Parasitism across kingdoms

Trying to think of all the possible combinations, and if they exist in reality:

Starting with same-kingdom:

  • We now know about virophages, the viruses that infect other viruses
  • Archaea do not seem to be parasitic on anything
  • I have not, however, found references to bacteria infecting other bacteria
  • Nor to protists parasitic on other protists
  • Fungi parasitic on other fungi: the “lobster mushroom” is an example
  • Plants parasitic on other plants: all of the mistletoes, broomrape family, and balanophores
  • Animals parasitic on other animals: roundworms, tapeworms, flukes, etc.

Now, considering cross-kingdom:

  • Viruses can infect all other kingdoms
  • Bacteria can infect fungi, plants, and animals
  • Protists can infect plants (downy mildew) and animals (malaria).
  • Fungi can be parasitic on plants and animals
  • Plants can be parasitic on fungi (saprophytes)
  • Animals can be parasitic on plants (gall-makers, nematodes)

So it seems that some possible combinations do not exist in reality: I cannot find any reference to a protist or an animal parasitic on a fungus, nor to a plant parasitic on an animal. If I am correct, is there some general explanation for these gaps?

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These definitely exist. Here’s an example regarding red algal parasites of other red algae: https://www.degruyter.com/view/journals/botm/60/1/article-p13.xml

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I have no answer for this since I have very little knowledge on this topic, but could it be due to food resource limits? Maybe there are certain nutrients a kingdom requires that aren’t provided by another?

Or there may be gaps in our understanding. Maybe the algae that one finds on many animals backs actually absorb some nutrients from the animal’s skin (that was just a random wild guess but hopefully the idea came across)?

EDIT: I think what I said is a bit too ridiculous, eg. algae and coral apparently seem to have a symbiotic relationship.

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There are plenty of insects that infest fungi and eat them from the inside. Mushroom hunters often have to cut open their finds to make sure they aren’t full of bugs before eating them. I’m under the impression that this pretty much always results in destruction of the host (or at least the fruiting bodies, even if they do not kill the hyphal networks), but the fungus is still alive while they’re eating it, so this does count as parasitism.

Here’s quite an old article on mushroom pests I found on the USDA’s website.

And another article from the UK Agri-food & Biosciences Institute on Sciarid flies, which are apparently a significant detriment to mushroom farming operations.

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Fungi can be parasites of protozoans (Myxomycetes).and on stramenopiles (brown algae).

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Some regard plants who use burs to stick onto animal skin in order to propagate “obligate parasites”

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Not only are there plants that are parasites to animals, they are parasitic to parasites, galls specifically. https://www.cell.com/current-biology/fulltext/S0960-9822(18)30815-7

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That’s quite an absurd statement they are making! They are pushing (really hard) the limits of what constitutes a parasitic interaction - parasitizing on the extended phenotype of the insect!?

I’m sure there’re many plants that might find certain animal “extended phenotypes” (like burrows, nests, whatever) suitable for growth and in some cases that would be to the detriment of the animal; by their definition that would be considered parasitism on the animal. If a vine is happy to grow on my house (my extended phenotype) and its roots erode the mortar - this would be detrimental to me, even though very slightly. So the vine is… parasitizing me?! Weeds growing in my garden (my extended phenotype) would be parasitizing me?! OMG

Even if we agree on their extended definition of parasitism, this would be far from being (as they claim) the first recorded such “parasitism”!

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There is only one fly which is parasitic on fungi in UK, but doubtless many elsewhere…
Agathomyia wankowiczii, the Yellow Flat-footed Fly… on Ganoderma applanatum, the Artists Bracket.

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I think before any discussion of parasitism starts, we need to define what parasitism means. As I understand it, an organism that must live within a host, and emerges with the host essentially intact, is a true parasite. Most insects are parasitoids - they live inside the host, but when they emerge, the host is dead. It’s a sort of advanced form of predation. If anyone has other thoughts to add, please do.

