Submitted to: Molecular Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2009
Publication Date: 12/1/2009
Citation: Viljakainen, L., Evans, J.D., Hasslemann, M., Rueppel, O., Tingek, S., Pamilo, P. 2009. Rapid evolution of immune proteins in social insects. Molecular Biology and Evolution. 26:1791-1801.
Interpretive Summary: Honey bees can battle parasites and pathogens through an elaborate immune response. Contrasting this immune response between honey bees and other social and solitary insects can identify weaknesses in the bee immune response as well as traits that could be enhanced through breeding. In this collaborative project, we characterize immune proteins across several honey bee species and contrast these proteins with those from ants and other insects. The results helped to identify protein regions that seem especially likely to be responsible for immune effectiveness. These results can limit the targets needed to explore in terms of finding honey bee breeding traits, a key goal of the bee research community.
Technical Abstract: In social insects the existence of behavioral traits connected to defense against pathogens manifests the importance of pathogens in the evolution of social insects. However, very little is known how the pathogen pressure has affected the evolution of genes involved in the innate immune system in social insects. We have studied the molecular evolution of several immune genes in ants and honeybees. The results show high evolutionary rates in both ants and honeybees as measured by the ratio of amino acid changes to silent nucleotide changes, that ratio being clearly higher than in Drosophila. This conforms to our expectations of higher pathogen pressure in social insects. However, by using a codon based likelihood method clear evidence of positive selection was found only in one ant gene. The evolution of immune defense genes in social insects seems to be affected by a balance between high pathogen pressure in densely populated societies and effective measures of behaviorally based colony-level defenses that reduce the selective pressure on immune genes.