Convergent evolutionary loss of chemosensory and blood-feeding pathways in non-blood-feeding mosquitoes

Mosquitoes possess a range of complex traits that involve many genes, systems, and development processes. Blood feeding is a trait that has been present in mosquitoes for millions of years, but has been independently lost in three distinct lineages. Understanding the genetic, physiological, and neural factors that contribute to blood feeding could provide insights into how this important trait is formed and dismantled.

To investigate these aspects, researchers assembled high-quality genomes for seven mosquito species, along with detailed brain reconstructions. By comparing genes shared among related species, they found instances of convergent gene loss in the three lineages that have lost blood feeding. These losses encompass the salivary platelet-aggregation inhibitor Aegyptin, blood-activated serine proteases like Chymotrypsin-1 and 2, and a carboxylesterase found in the female fat body and brain glia.

The loss of blood feeding also affected the mosquito's ability to detect chemicals, as non-blood feeders lacked certain odorant-binding proteins, ionotropic receptors tied to taste detection of blood components, and odorant receptors in a specific, predominantly female population of antennal neurons. Additionally, female-biased gene expression in the head regions was diminished in non-blood feeders.

Lastly, whole-brain reconstructions showed smaller antennal lobes in non-blood-feeding females, suggesting reduced olfactory input. These discoveries pinpoint a limited set of genes, expression patterns, and brain areas linked to blood feeding, providing a potential starting point for exploring the complex and potentially harmful nature of this trait.