A proximodistal gradient in bone structure and mechanics in the wings of Seba's short-tailed bat, Carollia perspicillata.

Bats possess the remarkable ability to fly, and with this, distinctive wing bone properties. We investigated the structural, mechanical, and compositional properties of the humerus, radius, metacarpals, and proximal and middle phalanges of Carollia perspicillata, an approximately 15 g fruit-eating bat native to the Neotropics. We used microcomputed tomography (micro-CT) to assess cross-sectional properties (cross-sectional area, second moment of area, circularity index), quantitative backscattered scanning electron microscopy (SEM) to assess mineral density in longitudinal sections, and nanoindentation to determine the elastic modulus along the length of each bone. Our findings revealed proximal to distal structural, mechanical, and mineral density gradients along the length of the wing. Proximal bones possessed larger cross-sectional area, second moment of area, mineral density, and elastic modulus than distal bones. Proximal bones were more circular in cross-section than the more elliptical distal bones, suggesting adaptation to torsional loading around the long axis and bending loading perpendicular to the long axis, respectively. This morphological and material properties gradient is linked to the bat's flight capabilities, reducing inertia and increasing ductility of the distal wing.