Genetic data from algae sedimentary DNA reflect the influence of environment over geography.

Kathleen R. Stoof-Leichsenring,Ulrike Herzschuh,Laura S. Epp,Juliane Klemm,Luidmila A. Pestryakova,Ralph Tiedemann

doi:10.1038/srep12924

Abstract

Genetic investigations on eukaryotic plankton confirmed the existence of modern biogeographic patterns, but analyses of palaeoecological data exploring the temporal variability of these patterns have rarely been presented. Ancient sedimentary DNA proved suitable for investigations of past assemblage turnover in the course of environmental change, but genetic relatedness of the identified lineages has not yet been undertaken. Here, we investigate the relatedness of diatom lineages in Siberian lakes along environmental gradients (i.e. across treeline transects), over geographic distance and through time (i.e. the last 7000 years) using modern and ancient sedimentary DNA. Our results indicate that closely-related Staurosira lineages occur in similar environments and less-related lineages in dissimilar environments, in our case different vegetation and co-varying climatic and limnic variables across treeline transects. Thus our study reveals that environmental conditions rather than geographic distance is reflected by diatom-relatedness patterns in space and time. We tentatively speculate that the detected relatedness pattern in Staurosira across the treeline could be a result of adaptation to diverse environmental conditions across the arctic boreal treeline, however, a geographically-driven divergence and subsequent repopulation of ecologically different habitats might also be a potential explanation for the observed pattern.

Highlights

Environmental DNA and the analysis of evolutionary relationships between closely-related lineages has not been considered in the context of biogeographic patterns in eukaryotic microbes
We hypothesize that if the biogeographic pattern in closely-related lineages of Staurosira is driven by geographic distance, we would expect to see a higher degree of relatedness among Staurosira lineages within geographic areas, and would not expect changes within a single sediment core through times of environmental change
If the establishment is linked to environmental change, rather than to geographic constraints, we would expect to see a high degree of relatedness among Staurosira lineages within similar vegetation types, and this association should be stable through time

Summary

Introduction

Environmental DNA and the analysis of evolutionary relationships between closely-related lineages has not been considered in the context of biogeographic patterns in eukaryotic microbes. A prevalent and diverse group of diatoms in the abundant thermokarst lakes of the Siberian treeline ecotone is Staurosira and related taxa[22,23], and their spatial turnover is known to be correlated with changing environments across this ecotone[16,20,24]. Phylogenetic relationships within this group have recently been reassessed using molecular genetic data, and due to a strong evolutionary relationship between the morphologically similar genera Staurosira, Staurosirella and Pseudostaurosira, a taxonomic integration into a single genus Staurosira has been suggested[25]. We would expect to see a turnover in Staurosira lineages contemporaneous with environmental change in the dynamic treeline area

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