[en] Black rat ; skull morphology ; size increase ; Azores archipelago
[en] The present paper deals with an analysis of metric (cranial measurements) and non metric (epigenetic cranial characters) variation in black rat populations from S. Miguel and Terceira islands compared to a continental sample. Assuming the Azorean rats originate from the European continent, we tested the similarity between the samples, considering only adult and subadult animals. Having verified that there was no sexual dimorphism in the characters studied, we computed discriminant functions and made a PCA with the most discriminant variables. The three samples are clearly separated by these functions, the Azorean rats showing a larger general skull size and differing between the two islands. The Mean Measure of Divergence (MMD), based on non metric cranial traits frequencies, was also used to express the interpopulational differences: the rats of Terceira differ significantly either from the continental ones or from those of S. Miguel. Finally, the possible origin of these differences is disussed.