Factors contributing to the potential expansion of Limnomonas gaiensis (Chlamydomonadales, Chlorophyta) in freshwater lakes in Northern Europe

ABSTRACT

Limnomonas gaiensis is a recently described green microalga inhabiting freshwater lakes in northern Europe (England, Sweden). There is little information on the species’ tolerance to environmental factors and its capacity to spread to unconnected lakes. Using a barcoding approach, we investigated the phylogeography of L. gaiensis along a latitudinal gradient spanning 54–60°N. Experimental long-term exposure to a gradient of water temperatures, mimicking natural conditions, was performed to assess its thermal tolerance. Genetic analyses showed that this limnic species is easily identified at the species level. Phylogeographic analyses revealed the existence of two genetically similar haplotypes over the mitochondrial cytochrome C oxidase subunit 1 gene in different countries, suggesting that the range of L. gaiensis has recently expanded from a common source lineage, despite geographic isolation. Heterogeneity in the Helix III of the nuclear Internal Transcribed Spacer 2 region of the English strain suggested past hybridization. Physiological analyses showed that L. gaiensis can survive and reproduce asexually, potentially year-round. Optimal growth was observed at 15°C, with a doubling time of 1.1 days. The species is able to survive short periods of desiccation. The lack of connectivity between the lakes where the species was sampled rules out aquatic dispersal of this species. However, its physiological features make L. gaiensis a good candidate for propagule dispersal by either wind or human/animal-mediated transportation. Our study calls for further investigation into limnic systems, using rapid barcoding, with concurrent atmospheric and physiological analyses to establish its distribution over wider geographic scales and to understand how L. gaiensis disperses.

Highlights

• Limnomonas gaiensis survives in a wide range of water temperatures.

• Phylogeographic analyses indicate its recent expansion in Northern Europe.

• Physiological features suggest airborne/animal-mediated dispersal between unconnected freshwater lakes.

KEYWORDS:

• Dispersal
• growth rate
• phylogeography
• survival
• thermal tolerance

Acknowledgements

The authors thank Lenne Nigul and Marlene Kaljumäe for technical support. The authors are grateful to GenBank staff for their help with sequence submission. The manuscript has been proofread by a native English speaker.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

S. Sildever: analysis of molecular data, drafting and editing manuscript; R. Stewart: data analysis, editing manuscript; S. Tesson: original concept, culture experiments, data analysis, drafting and editing manuscript.

Data availability statement

Genetic data are available in GenBank: 23S (OQ034578-OQ034608), ITS (ON124901- ON124904 and OQ048161-OQ048193) and COI (OQ104382- OQ104412).

Strains are deposited at the Culture Collection of Algae at the University of Göttingen, Germany (SAG): VR66-07 (SAG 2637), VR66-10 (SAG 2636), R86-45 (SAG 2638) and R86-47 (SAG 2639). Data are available from the authors upon reasonable request.

Additional information

Funding

The research was funded by Sven och Lilly Lawski foundation, by Helge Ax:son Johnsons Stiftelse [F18-0510], by The Royal Physiographic Society of Lund [FO2016-0224] and by The Royal Swedish Academy of Sciences, Anna-Greta and Holger Crafoord Foundation [CR2018-0023]. S.T. is funded by the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement no. 754513 and The Aarhus University Research Foundation. S.S. is funded by the Estonian Research Council grant [PSG735].