Morphological diversity of dental and mandibular deformities in Microtus hartingi (Rodentia, Arvicolinae)

We analyzed 104 labial and lingual projections of Harting's vole (Microtus hartingi) mandibles using linear and geometric morphometrics. Incisor and molar overgrowth and mandibular deformations were described in 2 Harting's vole populations. Over a 6-year research period, excessive incisor growth was observed in 15.4% of the Rhodopean M. hartingi population and in 10.3% of the Central Anatolian form M. h. ankaraensis. Maxillary incisors lengthening up to 2.3x the norm was noted, often accompanied by mandibular incisor shortening. Nevertheless, voles with overgrown incisors were able to feed and breed until the late stages of the pathology, where overgrown incisors made feeding impossible. The mandibular deformations were always accompanied by incisor overgrowth and never manifested on their own. Geometric morphometrics analysis revealed similar patterns of mandibular deformation and incisor overgrowth in both vole populations: extension of the coronoid process and the body of the mandible, elevated molar alveolus, deformation of the incisor alveolus, shortening of the diastema and narrowing of the spaces between the mandibular processes. Linear morphometry did not reveal any significant changes in the mandibular morphoecological indices; however, the distances between landmarks changed significantly. Due to the mandibular shape change, the methiorphoecological index values of the deformed mandibles remained the same as those of the normal mandibles. The excessive tooth growth and deformed mandible morphotype in Harting's vole may be the result of genetic and epigenetic factors induced by environmental stress which lead to developmental anomalies.