Social distancing in nature : insights from vampire bats

I am broadly interested in how animals change their social behaviors in response to infection and how these changes affect pathogen spread across groups or populations. Hence, my research integrates ideas from behavioral ecology, epidemiology, and immunology to better understand the ultimate and proximate consequences of social distancing. In my first chapter, I synthesize literature on pathogen-induced changes in sociality in non-human animals and in humans. These include active and passive changes in pathogen-exposed and unexposed group members, occurring both before and after individuals develop an active infection. Behavioral changes that reduce social interactions and thus pathogen spread include changes driven by infectious hosts, such as sickness behaviors and active self-isolation, as well as changes driven by healthy hosts, including active avoidance or exclusion of infectious individuals and proactive social distancing in the face of pathogenic threats. I review what is known about underlying mechanism and consider implications for evolution and epidemiology. I also highlight the value of studying social distancing behaviors in non-human animals to better understand how these behaviors alter traits relevant to human public health, including pathogen spread and virulence. The remaining three chapters present my experimental work on common vampire bats (Desmodus rotundus) in Panama. In my second chapter, I established a method to experimentally induce transient symptoms of sickness in vampire bats by using injections of lipopolysaccharide (LPS). LPS injections mimic a bacterial infection including physiological, as well as behavioral symptoms (commonly termed ‘sickness behaviors’) in vampire bats (Stockmaier et al., 2018). Importantly, vampire bats also expressed a form a social distancing by reducing their allogrooming efforts towards others in this study (Stockmaier et al., 2018). In my third chapter I explored how this social distancing behavior in vampire bats is affected by what type of behavior is observed (allogrooming versus food sharing), how sociality as a biological trait is defined (e.g. network degree versus mean edge strength), and the type of relationship between two interacting individuals (kin versus non-kin relationship). Immune-challenged bats experienced a greater reduction in grooming than food sharing which potentially bestows greater fitness benefits (Stockmaier et al., 2020a). I also found that sickness effects on social behaviors might vary with relationship type because the immune challenge had smaller effects on mother-offspring interactions (Stockmaier et al., 2020a). Finally, I found that sickness effects depend on how a social interaction is defined (e.g. number of grooming partners versus grooming duration). I found that sickness reduced the number of grooming partners but less so the overall duration of social encounters (Stockmaier et al., 2020a). This reduction in grooming partners could be driven by reduced movement but could be augmented by reduced social vocalizations. When isolated, vampire bats produce contact calls that attract highly associated group mates. In my fourth chapter I explore whether LPS injections affect contact calling behavior. I show that LPS-induced sickness behavior mainly reduces the number of contact calls produced by isolated vampire bats (Stockmaier et al., 2020b). This effect is relevant for pathogen transmission in social animals that rely on vocalizations to maintain physical contact.