Genetic structure and demographic inference of the regular sea urchin Sterechinus neumayeri (Meissner, 1900) in the Southern Ocean: The role of the last glaciation.

Angie Díaz,Thomas Saucède,Elie Poulin,Karin Gérard,Claudio González-Wevar,Bruno David,Jean-Pierre Féral,Claudia Maturana

doi:10.1371/journal.pone.0197611

Abstract

One of the most relevant characteristics of the extant Southern Ocean fauna is its resiliency to survive glacial processes of the Quaternary. These climatic events produced catastrophic habitat reductions and forced some marine benthic species to move, adapt or go extinct. The marine benthic species inhabiting the Antarctic upper continental shelf faced the Quaternary glaciations with different strategies that drastically modified population sizes and thus affected the amount and distribution of intraspecific genetic variation. Here we present new genetic information for the most conspicuous regular sea urchin of the Antarctic continental shelf, Sterechinus neumayeri. We studied the patterns of genetic diversity and structure in this broadcast-spawner across three Antarctic regions: Antarctic Peninsula, the Weddell Sea and Adélie Land in East Antarctica. Genetic analyses based on mitochondrial and nuclear markers suggested that S. neumayeri is a single genetic unit around the Antarctic continent. The species is characterized by low levels of genetic diversity and exhibits a typical star-like haplotype genealogy that supports the hypothesis of a single in situ refugium. Based on two mutation rates standardized for this genus, the Bayesian Skyline plot analyses detected a rapid demographic expansion after the Last Glacial Maximum. We propose a scenario of rapid postglacial expansion and recolonization of Antarctic shallow areas from a less ice-impacted refugium where the species survived the LGM. Considering the patterns of genetic diversity and structure recorded in the species, this refugium was probably located in East Antarctica.

Highlights

The marine benthic fauna of the Southern Ocean is unique and considered to be the most isolated on the planet [1,2,3,4,5]
A fragment of 931 base pairs coding for 310 amino acids of the mtDNA c oxidase subunit I (COI) gene was amplified, corresponding to nucleotides 79 to 1008 of the gene (Genbank accession AY275548, total size 1077 bp)
Sterechinus neumayeri exhibited low levels of genetic diversity across the Antarctic continent, even though at first glance Fildes Bay in Antarctic Peninsula exhibited higher levels of diversity measured as the number of polymorphic sites (S) and the number of haplotypes (k)

Summary

Introduction

The marine benthic fauna of the Southern Ocean is unique and considered to be the most isolated on the planet [1,2,3,4,5]. The ACC and the APF represent an important boundary in terms of high current speeds and strong horizontal gradients in density, temperature, salinity and air-sea fluxes [10]; they isolate the Antarctic continent and its associated archipelagos and islands from the other continental landmasses [11]. Antarctic continental glacial ice sheet expansions have been associated with one of the most important extinctions on the continent and of the evolution of the Antarctic marine life [13,20,21]. The geographic isolation of the continent, major oceanic currents and the bathymetry all act as strong barriers surrounding the Antarctic Continent, explaining the high levels of endemism recorded in the Antarctic marine benthic biota

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