Genes in animal immune systems may evolve in one of two main ways in the constant fight against pathogens: They may evolve diverse forms of genes (alleles) to fight a wide variety of pathogens, or when only a few pathogens dominate, they may evolve one or a few alleles that specialize against common infections.

The Cornell researchers have found evidence of both these adaptive strategies occurring in the same immune-defense genes in different subpopulations of the human malaria vector mosquito, Anopheles gambiae.

The research, appearing March 8 in the open-access journal PLoS Biology, focused on a cluster of genes called APL1, which are part of the mosquitoes' immune defense against malaria parasites and other pathogens. Malaria infects humans, but it also makes mosquitoes that transmit the disease sick.

"From a purely evolutionary biology perspective, seeing both of those patterns occur in a single gene is very unusual; it validates both models," said Brian Lazzaro, the study's principal investigator and a Cornell associate professor of evolutionary genetics in the Department of Entomology.