Sources of Assimilated Proteins in Old and New World Phytophagous Bats

Dietary proteins are considered crucial for growth and maintenance in mammals, but many fruit-eating mammals feed largely on a protein-poor diet. In the Chiroptera, frugivory has evolved twice, in the Old World Pteropodidae and in the New World Phyllostomidae, especially the Stenodermatinae. Recent studies based on the analysis of nitrogen isotope ratios (δ¹⁵N) suggest that phyllostomids feed to varying degrees on arthropods to meet their nitrogen (N) requirements. Arthropod feeding has rarely been observed in Pteropodidae. Thus, we asked whether pteropodids meet their N requirements by feeding exclusively on plant matter. We predicted that tissue from pteropodid wing membranes should be depleted in ¹⁵N relative to those of obligate insectivorous rhinolophoid, vespertilionid or emballonurid bats, if pteropodids acquire proteins exclusively from fruits, leaves or nectar. We found that δ¹⁵N in pteropodids were significantly lower than in obligate insectivorous bats. In addition, mean δ¹⁵N of Old World pteropodids was similar to that of obligate frugivorous stenodermatines of the New World tropics. We infer from these data that pteropodids are predominantly phytophagous bats. From a nutritional perspective, pteropodids and stenodermatines are very similar, suggesting that they share convergent physiological adaptations to compensate for the lack of dietary nitrogen.