Niche adaptation promoted the evolutionary diversification of tiny ocean predators

Area of Science:

• Marine microbial ecology
• Genomics
• Evolutionary biology

Background:

• Unicellular eukaryotic predators are vital for ocean nutrient cycling but often grouped together, masking diversity.
• Marine stramenopiles (MAST)-4 are cosmopolitan, uncultured picoeukaryotic predators.
• Previous studies overlooked organismal differences within functional groups of marine predators.

Purpose of the Study:

• Investigate genomic content and biogeography of four closely related MAST-4 species (A, B, C, E).
• Determine if spatial distribution patterns correlate with genomic divergence.
• Explore niche diversification driven by temperature adaptation and prey digestion.

Main Methods:

• Single-cell genomics to recover MAST-4 genomes.
• Co-occurrence and distribution analyses in the global surface ocean.
• Comparative genomic analysis focusing on functional gene categories, especially glycoside hydrolases (GHs).

Main Results:

• Recovered 66-83% of genomes for MAST-4A/B/C/E, revealing substantial interspecies divergence.
• MAST-4A and C showed contrasting distribution patterns, suggesting temperature adaptation.
• Species with similar GH composition (A and C) coexcluded, while those with different GHs (B and C) coexisted, indicating niche partitioning.

Conclusions:

• Differential niche adaptation to temperature and prey type promotes adaptive evolutionary diversification in MAST-4.
• Minute ocean predators within the same phylogenetic group exhibit distinct biogeography and genomic content.
• Understanding these differences is crucial for accurately modeling marine food webs.