Massive introgression drives species radiation at the range limit of Anopheles gambiae
Impacts of introgressive hybridisation may range from genomic erosion and species collapse to rapid
adaptation and speciation but opportunities to study these dynamics are rare. We investigated the
extent, causes and consequences of a hybrid zone between Anopheles coluzzii and Anopheles gambiae
in Guinea-Bissau, where high hybridisation rates appear to be stable at least since the 1990s. Anopheles
gambiae was genetically partitioned into inland and coastal subpopulations, separated by a central
region dominated by A. coluzzii. Surprisingly, whole genome sequencing revealed that the coastal
region harbours a hybrid form characterised by an A. gambiae-like sex chromosome and massive
introgression of A. coluzzii autosomal alleles. Local selection on chromosomal inversions may play a
role in this process, suggesting potential for spatiotemporal stability of the coastal hybrid form and
providing resilience against introgression of medically-important loci and traits, found to be more
prevalent in inland A. gambiae.