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Regurgitated food sharing in vampire bats is a cooperative behavior that has garnered scientific interest as an example of reciprocal helping among kin and non-kin. The amount of food given is estimated via the duration of mouth-licking. However, a growing body of evidence across other animal taxa, especially social insects, shows that mouth-to-mouth material transfer can serve many functions besides food sharing. In this review, we asked whether and to what extent mouth-licking in the common vampire bat (Desmodus rotundus) could be explained by functions other than regurgitated food sharing. We first review the evidence, including new analyses of published data, that food sharing occurs during mouth-licking bouts in vampire bats. We then review interpretations of mouth-licking in other mammal species and assess the likelihood that various hypothetical functions suggested in other species could occur in vampire bats. We conclude that the primary function of prolonged bouts of mouth-licking in vampire bats is sharing of ingested blood, but that microbial sharing is another likely benefit, and that short bouts of mouth-licking also function as social signals of begging or offering of food. Future work on this behavior should keep alternative explanations in mind when interpreting observations. 

Abstract In many group‐living animals, survival and reproductive success depend on the formation of long‐term social bonds, yet it remains largely unclear why particular pairs of groupmates form social bonds and not others. Can social bond formation be reliably predicted from each individual's immediately observable traits and behaviors at first encounter? Or is social bond formation hard to predict due to the impacts of shifting social preferences on social network dynamics? To begin to address these questions, we asked how well long‐term cooperative relationships among vampire bats were predicted by how they interacted during their first encounter as introduced strangers. In Study 1, we found that the first 6 h of observed interactions among unfamiliar bats co‐housed in small cages did not clearly predict the formation of allogrooming or food‐sharing relationships over the next 10 months. In Study 2, we found that biologger‐tracked first contacts during the first 4–24 h together in a flight cage did not strongly predict allogrooming rates over the next 4 months. These results corroborate past evidence that social bonding in vampire bats is not reducible to the individual traits or behaviors observed at first encounter. Put simply, first impressions are overshadowed by future social interactions. 

Social structure can emerge fromhierarchically embedded scales of movement, where movement at one scale is constrained within a larger scale (e.g. among branches, trees, forests). In most studies of animal social networks, some scales of movement are not observed, and the relative importance of the observed scales of movement is unclear. Here, we asked: how does individual variation in movement, at multiple nested spatial scales, influence each individual's social connectedness? Using existing data from common vampire bats (Desmodus rotundus), we created an agent-based model of how three nested scales of movement—among roosts, clusters and grooming partners—each influence a bat's grooming network centrality. In each of 10 simulations, virtual bats lacking social and spatial preferences moved at each scale at empirically derived rates that were either fixed or individually variable and either independent or correlated across scales. We found that numbers of partners groomed per bat were driven more by within-roost movements than by roost switching, highlighting that co-roosting networks do not fully capture bat social structure. Simulations revealed how individual variation in movement at nested spatial scales can cause false discovery and misidentification of preferred social relationships. Our model provides several insights into how nonsocial factors shape social networks. 

There is increasing awareness that data science and computational thinking are critical skills for undergraduates to develop but these can be difficult to integrate into undergraduate Biology classes. In this module, we describe how we have used a system for learning the programming language R that focuses on building students? skills and confidence in data exploration, management, and visualization. This activity pairs a hands-on virtual experiment where students simulate animal movements and social interactions to provide a friendly introduction to basic data science for biologists. During the activity, students play the ?Bat Game?, an online game which students access via an internet browser. Each student controls the movement decisions of one bat within a social group. The bats must search for cows they can bite to get a meal of blood. Students take the roles of bats in a series of foraging tasks. Students must follow ?rules? and attempt to match their overall actions to those of their group members under different scenarios. The game platform collects all the locations of all bats in the game. After playing the game, students export the data they just created and analyze it to learn how to detect known patterns through basic summaries and plotting in R. All analyses and programming skills are presented in one cohesive R Markdown file, where students can read about the goals of each coding chunk, can run each chunk, and then answer questions about the biology of the social system as well as basic questions about the code used in the analyses. This approach decouples coding from statistics, assumes no prior knowledge, and uses a charismatic species to incentivize student participation. This module can be used in many courses including lab sections of large-enrollment introductory biology courses as well as smaller upper-level courses 

