Biochemical controls: parasites control hosts (Introduction)

by David Turell , Thursday, July 20, 2023, 18:05 (490 days ago) @ David Turell

while losing unneeded genes:

https://www.sciencedaily.com/releases/2023/07/230718164256.htm

"Parasitic hairworms manipulate the behavior of their hosts in what's sometimes called 'mind control.' A new study reveals another strange trait shared by different hairworm species: they're missing about 30% of the genes that researchers expected them to have. What's more, the missing genes are responsible for the development of cilia, the hair-like structures present in at least some of the cells of every other animal known.

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"Hairworms are found all over the world, and they look like skinny strands of spaghetti, a couple inches long. Their simple bodies hint at their parasitic lifestyle -- they have no excretory, respiratory, or circulatory systems, and they spend almost their entire lives inside the bodies of other animals. "One of the coolest things, maybe the thing that they are most known for, is that they can affect the behavior of their hosts and make them do things that they wouldn't do otherwise," says Tauana Cunha, a postdoctoral researcher at Chicago's Field Museum.

"There are a few hundred species of freshwater hairworms. Their eggs hatch in water, and the hairworm larvae get eaten by tiny water-dwelling predators like mayfly larvae, which in turn get eaten by bigger, land-dwelling predators like crickets. After growing into adulthood inside of their new hosts' bodies, the hairworms manipulate the hosts' behavior, causing them to jump into water. There, the worms swim out of their hosts' butts and seek out mates, knotting themselves together, to begin the cycle anew. (There are also five species of hairworms that live in marine environments and parasitize water-dwelling creatures like lobsters, but it's not clear if those ones also have host manipulation capabilities -- there's no pressure for the worms to get back to the water, since the hosts already live there.)

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"'What we found, which was very surprising, was that both hairworm genomes were missing about 30% of a set of genes that are expected to be present across basically all groups of animals," says Cunha.

"Results like that often make scientists wonder if they've made a mistake. But there was a connection between the missing genes in the two worm species. "The large majority of the missing genes were exactly the same between the two species. This was just implausible by chance," says Cunha.

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"'Based on previous observations, it didn't seem like hairworms had any cilia, but we didn't really know for sure," says Cunha. "Now with the genomes, we saw that they actually lack the genes that produce cilia in other animals -- they don't have the machinery to make cilia in the first place."

"What's more, the fact that both the freshwater and marine hairworm species had lost the genes for cilia indicates that this evolutionary change happened in the deep past to the two species' common ancestor.

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"Hairworms aren't the only parasites capable of "mind control" -- it's a behavior that's cropped up in protozoans like the organism responsible for toxoplasmosis, which reduces rodents' fear of cats, and in the fungus Ophiocordyceps, which manipulates ants into spreading the fungus's spores. While these organisms are only distantly related to hairworms, Cunha says that the new study could help scientists find common threads for how this behavior works. "By doing this comparative analysis across organisms in the future, we might be able to look for similarities. Or maybe these organisms evolved similar behaviors in completely different ways from each other," says Cunha."

Comment: no question parasites lose genes whose functions are handled by the host organism. The last paragraph above reviews all the previous articles presented here about parasitism and mind control.