Along-shelf connectivity and circumpolar gene flow in Antarctic silverfish (Pleuragramma antarctica)

Jilda Alicia Caccavo,Maj Wetjen,Rainer Knust,Chiara Papetti,Lorenzo Zane,Julian R Ashford

doi:10.1038/s41598-018-36030-x

Abstract

The Antarctic silverfish (Pleuragramma antarctica) is a critically important forage species with a circumpolar distribution and is unique among other notothenioid species for its wholly pelagic life cycle. Previous studies have provided mixed evidence of population structure over regional and circumpolar scales. The aim of the present study was to test the recent population hypothesis for Antarctic silverfish, which emphasizes the interplay between life history and hydrography in shaping connectivity. A total of 1067 individuals were collected over 25 years from different locations on a circumpolar scale. Samples were genotyped at fifteen microsatellites to assess population differentiation and genetic structuring using clustering methods, F-statistics, and hierarchical analysis of variance. A lack of differentiation was found between locations connected by the Antarctic Slope Front Current (ASF), indicative of high levels of gene flow. However, gene flow was significantly reduced at the South Orkney Islands and the western Antarctic Peninsula where the ASF is absent. This pattern of gene flow emphasized the relevance of large-scale circulation as a mechanism for circumpolar connectivity. Chaotic genetic patchiness characterized population structure over time, with varying patterns of differentiation observed between years, accompanied by heterogeneous standard length distributions. The present study supports a more nuanced version of the genetic panmixia hypothesis that reflects physical-biological interactions over the life history.

Highlights

The Antarctic silverfish (Pleuragramma antarctica) is a critically important forage species in the Southern Ocean that connects higher and lower trophic levels in the continental shelf ecosystem[1,2]
Given that the effect size is quite small for the majority (20 of 22) of the instances of Hardy Weinberg Disequilibrium (HWD), it is unlikely that these departures from Hardy Weinberg Equilibrium (HWE) are of biological importance[41]
Evidence of high gene flow between regions connected by the Antarctic Slope Front (ASF) and associated Antarctic Slope Front Current on a circumpolar scale was accompanied by indications of reduced gene flow in regions not reached by the ASF

Summary

Introduction

The Antarctic silverfish (Pleuragramma antarctica) is a critically important forage species in the Southern Ocean that connects higher and lower trophic levels in the continental shelf ecosystem[1,2]. Assemblages of silverfish eggs and larvae have been found in the summer polynya of the eastern Weddell Sea[22], in waters along the Antarctic Peninsula[23], under sea ice in the western Ross Sea[4,12,24], and in the Dumont d’Urville Sea[25] (see Fig. 1 for place names) These observations suggest a life cycle in which adults return to coastal areas each winter to spawn. The discovery of newly hatched larvae in trough systems along the Weddell Sea, Ross Sea, and Antarctic Peninsula[6,13,22,26] implies this cycle of dispersion and retention occurs in multiple areas around the Antarctic Such a cycle would be vulnerable to advective losses along the shelf in the AACC, and along the slope in the ASF or ACC, resulting in transport to locations downstream[6]

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Conclusion