Insularity induces changes on body and mandible morphology in a Mediterranean population of the greater white-toothed shrew Crocidura russula (Hermann, 1780)

Island populations of terrestrial mammals often undergo extensive behavioural and morphological changes when separated from mainland populations. Within small mammals these changes have been mainly reported in rodents but were poorly assessed in soricomorphs. In this study we compared mandible morphology and body condition between mainland and island populations of the greater white-toothed shrew, Crocidura russula. The results indicated that island specimens were bigger and heavier than the mainland counterpart, and they showed changes in mandible shape that were associated with higher mechanical potentials. We suggest that these changes might be the result of the interaction of two main factors taking place in the island population: ecological release (i.e. the decrease of predation and interspecific competition), and consequently the increase of intraspecific competition. While the increase in size and body condition in island shrews could be a direct result from reduced predation and interspecific competition, the changes in mandible shape and the increase of both mechanical potential and sexual dimorphism could have arisen indirectly as a response to stronger intraspecific competition.