The evolution of immune-related genes from disease carrying mosquitoes: diversity in a peptidoglycan- and a thioester-recognizing protein.

Adaptive polymorphism may be common in immune system genes as co-evolutionary interactions foster diversity; either through ongoing positive selection (arms races), or balancing selection. DNA sequence diversity in two putative immune system genes was examined in species of the genus Anopheles and from Aedes aegypti. For one gene, encoding the peptidoglycan recognizing protein PGRPLB, there was evidence of purifying selection, suggesting that selection acts to eliminate sequence variation. For another gene, encoding the thioester-containing protein TEP3, higher levels of amino acid replacement were found than would be expected under neutral models of evolution - an indication that this gene has been subject to repeated bouts of positive selection.