Distinct haplotype structure at the innate immune receptor Toll-like receptor 2 across bank vole populations and lineages in Europe

Parasite-mediated selection may contribute to the maintenance of genetic variation at host immune genes over long time scales. To date, the best evidence for the long-term maintenance of immunogenetic variation in natural populations comes from studies on the major histocompatibility complex (MHC) genes, whereas evidence for such processes from other immune genes remains scarce. In the present study, we show that, despite pronounced population differentiation and the occurrence of numerous private alleles within populations, the innate immune gene Toll-like receptor 2 (TLR2) displays a distinct haplotype structure in 21 bank vole (Myodes glareolus) populations across Europe. Haplotypes from all populations grouped in four clearly differentiated clusters, with the three main clusters co-occurring in at least three previously described mitochondrial lineages. This pattern indicates that the distinct TLR2 haplotype structure may precede the split of the mitochondrial lineages 0.19-0.56 Mya and suggests that haplotype clusters at this innate immune receptor are maintained over prolonged time in wild bank vole populations.