Counties not countries: Variation in host specificity among populations of an aphid parasitoid

Authors: Hopper, Keith; OPPENHEIM, SARA - American Museum Of Natural History; Kuhn, Kristen; Lanier, Kathryn; Hoelmer, Kim; HEIMPEL, GEORGE - University Of Minnesota; Meikle, William; O'NEIL, ROBERT - Purdue University; VOEGTLIN, DAVID - Illinois Natural History Survey; WU, KONGMING - Chinese Academy Of Agricultural Sciences; WOOLLEY, JAMES - Texas A&M University; HERATY, JOHN - University Of California (UCLA)

Submitted to: Evolutionary Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2018
Publication Date: 1/1/2019
Citation: Hopper, K.R., Oppenheim, S.J., Kuhn, K.L., Lanier, K., Hoelmer, K.A., Heimpel, G.E., Meikle, W.G., O'Neil, R.J., Voegtlin, D.G., Wu, K., Woolley, J.B., Heraty, J.M. 2019. Counties not countries: Variation in host specificity among populations of an aphid parasitoid. Evolutionary Applications. 12(4):815-829. https://doi.org/10.1111/eva.12759.
DOI: https://doi.org/10.1111/eva.12759

Interpretive Summary: Levels of parasitism by populations of Aphelinus certus, a parasitoid of the soybean aphid, varied among aphid species, suggesting adaptation to locally abundant aphids. Differences in host specificity among parasitoid populations correlated with genetic differences among them. Whether different populations of the same natural enemy species vary in host specificity and the genetic basis of these differences are important because a major part of the search for natural enemies for introduction against invasive pests involves evaluating host specificity in laboratory experiments.

Technical Abstract: Parasitic wasps are among the most species-rich groups on Earth. A major cause of this diversity may be local adaptation to host species. However, little is known about variation in host specificity among populations within parasitoid species. Not only is such knowledge important for understanding host-driven speciation, but because parasitoids often control pest insects and narrow host ranges are critical for the safety of biological control introductions, understanding variation in specificity and how it arises are crucial applications in evolutionary biology. Here we report experiments on variation in host specificity among 16 populations of an aphid parasitoid, Aphelinus certus. We addressed several questions about local adaptation: Do parasitoid populations differ in host ranges or in levels of parasitism of aphid species within their host range? Are differences in parasitism among parasitoid populations related to geographic distance, suggesting clinal variation in abundances of aphid species? Or do nearby parasitoid populations differ in host use, as would be expected if differences in aphid abundances, and thus selection, were mosaic? Are differences in parasitism among parasitoid populations related to genetic distances among them? To answer these questions, we measured parasitism of a taxonomically diverse group of aphid species in laboratory experiments. Host range was the same for all the parasitoid populations, but levels of parasitism varied among aphid species, suggesting adaptation to locally abundant aphids. Differences in host specificity did not correlate with geographical distances among parasitoid populations, suggesting that local adaption is mosaic rather than clinal, with a spatial scale of less than 50 kilometers. We sequenced and assembled the genome of A. certus, made reduced representation libraries for each population, analyzed for single nucleotide polymorphisms, and used these polymorphisms to estimate genetic differentiation among populations. Differences in host specificity correlated with genetic distances among the parasitoid populations.