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Parasite of the Day
February 18, 2013 7:04 AM   Subscribe

Does just what it says on the tin,
"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum." - Jonathan Swift
posted by Blasdelb (13 comments total) 8 users marked this as a favorite

 
The pattern of branches in the schistosome family indicates that at some point in the past, the mammal-infecting group had evolved in a divergent direction (in terms of host use) to the rest of the family which is composed of species that infect birds. This raises intriguing questions about the deep evolutionary history of this group of parasites.

Evolved in a divergent direction or just born that way?
posted by three blind mice at 7:20 AM on February 18, 2013


Tommy Leung, one of the co-bloggers, has a great google+ feed as well. I work with him on Science Sunday and some other google+ science projects.
posted by ChuraChura at 7:22 AM on February 18, 2013


I love this idea, but Toxoplasmosis didn't get its just due on January 9th. Because UR CAT IZ MAKING U TEH CRAZEE
posted by mcstayinskool at 7:38 AM on February 18, 2013


and these have smaller still to bite ’em; and so proceed ad infinitum.

I wonder how far that actually goes. I know it's not turtle parasites all the way down, so what is the tallest parasite stack (parasite on a parasite on a parasite...) occurring in nature? I'm betting it doesn't go down much farther than something like dog(dog flea(parasite on or in a dog flea)) or, if you allow for symbiotes, rhino(tick bird(tick bird flea(parasite on or in a tick bird flea))).
posted by pracowity at 7:41 AM on February 18, 2013


"Evolved in a divergent direction or just born that way?"

Umm, yes.

The sentence you quoted can be a little difficult to parse. What it is saying is that both of the two populations of schistosomes that we see, the ones that infect birds and the ones that infect mammals, are likely descended from an ancient population of schistosomes that infected birds. The authors of the cited paper sequenced two widely conserved genes found in eggs of the one known sample to get an idea of how related it was to other schistosomes by comparing what they found to known sequences of other related strains. By mathematically looking at the patterns of similarity between a group of sequences, using magical programs that informaticians code for us, biologists can infer things like this. Generally the kinds of patterns that would indicate something like this would be things like a lot more diversity in one strain, which would then be inferred as ancestral, and a high level of relatedness between one subset of that strain and the entirety of the other, which would be inferred as divergent.
Molecular phylogenetics of the elephant schistosome Bivitellobilharzia loxodontae (Trematoda: Schistosomatidae) from the Central African Republic.
One of the most poorly known of all schistosomes infecting mammals is Bivitellobilharzia loxodontae. Nearly all of our available information about this species comes from the original description of worms that were obtained from an animal park-maintained elephant in Germany, probably a forest elephant Loxodonta cyclotis, originating from the present-day Democratic Republic of Congo. We obtained schistosome eggs from faecal samples from wild forest elephants from the Central African Republic. The eggs, which were similar in size and shape to those of described B. loxodontae, were sequenced for the 28S nuclear ribosomal gene and the mitochondrial cytochrome oxidase I (cox1) gene. In a phylogenetic analysis of 28S sequences, our specimens grouped closely with B. nairi, the schistosome from the Indian elephant Elephas maximus, to the exclusion of schistosomes from other genera. However, the eggs were genetically distinct (12% distance cox1) from those of B. nairi. We conclude the specimens we recovered were of B. loxodontae and confirm this is a distinct Bivitellobilharzia species. In addition to providing the first sequence data for B. loxodontae, this report also supports Bivitellobilharzia as a monophyletic group and gives the relative phylogenetic position of the genus within the Schistosomatidae. We also provide a review of the biology of this poorly known schistosome genus.
posted by Blasdelb at 7:43 AM on February 18, 2013 [1 favorite]


"I wonder how far that actually goes. I know it's not turtle parasites all the way down, so what is the tallest parasite stack (parasite on a parasite on a parasite...) occurring in nature? I'm betting it doesn't go down much farther than something like dog(dog flea(parasite on or in a dog flea)) or, if you allow for symbiotes, rhino(tick bird(tick bird flea(parasite on or in a tick bird flea)))."

It goes much much deeper than fleas, previously;

Farmer > Legume > Aphid > Parasitoid Wasp + Secondary Endosymbiont > Temperate Bacteriophage

or

Woman's Eye > Acanthamoeba polyphaga > Mimiviridae (Lentille virus) > virophage (Sputnik 2) > mobile genetic elements
posted by Blasdelb at 7:50 AM on February 18, 2013 [1 favorite]


What it is saying is that both of the two populations of schistosomes that we see, the ones that infect birds and the ones that infect mammals, are likely descended from an ancient population of schistosomes that infected birds.

