Polygenic Selection within a Single Generation Leads to Subtle Divergence among Ecological NichesINc

Area of Science:

• Evolutionary Biology
• Genetics
• Ecology

Background:

• Demonstrating rapid adaptation via polygenic selection in natural populations is challenging.
• Fundulus heteroclitus (killifish) in marine estuaries offers a model for studying adaptation due to high environmental heterogeneity and replicate populations.
• These populations possess high within-population genetic variation but negligible among-population variation.

Purpose of the Study:

• To investigate rapid adaptation to distinct niche environments within a single generation.
• To quantify allele frequency changes and spatial divergence in response to selection pressures.
• To determine if polygenic selection drives local adaptation in heterogeneous environments.

Main Methods:

• Identified 10,861 single nucleotide polymorphisms (SNPs) in a panmictic Fundulus heteroclitus population across distinct niches (coastal basin, tidal ponds).
• Sampled populations at two time points within a single generation to measure allele frequency changes and spatial divergence.
• Analyzed allele frequency shifts to assess concordance and magnitude of changes among niche subpopulations.

Main Results:

• Observed a significant number of moderate allele frequency changes exceeding neutral expectations (10-100%).
• Found allele frequency changes to be concordant in direction and magnitude across all niche subpopulations, suggesting parallel selection.
• Detected within-generation allele frequency changes leading to significant niche divergence, indicating local adaptation.

Conclusions:

• Polygenic selection, acting on standing genetic variation, can drive rapid local adaptation to distinct niches within a single generation.
• Parallel selection across replicate niches suggests a predictable evolutionary response to environmental pressures.
• Polygenic traits influencing fitness and/or migration are likely drivers of rapid, within-generation adaptation in heterogeneous environments.