Balance nature: important role of parasites in ecosystems (Introduction)

by David Turell , Sunday, May 08, 2022, 15:20 (930 days ago) @ David Turell

Involved in many ways:

https://knowablemagazine.org/article/living-world/2018/praise-parasites?utm_campaign=K_...

"Lafferty is not a medical doctor — he’s a PhD ecologist who studies parasites, mostly in fish and other marine creatures, a fact he’s always careful to explain to his correspondents. He’s sympathetic to these desperate people, even if what ails them is more imagined than real. Parasites, after all, have wormed into every corner of the tapestry of life, including hooking up with human beings in the most unpleasant of ways.

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"Parasites have an underappreciated importance, he adds — as indicators and shapers of healthy ecosystems. They thrive where nature remains robust, their richness and abundance keeping pace with biodiversity. They can serve important roles in maintaining ecosystem equilibrium. For all these reasons and others, he urges fellow scientists to take a more neutral view of them and adopt well-established theoretical approaches for studying diseases on land to better understand how marine parasites operate. If scientists want to better predict when infections and infestations will recede, remain innocuous or spiral out of control, he says, they need to start thinking like parasites.

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"The flatworms in these snails may not be destined for a lowly existence in the mud, though: Their future holds an opportunity to swim, and even fly. Larvae of the most common species go on to penetrate the gills of a California killifish, then attach themselves by the hundreds to the fish’s brain, manipulating the new host to dart to the surface or roll on its side and flash its silvery belly.

"That conspicuous behavior makes the infected fish 10 to 30 times more likely to be eaten by a predatory heron or egret. And it’s in that bird’s intestine that the trematode finally matures, excreting eggs that are dispersed with guano all over the salt marsh or in other estuaries — before being picked up, again, by horn snails.

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"By some estimates, nearly half of the species in the animal kingdom are parasites. Most of them remain largely out of sight because they are small, even microscopic. Their ancestors didn’t always start with a parasitic lifestyle: Researchers have so far found 223 incidents where parasitic insects, worms, mollusks or protozoans evolved from non-parasitic predecessors. Some ate dead things. Others killed their prey and consumed it. Then their life strategy evolved because they proved more successful if they kept their prey alive, kept their victims close — so they could feed on them longer. It’s a strategy distinct from those of parasitoids, which outright kill their hosts, Lafferty explains, a glint of mischief in his eye. “Think about the movie Alien. Remember when the alien sock puppet bursts its head out of John Hurt’s chest? That’s a classic parasitoid.”

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"As illustrated by the trematode in the killifish, Lafferty says, “parasites are determining who lives and who dies in a way that benefits them.”

"Moreover, parasites are a useful way to explore broader ecological questions: How does energy flow through those food webs? What forces maintain ecological stability and keep one species from overrunning all others? What are the implications of robust and healthy biodiversity on human health? Ecologists debate all sorts of competing theories, Lafferty says. What’s clear to him and other like-minded parasitologists: “We cannot answer these questions if we are going to ignore the parasite part of the equation.”

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"He and colleagues worked out how to halt an epidemic of schistosomiasis in Senegal by reintroducing freshwater river prawns that eat the intermediate host of the blood fluke that causes the disease. He discovered how the eradication of rats on Palmyra Atoll in the Central Pacific had a second benefit: the local extinction of the Asian tiger mosquito, a vector for the dengue and Zika viruses."

Comment: again, we see clear evidence of the importance of ecosystems maintaining the necessary balance for all living intertwined organisms. What parasites do could be seen as evil if humans were severely involved and some humans are. dhw will react by wishing no evil were present, but the examples in this article (not all included here) show beneficial effects, not evil. No more evil than ants controlled by fungus, discussed before. Theodicy is really as seen in the eye of the beholder, not the realist believer in God. Giant article worth reading