Histomorphometric changes in the wing bones of the fruit bat, Pteropus poliocephalus, (Megachiroptera: Pteropidae) in relation to increased bone strain and the failure of a good (?) hypothesis

Fluorochrome labelling of bone formation was used to examine the effect of exercise (flight) on the wing skeleton of fruit bats, Pteropus poliocephalus, over a 194 day period. The bats in this study had been born and raised in captivity and it was hypothesised that the large increases in bone strain that accompanied active flight would result in bone formation at the periosteal bone surface, leading to increased mechanical stiffness and strength. This hypothesis was not supported by the results. Bone formation rates, percentage mineralising surface and mineral apposition rates at the mid-shaft periosteal surface of the radius, metacarpal III and metacarpal V were small. The proximal phalanx of digit V did not display any bone formation at this surface. Bone appositional activity was not significantly different between baseline, control (non-flight) and treatment (flight) groups at any time-point of the experiment. Apposition, although limited, occurred primarily at the endocortical surface in all bones of all animals. No correlation was found between activity and bone formation. Active intracortical remodelling (a total of four secondary osteons) was only seen in three individuals. There was evidence of earlier remodelling activity in most bones, although there was no evidence of any secondary remodelling in the proximal phalanx.