define the mechanism involved in secretion release. Different histological, histochemical and immunohistochemical techniques were used to achieve these goals. The results revealed that the size and composition of this gland are variable and are mostly related to the lipid content during the reproductive season. The results also documented, for the first time, the occurrence of mechanoreceptors associated with the surface of the glandular duct by detecting an S100 protein, indicating that an external stimulus activates secretion. Previous studies on other species have classified the gland using obsolete criteria; hence, we adopted a new classification of adenomeres in this study. Moreover, we investigated the gland secretion mechanism previously proposed. This study defines the implications of this gland in the reproduction of this species. Our preliminary interpretation of the function of the gular gland is that it is a cutaneous exocrine gland activated by mechanoreceptors involved in the reproductive behaviour of the Molossidae family.