The clue to why Anopheles mosquitoes are unique in their ability to transmit malaria to humans could be found in their evolution of sexual biology.
Through analysis of 16 Anopheles genomes, the researchers found that these mosquitoes' reproductive traits evolved along with their capacity to transmit the Plasmodium parasite that causes malaria.
"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 at Harvard T. H. Chan School of Public Health.
By identifying factors critical for increasing the ability of mosquitoes to transmit malaria, compounds developed to specifically target those factors could be incorporated into existing mosquito control technologies, boosting their overall effectiveness.
The researchers analysed 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 were acquired and evolved together over time: the mating plug, and the ability to synthesise 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.
Sexual transfer of 20E induces a series of dramatic changes in the female, fundamentally altering her physiology and behaviour. These changes affect a female's reproductive output, longevity and immune response to Plasmodium parasites, all key factors in malaria transmission, the study noted.
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.
The study was published online in the journal Science.
