Spatial eco-climatic gradients drive adaptive 2La chromosomal inversion polymorphism in Anopheles coluzzii, a major...

Chromosomal inversions are important genetic mechanisms that facilitate local adaptation, ecological flexibility, and behavioural variation in mosquito populations. In Anopheles coluzzii, a dominant malaria vector in West Africa, the 2La inversion has been associated with desiccation tolerance, thermal resistance, and insecticide resistance. Despite Nigeria's ecological diversity and substantial malaria burden, the spatial distribution and clinal dynamics of 2La inversion polymorphism in An. coluzzii remain poorly characterized. This study investigated the distribution of 2La inversion karyotypes across major Nigerian ecozones and examined their association with climatic gradients.

Larvae of Anopheles mosquitoes were sampled across 12 states representing Nigeria's southern, central, and northern ecological zones. Species identification was conducted morphologically and confirmed with PCR diagnostics. The 2La inversion was determined using established molecular assays, and allele frequencies were analyzed with respect to ecozone and climatic gradients. Spatial distribution maps and statistical analyses, including correlation and clinal trend assessment, were done in R version 4.4.

A clear geographic structuring of 2La inversion polymorphism was observed in An. coluzzii populations. The 2La/2La homokaryotype was strongly predominant in the northern Sahelian and Sudan savanna ecozones, reflecting adaptation to hot and arid conditions. In contrast, the standard 2La+/2La+ arrangement was predominant in humid southern forest and mangrove regions. The heterokaryotype (2La/2La+) occurred at intermediate frequencies within the central transitional belt, where ecological gradients overlap. Karyotype frequencies exhibited a pronounced latitudinal cline, with heterozygosity peaking in central Nigeria. The spatial patterns indicate that climatic pressures, particularly aridity and humidity, might be a major determinant of inversion distribution in An. coluzzii from Nigeria.

This study provides the first detailed nationwide characterization of 2La inversion polymorphism in An. coluzzii across Nigeria's ecological zones. The strong alignment between inversion frequency and eco-climatic gradients highlights the role of chromosomal rearrangements in promoting vector survival and ecological fitness. These adaptive patterns have significant implications for malaria control, as inversion-mediated adaptability may influence resting behaviour, insecticide response, and vector persistence under climate change. Integrating chromosomal inversion surveillance into entomological monitoring frameworks will be essential for designing ecologically tailored vector control strategies in Nigeria.