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1. Social foraging in vampire bats is predicted by long-term cooperative relationships

   https://doi.org/10.1371/journal.pbio.3001366  

   Ripperger, Simon P.; Carter, Gerald G. (September 2021, PLOS Biology)

   Hobaiter, Catherine (Ed.)

   Stable social bonds in group-living animals can provide greater access to food. A striking example is that female vampire bats often regurgitate blood to socially bonded kin and nonkin that failed in their nightly hunt. Food-sharing relationships form via preferred associations and social grooming within roosts. However, it remains unclear whether these cooperative relationships extend beyond the roost. To evaluate if long-term cooperative relationships in vampire bats play a role in foraging, we tested if foraging encounters measured by proximity sensors could be explained by wild roosting proximity, kinship, or rates of co-feeding, social grooming, and food sharing during 21 months in captivity. We assessed evidence for 6 hypothetical scenarios of social foraging, ranging from individual to collective hunting. We found that closely bonded female vampire bats departed their roost separately, but often reunited far outside the roost. Repeating foraging encounters were predicted by within-roost association and histories of cooperation in captivity, even when accounting for kinship. Foraging bats demonstrated both affiliative and competitive interactions with different social calls linked to each interaction type. We suggest that social foraging could have implications for social evolution if “local” within-roost cooperation and “global” outside-roost competition enhances fitness interdependence between frequent roostmates. 

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2. Social convergence of gut microbiomes in vampire bats

   https://doi.org/10.1098/rsbl.2021.0389  

   Yarlagadda, Karthik; Razik, Imran; Malhi, Ripan S.; Carter, Gerald G. (November 2021, Biology Letters)

   The ‘social microbiome’ can fundamentally shape the costs and benefits of group-living, but understanding social transmission of microbes in free-living animals is challenging due to confounding effects of kinship and shared environments (e.g. highly associated individuals often share the same spaces, food and water). Here, we report evidence for convergence towards a social microbiome among introduced common vampire bats, Desmodus rotundus , a highly social species in which adults feed only on blood, and engage in both mouth-to-body allogrooming and mouth-to-mouth regurgitated food sharing. Shotgun sequencing of samples from six zoos in the USA, 15 wild-caught bats from a colony in Belize and 31 bats from three colonies in Panama showed that faecal microbiomes were more similar within colonies than between colonies. To assess microbial transmission, we created an experimentally merged group of the Panama bats from the three distant sites by housing these bats together for four months. In this merged colony, we found evidence that dyadic gut microbiome similarity increased with both clustering and oral contact, leading to microbiome convergence among introduced bats. Our findings demonstrate that social interactions shape microbiome similarity even when controlling for past social history, kinship, environment and diet. 

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3. Co‐option and the evolution of food sharing in vampire bats

   https://doi.org/10.1111/eth.13146  

   Carter, Gerald G.; Taborsky, ed., Barbara (September 2021, Ethology)

   Abstract The function of cooperative traits can change over time. For example, helping behaviors that originally evolved by kin selection can later yield direct fitness benefits and be stabilized by partner choice. In such cases, there may be multiple interacting factors that drive cooperation. Here, I review evidence that food sharing in vampire bats evolved as form of extended maternal care that was co‐opted to yield reciprocal benefits, and that such reciprocal relationships may have led to investment strategies that balance the trade‐offs between greater quality and quantity of cooperative relationships. 

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4. Social dominance and cooperation in female vampire bats

   https://doi.org/10.1098/rsos.210266  

   Crisp, Rachel J.; Brent, Lauren J.; Carter, Gerald G. (July 2021, Royal Society Open Science)

   When 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. 

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5. Non-kin adoption in the common vampire bat

   https://doi.org/10.1098/rsos.201927  

   Razik, Imran; Brown, Bridget K.; Page, Rachel A.; Carter, Gerald G. (February 2021, Royal Society Open Science)

   Individual animals across many different species occasionally ‘adopt’ unrelated, orphaned offspring. Although adoption may be best explained as a by-product of adaptive traits that enhance parental care or promote the development of parental skills, one factor that is possibly important for the likelihood of adoption is the history of cooperative interactions between the mother, adopted offspring and adopter. Using 652 h of behavioural samples collected over four months, we describe patterns of allogrooming and food sharing before and after an instance of non-kin adoption between two adult female common vampire bats ( Desmodus rotundus ) that were captured from distant sites (340 km apart) and introduced to one another in captivity. The first female died from an illness 19 days after giving birth. The second female groomed and regurgitated food to the mother more often than any other group member, then groomed, nursed and regurgitated food to the orphaned, female pup. The substantial increase in alloparental care by this female after the mother's death was not observed among the 20 other adult females that were present in the colony. Our findings corroborate previous reports of non-kin adoption in common vampire bats and are consistent with the hypothesis that non-kin adoption can be motivated, in part, by a history of cooperative interactions. 

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