Evolutionary processes and cellular functions underlying divergence in Alexandrium minutum.

Area of Science:

• Marine biology
• Genomics
• Evolutionary biology

Background:

• Pelagic environments pose challenges for studying organismal divergence.
• Alexandrium minutum, a globally significant harmful algal bloom (HAB) dinoflagellate, is difficult to study due to its small size, complex genome, and dynamic habitat.

Purpose of the Study:

• To investigate the functional basis of a divergence event in Alexandrium minutum.
• To understand the role of selective pressures and gene flow in dinoflagellate speciation.

Main Methods:

• Transcriptome-wide mRNA sequencing of 18 Alexandrium minutum strains.
• Morphological analysis.
• Joint Site Frequency Spectrum (JSFS) analysis to infer population history and gene flow.

Main Results:

• Evidence suggests an ancestral isolation followed by secondary contact with heterogeneous gene flow.
• Fixed single nucleotide polymorphisms (SNPs) indicate restricted gene flow and strong selective pressures.
• Highly divergent transcripts are associated with calcium/potassium fluxes, calcium signaling, and saxitoxin production.

Conclusions:

• Selective pressures, particularly on genes related to ion transport and toxin synthesis, are key drivers of Alexandrium minutum divergence.
• These genetic differences likely contribute to ecological divergence and reproductive isolation.
• High-throughput sequencing can reveal ecologically and evolutionarily important traits in challenging organisms like dinoflagellates.