A historical biogeographical scenario explaining the presence of Triturus karelinii mitochondrial DNA in T. macedonicus . The ranges of T. karelinii and T. macedonicus are shown in blue and green and the region where T. macedonicus contains T. karelinii mitochondrial DNA is shown in red. During the last glaciation, both species’ ranges were repressed (a). After glacial conditions alleviated, T. karelinii derived from Turkey colonized a considerable part of the Balkan Peninsula and T. macedonicus expanded its range and came into contact with T. karelinii (b). Subsequently, T. macedonicus displaced T. karelinii over part of its range and in the process cut off a T. karelinii enclave; due to mitochondrial DNA introgression, T. macedonicus possessed T. karelinii mitochondrial DNA, there where it displaced T. karelinii (c). Finally, T. macedonicus expanded its range further and, as part of the source population contained T. karelinii mitochondrial DNA, this mitochondrial DNA spread, via the bodies of T. macedonicus, into an area not inhabited by T. karelinii itself (d).
Wielstra and Arntzen BMC Evolutionary Biology 2012 12:161 doi:10.1186/1471-2148-12-161