Morphological and molecular phylogenetic analyses ofZepedanulus ishikawai(Arachnida: Opiliones: Laniatores: Epedanidae) in the southern part of the Ryukyu Archipelago

Ryo Arakawa,Jun Yokoyama,Osamu Miura,Tatsuya Fukuda,Yoshimasa Kumekawa,Haruka Fujimoto

doi:10.4039/tce.2021.42

Abstract

AbstractHarvestmen (Arachnida: Opiliones) are soil animals with extremely low dispersal abilities that experienced allopatric differentiation. To clarify the morphological and phylogenetic differentiation of the endemic harvestmanZepedanulus ishikawai(Suzuki, 1971) (Laniatores: Epedanidae) in the southern part of the Ryukyu Archipelago, we conducted molecular phylogenetic analyses and divergence time estimates based onCO1and16SrRNA sequences of mtDNA, the28SrRNA sequence of nrDNA, and the external morphology. A phylogenetic tree based on mtDNA sequences indicated that individuals ofZ. ishikawaiwere monophyletic and were divided into clade I and clade II. This was supported by the nrDNA phylogenetic tree. Although clades I and II were distributed sympatrically on all three islands examined (Ishigaki, Iriomote, and Yonaguni), heterogeneity could not be detected by polymerase chain reaction–restriction fragment length polymorphism of nrDNA, indicating that clades I and II do not have a history of hybridisation. Also, several morphological characters differed significantly between individuals of clade I and clade II. The longstanding isolation of the southern Ryukyus from the surrounding islands enabled estimation of the original morphological characters of both clades ofZ. ishikawai.

Highlights

Continental archipelagos are suitable for examining causal connections between geographical barriers, disjunct distributions, and genetic differentiation (Hedges et al 1992; Hisheh et al 1998; Atkins et al 2001; Ohdachi et al 2001; Poulakakis et al 2003; Bittkau and Comes 2005; VeloAnton et al 2012)
Even though only one sample of Epedanellus tuberculatus was used in the analysis of the 16S ribosomal RNA (rRNA) and CO1 sequences, four samples of Penaeus japonicus and two of K. insulanus were analysed because previous studies indicated that these species are divided into four and two groups, respectively (Kumekawa et al 2014, 2015)
The phylogenetic trees based on the CO1 and 16S rRNA genes indicated that individuals of Z. ishikawai composed a monophyletic group with a high bootstrap value (96%) and high posterior probability (1.00)

Summary

Introduction

Continental archipelagos are suitable for examining causal connections between geographical barriers, disjunct distributions, and genetic differentiation (Hedges et al 1992; Hisheh et al 1998; Atkins et al 2001; Ohdachi et al 2001; Poulakakis et al 2003; Bittkau and Comes 2005; VeloAnton et al 2012). The Ryukyu Archipelago was the eastern margin of continental East Asia in the middle to late Miocene (15.97–5.333 million years ago). In the late Miocene to the early Pleistocene (5.333–0.774 million years ago), it fragmented into large islands and includes approximately 140 islands scattered in an arc between Kyushu Island of Japan and Taiwan. The islands are the product of the repeated formation and division of a land bridge to continental Asia that extended through Taiwan and Kyushu. Expansion and regression of the land bridge have been attributed to climatic oscillations in the Pliocene and Quaternary periods (Kimura 1996, 2000; Kizaki and Ohshiro 1977, 1980; Ujiie 1990; Ohshiro 2003; Keally 2005; Shinjo 2015). A number of biogeographic and evolutionary studies on the organisms of the Ryukyu Archipelago have been conducted and have enhanced our understanding of the biogeographic and evolutionary histories of organisms in continental archipelagos (e.g., Ota 1998; Maekawa et al 1999; Seo et al 2004; Chiang and Schaal 2006; Seki et al 2007; Nakamura et al 2015; Kaito and Toda 2016)

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