Assessing geographic differences in skulls of Neomys fodiens and Neomys anomalus using linear measurements, geometric morphometrics, and non-metric epigenetics

Abstract

Previous morphological studies on Neomys fodiens and Neomys anomalus describe a pronounced ecological variance, mainly attributed to altitudinal and/or climatic conditions especially for Neomys fodiens. The major aim of this study was to find out whether there are intraspecific geographic variations related to cranial morphometry. Two different methods were used: classical linear measurements and modern geometric morphometric 2D method. Shrew skulls from Germany and Slovakia separated into different regional groups were studied. For Neomys fodiens, the linear method showed a clearer separation than the geometric method, whereby the skull measures CBL and CORH followed Bergmann’s rule, which could be explained with an allopatric living. Both methods produced various results for the characters in which the groups differed the most. For N. anomalus, the selectivity was high in both methods, with similar results. The linear skull measures were heterogeneous, which may possibly have been caused by an interspecific competition with N. fodiens. The lengths of the unicuspid teeth of the maxilla showed the strongest variation between the regions, which might be associated with a different prey selection. Likewise, a non-metric study on N. fodiens was performed to obtain knowledge about the epigenetic variability. There was no sign for significant epigenetic impoverishment (Iev = 0.42), and the degrees of the epigenetic distances (MMD = 0.01 to 0.06) indicated a small differentiation between the N. fodiens groups. The fluctuating asymmetry (FA = 0.15 to 0.21) is rather small by comparison with other mammals. So, there is only a small indication of reduced developmental stability in all regional groups, but with an increase from south to north.