Urban enrichment of molestus ancestry and opposing temperature clines in a metropolitan Culex pipiens hybrid zone

The hybrid zone where ecologically distinct lineages of Culex pipiens meet in the mid-Atlantic intersects with temperature and urbanization gradients. Researchers examined whole-genome Pool-seq data from 24 field populations and three lineage-reference pools across the Baltimore-Washington corridor.

The findings reveal a weakly differentiated, Cx. pipiens f. pipiens-like background enriched in molestus- and quinquefasciatus-like ancestry towards warmer regions of the corridor. Urbanization has a significant impact on allele frequencies across the genome, with molestus-like ancestry rising independently of temperature and position as impervious surfaces increase. In contrast, Cx. quinquefasciatus-like ancestry does not correlate with urbanization.

A 11.6 Mb chromosome 3 inversion is molestus-like in every population, particularly in urban ones, and follows the trend of genome-wide molestus-like ancestry. Temperature affects the genome locus by locus. On chromosome 1, a cluster of six CYP6 paralogs, implicated in insecticide resistance and thermal-stress response, exhibits rising Cx. quinquefasciatus-like ancestry and read depth with increasing temperature.

A chromosome 2 interval centered on a Yan ortholog, a repressor of cell differentiation, shows increasing non-quinquefasciatus ancestry with temperature, suggesting selection against Cx. quinquefasciatus-like introgression.

These observations indicate that urban populations carry more ancestry from the human-commensal lineage, while temperature influences ancestry differently at individual loci. The presence of molestus and Cx. quinquefasciatus traits in both donor lineages suggests that these patterns could influence how warming and urbanization will shape arboviral risk.