Social benefits of non-kin food sharing by female vampire bats

Abstract

Regurgitations of blood among vampire bats appear to benefit both direct and indirect fitness. To maximize inclusive fitness, reciprocal food sharing should occur among close kin. Why then do females with kin roost-mates help non-kin? We tested the hypothesis that helping non-kin increases a bat's success at obtaining future donations by expanding its network of potential donors. On six occasions, we individually fasted 14 adult females and measured donations from 28 possible donors. Each female was fasted before, during and after a treatment period, when we prevented donations from past donors (including 10 close relatives) by simultaneously fasting or removing them. This experiment was designed to detect partner switching and yielded three main results. First, females received less food when we prevented donations from a past donor versus a control bat. Donors within a group are therefore not interchangeable. Second, the treatment increased the variance in donors' contributions to food received by subjects, suggesting the possibility of alternative responses to a partner's inability to reciprocate. Finally, bats that fed more non-kin in previous years had more donors and received more food during the treatment. These results indicate that a bat can expand its network of possible donors by helping non-kin.

Non-kin cooperation in bats

“…In an attempt to determine how vampire bats respond to non-reciprocation, we prevented food sharing between targeted pairs of bats with a history of sharing so that each could only be fed by other bats for several weeks. When sharing was then allowed between the pair, five targeted donors refused to share any blood while six others increased their relative contributions [79]. These divergent responses suggest that vampire bats do not follow a simple tit-for-tat rule [85] and may use alternative strategies for dealing with non-reciprocation.…”

“…Recent work shows that helping non-kin expands the network of possible donors beyond that possible if sharing were limited to close kin [79]. When primary donors, many of whom were relatives, were prevented from sharing, females that previously shared food with more non-kin were fed by more individuals and received more food [79]. When kin donors are unavailable, non-kin can therefore act as a 'safety net'.…”

“…Given the opportunity to accrue both direct and indirect fitness benefits by exclusively helping kin, why should vampire bats ever feed non-kin? Recent work shows that helping non-kin expands the network of possible donors beyond that possible if sharing were limited to close kin [79]. When primary donors, many of whom were relatives, were prevented from sharing, females that previously shared food with more non-kin were fed by more individuals and received more food [79].…”

The influence of social relationship on food tolerance in wolves and dogs

“…Food sharing incurs a cost to the food possessor and, as such, is the most commonly seen prosocial behavior in non-human animals, with evidence of its occurrence in a wide variety of species (e.g., Clutton-brock 1991; Vahed 1998; Carter and Wilkinson 2015). However, although food sharing has been observed in many species, the mechanisms and principles regulating an individual’s choice to share food with another are still under debate.…”

Ultimate and proximate mechanisms of reciprocal altruism in rats

“…Zentall (2016) observed correctly that from an evolutionary perspective, reciprocal altruism can only be selected for if the cost of occasionally sharing one's resources with others is outweighed by the benefit of receiving resources from others. Recent findings, such as the reciprocal cooperation in vampire bats (Carter & Wilkinson, 2013, reveal mechanisms maintaining cooperation based on a social network, which implies that either simple reciprocity rules (van Doorn & Taborsky 2012) or more elaborate exchange mechanisms (Carter & Wilkinson, 2015) might be commonly applied in species living in complex societies. It is a great challenge for future research to unravel which cognitive skills are required for reciprocal cooperation in species characterized by complex social network structures (Carter & Wilkinson, 2015, 2016.…”