50,000 years of ice and seals: Impacts of the Last Glacial Maximum on Antarctic fur seals.

Alison C Cleary,Joseph I Hoffman,Christian Lydersen,Kit M Kovacs,Andrew D Lowther,Jaume Forcada

doi:10.1002/ece3.8104

Abstract

Ice is one of the most important drivers of population dynamics in polar organisms, influencing the locations, sizes, and connectivity of populations. Antarctic fur seals, Arctocephalus gazella, are particularly interesting in this regard, as they are concomitantly reliant on both ice‐associated prey and ice‐free coastal breeding areas. We reconstructed the history of this species through the Last Glacial Maximum (LGM) using genomic sequence data from seals across their range. Population size trends and divergence events were investigated using continuous‐time size estimation analysis and divergence time estimation models. The combined results indicated that a panmictic population present prior to the LGM split into two small refugial populations during peak ice extent. Following ice decline, the western refugial population founded colonies at the South Shetlands, South Georgia, and Bouvetøya, while the eastern refugial population founded the colony on Iles Kerguelen. Postglacial population divergence times closely match geological estimates of when these coastal breeding areas became ice free. Given the predictions regarding continued future warming in polar oceans, these responses of Antarctic fur seals to past climate variation suggest it may be worthwhile giving conservation consideration to potential future breeding locations, such as areas further south along the Antarctic Peninsula, in addition to present colony areas.

Highlights

Ice is a key environmental driver for many polar organisms, with glaciers, snow, and sea ice often determining the size and connectivity of populations through diverse mechanisms
Changes in sea ice algae can drive bottom-up ecosystem effects, while changes in the availability of sea ice as a hunting platform for organisms such as leopard seals and polar bears can result in top-down effects (Kovacs et al, 2011; Reid et al, 2005; Siniff et al, 2008)
During the Last Glacial Maximum (LGM), approximately 25–15 thousand years ago, glaciers covered most of the Antarctic continent and the sub-Antarctic islands, seasonal sea ice extended to 45°S, and primary productivity was reduced (Allcock & Strugnell, 2012; Fraser et al, 2012; Hall, 2004; Mortlock et al, 1991)

Summary

| INTRODUCTION

Ice is a key environmental driver for many polar organisms, with glaciers, snow, and sea ice often determining the size and connectivity of populations through diverse mechanisms. During the LGM, approximately 25–15 thousand years ago, glaciers covered most of the Antarctic continent and the sub-Antarctic islands, seasonal sea ice extended to 45°S, and primary productivity was reduced (Allcock & Strugnell, 2012; Fraser et al, 2012; Hall, 2004; Mortlock et al, 1991) These changes in ice had diverse impacts across species, including changes in geographic distributions (range shifts, contractions, and expansions), changes in population structure (merging or splitting of populations), and changes in population size (increases and decreases), with some species showing very large effects, while others were less impacted (Allcock & Strugnell, 2012; Younger et al, 2016). These analyses combine to provide a new picture of the history of this species across a period of dramatic climate change

| MATERIALS AND METHODS

Findings

| DISCUSSION