Researchers at Harvard T. H. Chan School of Public Health and University of Perugia, Italy may have found the key to uncovering why Anophelesmosquitoes are unique in their ability to transmit malaria to humans. A Greek researcher was a part of the team.

The paper’s senion author is Flaminia Catteruccia and co-lead authors are Sara Mitchell and Adam South of Harvard Chan School and Evdoxia G. Kakani of University of Perugia and the Harvard Chan School.

Through analysis of 16 Anophelesgenomes, they found that these mosquitoes’ reproductive traits evolved along with their capacity to transmit the Plasmodium parasite that causes malaria. These findings may provide a new target for malaria control, particularly in regions hardest hit by the disease.

“Our study is the first to reveal the evolutionary dynamics between the sexes that are likely responsible for shaping the ability of Anopheles mosquitoes to transmit malaria to humans,” said senior author Flaminia Catteruccia, associate professor of immunology and infectious diseases at Harvard Chan School and University of Perugia.

The study was published online February 26, 2015 in Science.

Anopheles mosquitoes are the only mosquitoes capable of transmitting human malaria; however, the species within this genus vary widely in their ability to do so, for reasons that remain unknown. The researchers analyzed nine globally dispersed Anopheles species, enabling reconstruction of the evolutionary history of their reproductive traits and capacity to transmit malaria.

They found that two key male reproductive traits in Anopheles are acquired and evolved together over time: transferring ejaculate as a gelatinous rod-shaped structure called the mating plug, and the ability to synthesize a steroid hormone contained in that plug called 20-hydroxyecdysone (20E). The researchers also demonstrated that the evolution of these male traits drove reciprocal adaptations in females strongly linked to the mosquitos’ capacity to transmit malaria.

This study adds to previous findings from this research group showing that sexual transfer of 20E induces a series of dramatic changes in the female, fundamentally altering her physiology and behavior. These changes affect a female’s reproductive output, longevity and immune response to Plasmodium parasites, all key factors in malaria transmission. All four species of Anopheles mosquitoes that transfer large levels of 20E are major malaria vectors originating from Africa and India, the regions of highest malaria burden.