Identification and characterization of the contact zone between short-tailed shrews (Blarina) in Iowa and Missouri

Short-tailed shrews (genus Blarina Gray, 1838) are characterized by divergent karyotypes and are genetically distinct. Blarina species are similar morphologically but, in most cases, can be distinguished morphometrically. Blarina distributions tend to be parapatric along well-defined contact zones; however, it has been suggested that the northern short-tailed shrew (Blarina brevicauda (Say, 1823)) and Elliot's short-tailed shrew (Blarina hylophaga Elliot, 1899) occur sympatrically in Iowa and Missouri. To evaluate this possibility, 179 specimens were collected in southwestern Iowa and northwestern Missouri. Karyotypes and total length were used for field identification, and amplified fragment length polymorphism (AFLP) analysis was used to verify field identifications and to investigate the extent of hybridization. One hundred seventy-eight of 179 specimens were identified to species. The one exception had a karyotype of B. brevicauda (2n = 50, FN = 48); however, AFLP analysis indicated that this individual was likely an F-1 hybrid. No backcrosses were detected, so it appears that introgression is minimal. The putative hybrid was trapped at a locality with B. brevicauda just north of a locality having only B. hylophaga. No locality contained both species. Therefore, these species are not broadly sympatric as has been suggested, but rather exhibit a distribution similar to the pattern of parapatry seen in most of the contact zones of Blarina