Geological and paleoclimatic events reflected in phylogeographic patterns of intertidal arthropods (Acari, Oribatida, Selenoribatidae) from southern Japanese islands

A comprehensive study of the intertidal oribatid mite fauna of southern Japanese islands revealed the presence of the selenoribatid Arotrobates granulatus Luxton, 1992 and two yet undescribed species. The latter are herein described as Indopacifica taiyo n. sp., occurring from the Southern to the Central Ryukyus, and Indopacifica tyida n. sp., which was only found on the most western island of the Ryukyus, namely Yonaguni. A concomitant molecular genetic study using mitochondrial COI and 18S rRNA gene sequences, demonstrated that the phylogeographic pattern of I. taiyo n. sp. reflects recent expansion on the Southern and Central Ryukyus, probably due to existing land bridges during the late Pleistocene. Arotrobates granulatus , on the other hand, shows three distinct lineages, one on Japanese mainland, another on the island of Amami, and the third on part of the Central and Southern Ryukyus. These lineages are most likely the result of the break‐up of a large peninsula reaching from China to the Northern Ryukyus about 1.2–1.7 million years ago. Despite emerging land bridges in the late Pleistocene, this species was not able to expand its range again which indicates very low dispersal abilities. Morphometric data of I. taiyo n. sp. show considerable intraspecific variation between island populations correlating with geography. This found variation is suggested to be a result of phenotypic plasticity caused by diverging local environmental factors. From an ecological perspective, all three found species are classified as intertidal rock‐dwellers feeding on diverse algae, whereas I. taiyo n. sp. and Arotrobates granulatus occasionally occur in mangrove habitats.