Food sharing is often evolutionarily puzzling, because the provider's benefits are not always clear. Sharing among kin may increase indirect fitness , but when non-kin are involved, different mechanisms were suggested to act. Occasionally, “tolerated theft” [2, 3] is observed, merely because defending a resource is not cost effective. Sharing may also be explained as “costly signaling” [4, 5], where individuals signal their high qualities by distributing acquired resources, as has been suggested to occur in certain human cultures . Alternatively, a transferred food item might be compensated for in later interactions . In vampire bats, blood sharing reflects reciprocity between non-kin colony members [8–10], and long-term social bonds affect food sharing in chimpanzees . Food may also be exchanged for other goods or social benefits [12–14]. One reciprocity-based explanation for intersexual food sharing is the food-for-sex hypothesis [15–17]. This hypothesis proposes that males share food with females in exchange for mating opportunities. Studies on human hunter-gatherer societies suggest that males with increased foraging success have higher reproductive success [18, 19]. Male chimpanzees, which in contrast to humans do not maintain pair bonds, were suggested to share food with females to increase their mating opportunities  (but see ). Bats, which are long-lived social mammals [21, 22], provide an opportunity to study long-term social reciprocity mechanisms. We monitored producer-scrounger interactions of a captive Egyptian fruit bat (Rousettus aegyptiacus) colony for more than a year and genetically determined the paternity of the pups that were born in the colony. We found that females carry the young of males from which they used to scrounge food, supporting the food-for-sex hypothesis in this species. Harten et al. follow the social foraging activity of a captive colony of Egyptian fruit bats. They use genetic paternity analysis of pups to reveal that producer-scrounger interactions promote reproductive intersexual relationships. These findings demonstrate an interesting case of food-for-sex reciprocity in a social mammal.
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