Genetic structure and dispersal patterns in Limnoria nagatai (Limnoriidae, Isopoda) dwelling in non-buoyant kelps, Eisenia bicyclis and E. arborea, in Japan.

Hiroki Yoshino,Takeshi A Ohsawa,Futa Yamaji,Tzen-Yuh Chiang

doi:10.1371/journal.pone.0198451

Abstract

The marine isopod genus Limnoria contains algae-eating species. Previous phylogeographic studies have suggested that Limnoria species feeding on buoyant kelp underwent low genetic differentiation on a large spatial scale because rafting on floating host kelps promotes high levels of gene flow. In this paper, we survey the genetic structure of Limnoria nagatai, which bores into the non-buoyant kelps Eisenia bicyclis and E. arborea. We analyze the mitochondrial DNA (cytochrome oxidase subunit I [COI] gene) and morphological traits of L. nagatai, and the host kelps E. bicyclis and E. arborea from 14 populations along the Japanese archipelago of the Pacific Ocean and the Sea of Japan. Four major lineages are recognized within L. nagatai: three lineages in the Pacific Ocean, and one lineage in the Sea of Japan which might be a cryptic species. For L. nagatai, we show high genetic differentiation between geographically separated habitats in the Pacific Ocean, while low differentiation is found among continuous host kelps habitats in the Pacific Ocean as well as the Sea of Japan. L. nagatai in E. bicyclis in the Pacific Ocean has experienced large population expansion after the Last Glacial Maximum (LGM), whereas the lineage in E. bicyclis in the Sea of Japan has not. We suggest that Limnoria feeding on non-buoyant kelps, may attain low genetic differentiation because they might be able to disperse long distance if the habitat of host kelps is continuous. The historical events affecting Limnoria after the LGM may differ between the coasts of the Pacific Ocean and the Sea of Japan.

Highlights

Dispersal ability affects the levels of gene flow and complexity of population genetic structure [1]
In marine benthic invertebrates with low mobility, dispersal potential at the pelagic larval stage has been recognized as an important determinant of genetic structure [2,3]
Genetic analyses of Limnoria nagatai from the host kelp Eisenia in Japan revealed that L. nagatai comprised three allopatric lineages in the Pacific Ocean and one lineage in the Sea of Japan

Summary

Introduction

Dispersal ability affects the levels of gene flow and complexity of population genetic structure [1]. In marine benthic invertebrates with low mobility, dispersal potential at the pelagic larval stage has been recognized as an important determinant of genetic structure [2,3]. Recent genetic studies on some marine species suggest that the presence or absence and the length of a planktonic larval stage do not explain the variance in the genetic structure [4,5,6]. Some alternative factors caused dispersal across distant geographic areas, for example, vicariant effects of historic patterns, anthropogenic introduction, and rafting on floating objects [3]. Excellent discussions on genetic structures of benthic animals affected by long-distance dispersal via rafting on floating objects have been presented in phylogenetic works on the isopods of the genus Limnoria Leach (Limnoriidae, Crustacea) [7,8]

Methods

Results

Discussion

Conclusion