Causes and consequences of living in closed societies: lessons from a long‐term socio‐genetic study on Bechstein’s bats

Abstract

Understanding the ecological, behavioural and genetic factors influencing animal social systems is crucial to investigating the evolution of sociality. Despite the recent advances in population genetic methods and the analysis of social interactions, long-term studies exploring the causes and consequences of social systems in wild mammals are rare. Here, we provide a synthesis of 15 years of data on the Bechstein's bat (Myotis bechsteinii), a species that raises its young in closed societies of 10-45 females living together for their entire lives and where immigration is virtually absent. We discuss the potential causes and consequences of living in closed societies, based on the available data on Bechstein's bat and other species with similar social systems. Using a combination of observational and genetic data on the bats together with genetic data on an ecto-parasite, we suggest that closed societies in Bechstein's bats are likely caused by a combination of benefits from cooperation with familiar colony members and parasite pressure. Consequences of this peculiar social system include increased sensitivity to demographic fluctuations and limits to dispersal during colony foundation, which have broad implications for conservation. We also hope to illustrate by synthesizing the results of this long-term study the diversity of tools that can be applied to hypothesize about the factors influencing a species' social system. We are convinced that with the expansion of the number of social mammals for which comparably detailed socio-genetic long-term data are available, future comparative studies will provide deeper insights into the evolution of closed societies.

Lyssavirus-reactive antibodies in Swedish bats

“…Daubenton's bats live in ‘fusion-fission colonies’, in which the bats in the same roosting refuge form a ‘loose colony’ (40). The ‘fused colony’ is built by several subgroups, while fission occurs at the time of roost switching by subgroups breaking apart and mixing, ending up in various new roosts (41). This strategy has several ecological advantages, but unfortunately it also facilitates the efficient spreading of infections.…”

Host social organization and mating system shape parasite transmission opportunities in three European bat species

“…As a result, unlike most other mammalian systems (Schalk and Forbes 1997; Zuk and McKean 1996), females of most temperate zone bats have higher levels of parasite infection than males (e.g., Reckardt and Kerth 2009). Contact between the philopatric, closed female maternity colonies, and between females and males, is very rare during summer (Burland and Wilmer 2001; Kerth and van Schaik 2012). This results in limited horizontal transmission (used here as parasite exchange between different host colonies) opportunities for contact-transmitted parasites during this time (Bruyndonckx et al 2009b; van Schaik et al 2015).…”

“…Mite infection increases host grooming activity and metabolism (Giorgi et al 2001), and thus may impose a substantial cost, especially to juvenile hosts in maternity colonies (Lourenço and Palmeirim 2007). A study of mite population genetic structure across maternity colonies in M. myotis and Myotis bechsteinii , the latter having a similar social organization as M. nattereri (Kerth and van Schaik 2012; Rivers et al 2005), found contrasting levels of genetic diversity and genetic differentiation between the maternity colonies of the two host species (van Schaik et al 2014). Nevertheless, in both M. myotis and M. bechsteinii , substantial horizontal transmission of mites during the autumn mating season was implicated but could not be examined.…”

The complete mitochondrial genome of the Bechstein’s bat, Myotis bechsteinii (Chiroptera, Vespertilionidae)

“…M. bechsteinii were wild caught in a forest near the city of W€ urzburg, Germany (latitude: N49 43 0 , longitude: E9 49 0 ), where the species has been studied for more than two decades (Kerth & van Schaik 2012). A 3 mm diameter wing biopsy was taken and stored in silica beads prior to DNA extraction.…”

“…In this study, we sequenced, assembled, and phylogenetically validated the mitogenome of M. bechsteinii, a species whose population genetic structure and social behaviour has been intensively studied (Kerth & van Schaik 2012). This mitogenome is a resource for phylogenetic, biomedical, and on-going conservation studies.…”