Parasites are fascinating and thanks for the exposition Blasdelb. Why an organism that has evolved to do one thing suddenly (more or less) starts doing something else is really a paradox. Why does a parasite - which is a particularly host-dependent organism - that infects birds suddenly start infecting mammals? The hand-waving explanation of "random" mutations would not seem to give rise to such enormous difference in behavior and there is a chicken-or-egg mystery about all of it.
posted by three blind mice at 8:12 AM on February 18, 2013


Well one thing that happens to cause parasite lineages to diverge is vertical transmission in different host lineages, three blind mice. The ancient version of the bird schistosome may have been perfectly capable of infecting mammals, but its life history may be be such that it almost never got a chance to infect a host other than its normal bird host.

It's possible that some ways back in evolutionary time a small population of bird schistosomes managed (through some unusual series of events) to infect a mammal and that mammalian lineage managed to persist to this day. If there was no subsequent cross-transmission between the mammalian lineage and the avian lineage, then the two parasite lineages would've evolved along divergent paths and gradually become more specialized to their particular hosts to the point where they could now quite easily represent different species.

Mutation isn't necessarily (or even normally) the original event that causes two populations of a species to set out on diverging evolutionary paths. More often it is something like a change in behavior, or a change in resource preference, or a physical separation that prevents cross-breeding. Once two populations become isolated from each other, then evolution can start the process of divergence.
posted by Scientist at 8:45 AM on February 18, 2013


"Parasites are fascinating and thanks for the exposition Blasdelb. Why an organism that has evolved to do one thing suddenly (more or less) starts doing something else is really a paradox. Why does a parasite - which is a particularly host-dependent organism - that infects birds suddenly start infecting mammals? The hand-waving explanation of "random" mutations would not seem to give rise to such enormous difference in behavior and there is a chicken-or-egg mystery about all of it."

Well it does happen all the time. One thing I was always sure to stress to undergrads when I had lectures to give was that more or less everything you see or touch is covered in a thin film of fecal matter, even with the benefits of modern sanitation. Poop is everywhere and even we, in this miraculous modern age of toilets and sporadic hand washing, are constantly consuming it when critters shit in our attics, birds poop in the intake vents of our ventilation, or cow shit leeches onto our vegetable fields, or we don't wash our hands after touching a bathroom door handle or a belt buckle much less wipe our asses. One the other hand, the quantity of poop that animals in the wild consume, mostly the poop of other creatures, is intense. At the same time every single parasite in all of that poop that would ordinarily infect one of those other critters is a member of a population made diverse through mostly random mutation and each individually gets a shot at trying to infect the critters with the poor taste to east something covered in shit.

Really when you see the metazoan life they infect with the, IMO clearer, perspective of our pathogens; we all don't really look that different. Especially among mammals, our immune systems have important differences but all operate along roughly the same principles. Terrestrial animals are also all generally active at more or less the same temperature, though with some important exceptions, for example birds are generally a few degrees centigrade hotter, and indeed most pathogens we share with them get our immune systems to helpfully raise our body temperatures with a fever to accommodate them. From a human perspective there is indeed still a great deal of risk from pathogens that are new to us crossing the barrier into human disease from some animal to us and spreading wildly, where the googleable term d'art is emerging zoonoses (PDF)
posted by Blasdelb at 8:54 AM on February 18, 2013


Nature is wonderful.
posted by Artw at 9:04 AM on February 18, 2013


I love this blog, though I often find it unbearably squicky. I think my favorite parasite from it is this bird, Fregata minor. It is a kleptoparasite(!) which gets part of its food by chasing other birds around in the air until they throw up(!) and then diving to eat the falling vomit before it hits the water(!!!).
posted by whir at 10:51 AM on February 18, 2013 [3 favorites]


This interested me since I just learned about pallasite meteors, and my birthstone being peridot, I asked my SO for a pallasite. He offered a parasite instead and we laughed (I'd get eight fleas, up from one since he'd "splurge"). So I click through to the parasite of the day, hoping to find something more interesting than a run-of-the mill flea to continue this odd bargaining I've got going on.

I'm reading about the nematode that infects mosquitoes, and there's a video of the little wormy thing coming out of the mosquito larva. Pretty cool.

But then there's a related video titled "WTF IS THIS?!?" and I click through to see a huge wormy thing coming out of a huntsman spider. I'm terrified. But I can't help clicking through to the other related videos, showing nematodes coming out of spiders.

So now I'm all squicked out even though I usually don't mind creepy crawlies, but OMG PARASITES KILLING HUGE SPIDERS. Thanks, MetaFilter. I'm going to go crawl out of my own skin now.
posted by youngergirl44 at 12:53 PM on February 18, 2013 [4 favorites]


"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum." - Jonathan Swift

“There’s a bacterium on a diatom on an amphipod on a frog on a bump on the log in the hole in the bottom of the sea!”
posted by radwolf76 at 12:19 PM on February 19, 2013


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