Host-pathogen evolutionary signatures reveal dynamics and future invasions of vampire bat rabies

Anticipating how epidemics will spread across landscapes requires understanding host dispersal events that are notoriously difficult to measure. Here, we contrast host and virus genetic signatures to resolve the spatiotemporal dynamics underlying geographic expansions of vampire bat rabies virus (VBRV) in Peru. Phylogenetic analysis revealed recent viral spread between populations that, according to extreme geographic structure in maternally inherited host mitochondrial DNA, appeared completely isolated. In contrast, greater population connectivity in biparentally inherited nuclear microsatellites explained the historical limits of invasions, suggesting that dispersing male bats spread VBRV between genetically isolated female populations. Host nuclear DNA further indicated unanticipated gene flow through the Andes mountains connecting the VBRV-free Pacific coast to the VBRV-endemic Amazon rainforest. By combining Bayesian phylogeography with landscape resistance models, we projected invasion routes through northern Peru that were validated by real-time livestock rabies mortality data. The first outbreaks of VBRV on the Pacific coast of South America could occur by June 2020, which would have serious implications for agriculture, wildlife conservation, and human health. Our results show that combining host and pathogen genetic data can identify sex biases in pathogen spatial spread, which may be a widespread but underappreciated phenomenon, and demonstrate that genetic forecasting can aid preparedness for impending viral invasions

Effects of experience on the development of social behaviour of house-dwelling bats

This study aims at clarifying the mechanisms underlying the formation and maintenance of stable social units in bats (Chiroptera), a characteristic shared by most species of this group of mammals, by investigating the effects of the early social environment, i.e. pursuing the hypothesis that imprinting-like influences on the development of social behaviour exist and may have a profound impact on the social lives of bats. First I present an overview on bats' social behaviour and systems: these mammals comprise a high number of species and thus constitute an excellent group for testing general hypotheses about evolution and development of social behaviour. Bat social systems in fact range from solitary species to others aggregating in conspicuous groups of up to millions individuals. Such complexity leads to a variety of social behaviours rarely found in other taxonomic groups: there is increasing evidence that bats are able of cooperative social behaviours such as allogrooming, communal nursing, group hunting and social learning, all interactions that require high-level cognitive skills. Investigating such a complex system needs a multi-disciplinary approach, fundamental for disentangling the mechanisms through which bat sociality develops. I performed a series of experiments and used classical ethological and statistical methods (ethogram composition, general linear models) together with social network analysis (SNA), developing the analyses of social interactions on an individual-based approach. Experiment 1 deals with the ability of bats to modulate their behaviour (e.g. aggressiveness) according to intrinsic (e.g. age, sex) and extrinsic (familiarity) factors during a social interaction. I performed dyadic arena-encounters where two bats per test were allowed to freely interact. I recorded aggressive and affiliative behaviours and measured the degree of affiliation towards familiar and unfamiliar individuals of captive European free-tailed bats 9 (Tadarida teniotis). By testing individuals from different captive colonies and of different age, I measured the effects of familiarity, sex and age on the aggressive behaviour of this species, using aggressiveness as a proxy for xenophobia. I found significant effects of all the selected factors upon the degree of affiliation among individuals: familiar bats were more prone to perform affiliative behaviours, behaving xenophobically towards non-group members. This xenophobic attitude was lower in females and almost null towards juveniles. These results indicate that adult bats' behaviour is influenced by previous social experiences, also suggesting that social bonds formed inside colonies are long lasting regardless of genetic relatedness existing between individuals. With experiment 2 I investigate the mechanisms leading to the formation of social subunits in groups bats, using Pipistrellus kuhlii as a model species. By manipulating the early social environment of young bats and describing their pattern of association inside artificial roost as well as measuring their rates of interaction, I demonstrate that spatial proximity inside roosts promotes social cohesion. These associations are maintained by bats throughout adulthood by means of cooperative behaviours such as allogrooming and social thermoregulation. Both classical approach and social network analysis of interacting bats indicate that physical contacts and cooperative behaviours among bats inside a colony are non-random and are more frequently performed between individuals that already had contacts at a very young age. Following the same approach and techniques of Experiment 2, with Experiment 3 I test the hypothesis that the same mechanisms that produce group cohesion inside roosts can lead to the formation of multi-specific associations of bats. Such multi-specific groups are widespread among mammals, and in bats they are assumed to form due to eco-physiological reasons (i.e. species sharing micro-climatic requirements). I manipulated the early social environment of two species that naturally occur inside the same roosts; very young Kuhl's (P. kuhlii) and Savi's (Hypsugo savii) bats were exposed to artificial multi-specific social contacts in captivity. I demonstrate that early social experience does influence social bonding also beyond the species' boundaries. Independent young bats in fact selected previous groupmembers for social thermoregulation and reciprocal grooming, regardless of species membership. Results from all experiment clearly indicate a strong effect of early social environment on the interaction and association patterns in bats, both at short (Experiments 2-3) and long (Experiment 1) time scales, suggesting the existence of imprinting-like mechanisms. Such mechanisms lead to the formation of cryptic social subunits within bat colonies and probably enhance the cohesion of the entire social structure, with obvious and strong consequences on behavioural and ecological (e.g. demographic and epidemiological) scales

