Parasites' Genetic Variety May Be Best Way To Track Salmon May 05, 2006

Researchers at Oregon State University have discovered that the best way to tell where an animal came from, such as salmon that scientists are trying to track, may not be the genetics of the animal itself, but rather the parasites that are hitching a ride.   In a pioneering study that should give wildlife biologists an important new tool to track migrating animals, the OSU researchers found that genetic "fingerprinting" of parasites can be up to four times more effective for identifying the origin of a host animal than the DNA of the host animal itself.   The findings were just published in Ecology, a professional journal.   "We did this study with fish, but ultimately this approach could be very important with many animal species," said Michael Blouin, an OSU associate professor of zoology. "No one had ever demonstrated before that that the genetic study of parasites could give you the most accurate information about where the host animal came from."   In many wildlife monitoring and management situations, Blouin said, it can be quite important to know the original home or territory of individual animals. If a salmon population in one area is in severe decline, for instance, it may be critical to understand where those fish are going, or being caught.   "Sometimes, unfortunately, there just is not that much genetic difference between animals from different geographic locations over a wide area," Blouin said. "Thus, you can't use an animal's DNA to accurately identify its population of origin. On the other hand, it appears that parasites from different locations tend to be much more genetically distinct than their hosts from the same locations."   The OSU scientists studied the genetic markers found in trematodes, a flatworm that can infect fish when they enter fresh water and which often live in the gut of salmon. They discovered that in a genetic sense, the trematodes vary much more from one area to another than the salmon.   "On one level, this is just basic DNA fingerprinting, the type used in everything from human paternity testing to crime scenes and wildlife biology," said Blouin. "It's existing technology that's fairly efficient and cost effective. But no one had ever considered the wide genetic variation found in parasites and the much more accurate information that might give us."   In one test, the scientists tried to identify the origin of fish from two important "evolutionally significant units" of salmon, one in Oregon and one in Northern California . Conventional genetic testing of fish was only 80 percent accurate in determining where they came from; the testing of parasites was 100 percent accurate.   Parasites of one type or another are common in many animals, Blouin said, such as the trematodes in fish, nematodes in many animals, or lice common to birds and mammals. The study also found that hosts that carry two or more parasites can be tracked to their ancestral home with extremely high accuracy, even better than those with a single parasite.   This technology might also aid in prevention of smuggling of valuable exotic animals, researchers say, such as parrots from tropical jungles. The technology is sufficiently accurate that it should be useful to law enforcement officers, Blouin said.