Evidence that the ancestral lineage leading to Aedes aegypti colonization of America is present in Argentina

Aedes aegypti mosquito is a major mosquito vector of viruses that cause human disease. There are two known subspecies: Aedes aegypti formosus (Aaf), is found exclusively in sub-Saharan Africa, breeds in nonhuman-disturbed habitats, and uses nonhumans for bloodmeals; and Aedes aegypti aegypti (Aaa), which is widely distributed around world, breeds in human habitats, and prefers human bloodmeals. The two subspecies are genetically different.

Populations of Ae. aegypti in Argentina display a mixed genetic signature between both subspecies. This admixture pattern may be explained by two hypotheses. One is that African Aaf populations were recently reintroduced into Argentina and interbred with the local Aaa populations. Alternatively, Argentinian populations represent the remnant of the original African proto-Aaa population that arrived in America ~500 years ago with the slave trade.

To test these hypotheses, we used pair-wise comparisons of phased genomes of Aedes aegypti mosquitoes from Africa, outside Africa and from El Dorado (Argentina) to infer times of divergence based on coalescence time estimation implemented by MSMC2. An isolation-migration model through MSMC-IM tool was then applied to differentiate recent admixture events from shared ancestral population background.

Our analysis uncovered a single high migratory peak that coincides with the timing of the slave trade, likely representing the mosquito’s migration from Africa to America. Moreover, the analysis did not detect any evidence of recent introduction of Aaf into Argentina. These results suggest that modern populations from Argentina are closely related to the proto-Aedes aegypti populations thatfirst emigrated to America.