Differential expression of immune genes between two closely related beetle species with different immunocompetence following attack by Asecodes parviclava

Endoparasitoid wasps are important natural enemies of many insect species and are a major driving force of the variation in the host immune system. Despite increased interest in insect anti-parasitoid immunity, there is sparse information on the evolutionary dynamics of biological pathways and gene regulation involved in host immune defence outside the Drosophila species. We de novo assembled two beetle transcriptomes and used time-course differential expression analysis to understand the differences underlying the genetic basis of host immunocompetence between two closely related Galerucella species, G. pusilla and G. calmariensis. These two species were chosen because G. pusilla and G. calmariensis are, respectively, resistant and susceptible against parasitoid infection by Asecodes parviclava. More immune genes were differentially expressed in G. pusilla than in G. calmariensis, in particular with genes involved in hematopoiesis. Temporal gene expression responses to parasitoid infection were observed in G. pusilla. Genes involved in signalling, recognition, protease, melanisation and hematopoiesis showed the greatest differential expression four hours after parasitism in G. pusilla. Our study characterizes important genes and pathways involved in different immune functions after parasitoid infection, and supports the role of hematopoiesis genes as key players in host immunity in Galerucella against parasitoid wasps. Among these, genes involved in hemocyte proliferation, lamellocyte differentiation and crystal cell differentiation are particular enriched in the resistant species G. pusilla.