Aedes aegypti female. Image credit: Public domain
Sexual dimorphism is a phenomenon among animals, insects and plants where the two sexes of a species show differences in body size, physical features or colors. The bushy mane of a male lion, for example, is nowhere to be seen on a female lioness, and only male peacocks have extravagant tails. Most examples of sexual dimorphism, such as elaborate visual displays or courtship behaviors, are linked to mating.
However, there are a few species where behavioral differences between the sexes are not connected to mating. Mosquitoes are an example: while female mosquitoes feed on humans, and are attracted to a person’s body heat and odor, male mosquitoes have little interest in biting humans for their blood. Therefore, female mosquitoes are the ones responsible for transmitting the viruses that cause certain blood-borne diseases such as dengue fever or Zika. Determining which genes are linked to feeding behaviors in mosquitoes could allow researchers to genetically engineer females so they no longer bite people, thus stopping the spread of these diseases. Unfortunately, the genes that control mosquito feeding behaviors have not been well studied.
In other insects, some of the genes that control mating behaviors that depend on sex have been identified. For example, a gene called fruitless controls courtship behaviors in male flies and silkworms, and is thought to be the ‘master regulator’ of male sexual behavior across insects. Yet it remains to be seen whether the fruitless gene has any effect in mosquitoes, where sex differences relate to feeding habits.
To investigate this, Basrur et al. removed the fruitless gene from Aedes aegypti mosquitoes. The genetically altered male mosquitoes became unable to mate successfully, but – similar to unmodified males – still preferred sugar water over blood when feeding. Unlike unmodified males, however, the male mosquitoes lacking fruitless were attracted to the body odor of a person’s arm (like females).
These results reveal that fruitless, a gene that controls sex-specific mating behaviors in other insects, controls a sex-specific feeding behavior in mosquitoes. The fruitless gene, Basrur et al. speculate, likely gained this role controlling mosquito feeding behavior in the course of evolution. More research is required to fully understand the effects of the fruitless gene in male and female mosquitoes.
