Parent-Offspring Recognition and Alloparental Care in Greater Spear-Nosed Bats

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Selection should insure that parents selectively care for their own offspring. Thus, alloparental care, or care of other's young, seems counterintuitive to evolutionary theory. Alloparental care is often attributed to: 1) mistaken identity, when individuals confuse their young with others or 2) cooperation, when the alloparent and young mutually benefit. Cooperative care, in turn, is often explained by kin selection, where animals selectively care for genetic relatives. In this dissertation, I examine these alternative explanations for alloparental care in greater spear-nosed bats (Phyllostomus hastatus). In this species, females form stable social groups of relatively unrelated individuals. Females give birth once a year to nonvolant pups that frequently fall from roost sites in cave ceilings and likely perish unless retrieved by an adult. In this context, pups emit vocalizations, termed isolation calls, that are used in parent-offspring recognition.

I examine parent-offspring recognition in P. hastatus by examining isolation call variability and both detection and perception of isolation calls by adults. I found that pups emit individually distinctive calls but that pups from the same social group have more similar calls than pups from different social groups. Psychoacoustic experiments in the laboratory showed that greatest hearing sensitivity and frequency selectivity in adult P. hastatus is at the fundamental frequency of isolation calls. I found that this is a common phenomenon in bats using comparative phylogenetic methods. Finally, using psychoacoustic experiments I demonstrated that P. hastatus females could discriminate between pups' isolation calls regardless of the pups' social groups.

Next, I examine parental care in the natural habitat of P. hastatus. I found that females respond more frequently and spend more time visiting group mates' pups than non-group mates pups, even though many of these females are not missing pups of their own. These results, combined with the results from psychoacoustic studies, indicate that mistaken identity cannot explain this visiting behavior. By visiting group mates' pups, females protect them from non-group mates who attack and sometimes kill them. However, kin selection cannot explain this behavior because females are unrelated to group mates' pups that they visit.