Blood-feeding (sanguivory) has evolved more than two dozen times among birds, fishes, insects, arachnids, molluscs, crustaceans, and annelids; however, among mammals, it is restricted to the vampire bats. Here, the authors revisit the question of how it evolved in that group. Evidence to date suggests that the ancestors of phyllostomids were insectivorous, and that carnivory, omnivory, and nectarivory evolved among phyllostomids after vampire bats diverged. Frugivory likely also evolved after vampire bats diverged, but the phylogeny is ambiguous on that point. However, vampire bats lack any genetic evidence of a frugivorous past, and the behavioural progression from frugivory to sanguivory is difficult to envision. Thus, the most parsimonious scenario is that sanguivory evolved in an insectivorous ancestor to vampire bats via ectoparasite-eating, wound-feeding, or some combination of the two—all feeding habits found among blood-feeding birds today. Comparing vampire bats with other sanguivores, the authors find several remarkable examples of convergence. Further, it was found that blood-feeding has been ca. 50 times more likely to evolve in a vertebrate lineage than in an invertebrate one. The authors hypothesize that this difference exists because vertebrates are more likely than invertebrates to have the biochemical necessities required to assimilate the components of vertebrate blood. 

Abstract Reciprocity and pseudo‐reciprocity are two important models for the evolution of cooperation and often considered alternative hypotheses. Reciprocity is typically defined as a scenario where help givencauseshelp received: cooperation is stabilized because each actor's cooperative investments are conditional on the cooperative returns from the receiver. Pseudo‐reciprocity is a scenario where helpenablesbyproduct returns: cooperation is inherently stable because the actor's cooperative investments yield byproduct returns from the receiver's self‐serving behavior. These models are strict alternatives only if reciprocity is defined by the restrictive assumption of zerofitness interdependence, meaning that the helper has no “stake” in the receiver's fitness. Reciprocity and interdependence are, however, not mutually exclusive when helping can increase both reciprocal help and byproduct returns. For instance, helping partners survive can simultaneously increase their willingness to reciprocate, their ability to reciprocate, and byproduct benefits of their existence. Interdependence can “pave the road” to reciprocal helping, and partners who reciprocate help can also become interdependent. However, larger cooperative investments can increase the need for responsiveness to partner returns. Therefore, most long‐term cooperative relationships involve both responsiveness and interdependence. Categorizing these relationships as “reciprocity” can be viewed as ignoring interdependence, but calling them ‘pseudo‐reciprocity’ is confusing because stability also comes from the cooperative investments being conditional on returns. Rather than conceptualizing cooperation intodiscrete categories, it is more insightful to imagine a coordinate system with responsiveness and interdependence ascontinuous dimensions. One can ask: To what degree is helping behavior responsive to the partner's behavior? And to what degree does the helper inherently benefit from the receiver's survival or reproduction? The amounts of responsiveness and interdependence will often be hard to estimate, but both are unlikely to be zero. Identifying their relative importance, and how that changes over time, would greatly clarify the nature of cooperative relationships. 

Selection of habitat is a key determinant of reproductive success, and the process of finding and choosing these sites is often influenced by the presence of conspecifics. Many bats frequently switch roosts, and some bats repeatedly find new roosts. To find roosts with conspecifics or group members, bats can use social cues. However, most research on how bats use social cues for roost-finding has focused on acoustic cues. Here, we review and discuss the evidence for bat roost selection using scent cues from guano and urine stains, which are present at most bat roosts. We outline reasons why bats might, or might not, use scent in roost detection and selection, and we review evidence on the possible use of guano and urine in roost-finding from eight studies with 12 bat species (across four families). Overall, the sparse evidence that exists indicates that scent cues from guano and urine are not a strong and consistent lure in the species and situations that were tested. Most studies had unclear results or found no effect. Two of the eight studies found weak experimental evidence for bats using guano or urine to select a roosting site. Even if guano and urine can indicate the presence of bats at a roost, it is possible that the resulting olfactory cues do not contain sufficient social information to be used in roost selection, in contrast to olfactory cues from scent marking. Studies of how bats use sensory cues beyond sound could contribute to a better understanding of bat social behavior and roosting ecology.