Geographical patterns in mandible variation of the common shrew (Sorex araneus) in Europe

The common shrew (Sorex araneus) is one of the most studied shrew species of the Western Palaearctic. Despite this, the general drivers underlying morphological variation still remain unclear. Here we provide evidence for contradictory effects of climatic and geographical factors on the mandible of the common shrew. At the continental scale there is a negative correlation between body- and skull-size and latitude and longitude but at regional scales such an association is often not apparent; in fact, in some cases body size and skull size follow the opposite trend and observations at various scales yielded contradictory results. We studied shrew mandibles using geometric morphometrics and tested for correlations of their size and shape with selected geographical and climatic variables. We examined 1155 mandibles from 29 European localities and found significant interpopulation differences in both size and shape. Centroid size negatively correlated with latitude. We also found that centroid size was significantly correlated with altitude and annual precipitation. Our results confirmed an inverse Bergmann's rule relationship in S. araneus along the transect from the Baltic to the Adriatic Sea. Regarding mandible shape, Slovenian shrews were the most distant from all other studied populations. We discuss how altitude and precipitation can influence the morphology of the common shrew.