Evolution of scapula shape in several families of bats (Chiroptera, Mammalia)

Abstract

The morphological variation of the scapula of bats, in a phylogenetic context, is still unknown. However, several descriptive-comparative and morphofunctional studies about the scapular girdles and forelimbs and their importance in the wing-beat cycle, are well known and documented. In this study, we tested the hypothesis that there is a conjunction of factors that influences the size and shape of the scapula in bats, such as phylogenetic effects and lifestyle traits. We analyzed the variation in size and shape of the scapula of six families of bats (277 specimens from 91 species) using geometric morphometrics in a phylogenetic context. The results indicate that phylogenetic signal for both size and shape of the scapula is strong. The phylomorphospace indicates a clear separation by families, with Phyllostomidae and Molossidae being the most different from each other. Phylogenetic signal was also strong for size and shape of the scapula within the family Phyllostomidae. According to phylogenetic analyses of variance, the shape and size of the scapula are not affected by the lifestyle of the bats, independently of phylogeny, except for the type of flight in Vespertilionidae. The results in this family indicate that, in addition to strong phylogenetic signal in scapular morphology, there is evidence of some evolutionary convergence that supports an adaptive interpretation. However, the assessments to test morphological convergence failed to find phenotypic similarity within states of lifestyle traits, except for insectivore species which presented some degree of morphological resemblance in the shape of the scapula. Thus, it seems that at higher taxonomic levels (for example, among families) the morphology of the scapula is phylogenetically conserved, whereas patterns of convergent evolution are visible at lower taxonomic levels (for example within families).