PS 76-172
Limited range expansion of an introduced parasitoid is not caused by a genetic bottleneck
The ability for an introduced parasitoid to succeed in a novel environment may correlate with increased genetic diversity, resulting from different introductions from multiple source populations. The parasitoid, Copidosoma sosares, has followed the plant-herbivore system consisting of wild parsnip (Pastinaca sativa) and parsnip webworm (Depressaria pastinacella) to the US from Europe. While the wild parsnip and webworm are widespread throughout North America and the webworm has established a novel association with the native cowparsnip (Heracleum lanatum), C. sosares is absent from locations east of the Rocky Mountains and is present in only some webworm populations scattered throughout western North America. The lack of C. sosares in some parsnip webworm populations in the western US could be a result of introductions of a single (or few) European source population(s) that are poorly adapted to variable plant-herbivore associations. To test this hypothesis DNA was extracted from C. sosares adults from western US and European sites. The mitochondrial cytochrome b gene (cyt b) and microsatellite markers were used to infer the genetic structure among/between populations. Analyses were performed using Bayesian inference and maximum likelihood using RAxML, AMOVA in Arlequin and STRUCTURE to determine spatial genetic structure of populations.
Results/Conclusions
Currently 550 samples have been sequenced revealing 306 unique haplotypes and five well supported clades of C. sosares. Primers have been developed for 9 microsatellite loci and genotyping has been conducted on 7 of these loci for a total of 265 C. sosares individuals. MtDNA data indicates western US C. sosares populations originated from multiple introductions of European origin, suggesting genetic variability to tolerate novel associations between parsnip webworm and cowparsnip is not likely preventing the spread of C. sosares more widely. Instead, different patterns of spread of parasitoid and webworm may indicate that conditions, such as plant chemistry, permitting the range expansion of one trophic level are not the same for other trophic levels. A series of reciprocal cross parasitism experiments to test the role of plant chemistry in shaping webworm and C. sosares interactions would address this hypothesis and is currently being investigated. Ultimately, our research into the coevolutionary dynamics of interactions between plants, herbivores, and their natural enemies as a function of geography will be of considerable value in designing programs for invasive species management, biodiversity conservation, and classical biological control programs, which should aid in their sustainable implementation.