Hypophysis Size Evolution in Chiroptera

Abstract

The hypophysis influences biological functions in mammals at various levels, and its volumetric variation in Chiroptera is recently well known. We explored the relation of the hypophysis size as a whole (Hyp) and its separate components, adenohypophysis (Adh) and neurohypophysis (Neh), from 96 species of bats (Yinpterochiroptera and Yangochiroptera), with social (roosting association), reproductive (testes mass, mating system, female promiscuity), body size (body mass) and foraging (diet) variables (when available for the sampled species), through ANCOVA and linear regressions analyses. We also explored the phylogenetic legacy of the volumetric changes of Hyp, Adh and Neh over a well-resolved phylogenetic tree, through Phylogenetically independent contrasts analysis, phylogenetic signal, and character optimizations. Hyp, Adh, Neh volumes and testes mass showed significant relation with body mass. When body mass effect was excluded, Hyp, Adh and Neh showed no significant relation with testes mass nor significant differences within roosting association, mating system and female promiscuity variables. However, Hyp, Adh and Neh volumes showed a pattern with diet, probably related to the regulatory role of the hypophysis at the endogenous protein metabolism in Mammals. The significant phylogenetic effect at linear regressions of Hyp, Adh and Neh volumes against body mass suggests the hypophysis volume and the body mass has coevolved, which was also supported by the significant phylogenetic signal and the optimizations considering body mass. Optimizations excluding body mass also showed significant phylogenetic signal, demonstrating that the volumetric changes bear phylogenetic information beyond body size. Our results suggest that the hypophysis size variations in bats are rather explained by phylogenetic legacy, as phylogenetic inertia linked to the ecology of the ancestors of the different clades, than current ecological aspects related to the natural history of the extant species.