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Well, since I started the thread, I will state what I meant. If the insects eating the inside of the fungus are parasites, “because it is still alive while they are eating it,” that would make almost every grazing herbivore a “parasite,” too. The caterpillar’s host plant is also still alive as the caterpillar eats it, after all. This is why I specifically did not cite fungivorous insects, which I certainly knew about.

In single celled organisms like bacteria, it is difficult to stick to the strict definition of a parasite; a virus that infects a bacterium is more like a parasitoid in that the host will always be dead at the end. But unlike parasitoid insects, I know of no virus that is a parasitoid on any multicellular host, so that’s why I counted it: what it does to a bacterial cell is the same as what it does to an animal cell.

What I had in mind by parasitism was some part of the host tissue being invaded by parasite tissue – like the mistletoe “root” invading the tree branch, or the liver fluke invading the liver. The example of the dodder laurel invading the gall is to me just another case of plant-on-plant parasitism, since the gall is made of the host plant’s tissue.

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I think living inside the host is only a requirement of endoparasites; ectoparasites such as lice or ticks live outside.

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Perhaps the host simply being alive while it is consumed is insufficient by itself, but I still think the fungus-eating insects should count. Obviously grazing herbivores are a little different in that they are neither internal to nor in some way attached to the host while feeding on it, so I don’t think you could extend the definition of parasite to them. The same applies to the caterpillar. The fungus-eating insects do infest the inside of the fungus, however, so they would be considered an internal parasite (or at least some do. I suppose in that case only the subset of fungus-eating insects that eat the host fungus from the inside should count).

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Is fact that they usually take a blood meal sufficient to call them parasites? Are they not specialised predators? We have all sorts of organisms that live on us, feed on skin cells or whatever. Are those parasites as well? Are biting flies parasites or predators?
I’m playing a bit of Devils Advocate here - it’s been decades since I did my Parasitology, so much may have changed. I have a lot of respect for internal parasites - not only are they in a dangerous environment, it’s an environment that is actively trying to kill them!

Perhaps parasitism can only develop in phyla that are predatory in some way. There are no bivalve parasites, possibly because they are filter feeders (I believe). Arthropods eat a whole range of things, so it is no surprise that parasitism has developed in them. From what I understand, Fungi are not a rich source of nutrients which may explain the relative lack of parasitism on them. As for galls, are these a response to feeding (albeit internal)? Oddly, leaves don’t respond in the same way to leaf mining insects. I’m only spitballing here - I know very little about mollusks, fungi, or most plants. I just find the whole notion of parasitism fascinating.

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I am afraid, you are wrong here. Fungi have many parasites, but almost all of them are other fungi.

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definitely. Ripped straight from wikipedia:
“Like predation, parasitism is a type of consumer-resource interaction,[3] but unlike predators, parasites, with the exception of parasitoids, are typically much smaller than their hosts, do not kill them, and often live in or on their hosts for an extended period.”

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There is more than one definition of parasite. The biomedical definition of parasite that frames the field of Parasitology includes a wide range of eukaryotic organisms that derive their energetic needs from other species without immediately killing them or, as E.O. Wilson put it, “predators that eat prey in units of less than one”. The formal field of study generally excludes prokaryotes, viruses and vertebrates.

Ecologists and evolutionary biologists have a broader view of parasitism, including behaviour that appropriates the investment of energy from one species to the benefit of another with corresponding effects on their respective fitnesses. Brood parasitism is an example.

Like a lot of terminology in biology, parasitism’s origins predate modern biological and evolutionary theory and the original concept doesn’t really fit modern understanding. There are no hard boundaries between consumption, predation and parasitism.

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Thanks for correcting me. I don’t know much about fungi.

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Thanks for the discussion folks. As I said, my knowledge of parasitism was laid down in the early 1980’s, so it’s good to have some updates. @pmeisenheimer, I would agree there are few hard boundaries. I would even extend it to any type of organism.
Now, perhaps we could get back to the OP’s question, after I derailed the conversation!

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