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Parasites change life history of snails



With 4.5 billion humans infected with parasitic worms, it's no surprise that half of all living creatures are parasites.

While the mere mention of internal parasites may make some queasy, Den- nis Minchella finds their unique life- styles and "cleverness" fascinating.

Minchella, a professor of biological sciences and associate dean of the Col- lege of Science, became interested in parasites while taking an invertebrate zoology course as an undergraduate stu- dent. He enjoyed learning about para- sites' mechanisms for survival and how they can transmit themselves to differ- ent hosts.

Coevolution between hosts and para- sites is one of the main areas Minchella studies. As hosts develop defense mech- anisms against parasitic infection, the parasites find intelligent ways of adapting against the host's defenses, entering what is known as a coevolutionary arms race.

"Within a coevolutionary arms race, hosts are coming up with ways to thwart their parasites and then their parasites are getting over those obstacles," said Alyssa Gleichsner, a Ph.D. candidate in biology and assistant in Minchella's lab.

Minchella works mainly with schis- tosomes, parasites which penetrate hu- mans' skin after their larvae complete a stage of their life cycle in snails. Within his lab in Lilly Hall, Minchella replicates the schistosomes' entire life cycle ... mi- nus the human host.

"We have tanks of freshwater snails, and we run (the parasites) through mice, so mice are the vertebrate host," Minchella said. "If you want to study the parasite, you have to be able to have it in a life cycle. It has to be alive and the only way to keep it alive is to keep it cycling through snails and ver- tebrate hosts."

Minchella said some of the parasites come from endemic areas, and most are collected from the wild to maximize ge- netic variability. He has strains of para- sites from Egypt, Brazil and Kenya.

After many years of research and 80 publications, Minchella said he was most surprised by snails' having what he called "fecundity compensation." After the parasite enters the snail, the snail is no longer able to produce offspring. To compensate for this, the snail has a "burst of reproduction" before the para- site renders it infertile.

"The surprise was that hosts are able to change their life history strategy in order to deal with a parasitic infection," Minchella said. "Before that, people just said, 'You're resistant or you're not re- sistant,' and there was nothing in be- tween. I think people are much more willing to not think about life history changes and how that can help you deal with parasitic infections."

By Alyssa Fanara
Assistant Campus Editor

Michael Takeda
Photo Editor

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