Low genome-wide divergence between two lizard populations with high adaptive phenotypic differentiation.

Area of Science:

• Evolutionary Biology
• Population Genetics
• Ecology

Background:

• Adaptive phenotypic differentiation typically correlates with genetic divergence.
• However, adaptation can occur with minimal genetic differentiation, especially with high gene flow or recent population splits.
• Understanding the frequency of such non-genetic divergence is crucial for evolutionary studies.

Purpose of the Study:

• To investigate genome-wide genetic divergence in two populations of *Psammodromus algirus* separated by an elevational gradient.
• To determine if local phenotypic adaptation is associated with genetic differentiation, despite previous findings of low genetic divergence.
• To explore the role of gene flow in maintaining phenotypic adaptation without genetic isolation.

Main Methods:

• Analysis of genome-wide single nucleotide polymorphisms (SNPs) from over 70,000 loci.
• Utilized F_ST-based outlier detection tests to identify loci under selection.
• Compared genetic divergence with phenotypic variation across populations.

Main Results:

• No significant genome-wide genetic differentiation was found between the lizard populations.
• Phenotypic adaptation was evident across a range of traits despite the lack of genetic divergence.
• Outlier tests did not reveal loci with significantly higher F_ST values than expected by chance.

Conclusions:

• Local adaptation can occur without concurrent genome-wide genetic differentiation or isolation.
• High gene flow may maintain phenotypic divergence while preventing genetic divergence.
• These findings support scenarios of local adaptation without isolation by environment, challenging traditional models of speciation.