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Marine Whelks Expanding Their Ranges Encounter Less Parasites

Paper Reviewed
Hopper, J.V., Kuris, A.M., Lorda, J., Simmonds, S.E., White, C. and Hechinger, R.F. 2014. Reduced parasite diversity and abundance in a marine whelk in its expanded geographical range. Journal of Biogeography 41: 1674-1684.

In a study conducted off the coast of western North America, Hopper et al. (2014) sought to determine "how parasitism interacts with geographical range expansions by quantifying diversity and abundances of parasites in 25 populations of a large marine snail, Kellet's whelk (Kelletia kelletii), throughout its historical and recently-expanded range," the former of which stretches from Mexico's Isla Asuncion to Point Conception on the coast of California, and the latter of which continues from there to Monterey, California.

Conducting parasitological examinations of 199 whelks collected from 25 sub-tidal reefs found throughout the species' expanded and historical ranges, the six scientists learned a great deal, including the facts that (1) "the average whelk in the expanded range was less than 20% as likely to be infected by parasites than was a whelk in the historical range, despite considerable variation among sites and across geographical regions," that (2) "the average infected whelk in the expanded range had [only] 5.6% the intensity (parasite numbers) of the average infected historical-range whelk," that (3) "the average expanded-region whelk was infected by 0.11 parasite species, compared with 0.77 parasite species infecting the average historical-range whelk," and that (4) parasite "species richness among sites in the expanded range was 22% of the richness found in the historical range."

In further discussing their findings, Hopper et al. write that "Kellet's whelk provides an example contrary to the hypothesis that disease will generally increase with warming-induced range shifts." And they say that "these findings, when combined with previous empirical (Menendez et al., 2008) and theoretical (Phillips et al., 2010) results, suggest that species range-margin expansions in both terrestrial and marine biomes may generally be characterized by a release from parasitism." In addition, they remark that "if such reduced parasitism generally characterizes range expansions, then increased infectious disease may not be one of the pervasive impacts of climate change-induced range expansion." Indeed, they state that "climate change may lead to the expansion into new areas of species lacking disease."

References
Menendez, R., Gonzalez-Megias, A., Lewis, O.T., Shaw, M.R. and Thomas, C.D. 2008. Escape from natural enemies during climate-driven range expansion: a case study. Ecological Entomology 33: 413-421.

Phillips, B.L.,Kelehear, C., Pizzatto, L., Brown, G.P., Barton, D. and Shine, R. 2010. Parasites and pathogens lag behind their host during periods of host range advance. Ecology 91: 872-881.

Posted 20 January 2015