Targeted resequencing reveals geographical patterns of differentiation for loci implicated in parallel evolution

Area of Science:

• Evolutionary biology
• Genetics
• Speciation

Background:

• Parallel divergence and speciation are key to understanding biological diversity.
• Recent studies suggest divergent selection's genetic basis may vary geographically.
• Outlier loci, indicative of divergent selection, are often not shared across parallel evolutionary instances.

Purpose of the Study:

• To test if limited sharing of outlier loci is due to technical issues (false positives).
• To investigate the genetic basis of parallel ecotype evolution in the marine snail Littorina saxatilis.
• To determine if outlier loci show consistent patterns of elevated FST across geographical locations.

Main Methods:

• Capture sequencing targeting previously identified outlier loci and control loci.
• Hierarchical sampling design (within and between countries) in Littorina saxatilis populations.
• Analysis of FST (a measure of genetic differentiation) to identify loci under divergent selection.

Main Results:

• Outlier loci consistently showed elevated FST in their original locations, refuting sampling effects.
• Outliers were more likely to show increased FST in geographically close locations.
• Unexpectedly, some outlier types also exhibited elevated FST in geographically distant locations.

Conclusions:

• The genetic basis of parallel phenotypic divergence is not solely due to sampling effects.
• Geographical proximity influences the sharing of outlier loci, potentially due to gene flow or shared ancestral variation.
• Further research is needed to explain the presence of shared outlier loci in distant populations.