The History of Tree and Shrub Taxa on Bol'shoy Lyakhovsky Island (New Siberian Archipelago) since the Last Interglacial Uncovered by Sedimentary Ancient DNA and Pollen Data.

Heike Zimmermann,Elena Raschke,Kathleen Stoof-Leichsenring,Lutz Schirrmeister,Laura Epp,Georg Schwamborn,Ulrike Herzschuh

doi:10.3390/genes8100273

Abstract

Ecosystem boundaries, such as the Arctic-Boreal treeline, are strongly coupled with climate and were spatially highly dynamic during past glacial-interglacial cycles. Only a few studies cover vegetation changes since the last interglacial, as most of the former landscapes are inundated and difficult to access. Using pollen analysis and sedimentary ancient DNA (sedaDNA) metabarcoding, we reveal vegetation changes on Bol’shoy Lyakhovsky Island since the last interglacial from permafrost sediments. Last interglacial samples depict high levels of floral diversity with the presence of trees (Larix, Picea, Populus) and shrubs (Alnus, Betula, Ribes, Cornus, Saliceae) on the currently treeless island. After the Last Glacial Maximum, Larix re-colonised the island but disappeared along with most shrub taxa. This was probably caused by Holocene sea-level rise, which led to increased oceanic conditions on the island. Additionally, we applied two newly developed larch-specific chloroplast markers to evaluate their potential for tracking past population dynamics from environmental samples. The novel markers were successfully re-sequenced and exhibited two variants of each marker in last interglacial samples. SedaDNA can track vegetation changes as well as genetic changes across geographic space through time and can improve our understanding of past processes that shape modern patterns.

Highlights

The Pleistocene epoch is characterised by glacial-interglacial cycles leading to pronounced changes of temperature and sea level [1,2,3], which in turn affect the prevailing ecosystems [4,5,6] and periglacial landscapes [7,8]
To validate the presence of Larix-derived DNA in these samples and to assess the potential of analysing single-nucleotide polymorphisms (SNPs) in sedimentary ancient DNA we developed new genetic markers
In contrast to previous pollen and macrofossil studies, which have reconstructed shrub-tundra as the prevailing vegetation on Bol’shoy Lyakhovsky Island, our proxies of pollen and sedimentary ancient DNA (sedaDNA) indicate that trees were present during MIS 5 and during the transition from MIS 2 to MIS 1

Summary

Introduction

The Pleistocene epoch is characterised by glacial-interglacial cycles leading to pronounced changes of temperature and sea level [1,2,3], which in turn affect the prevailing ecosystems [4,5,6] and periglacial landscapes [7,8]. During glacial periods sea level was much lower than today, exposing the shallow arctic shelf, which extended the Eurasian continent northwards and connected it with the North. Genes 2017, 8, 273 rising sea level [9,10,11] that submerged the shallow shelf systems. These climate-coupled dynamics affected species distributions, which responded by range contractions or expansions [12,13]. The spatial position of ecosystem boundaries changed through time One such boundary is the Siberian treeline, called the tundra-taiga ecotone, as it is a zone where boreal larch forest gradually changes into tundra [14]. The treeline is thought to have retreated southwards during glacial periods and to have shifted northwards during interglacial periods [5], but the northern limit of larch in Siberia during past interglacials is still unknown

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