Selection Over Small and Large Spatial Scales in the Face of High Gene Flow

Area of Science:

• Marine biology
• Evolutionary genetics
• Ecology

Background:

• Local adaptation balances selection and gene flow, often occurring at small spatial scales.
• Marine species with high dispersal can experience environmental heterogeneity across multiple scales.
• The Pacific purple sea urchin (Strongylocentrotus purpuratus) exhibits local adaptation and high gene flow.

Purpose of the Study:

• Investigate microgeographic adaptation in Strongylocentrotus purpuratus across its California range.
• Determine if environmental factors like sea surface temperature and tidal zones influence genetic structure.
• Examine the role of balanced polymorphisms in adaptation across varying spatial scales.

Main Methods:

• Fine-scale genetic sampling of Strongylocentrotus purpuratus populations.
• Analysis of genetic variation in relation to satellite-derived sea surface temperature and tidal zone data.
• Identification of divergent genetic variants and gene expression patterns.

Main Results:

• Subtle genetic differences were found among populations despite a lack of neutral population structure.
• Sea surface temperature and tidal zone were associated with genetic variation, indicating adaptation across latitudinal and small scales.
• Some genetic variants differentiated populations at both large and small spatial scales, linked to temperature.

Conclusions:

• Balanced polymorphisms contribute to local adaptation in marine species across complex environmental mosaics.
• Even with high gene flow, genetic variation can be sorted across spatial scales, driving adaptation.
• Genes with tissue- or stage-specific expression show higher divergence, suggesting roles in phenotypic variation for adaptation.