Disease causing organisms can be present in some areas where their hosts are not. If their hosts arrive, novel disease outbreaks may result. In the first comprehensive genetic analysis of an invasive marine host and its parasites, researchers trace invasion pathways of snails and trematodes from Japan to North America.
Their results, published in the Proceedings of the National Academy of Sciences, have broad implications for identifying and mitigating spreading disease in a global economy. Simultaneously understanding the invasion pathways of disease-causing organisms and their hosts will be key in limiting future disease outbreaksin humans, agriculture and wildlife.
Invasive populations of Asian mud snails, Batillaria attramentaria, probably arrived in North America with Pacific oysters, Crassostrea gigas, imported from northern Japan in the early 1900's. Genetic research by Osamu Miura, Tohoku University, and colleagues from the Smithsonian Institution and UC Santa Barbara confirmed this. "We saw a lot of genetic variation among snail populations in Japan but the North American snails are genetically most similar to those from northern Japan, the source of the imported oysters," Miura reports.
Of the eight species of trematode parasites that plague the snails in Japan, only the most common, Cercaria batillariae, has arrived in America. Luckily for the researchers, gene sequencing showed that this single species actually consisted of several genetically distinct cryptic species in its home range in Japan. In North America, they commonly found two of the cryptic species. One parasite shows much less genetic diversity in America than in Japan, whereas the other parasite is equally diverse in both regions.
"Genetic evidence suggests that while one cryptic parasite species experienced a bottleneck and probably came with the snails, the other was probably historically dispersed by migratory birds and could only establish i
Contact: Mark Torchin
202-786-2094 ext. 8713
Smithsonian Tropical Research Institute