|BREDLAU, JUSTIN - Virginia Commonwealth University|
|KESTER, KAREN - Virginia Commonwealth University|
Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2019
Publication Date: 5/29/2019
Citation: Bredlau, J., Kuhar, D.J., Gundersen, D.E., Kester, K. 2019. The parasitic wasp, Cotesia congregata, consists of two incipient species isolated by asymmetric reproductive incompatibility and hybrid inability to overcome host defenses. Frontiers in Ecology and Evolution. https://doi.org/10.3389/fevo.2019.00187.
Interpretive Summary: Parasitic wasps have potential for control of moth species that are pests of agricultural crops and forests. The survival of many of these wasps is enhanced by a virus, called a polydnavirus, that is injected along with the wasp egg into the host caterpillar pest. Different populations of a parasitoid wasp known as Cotesia congregata were reared on different host plants and caterpillar hosts displayed differences in development, reproduction, and genetics of wasp-encoded polydnavirus depending on which characteristics were present in male and female parent that may help explain the fitness of certain populations over others. Understanding the genetic relationships among ecologically differentiated populations of parasitic wasps and their symbiotic PDVs is essential for ensuring their effective use as biological control agents. This information will be of interest to university and industry scientists who are interested in evolution, how viruses contribute, and/or in developing new strategies to control pests.
Technical Abstract: Parasitic wasps are highly diverse and play a major role in suppression of herbivorous insect pest populations. Several parasitic wasp species have been found to be complexes of cryptic species resulting from adaptations to specific hosts or host foodplants. Cotesia congregata, which has long served as a model system for host-parasitoid interactions, provides a system for investigating diversification among sympatric populations that differ in host-host foodplant usage. Two incipient species of C. congregata have been identified in the USA mid-Atlantic region, one utilizes Manduca sexta on tobacco (“MsT”) and the other utilizes Ceratomia catalpae on catalpa (“CcC”). Both can develop in either host; however, hybrids resulting from CcC'xMsT' crosses are typically sterile with hosts developing normally, whereas the reciprocal cross produces fertile hybrids. In this study, we tested hybrid sterility with additional host-foodplant sources and compared in vivo expression of bracovirus (BV) genes associated with host immune response suppression. Crosses between MsT or CcC wasps and four additional host-foodplant complex sources of C. congregata displayed a pattern of asymmetric hybrid sterility in which crosses with either CcC' or MsT' produced sterile hybrids that lack mature ovaries but the other crosses produced fertile hybrids. Relative expression of seven C. congregata BV (CcBV) genes in hosts, M. sexta and C. catalpae, parasitized by individual MsT or CcC wasps, and in M. sexta parasitized by individual MsT and CcC hybrids were compared. Patterns of relative in vivo expression of MsT and CcC CcBV genes differed; a few were not expressed in hosts parasitized by CcC wasps. Overall, patterns of relative expression did not differ with respect to the host species parasitized. Low or absent expression of CcBV genes was found in hosts parasitized by sterile hybrids. Select CcBV genes were sequenced from each wasp source and some differed between MsT and CcC wasps. Differences in CcBV gene expression and sequences, in addition to the pattern of reproductive incompatibilities among hybrid crosses suggest that C. congregata is composed of two sympatric incipient species that can utilize multiple host species.