Cryptic speciation in the field vole: a multilocus approach confirms three highly divergent lineages in E urasia

Species are generally described from morphological features, but there is growing recognition of sister forms that show substantial genetic differentiation without obvious morphological variation and may therefore be considered ‘cryptic species’. Here, we investigate the field vole ( M icrotus agrestis ), a E urasian mammal with little apparent morphological differentiation but which, on the basis of previous sex‐linked nuclear and mitochondrial DNA (mt DNA ) analyses, is subdivided into a N orthern and a S outhern lineage, sufficiently divergent that they may represent two cryptic species. These earlier studies also provided limited evidence for two major mt DNA lineages within Iberia. In our present study, we extend these findings through a multilocus approach. We sampled 163 individuals from 46 localities, mainly in I beria, and sequenced seven loci, maternally, paternally and biparentally inherited. Our results show that the mt DNA lineage identified in P ortugal is indeed a distinct third lineage on the basis of other markers as well. In fact, multilocus coalescent‐based methods clearly support three separate evolutionary units that may represent cryptic species: N orthern, S outhern and P ortuguese. Divergence among these units was inferred to have occurred during the last glacial period; the P ortuguese lineage split occurred first (estimated at c. 70 000 bp ), and the N orthern and S outhern lineages separated at around the last glacial maximum (estimated at c. 18 500 bp ). Such recent formation of evolutionary units that might be considered species has repercussions in terms of understanding evolutionary processes and the diversity of small mammals in a E uropean context.