Considerable research in a wide variety of organisms has established that there is extensive variation for immune function among different individuals. The fruit fly, Drosophila melanogaster, provides a useful model system for studying the underlying genetic basis for that variation. A key component of understanding genetic variation for complex traits such as immune function is deciphering how much of that variation represents additive variation, which determines how rapidly a trait can evolve. By using standard crossing designs, this work will measure the additive genetic variation for immune system function in D. melanogaster, as well as additive genetic variation for expression of key candidate genes in the immune pathway.
In addition to predicting how variation will respond to selection in the future, patterns of additive genetic variation can be used to infer the evolutionary forces that have likely acted on the genetic variation we observe. Therefore, understanding the extent of additive genetic variation in the Drosophila immune system will help determine whether functional variation in the immune system is due to pleiotropic effects, where variants that are beneficial for some aspect of immune function have negative consequences for other traits, or whether functional variation in the immune system is due to deleterious mutations segregating at low frequency in the population. These results will have implications for understanding how immune systems evolve, and how evolutionary forces shape variation in crucial fitness traits.
