Fine-scale genetic structure due to adaptive divergence among microhabitats

Area of Science:

• Evolutionary biology
• Population genetics
• Ecology

Background:

• Adaptive evolution is proposed to shape ecological communities.
• Adaptation across environments typically requires isolation or strong selection, which can be limited by gene flow.
• Polygenic adaptation, involving small allele frequency changes at many loci, may facilitate adaptation in the face of migration.

Purpose of the Study:

• To investigate whether individuals can evolve adaptation to fine-scale habitat variation (microhabitats).
• To analyze the genetic divergence of Fundulus heteroclitus among microhabitats.

Main Methods:

• Analysis of 4741 single-nucleotide polymorphisms (SNPs) in Fundulus heteroclitus.
• Comparison of genetic divergence among microhabitats (<200 m apart) within three saltmarshes.
• Identification of outlier SNPs with significant differences among microhabitats.

Main Results:

• 1.3-2.3% of SNPs showed large, significant genetic differences among microhabitats (mean FST=0.15).
• Microhabitat divergence for outlier SNPs exceeded population-level divergence and neutral expectations.
• Evidence of surprising population structure among closely situated microhabitats.

Conclusions:

• Polygenic selection is effective in altering allele frequencies at numerous SNPs in response to fine-scale environmental differences.
• Significant genetic divergence can occur over very small geographic distances due to adaptation.
• Further research is needed to confirm natural selection's role in fine-scale genetic divergence.