Gene flow-dependent genomic divergence between Anopheles gambiae M and S forms

Area of Science:

• Genetics
• Evolutionary Biology
• Entomology

Background:

• Anopheles gambiae sensu stricto comprises M and S molecular forms with distinct genetic profiles.
• Genomic islands with extreme divergence were previously thought to drive speciation in these forms.
• The role of these islands in reproductive isolation versus ancestral differentiation remains debated.

Purpose of the Study:

• To investigate the role of genomic islands in Anopheles gambiae speciation.
• To test whether genomic islands represent ancestral polymorphism or are actively driving divergence.
• To assess the impact of varying introgression rates on genomic differentiation.

Main Methods:

• Genotyping of 871 single nucleotide polymorphisms (SNPs) in Anopheles gambiae.
• Analysis of genomic variation across sympatric and allopatric M and S form populations.
• Quantification of hybridization rates and genomic divergence.

Main Results:

• Genomic differentiation between M and S forms was evident despite ongoing introgression.
• The extent and pattern of genomic divergence correlated with introgression levels.
• Key divergent regions, including speciation islands, were identified, with some outside low-recombination zones.

Conclusions:

• Genomic islands exhibit divergence resilient to substantial gene flow, refuting the ancestral polymorphism hypothesis.
• These islands contribute significantly to early-stage speciation in Anopheles gambiae.
• Genomic islands, despite their small size, are crucial for reproductive isolation.