A small bug manipulates the behavior of its hosts to ensure its amazing life cycle
Parasites give new meaning to the “eat or be eaten” cliché. Often their life cycle can only be completed if they are ingested by a host – repeatedly for some – making their chances of survival seemingly slim. To improve their chances, certain parasites manipulate the behavior of their hosts to make it more likely that the person will be eaten.
The parasitic cestode Schistocephalus solidus it requires a much larger host—specifically a three-spined woodpecker—to develop and then a bird to breed. But the parasite’s larvae, less than a millimeter long, are too small for the fish to eat.
Instead, the larva must first be ingested by a copepod, a small shrimp-like crustacean. When ready for its next host, the larva causes the copepods to twitch. If all goes well (for the parasite), the three-spined tadpole eats the copepods. Inside the fish, the larva grows prodigiously, causing the poor stickleback to suffocate to the surface of the water, where it is likely to be eaten by a bird. Inside the bird, the parasite matures and mates, sending its eggs back into the water through the bird’s feces. And so the cycle begins again.
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This article was originally published under the title “An incredible life cycle” in Scientific American 327, 4, 78 (October 2022)
doi:10.1038/scientificamerican1022-78
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https://www.scientificamerican.com/article/see-how-a-parasite-travels-from-tiny-crustacean-to-fish-to-bird/
