Autogenous and anautogenous Culex pipiens bioforms exhibit insulin-like peptide signaling pathway gene expression differences that are not dependent upon larval nutrition

Abstract

Culex pipiens form pipiens and Cx. pipiens form molestus differ in their ability to produce eggs without a bloodmeal. Autogenous mosquitoes, such as the molestus bioform of Cx. pipiens, depend on nutrition acquired as larvae instead of a bloodmeal to fuel the energy intensive process of vitellogenesis, which requires abundant production of yolk proteins. In anautogenous mosquito systems, ovary ecdysteroidogenic hormone (OEH) and insulin-like peptides (ILPs) transduce nutritional signals and trigger egg maturation in response to a bloodmeal. It is unclear to what extent the process is conserved in autogenous mosquitoes and how the bloodmeal trigger has been replaced by teneral reserves. Here, we measured the effects of a series of nutritional regimens on autogeny, time to pupation, and survival in Cx. pipiens form molestus and form pipiens. We find that abundant nutrients never result in autogenous form pipiens and extremely poor food availability rarely eliminates autogeny from form molestus. However, the number of autogenous eggs generated increases with nutrient availability. Similarly, using qPCR to quantify gene expression, we find several differences in the expression levels of ilps between bioforms that are reduced and delayed by poor nutrition, but not extinguished. Changes in OEH expression do not explain bioform-specific differences in autogeny. Surprisingly, the source of most of the gene expression differences correlated with autogeny is the abdomen, not the brain. Overall, our results suggest that autogeny is modulated by nutritional availability, but the trait is encoded by genetic differences between forms and these impact the expression of ILPs.