The passage is adapted from Carter G, Leffer L (2015) “Social Grooming in Bats: Are Vampire Bats Exceptional?” © 2015 Carter, Leffer

大多数evide长期合作关系nt in primates, but evidence for similar social relationships has been accumulating for several other social vertebrate groups including cetaceans, bats, elephants, hyenas and ravens. The functional importance of these complex social relationships across different species may have led to similar cognitive or behavioral mechanisms for manipulating social bonds. A prime example of such a mechanism is social grooming—the cleaning of the body by a partner. Experimental and observational studies show that primate social grooming can be ‘exchanged’ for multiple social benefits, including reciprocal grooming, social tolerance, access to food, and agonistic support. Individuals can spend up to 20% of their time grooming others, and the behavior provides proximate physiological rewards for both givers and receivers. Although most of what is known about social grooming comes from studies of primates, evidence for a role of social grooming in maintaining social ties is emerging from several other mammals (marsupials, deer, cows, horses, voles, mice, meerkats, coati, lions) and group-living birds.

In bats, adult social grooming is female-biased in species with female philopatry and has been most studied in the common vampire bat (Desmodus rotundus). Kerth et al. compared social grooming rates of vampire bats with the temperate and insectivorous Bechstein’s bat (Myotis bechsteinii). These two species both have long lifespans and demonstrate fission-fusion social dynamics, where individuals maintain long-term social associations while moving between several roost trees. In both species, social grooming rates among individuals were not predicted by self-grooming or numbers of parasites. Bechstein’s bats spent more time grooming themselves (38% of their time in roosts) compared with vampires (23% of their roosting time), but wild vampire bats spent about 5% of their roosting time grooming others, which is 2–4 times higher than Bechstein’s bats.

Patterns of social grooming among categories of individuals also differed between the two species. In the Bechstein’s bat, adult female social grooming was not detectably symmetrical, and was predicted by kinship, occurring mostly between adult mothers and daughters, sometimes between sisters, and only rarely between non-kin. In vampires, female social grooming was highly symmetrical and relatively common among non-kin, where it correlated with co-roosting association and food sharing.

It is not entirely clear if vampire bat social grooming is typical or exceptional when compared to other bats or non-primate mammals. One hypothesis is that social grooming in vampire bats is exceptional in quantity and quality, because it is related to their uniquely cooperative food sharing behavior. Like many primates, reciprocal patterns of vampire bat food sharing and social grooming extend beyond mother-offspring bonds, suggesting they may provide both direct and indirect fitness benefits. Among bats, the common vampire has an extraordinarily large brain and neocortex for its body size. In primates, increased neocortex size has been linked to higher metrics of social complexity, such as social grooming network size and strategic deception.

Alternatively, the apparent distinctiveness of vampire bat social grooming might stem from purely ecological factors. Social grooming may be more obvious in vampire bats due to higher levels of ectoparasite infestation. Bat fly density has been linked to species-level grooming rates and the two vampire species that were observed ranked 5th and 6th place out of 53 neotropical bats for average number of parasitic streblid flies per bat. A sampling bias could also over-emphasize social grooming in vampire bats, because there is much effort focused on studying vampire bat social behavior and a lack of data on social grooming in other bats.

Comparing social grooming data across studies can be difficult due to study differences in ectoparasite density, temperature, sampling method, visibility, and level of human disturbance. Still, there are important conclusions that can be made regarding social grooming among vampire bats from the studies that have been conducted. With even better studies in the future – for instance, ones that compare groups of adult bats that have fixed levels of social association (stable group composition) and no insect ectoparasites – we will get a clearer picture of social grooming among vampire bats and its significance.

According to the passage, Bechstein’s bats and vampire bats differ in their grooming habits in which of the following ways?