Contrasted phylogeographic patterns on mitochondrial DNA of shallow and deep brittle stars across the Atlantic-Mediterranean area.

Sergi Taboada,Rocío Pérez-Portela

doi:10.1038/srep32425

Abstract

Previous studies on Ophiothrix in European waters demonstrated the existence of two distinct species, Ophiothrix fragilis and Ophiothrix sp. II. Using phylogenetic and species delimitation techniques based on two mitochondrial genes (cytochrome c oxidase I and 16S rRNA) we prove the existence of a new congeneric species (Ophiothrix sp. III), occurring in the deep Atlantic coast of the Iberian Peninsula and the Alboran Sea. We compared phylogeographic patterns of these three Ophiothrix species to test whether closely related species are differentially affected by past demographic events and current oceanographic barriers. We used 432 sequences (137 of O. fragilis, 215 of Ophiothrix sp. II, and 80 of Ophiothrix sp. III) of the 16S rRNA from 23 Atlantic-Mediterranean locations for the analyses. We observed different geographic and bathymetric distributions, and contrasted phylogeography among species. Ophiothrix fragilis appeared genetically isolated between the Atlantic and Mediterranean basins, attributed to past vicariance during Pleistocene glaciations and a secondary contact associated to demographic expansion. This contrasts with the panmixia observed in Ophiothrix sp. II across the Atlantic-Mediterranean area. Results were not conclusive for Ophiothrix sp. III due to the lack of a more complete sampling within the Mediterranean Sea.

Highlights

Several benthic invertebrates, reaching in some cases different conclusions even when considering species with similar dispersal abilities e.g. refs 7, 8, 12 and 20, which may be explained by the effect of past historical processes differentially affecting the genetic diversity of these organisms
The aims of this work were: (i) to describe the distribution of Ophiothrix spp. across both space and depth, and to detect the possible occurrence of cryptic speciation; and (ii) to compare phylogeographic patterns based on mitochondrial DNA among congeneric species to determine whether present and past marine biogeographic barriers and demographic events may have differentially affected the distribution of genetic diversity among species, paying special attention to potential differentiation between the Atlantic and Mediterranean basins
Two different haplogroups were recovered for the 16S in O. fragilis corresponding to samples from the Mediterranean and from a mixture of samples from the Atlantic and Mediterranean (Fig. 2; fra_Med and fra_Atl-Med); these haplogroups, though, were not recovered in the COI phylogenetic tree because samples of this species from the Mediterranean were not available

Summary

Introduction

Several benthic invertebrates, reaching in some cases different conclusions even when considering species with similar dispersal abilities e.g. refs 7, 8, 12 and 20, which may be explained by the effect of past historical processes differentially affecting the genetic diversity of these organisms In this sense, the comprehensive study of congeneric species with a common evolutionary origin (i.e. sharing similar biological traits) and similar geographic distribution (i.e. being affected by similar hydrological and geological processes), has been proposed as a useful approach to identify phylogeographic signals and real permeability of major marine fronts[1,7,21]. To achieve our objectives we used two mitochondrial gene fragments, the 16S rRNA (hereafter 16S), which has been demonstrated to provide suitable resolution in population genetic studies of brittle stars[15,24], and the cytochrome c oxidase subunit I (hereafter COI)

Objectives

Methods

Results

Conclusion