Сomprehensive craniological analysis of geographically remote muskrat populations (Ondatra zibethicus Linnaeus, 1766)

In this article, a comprehensive craniological analysis of two geographically remote muskrat populations (Ondatra zibethicus Linnaeus, 1766) was carried out. The research material was samples of muskrat skulls from two geographical populations more than 2000 km away from each other: the vicinity of the village of Aristovo, Semenovsky district, Nizhny Novgorod region and the valley of the Ili River, Balkhash district of the Republic of Kazakhstan. A standard craniometric analysis of the samples from Nizhny Novgorod and Kazakhstan revealed inter-population differences in only one of eight linear measurements (the length of the incisive foramen). The analysis of skull shape based on digital 3D-models revealed inter-population differences in the symmetric component of the form. The analysis of the asymmetric component of the skull form revealed the presence of both fluctuating and directional asymmetry. At the same time the fluctuating asymmetry is about 10 times higher than the directional one. Procrustes ANOVA based on the asymmetric component of muskrat skull shape revealed that that directional asymmetry, in contrast to fluctuating asymmetry, is characterized by inter-population specificity, that is, muskrat skulls in different populations deviate differently from strict bilateral symmetry. At this stage of research, it is impossible to find out whether this specificity has an adaptive value or is the result of isolation and genetic-automatic processes. The obtained results complement our understanding of the processes of morphological adaptation in muskrat populations as an introduced species.