Genetic signature of Last Glacial Maximum regional refugia in a circum-Antarctic sea spider.

Anna Soler-Membrives,Claudia P Arango,Karen J Miller,Katrin Linse

doi:10.1098/rsos.170615

Abstract

The evolutionary history of Antarctic organisms is becoming increasingly important to understand and manage population trajectories under rapid environmental change. The Antarctic sea spider Nymphon australe, with an apparently large population size compared with other sea spider species, is an ideal target to look for molecular signatures of past climatic events. We analysed mitochondrial DNA of specimens collected from the Antarctic continent and two Antarctic islands (AI) to infer past population processes and understand current genetic structure. Demographic history analyses suggest populations survived in refugia during the Last Glacial Maximum. The high genetic diversity found in the Antarctic Peninsula and East Antarctic (EA) seems related to multiple demographic contraction–expansion events associated with deep-sea refugia, while the low genetic diversity in the Weddell Sea points to a more recent expansion from a shelf refugium. We suggest the genetic structure of N. australe from AI reflects recent colonization from the continent. At a local level, EA populations reveal generally low genetic differentiation, geographically and bathymetrically, suggesting limited restrictions to dispersal. Results highlight regional differences in demographic histories and how these relate to the variation in intensity of glaciation–deglaciation events around Antarctica, critical for the study of local evolutionary processes. These are valuable data for understanding the remarkable success of Antarctic pycnogonids, and how environmental changes have shaped the evolution and diversification of Southern Ocean benthic biodiversity.

Highlights

The Southern Ocean (SO) marine biota is unique in terms of ecology, phylogeography and diversity [1] as a consequence of the long isolation, the unique geological and climatological history, and recurrent glacial cycles
The number of haplotypes (k) was lowest in Antarctic islands (AI) (k = 6) and highest in East Antarctic (EA) (k = 50), this was probably related to the different sampling effort in each locality given that haplotype diversity was similar in these two locations
Genetic variation was low in the Weddell Sea (WS), which had around half the haplotypic diversity of the other localities, as well as the lowest average number of nucleotide differences (Π ) and mean nucleotide diversity (π )

Summary

Introduction

The Southern Ocean (SO) marine biota is unique in terms of ecology, phylogeography and diversity [1] as a consequence of the long isolation, the unique geological and climatological history, and recurrent glacial cycles. The most recent reconstructions of the Antarctic Ice sheet during the LGM suggest that it did not reach the shelf edge all around Antarctica and that the spatial pattern of deglaciation was highly variable, especially on inner shelves [11], enabling the presence of shelf refugia This variability in the nature of ice extent and the way in which it retreated probably had differential effects on the recolonization and expansion of marine populations, resulting in different evolutionary trajectories around Antarctica. The multi-national, SO-wide expeditions linked to the Census of Antarctic Marine Life (CAML) enhanced the collection, sharing and barcoding of specimens [12], enabling detailed phylogeographic analyses on selected taxa to study their relatively recent evolutionary history [8,9,13,14,15,16,17] These datasets are contributing to understanding how populations around Antarctica survived through past environmental change

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