The evolutionary genetics of immunity genes in the Anopheles gambiae complex

Recently much effort has been devoted to the study of immune genes involved in the resistance of Anopheles mosquitoes against Plasmodium. A variety of genes have been identified that affect the intensity of Plasmodium infection, but the importance of these genes in the field is not clear. Based on the evidence that Plasmodium and Anopheles co-evolve, we expect that immune genes that act specifically against malaria show signs of adaptive evolution in species that transmit malaria, but not in closely related species that do not vector the disease. We have studied the genetic variation in 20 anti-malarial genes in several species of the Anopheles gambiae complex, including vector and non-vector species. We have previously reported that LRIM1 is under positive selection in An. arabiensis. The remainder of the investigated genes are under purifying selection, with the exception of Tep1, which appears to carry two markedly different allele classes in several species. This may indicate that this gene is subject to balancing selection.