Behavioral differentiation and hybridization of the European and Asian forms of Harting' vole Microtus hartingi (Rodentia, Arvicolinae)

The final isolation of Europe from Asia took place comparatively not long ago - in the early Holocene - late Pleistocene which led to the division of Microtus hartingi area into two isolated parts (Asian-Central and West Anatolia and European-southern Balkans). The Northern Mediterranean was influenced by considerable climatic and habitat fluctuations that caused fragmentation of a potential area of Microtus hartingi and promoted microevolutionary processes. The purpose of the work was evaluation of the range disjunction influence on diversification of the species. We analyzed (1) copulatory behavior, (2) exploratory activity and ability to overcome the stress, (3) growth and development of pups, and also (4) hybridization success in the two nominal forms of M. hartingi - M. h. lydius and M. h. strandzensis. Considerable changes in behavior of individuals of two subspecies were obtained. As a result of the hybridization of the two forms, viable and prolific posterity of F1 was received, but the subsequent cross breeding including backcrossing sterility of males and high mortality of posterity began to be established. The testes and the epididymis of the hybrids were with smaller weight in comparison with parents' subspecies, especially M. h. lydius, reduced quantity of spermatozoa and small percent mobile of them which confirmed the lower level of spermatogenesis. We assume that evolution of the phenotypic characteristics of the voles was supported by gene drift and probably by the selection, induced by the stress more strongly, than changes in the genotypic characteristics, e.g. distinctions on cytochrome b and the karyotype are not significant. This can be explained as an influence of specific ecological conditions and fragmentation of the habitats in the Northern Mediterranean Region. Until recently M. h. lydius and M. h. strandzensis were considered as subspecies. However, they reached considerable degree of a divergence and the question of their specific status has to be considered additionally.