Craniological analysis of the muskrat (Ondatra zibethicus) from different river basins of Ukraine

Abstract

The paper presents the results of a comprehensive craniological analysis of muskrats (Ondatra zibethicus Linnaeus, 1766) from five river basins of Ukraine: Dnipro (Lower Dnipro, Kherson Oblast), Snihurivka (irrigation canal, Mykolaiv Oblast), Danube (Lower Danube, Odesa Oblast), Dnister (Middle Dnister, Lviv and Ternopil oblasts), and Donets (Siversky Donets, Luhansk and Kharkiv oblasts). In total, 72 skulls were analysed using methods of traditional and geometric morphometrics. The craniometrical analysis included 14 measurements that describe general dimensions of the skull and its elements, whereas shape analysis was carried out separately for the dorsal and ventral surfaces of the skull and the buccal surface of the left mandible. The study revealed that muskrats from the Donets basin have the smallest skulls, whereas the other four samples greatly overlap. According to the results of multivariate analyses (PCA, CVA), the length and height of the mandible contribute the most into the differentiation of the samples. Geometric morphometrics showed that the most important distinguishing features include the shape of the nasal and parietal bones on the dorsal side, and of structures mainly related to the diastema and proximal part of the hard palatine on the ventral side. The most significant differences between the five samples, however, depend on the shape and relative orientation of the elements of the ascending ramus of the jaw—the coronoid, condylar, and angular processes, as well as the shape of bights between them and of the adjacent curvatures on the dorsal and ventral sides of the ascending ramus. The revealed features allow suggesting that the main contributing factors into the variation of geographically distinct populations include diet and feeding adaptations on the one hand, and possible spatial relationships and origin on the other. The Ukrainian sample also notably differs from muskrats from geographically distant regions by the mean values of several craniometrical characters, also indicating that animals in areas of secondary introduction have smaller cranial dimensions.