Diet choice in frugivorous bats: gourmets or operational pragmatists?

Allocation to reproduction is based on trade-offs between competing functions and available energy and nutrients. Because fruit is generally protein poor, strict frugivores may require additional protein during periods of investment in young and, in mammals, periods of milk production. Observations of frugivores supplementing their diets with protein-rich insects are accumulating and this is likely an underappreciated common strategy. However, it is unclear if protein augmentation is determined by seasonal abundances of high-protein food or by behavioral changes to navigate physiological demands. We present the 1st study asking if frugivorous bats supplement their diets with insects to obtain required energy and nutrients that could be used for successful reproduction. Using naturally occurring stable isotopes of nitrogen, we examine the roles of fruit versus insects to determine if these frugivorous mammals are truly specialists, we also ask how diet breadth varies with season, sex, and by reproductive state. We test 2 new hypotheses regarding when insect supplementation occurs using the well-studied largely frugivorous Jamaican fruit bat, Artibeus jamaicensis. The 1st hypothesis suggests protein augmentation occurs seasonally but independent of reproduction (H1). Alternatively, females may supplement their frugivorous diets with insects during the nitrogen-demanding periods of pregnancy and lactation (H2). Finally, we test a 3rd independent hypothesis (H3) that these bats are specialists, consistent with both H1 and H2. We found dietary shifts relative to season, reproductive state, and sex. The largest portion of insect use was by pregnant females. Surprisingly, lactating females did not consistently supplement their diets with insects and exhibited fruit-focused diets. Males exhibited the narrowest dietary breadth and nonreproductive females the greatest. Diet breath of all reproductive groups varied by month. Our data indicate that, while fruits remain an important part of the diet, insects may be an extremely valuable source of nitrogen to females during pregnancy. [ABSTRACT FROM AUTHOR]