Abstract
Botryococcus braunii is a colonial microalga that appears early in the fossil record and is a sensitive proxy of environmental and hydroclimatic conditions. Palaeozoic Botryococcus fossils which contribute up to 90% of oil shales and approximately 1% of crude oil, co-localise with diagnostic geolipids from the degradation of source-signature hydrocarbons. However more recent Holocene sediments demonstrate no such association. Consequently, Botryococcus are identified in younger sediments by morphology alone, where potential misclassifications could lead to inaccurate paleoenvironmental reconstructions. Here we show that a combination of flow cytometry and ancient DNA (aDNA) sequencing can unambiguously identify Botryococcus microfossils in Holocene sediments with hitherto unparalleled accuracy and rapidity. The application of aDNA sequencing to microfossils offers a far-reaching opportunity for understanding environmental change in the recent geological record. When allied with other high-resolution palaeoenvironmental information such as aDNA sequencing of humans and megafauna, aDNA from microfossils may allow a deeper and more precise understanding of past environments, ecologies and migrations.
Highlights
We investigate the potential for purifying Botyrococcus microfossils and ancient DNA (aDNA) from sediments known to contain the microalga
Conventional palaeoenvironmental analysis was used to determine the composition of the sediment in combination with palynological techniques to identify and quantify the putative B. braunii microfossils throughout a sediment core extracted from Boswell Lake, British Columbia, Canada
A complete Holocene sediment record was recovered from Boswell Lake (Fig. 1), a carbonate lake located in British Columbia, Canada (52°32′24.72′′N 121°27′5.23′′W)
Summary
Botryococcus braunii is a colonial microalga that appears early in the fossil record and is a sensitive proxy of environmental and hydroclimatic conditions. We show that a combination of flow cytometry and ancient DNA (aDNA) sequencing can unambiguously identify Botryococcus microfossils in Holocene sediments with hitherto unparalleled accuracy and rapidity. We first performed a two-dimensional gas chromatography analysis of the hydrocarbons present in the sediment to verify that the Botryococcus microfossils identified using these conventional techniques are co-localised with their associated source signature geolipids, as seen in oil shales. No such co-localisation was observed due to the migration and degradation of the diagnostic Botryococcus derived geolipids[27]. The combination of FC purification and DNA sequencing has wider applications to other microfossil species and the interpretation of their fossil record
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