Variation in the white-toothed shrews ( Crocidura spp.) in the British Isles

Abstract Ten skull characters were measured on each of 300 specimens of Crocidura suaveolens (Pallas) and 99 specimens of C. russula Hermann from five of the Scilly Isles, four of the Channel Isles and one locality on the mainland of France. No place contained both species. The characters were skull length, skull width, lengths of upper and lower tooth rows, distance between the third upper molars, distance between the upper premolars, length from the palate to the foramen magnum, the combined length in ventral aspect of the third upper incisor and canine and the mandibular height. The means of each measurement at each locality were calculated. Analyses of variance were also calculated and from these variance components within locality groups were obtained. An analysis into canonical variates was made with a view to accounting for the largest possible part of the variation between groups using a limited number of linear combinations of the original measurements. Most of the variance (82%) was contained in the first canonical variate and from the dispersion of the means of the samples the popula­tions of Crocidura separated into two main groups. One contained animals from Alderney, Guernsey and Cap Gris Nez (C. russula) and the other the remainder (C. suaveolens). The latter group subdivided, particularly with reference to the second canonical variate, into animals from Sark and Jersey and those from the Isles of Scilly. Differences between popula­tions from the Scilly Isles are very small, suggesting origin from a common stock. The shrews from Sark and Jersey differ more from each other than do any pair of Scilly Island popula­tions. The three populations of C. russula do not form as close a cluster as the Scilly Island ones. The analyses of variance agree with these findings although for certain characters highly significant differences often occur between localities in a particular group.