Morpho-metric analysis of the insular and mainland Rattus in Tunisia

The genus Rattus is widely distributed in Tunisia. Rattus rattus and Rattus norvégiens coexist in continental areas, and only the black rat is present on islands. In the present work, we examined morpho-metric skull variations between continental and islands populations, a population of the Norway rat is used as comparative reference regarding the importance of variation. The influence of the environmental conditions of the Tunisian islands on skull dimensions was determined. The results show that the skull size of island specimens is larger than skulls from specimens in continental areas and even bigger for some mandibular parameters than the Norway rat. The morphological difference is driven by ecological factors such as lack of competition and the low prédation pressure and the nature of trophic resources rich in calcium, which might help increase the size of skulls of island Rattus . This difference seems to be a trait evolving faster in comparison with R. norvegicus .