COOPERATION AND SOCIAL BONDS IN COMMON VAMPIRE BATS

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

Dominance behaviour of female vampire bats

Female vampire bats (Desmodus rotundus) are a model for the study of cooperation in behavioural ecology, but we know very little of their conflict. This gap in knowledge is surprising given that competition over resources, and thus conflict, is an expected consequence of group living (Clutton-Brock & Huchard, 2013). Further, it is important to understand how vampire bats compete and resolve conflict because there is evidence to suggest that patterns of conflict are associated with patterns of cooperation (e.g. Schino & Aureli, 2008). We aimed to address this gap by observing competitive interactions occurring over food within a captive colony of 33 vampire bats which included adult females and their young aged 5 months and younger. To understand whether there was a pattern to competitive interactions we looked for evidence of a dominance hierarchy. We found strong evidence for a weakly linear dominance hierarchy, tested using three standard metrics: directional consistency, Landua’s h’, and triangle transitivity. Randomised Elo-ratings showed that the hierarchy was not steep. We also found no evidence that rank was predicted by body size, sex, age, reproductive status, social group origin, or kinship. Taken together, these results strongly indicate that vampire bat social interactions are predominantly egalitarian. To put our results in a broader context, we compared dominance hierarchy metrics in female vampire bats to 172 published datasets from other taxa. Female vampire bat dominance was less linear and less steep than over 95% of other taxa. This indicates that female vampire bats are exceptional in their lack of a strict dominance hierarchy. Our results are consistent with the prediction that egalitarian or low-sloped hierarchies will occur in species characterised by symmetrical and reciprocal cooperative relationships which supports the biological market theory of cooperation

Phylogeography of the common vampire bat (Desmodus rotundus): Marked population structure, Neotropical Pleistocene vicariance and incongruence between nuclear and mtDNA markers

Background: The common vampire bat Desmodus rotundus is an excellent model organism for studying ecological vicariance in the Neotropics due to its broad geographic range and its preference for forested areas as roosting sites. With the objective of testing for Pleistocene ecological vicariance, we sequenced a mitocondrial DNA (mtDNA) marker and two nuclear markers (RAG2 and DRB) to try to understand how Pleistocene glaciations affected the distribution of intraspecific lineages in this bat. Results: Five reciprocally monophyletic clades were evident in the mitochondrial gene tree, and in most cases with high bootstrap support: Central America (CA), Amazon and Cerrado (AMC), Pantanal (PAN), Northern Atlantic Forest (NAF) and Southern Atlantic Forest (SAF). The Atlantic forest clades formed a monophyletic clade with high bootstrap support, creating an east/west division for this species in South America. On the one hand, all coalescent and non-coalescent estimates point to a Pleistocene time of divergence between the clades. On the other hand, the nuclear markers showed extensive sharing of haplotypes between distant localities, a result compatible with male-biased gene flow. In order to test if the disparity between the mitochondrial and nuclear markers was due to the difference in mutation rate and effective size, we performed a coalescent simulation to examine the feasibility that, given the time of separation between the observed lineages, even with a gene flow rate close to zero, there would not be reciprocal monophyly for a neutral nuclear marker. We used the observed values of theta and an estimated mutation rate for the nuclear marker gene to perform 1000 iterations of the simulation. The results of this simulation were inconclusive: the number of iterations with and without reciprocal monophyly of one or more clades are similar. Conclusions: We therefore conclude that the pattern exhibited by the common vampire bat, with marked geographical structure for a mitochondrial marker and no phylogeographic structure for nuclear markers is compatible with a historical scenario of complete isolation of refuge-like populations during the Pleistocene. The results on demographic history on this species is compatible with the Carnaval-Moritz model of Pleistocene vicariance, with demographic expansions in the southern Atlantic forest.FAPESP grants number 03/01583 -3 and 04/08682-4CAPES grant number BEX4687/06-

Social dominance and cooperation in female vampire bats

This is the final version. Available on open access from the Royal Society via the DOI in this recordData accessibility: All data and R code can be found on Figshare: https://doi.org/10.6084/m9.figshare.14043794.v1When group-living animals develop individualized social relationships, they often regulate cooperation and conflict through a dominance hierarchy. Female common vampire bats have been an experimental system for studying cooperative relationships, yet surprisingly little is known about female conflict. Here, we recorded the outcomes of 1023 competitive interactions over food provided ad libitum in a captive colony of 33 vampire bats (24 adult females and their young). We found a weakly linear dominance hierarchy using three common metrics (Landau's h’ measure of linearity, triangle transitivity and directional consistency). However, patterns of female dominance were less structured than in many other group-living mammals. Female social rank was not clearly predicted by body size, age, nor reproductive status, and competitive interactions were not correlated with kinship, grooming nor food sharing. We therefore found no evidence that females groomed or shared food up a hierarchy or that differences in rank explained asymmetries in grooming or food sharing. A possible explanation for such apparently egalitarian relationships among female vampire bats is the scale of competition. Female vampire bats that are frequent roostmates might not often directly compete for food in the wild.Smithsonian Tropical Research Institute (STRI)National Science Foundation (NSF