Localization of candidate regions maintaining a common polymorphic inversion (2La) in Anopheles gambiae

Area of Science:

• Genomics
• Evolutionary Biology
• Population Genetics

Background:

• Chromosomal inversion polymorphisms are implicated in adaptive divergence.
• The specific genes driving adaptive benefits of inversions remain largely unknown.
• The 2La inversion in Anopheles gambiae is common and its frequency suggests adaptation to aridity.

Purpose of the Study:

• To map genomic differentiation across the Anopheles gambiae genome.
• To identify specific genes or regions under selection associated with the 2La inversion.
• To investigate the evolutionary forces maintaining the 2La inversion polymorphism.

Main Methods:

• Genomic DNA hybridization to oligonucleotide microarrays for genome-wide differentiation mapping.
• Comparison of genetic divergence between mosquitoes homozygous for alternative 2La arrangements.
• Targeted sequencing to validate regions of significant divergence.

Main Results:

• Highest genetic divergence was observed within the 2La rearranged region.
• Two approximately 1.5 Mb regions near inversion breakpoints showed significant divergence.
• The strong association of these regions with the 2La arrangement suggests selection, not just genetic drift.

Conclusions:

• Selection on genes within specific regions is likely responsible for maintaining the 2La inversion.
• The data support a model of migration-selection balance maintaining the inversion.
• Further research is needed to differentiate between local adaptation and coadaptation models for 2La maintenance.