The effect of host social system on parasite population genetic structure: comparative population genetics of two ectoparasitic mites and their bat hosts

Abstract

BackgroundThe population genetic structure of a parasite, and consequently its ability to adapt to a given host, is strongly linked to its own life history as well as the life history of its host. While the effects of parasite life history on their population genetic structure have received some attention, the effect of host social system has remained largely unstudied. In this study, we investigated the population genetic structure of two closely related parasitic mite species (Spinturnix myoti and Spinturnix bechsteini) with very similar life histories. Their respective hosts, the greater mouse-eared bat (Myotis myotis) and the Bechstein’s bat (Myotis bechsteinii) have social systems that differ in several substantial features, such as group size, mating system and dispersal patterns.ResultsWe found that the two mite species have strongly differing population genetic structures. In S. myoti we found high levels of genetic diversity and very little pairwise differentiation, whereas in S. bechsteini we observed much less diversity, strongly differentiated populations and strong temporal turnover. These differences are likely to be the result of the differences in genetic drift and dispersal opportunities afforded to the two parasites by the different social systems of their hosts.ConclusionsOur results suggest that host social system can strongly influence parasite population structure. As a result, the evolutionary potential of these two parasites with very similar life histories also differs, thereby affecting the risk and evolutionary pressure exerted by each parasite on its host.

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

“…In this study, we captured over 70  M. bechsteinii , but we did not find any to be infected with mites (see Table S1) despite the fact that such mites are common in several nearby (±100 km) German regions (Bruyndonckx et al 2009b; van Schaik et al 2014). This stochasticity in local extinction patterns can also have strong consequences for parasite population genetic structure in regions where the parasite does not go regionally extinct.…”

“…As a result, the mite meta-population should be well mixed and its effective population size is expected to be much larger than in the other investigated species. Support for this prediction is found in an analysis of mite population genetic structure across six M. myotis maternity colonies, which found high overall genetic diversity and very little genetic differentiation between mites from different M. myotis colonies (van Schaik et al 2014). …”

“…This stochasticity in local extinction patterns can also have strong consequences for parasite population genetic structure in regions where the parasite does not go regionally extinct. In M. bechsteinii , mite populations from different maternity colonies were temporally unstable as a result of the limited transmission and low number of founding individuals per host colony (Bruyndonckx et al 2009b; van Schaik et al 2014). …”

“…Mating in temperate zone bat species is promiscuous and predominantly occurs either in temporary harems (Zahn and Dippel 1997), locally with males in the summer home range of the females (Senior et al 2005), or during a behavior known as swarming, in which bats show intense flight activity at the entrance to underground sites used for hibernation in winter (Fenton 1969). During these encounters, parasites may be directly transmitted between females (in harems) or by males acting as a vector for parasite transmission between females from different colonies (van Schaik et al 2014). In winter, bats hibernate either solitarily or in clusters (Dietz et al 2007).…”

“…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.…”