Geographic variation and biogeography of the greater Japanese shrew mole Urotrichus talpoides (Eulipotyphla: Talpidae)

Abstract

The island rule has been generally studied as a morphological evolution between continents and islands. Recently, an evolution between islands of the larger main islands and smaller peripheral islands in Japan has been implied. This study revealed island–island biogeography and examined the island rule between islands. We studied the skull morphology of the greater Japanese shrew mole Urotrichus talpoides Temminck, 1841 (Eulipotyphla: Talpidae). Univariate and multivariate analyses were conducted on the basis of 20 measurements obtained from 296 specimens. Our results revealed morphological differences among islands, in the overall skull size, distance of the fourth premolar to the third molar in the upper and lower jaws (P4M3 and P4M3), and the slender–robust proportion of the rostrum and braincase. P4M3 and P4M3 were commonly larger in the peripheral island populations than in the main island populations. By contrast, the overall skull size and proportion of the rostrum and braincase diverged among the peripheral islands. Therefore, gigantism of P4M3 and P4M3 was suggested in the peripheral island populations, and the island rule was partially supported; however, the island–island morphological evolution should be considered to have a different direction from the island rule due to divergent morphology in small–large skull size and slender–robust proportion among peripheral island populations.