Features of reproduction and postembryonic ontogenesis in voles Microtus kermanensis and M. mystacinus of the subgenus Microtus (Rodentia, Arvicolinae)

The voles Microtus kermanensis Roguin, 1988 and M. mystacinus De Filippi, 1865 are representatives of the “mystacinus” group in the subgenus Microtus (2n = 54). A three-year study of reproduction of these species was conducted in the Laboratory of Theriology of the Zoological Institute RAS. The laboratory populations of voles were created from animals caught in Iran. In this study, 38 pairs of M. kermanensis and 18 pairs of M. mystacinus were under observation. For the study of postembryonic ontogenesis, 39 litters (166 pups) of M. kermanensis voles and 14 litters (51 pups) of M. mystacinus were examined. For comparison, 10 litters (47 pups) of M. arvalis Pallas, 1978 (form “arvalis” from the Vladimir region) were used. The breeding of animals continued all year round. The average number of pups per litter was 4.3 in M. kermanensis, 3.6 in M. mystacinus, and 4.7 in M. arvalis; the sex ratio in all species was close to 1:1. High mortality was noted in the larger M. kermanensis (28.3%), with lower rates in M. mystacinus (15.7%) and M. arvalis (17.0%). In general, the development of pups of all three species during the first 12 days of life is fast. Among the distinctive features, the early separation of the auricles in M. mystacinus is of note. The large M. kermanensis is characterized by earlier divergence of the fingers on the fore and hind limbs, which ends by day 10 (in M. mystacinus and M. arvalis by day 12). Also, in M. kermanensis the timing of incisor eruption is extended; the lower incisors begin to erupt on day 3 and appear by day 9 in 100% of the pups (by day 7 in the other two species). The upper incisors begin to erupt from day 4, and 100% of the pups have them by day 10 (in M. mystacinus and M. arvalis, they completely erupt on day 8). In all three species, their eyes start opening at 9 days and open completely by day 12; such uniformity can serve as confirmation of the phylogenetic proximity of these species. All three species are characterized by the avoidance of incest.