Incisor Adaptation to Fossorial Life in the Blind Mole-Rax Spalax ehrenbergi

Blind mole-rats ( Spalax ehrenbergi ) are aggressive and solitary fossorial rodents, highly specialized to their environment. They use their lower incisors mainly to excavate their tunnel systems. We found that the lower incisors of the mole-rat grow significantly faster than the upper incisors. Upper and lower incisors of males grow significantly faster than incisors of females. Density of incisors of males was significantly higher than in females and in male laboratory rats ( Rattus norvegicus ). In both sexes of mole-rats, maxillary bone density at the root apex area of the incisor was significantly higher than the anterior area where incisors emerge from the bone and the same area densities in male laboratory rats. We suggest that the rapid growth rate and high density of incisors in mole-rats compared with male laboratory rats represent an adaptation to their digging life-style and compensate for the extensive incisor attrition resulting from the mechanical forces of digging. Inter-sexual differences in mole-rat incisor growth and incisor plus maxillary bone densities are in accordance with intersexual behavioral differences: males excavate wider and longer tunnels than females and are more aggressive. Because incisors of males are used more extensively in digging and fighting than those of females, we suggest that male mole-rats develop stronger incisors with a higher compensatory growth rate than females.