<\/a>University of Alaska Fairbanks doctoral student Don Larson with a wood frog he captured in Ballaine Lake on the university campus in Fairbanks. (Courtesy Photo | Oivind Toien)<\/p><\/div>\n\t\t\t\t
Larson loves frogs, but he was even more interested in a parasite that lives part of its life in Alaska ponds and lakes. Ribeiroia ondatrae is — for part of its life — an oversized head with a whip tail. In ponds and lakes and puddles, it torpedoes into tadpoles, embedding itself near where a frog’s legs will emerge. Sometimes, a developing frog will react to the irritant by growing extra legs.<\/p>\n\t\t\t\t
Why would a parasite do that to the animal upon which it depends?<\/p>\n\t\t\t\t
“They want to create a zombie,” Larson said. “This parasite wants this frog to be eaten.”<\/p>\n\t\t\t\t
Ribeiroia ondatrae needs three other animals to complete its life cycle. It first requires a bird like a sandhill crane to eat an infected frog, which maybe is not moving well with those extra legs. Then it needs the crane to poop out adult parasites into water, which produce eggs that hatch into little blobs.<\/p>\n\t\t\t\t
Snails eat those blobs. Within snails, the parasites multiply like crazy, then depart as tadpole-seeking missiles, entering them through the anus or gills.<\/p>\n\t\t\t\t
Why would anything evolve to rely on three other organisms?<\/p>\n\t\t\t\t
“It’s like living with mom and dad well after high school,” Larson said. “The food, housing, and transport are all taken care of for parasites. They only need to expend energy to avoid the host’s immune system, and reproduce.”<\/p>\n\t\t\t\t
Though Larson did not find a deformed frog in Fairbanks, he found that the parasites can survive in overwintering wood frogs. He thinks the parasites endure winter by “hijacking” a frog’s glucose strategy. He wonders, if the air keeps warming, if the parasites will take that as an advantage, leading to more greenish zombies skittering through Alaska wetlands.<\/p>\n\t\t\t\t
<\/p>\n\t\t\t\t\u2022 Since the late 1970s, the University of Alaska Fairbanks\u2019 Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.<\/b><\/p>\n\t\t\t\t
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