Geographic variations of skull morphology in the Rhinolophus ferrumequinum species complex (Mammalia: Chiroptera)

Abstract

The greater horseshoe bat (Rhinolophus ferrumequinum), distributed from Europe and Northeast Africa through the temperate regions of Asia to Japan, is regarded as either a single, albeit polytypic, species or as representing a complex of two species, R. ferrumequinum sensu stricto in the western part and R. nippon in the eastern part of the seemingly continuous range. To evaluate patterns of geographic variation within the complex and to determine if distinguishing morphological characters exist between R. ferrumequinum and R. nippon, we performed a comprehensive comparative study of skull morphology, combining traditional linear measurements, geometric morphometric methods, and evaluation of non-quantitative discriminant characters. We analyzed 230 specimens from 19 localities in 10 geographic regions sampled from central Europe, Iraq, Nepal, China, North Korea, South Korea, and Japan. Our results revealed remarkable differences in skull morphology between the European-West Asian and East Asian groups; variation between these two groups was considerably larger than within-group variation. The two groups were separable by three main features: 1) the position of the anterior palatal edge in relation to the cusps of the upper first molar; 2) the position of the glenoid cavity; and 3) the robustness of the skull as expressed by the ratio of the zygomatic and mastoid widths. In line with recent molecular biological studies, we recommend recognizing R. ferrumequinum (Schreber, 1774) and R. nippon Temminck, 1835 as two distinct species. Our results also revealed unique size variations in island populations of R. nippon, presumably shaped by the island rule and the founder effect.