Next‐Generation Sequencing to Identify Lacustrine Haptophytes in the Canadian Prairies: Significance for Temperature Proxy Applications

The Great Plains of North America often experience prolonged droughts that have major economic and environmental impacts. Temperature reconstructions are thus crucial to help decipher the mechanisms responsible for drought occurrences. Long‐chain alkenones (LCAs), lipids produced by three major phylogenetic groups (Groups I, II, and III) of haptophyte algae within the order Isochrysidales, are increasingly used for temperature reconstructions in lacustrine settings. However, to select the most appropriate calibration of the LCA‐based temperature proxy, it is first essential to identify the LCA‐producing haptophyte species present. Here we used next‐generation sequencing to target the 18S rRNA haptophyte gene from sediments with distinct LCA profiles to identify the LCA‐producer(s) from five Canadian prairie lakes. In total, 374 operational taxonomic units (OTUs) were identified across the studied samples, of which 234 fell within the Phylum Haptophyta. Among the most abundant OTUs, three were characterized as LCA‐producers, one falling within the Group I haptophytes and two within the Group II haptophytes. The OTU from Group I haptophytes was associated with a single, highly specific LCA profile, whereas Group II OTUs showed higher variability in LCA distributions. Our study revealed that most of the LCA‐producing OTUs thriving in the Canadian lakes are included within the genus Isochrysis, which helps guide selection of the most appropriate calibration for down‐core temperature reconstructions. Our findings also suggest that the temperature dependency is likely consistent within different taxa from Group I and Group II haptophytes, but that other environmental parameters may influence the accuracy of the calibration. Plain Language Summary The Great Plains of North America are extremely sensitive to changes in temperature and moisture and often experience prolonged periods of droughts and floods that have major impacts on agriculture production and ecosystem function. Temperature reconstructions are thus crucial to help decipher the climate mechanisms responsible for drought and flood occurrences. In the present study, we identified the algae that biosynthesize a very specific class of lipids, the long‐chain alkenones (LCAs). LCAs have been successfully used for decades to reconstruct past temperature changes in marine environments, but it is important to identify the algae producing these lipids in lakes before we can use them as a paleo‐thermometer for