Integrative taxonomy on the rare sky-island Ligidium species from southwest China (Isopoda, Oniscidea, Ligiidae)

Abstract

Background The sky-island Ligidium species fauna in southwest China is poorly known. Before this study, six of the seven sky-island species of the genus were known to be endemic to southwest China. In morphology, Ligidium species are often difficult to identify, and an appraisal of integrative taxonomy is needed. Results We integrated morphology and molecular analyses to delimit Ligidium species. Molecular species delimitation based on distance- and evolutionary models recovered seven-candidate lineages from five gene markers (COI, 12S rRNA, 18S rRNA, 28S rRNA and NAK). We also estimated that the species divergences of sky-island Ligidium in southwest China started in late Eocene (40.97 Mya) to middle Miocene (15.19 Mya). Four new species (L. duospinatum Li, sp. nov., L. acuminatum Li, sp. nov., L. rotundum Li, sp. nov. and L. tridentatum Li, sp. nov.) are described. Morphological confusion among L. denticulatum Shen, 1949, L. inerme Nunomura & Xie, 2000 and L. sichuanense Nunomura, 2002 is clarified by integrative taxonomy. Conclusion This work confirms that an integrative approach to Ligidium taxonomy is fundamental for objective classification, and deduced the uplift of Qinghai-Tibetan Plateau in the late Eocene and middle Miocene as one of the principal reasons for the species divergences of sky-island Ligidium in southwest China. We also inferred that sky-island mountains have a huge reserve of higher Ligidium species diversity.

History of the terrestrial isopod genus Ligidium in Japan based on phylogeographic analysis

“…For example, in the Aegean Islands of Greece, Ligidium can be sorted into genetic clusters corresponding to their paleogeographic histories, suggesting that the islands’ isolation was a major determinant of their genetic diversity [ 12 ]. In China, the uplift of the Qinghai–Tibet Plateau likely affected Ligidium species divergence [ 13 ]. Our preliminary analysis showed that the Hokkaido population in northern Japan experienced a bottleneck caused by the Last Glacial Maximum (LGM) [ 14 ], suggesting that this genus is sensitive to glacial cycles.…”