Discrimination of the two subspecies of Microtus hartingi (Rodentia: Arvicolinae) by shape and linear features of the spermatozoon

The Asian and European populations of Microtus hartingi have been isolated for a long time by the Straits of Dardanelle and the Bosporus, which could cause different degrees of divergence of morphological structures. The aim of this study was to compare the shape and linear features of spermatozoa of two subspecies of M. hartingi using different methods — geometric and linear morphometrics. The results obtained showed that geometric morphometrics more precisely demonstrates the change in the shape of the spermatozoon of two taxa. The shape of the spermatozoa head of M. h. hartingi is globular, with retracted basal part compared to the slimmer head with a stronger developed basal protrusion in M. h. lydius. The variability of the head shape is insignificant within each taxon, while considerable polymorphism is shown for the shape of acrosome. We have identified several types of acrosome shape, of which two types dominate in the opposite ratio in the two subspecies. Other types of acrosome shape are rare. The question of the diversity of the acrosome shape is discussed. We recommend the method of geometric morphometry of spermatozoa to consider variations of this cell structure in mammals at species and subspecies levels.