Natures wonders: lung worm controls frogs' poop (Introduction)

by David Turell @, Thursday, May 03, 2018, 21:18 (438 days ago) @ David Turell

These controls allow the larvae to survive until the next life cycle:

"it’s not surprising that scientists recently discovered lungworms alter the behavior of their cane toad hosts to ensure things are most comfortable for them. But what is surprising, or at least a little unnerving, is what they actually do: the worms makes their hosts poop differently.

"The question of whether the parasites were manipulating toads arose after Patt Finnerty noticed that infected toads acted a little differently in other lab trials he was conducing. Further investigation revealed significant differences in behavior between infected and uninfected toads, particularly when it comes to their bowel movements.

"The parasite in question is the lungworm Rhabdias pseudosphaerocephala, a nematode that primarily infects cane toads (Rhinella marina). It came to the attention of scientists because its those toads—normally native to the Americas—have become invasive pests in places like Australia after they were introduced in 1935.


"That lifecycle involves a two-generation process with both parasitic and free-living stages. As the name implies, the parasitic lungworms live in their hosts lungs as adults feeding on blood (1). The eggs they lay there are essentially coughed up and swallowed, and hatch in the toad’s digestive tract (2). As larvae, they hang out in feces, which they consume (3), and a little after the frog defecates, they molt to become free-living adult worms (4), which find one another and mate. The female worm gets the short end of the parenting stick at this point, as she retains her fertilized eggs until after they hatch (5). The offspring develop inside her until they kill her as they burst free (6). They then wait in the soil (7) until the opportunity presents itself to burrow into the next unfortunate toad that stops by (8), starting the cycle anew.


"The researchers also noticed that infected toads defecated more often, and seemingly aimed for their water containers rather than the dry newspaper floor of their cages. When they weighed these poops out, the average wet mass of the infected animals’ feces was higher than that of the dewormed ones, but the dry mass was the same—infected poops were just about 15% moister. And that was especially intriguing, because when they put the lungworm larvae through the gauntlet, they found that over 15 times as many survived after three days if the soil was moist rather than dry.

"The same story emerged from the field data. Infected wild toads tended to poop closer to bodies of water, and on moister soils. And when the weather was dry, the infected toads stuck much closer to water.

“'We found that toads with lungworms behaved much differently than uninfected toads is several regards,” explained Greg Brown, a research fellow at the University of Sydney and co-author on the paper. “Most notably, infected toads tended to stay closer to water and poo in moister areas.”

“'These are the conditions that increase survival of the larval worms in the poo and increase their likelihood of encountering a new host.”


"then the results open a, well, can of worms, so to speak, because they are evidence that parasitic manipulation of hosts may be more subtle than scientists thought—and more common. “Lots of parasite larvae are transmitted to the environment through feces, so maybe parasite ability to manipulate host pooing is widespread,” said Brown. “It seems like a logical way for the parasite to increase the likelihood of its offspring surviving and infecting another host.”

"But if the worms are really manipulating their hosts, then more questions arise—like, how are the worms causing these behavioral changes? The researchers couldn’t say for sure, but they’re betting the worms tweak circulating cellular signals like neurotransmitters or hormones to get the toads to deposit moist, frequent poops near water. Learning exactly how they exert their control could help scientists better understand the toads’ physiology, or maybe even point to novel ways of getting rid of them.

"Controlling an invasive species by controlling its bowels—now wouldn’t that be something."

Comment: It seems reasonable that chemical influences from the are used for this control of the frog's body.

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