Cranial morphological homogeneity in two subspecies of water deer in China and Korea

The water deer (Hydropotes inermis) has conventionally been classifiedinto two subspecies according to geographic distribution and pelage color pattern:H. i. inermis from China and H. i. argyropus fromKorea. However, the results of a recent molecular study have called this into question. Tofurther reappraise this classification, we examined morphological variation incraniodental measurements of these 2 subspecies. Results of univariate and multivariateanalyses demonstrated that these 2 subspecies are not well-differentiated, suggesting thatindividuals of the 2 populations share common morphological traits. Despite thedistribution of the subspecies at different latitudes, no clear morphocline was detected,suggesting that Bergmann’s rule does not apply in this case. Discriminant analysisindicated that the characteristics of individuals are shared by both populations,suggesting that not all individuals can be assigned to their original population. Resultsof principal component analysis showed that the two populations shared more than 75% ofindividuals, congruent with the “75% rule” of subspecies classification. In both theneighbor-joining and unweighted pair group methods with arithmetic mean cluster analyses,specimens of H. i. argyropus and H. i. inermis werehighly mixed within the cladograms. These results suggest that the overall morphologicalvariation in the 2 subspecies overlaps considerably and that there is no coherentcraniofacial difference between the 2 groups. The present findings combined with priorobservations from molecular biogeography point out that the taxonomic division of waterdeer into 2 subspecies should be revisited.