Mosquitoes started biting humans 5,000 years ago

Genomic analysis of slave trade records has helped reveal when first yellow fever mosquitoes they bit humans – it happened about 5 thousand years ago, when the Sahara Desert was formed. These conclusions were reached by a team of US researchers in an article published on Science. To date, it was unclear how the yellow fever mosquito began biting humans causing it collectively hundreds of millions of infections every year.

Scientists agree that a subpopulation of A. aegypti she separated from a harmless ancestor who preferred to live in forests and feed on animals, not people. “The thing we didn’t know was when, how, or why this all happened,” she says Noah Rose, an evolutionary biologist at the University of California (UC), San Diego. Now, Rose has led agenomic analysis which concludes that the fateful split occurred about 5000 years ago, during a period of natural climate change in the West African Sahelon the southern border of the Sahara.

“We were able to tell the natural history of A. aegypti using the genome,” he says Athanase Badolo, an entomologist at Joseph Ki-Zerbo University in Ouagadougou, Burkina Faso, who co-authored the study. Those genomes also revealed a hint of rapid and continuous evolution that in just the last few decades has allowed the species to prey on humans and possibly spread disease even more efficiently in African cities. Rose’s team began by sampling different populations of yellow fever mosquitoes from both forests and cities. In 2020, researchers reported that mosquitoes showing the strongest preferences for human odors appeared to be clustered in arid urban communities in the Sahelsuggesting that the first human-focused mosquitoes likely evolved there, attracted to cities because they offered dense human populations and water for long periods even in dry seasons.

For their most recent analysis, Rose’s team turned to a computational technique typically applied to reconstructing human migrations from divergent genomes scattered around the world. Once two biological populations are separated and can no longer interbreed, their genomes diverge more and more over time. The accumulated mutations act as a clock that, when calibrated with known dates, can be rewound to pinpoint divergence dates. In this case, graphs comparing mosquito genomes collected in Africa and Brazil showed two intense migratory events: one between Africa and the Americas, and a separate, much earlier one, in which all populations of A. aegypti they initially diverged.

tutorials

Plants and natural remedies to keep mosquitoes away from balconies and gardens

by Gaetano Zoccali

06 August 2022

Ecologists believe that the transatlantic migration of mosquitoes may have peaked around the year 1800, during the height of the transatlantic slave trade. Along with an estimated 80,000 slaves kidnapped across the ocean each year, yellow fever mosquitoes lurk on these voyages, laying their eggs in barrels of water and feasting on the people aboard. That timing helped Rose calibrate the date of the earlier migratory event, when all A. aegypti insects first split into forest- and city-dwelling types.