Molecular phylogeography reveals multiple Pleistocene divergence events in estuarine crabs from the tropical West Pacific.

Adnan Shahdadi,Christoph D Schubart,Katharina Von Wyschetzki,Ka Hou Chu,Hung-Chang Liu

doi:10.1371/journal.pone.0262122

Abstract

Due to the lack of visible barriers to gene flow, it was a long-standing assumption that marine coastal species are widely distributed, until molecular studies revealed geographically structured intraspecific genetic differentiation in many taxa. Historical events of sea level changes during glacial periods are known to have triggered sequential disjunctions and genetic divergences among populations, especially of coastal organisms. The Parasesarma bidens species complex so far includes three named plus potentially cryptic species of estuarine brachyuran crabs, distributed along East to Southeast Asia. The aim of the present study is to address phylogeography and uncover real and hidden biological diversity within this complex, by revealing the underlying genetic structure of populations and species throughout their distribution ranges from Japan to West Papua, with a comparison of mitochondrial COX1 and 16S rRNA gene sequences. Our results reveal that the P. bidens species complex consists of at least five distinct clades, resulting from four main cladogenesis events during the mid to late Pleistocene. Among those clades, P. cricotum and P. sanguimanus are recovered as monophyletic taxa. Geographically restricted endemic clades are encountered in southeastern Indonesia, Japan and China respectively, whereas the Philippines and Taiwan share two clades. As individuals of the Japanese clade can also be found in Taiwan, we provide evidence of a third lineage and the occurrence of a potential cryptic species on this island. Ocean level retreats during Pleistocene ice ages and present oceanic currents appear to be the main triggers for the divergences of the five clades that are here addressed as the P. bidens complex. Secondary range expansions converted Taiwan into the point of maximal overlap, sharing populations with Japan and the Philippines, but not with mainland China.

Highlights

The biogeography of marine species is generally determined by different abiotic and biotic factors
The present study focuses on the coastal crab species occurring in this area, i.e. Parasesarma cricotum from Southeast Asia vs. P. sanguimanus and P. bidens from East Asia, in order to reveal underlying causes for species divergence and biogeographic distribution patterns in these two Asian subregions
cytochrome oxidase subunit 1 (COX1) sequences were obtained from 142 specimens of P. bidens species complex (Fig 2A, S1 Table), with variable lengths from different localities as the main ingroup of the present analyses

Summary

Introduction

The biogeography of marine species is generally determined by different abiotic and biotic factors. The lack of visible geographic barriers was responsible for the general belief that most marine species are widely, or some of them even globally, distributed and dispersed via oceanic currents [16]. Molecular comparisons have revealed genetic disjunctions and phylogeographic structures among and within many marine animals [17], including decapod crustaceans [18]. Such genetic disconnections and locally structured patterns are common among partly pelagic [19] and meroplanktonic (e.g. coastal crabs with planktonic larvae) species [20]

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Conclusion