Authors

Discussion

Many parasites infect multiple host species and transmission between sympatric hosts is assumed to be commonplace. Between-species transmission could be key to parasite persistence and spread, especially where host populations exist in highly heterogeneous landscapes, are small and prone to stochastic extinction. However, previous genetic studies of the multihost parasite Bartonella, found evidence of cryptic host specificity of bacterial strains, challenging the assumption of frequent between-species transmission. We investigate whether this finding of cryptic host specificity is universal or whether dynamics of between-species transmission may be context dependent. Using a whole-genome sequencing approach, we compare patterns of host specificity and between-species transmission of Bartonella grahamii strains in the context of two contrasting populations: a highly fragmented population of water voles (Arvicola amphibius) and sympatric field voles (Microtus agrestis) and a community of field and bank voles (Myodes glareolus) inhabiting more continuous habitat. Statistical analysis of single nucleotide polymorphism (SNP) patterns showed that B. grahamii strains were host generalists in the context of the fragmented population, commonly infecting both hosts. In contrast, in the continuous population B. grahamii showed indications of cryptic host specificity. We suggest that patterns of between-species transmission may be context dependent. In highly heterogenous landscapes and fragmented populations, host generalist  strains may have a competitive advantage over host specialists, as the ability increasing their persistence and spread.