A Fluke Migration

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Science  12 Jan 2007:
Vol. 315, Issue 5809, pp. 162
DOI: 10.1126/science.315.5809.162c

Parasites in the trematode family, which includes liver flukes and schistosomes, have fantastically complicated life cycles that often involve snails and other aquatic hosts, as well as birds and mammals that prey on the intermediate hosts. Mud snails are small estuarine species that can harbor the intermediate stages of many species of trematode. A century ago on the coast of California, the Japanese mud snail was accidentally introduced when oysters were imported; it can outcompete the native snails partly because it is victimized by fewer trematodes parasites—only three.

Miura et al. have studied the population genetics of these traveling trematodes and have found a different itinerary for each. The most common North American species is also the most common one in northeastern Japan, whereas the rarest one was found only at Elkhorn Slough and at the original oyster source in Matsushima Bay. The third showed a striking level of genetic diversity, rarely seen in introduced species and probably due to its repeated re-importation by migrating shore birds. Before the accidental entry of its preferred host (native mud snails simply won't do), this trematode was merely a passenger in transit. — CA

Proc. Natl. Acad. Sci. U.S.A. 103, 19818 (2006).

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