Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item COOPERATION AND SOCIAL BONDS IN COMMON VAMPIRE BATS(2015) Carter, Gerald; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Regurgitated food sharing among vampire bats is a classic textbook example of reciprocity ("reciprocal altruism"). But many authors have contested both the notion that reciprocity explains vampire bat food-sharing and the importance of reciprocity more generally. In Chapter 1, I review the literature on evolutionary explanations of cooperation. I show why reciprocity was once considered important but is now considered rare: overly literal translations of game theory strategies have resulted in problems for both defining and testing reciprocity. In Chapter 2, I examine the relative roles of social predictors of food-sharing decisions by common vampire bats (Desmodus rotundus) under controlled conditions of mixed relatedness and equal familiarity by fasting 20 individuals in 48 trials over two years. The food-sharing network was consistent, symmetrical, and correlated with mutual allogrooming. Non- kin food-sharing patterns were not consistent with harassment or byproduct explanations. I next attempted to manipulate food-sharing decisions in two ways. In Chapter 3, I administered intranasal oxytocin to test for effects on allogrooming and food sharing. I observed that inhaled oxytocin slightly increased the magnitude of food donations within dyads, and the amount of female allogrooming within and across all partners, without increasing number of partners. In Chapter 4, I assessed contingency of food-sharing in 7 female dyads (including four pairs of mother and adult daughters) with prior histories of sharing. To test for evidence of partner switching, I measured dyadic levels of food sharing before and after a treatment period where I prevented dyadic sharing (each bat could only be fed by others). A bat's sharing network size predicted how much food it received in the experiment. When primary donors were excluded, subjects did not compensate with donations from other partners. Yet, food-sharing bonds appeared unaffected by the non-sharing treatment. In particular, close maternal kin were clearly not enforcing cooperation using strict contingency. I argue that any contingencies within such bonds are likely to involve multiple services and long timescales, making them difficult to detect. Simple and dyadic `tit-for-tat' models are unlikely to predict cooperative decisions by vampire bats or other species with stable, mixed kinship, social bonds.Item Parent-Offspring Recognition and Alloparental Care in Greater Spear-Nosed Bats(2005-12-02) Bohn, Kirsten M; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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.