Posts Tagged 'Parasite'

Arthropods in pop culture: Tongue replacing isopods

Isopod crustaceans exhibit a wide variety of morphologies and lifestyles. For instance, the common pill bug or woodlouse, found under any log in North America, is an isopod. These isopods, of the suborder Oniscidea, are the most terrestrially adapted of the crustaceans (unless you count insects, which you probably should). However, it is in aquatic environments that you see the true breadth of isopod diversity. I talked about two good examples in a previous post: Serolid isopods have flattened, trilobite-like bodies and scavenge on marine sediment; and Antarcturid isopods are narrow, with long forelimbs for catching prey from the water column. Other isopod suborders have developed parasitic lifestyles.

Many aquatic isopods are parasites that live either on the surface or inside their hosts. Some, the Epicarids for example, display morphological modifications characteristic of parasites; including reduction of appendages and sensory organs as well as a loss of rigid segmentation. Also, the mouthparts are sometimes specialized into a suction apparatus, complete with piercing stylets, used for extracting fluid from their hosts. These isopods parasitize copepods as larvae and then decapods as adults; living inside the carapace or gill chambers of crabs and shrimp. Other isopods parasitize fish, attaching to the body or gill chamber and feeding on the scales, flesh, or blood of the animal. Some of these isopods attack and kill fish in large swarms.

Parasitic isopods do some some fairly gristly stuff that is typical of parasites…

…but then there’s this… Oh, god… the horror…

I added LoL speak to make this a little less revolting. Alternate caption: 'Oh hai! Your tongue used to be here, but I eated it. Om-nom nom.'

Meet Cymothoa exigua, a Cymothoid isopod. Most Cymothids are exoparasites that feed on the flesh of fish. However this lifestyle has the disadvantages of exposing the isopod to predation and requiring it to migrate from fish to fish. C. exigua solves these problems by doing something disturbing.

Photo: Matthew Gilligan, Savannah State College, Savannah, GA (1989)

C. exigua parasitizes rose spotted snappers. It enters the fish through the gills and lodges itself in the buccal cavity at the back of the mouth. There it severs blood vessels leading to the fish’s tongue, causing the tongue to atrophy and degenerate. The isopod then uses its hook like pereopods to attach to the tongue nub, effectively and functionally replacing the snapper’s tongue. There it stays, feeding on blood, mucus, and stray pieces of whatever the fish is eating for the rest of its life.

Imagine being a rose spotted snapper, cruising around the comfortable waters of the gulf of California. One day this hard, spikey creature enters your mouth through your breathing apparatus, violently removes your tongue, and takes up residence. You have no arms or hands to reach into your mouth and remove it: So there it stays, drinking your blood and stealing your food, unmolested, …for ever…

*shudder*

More posts on isopods.

Previous posts about parasites: Flies, Wasps

Previous posts on arthropods that turn up in pop culture: Trashcan crab, Samurai Crabs

References:

  • Brusca, R., & Gilligan, M. (1983). Tongue Replacement in a Marine Fish (Lutjanus guttatus) by a Parasitic Isopod (Crustacea: Isopoda) Copeia (3) DOI: 10.2307/1444352

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We contracted crabs from gorillas

And you were probably thinking that people only got crabs from coeds on spring break in Cancun!

Seriously though, I apologize for the sensationalist title, but this story is a really neat demonstration of the application of phylogenetic comparison and evolutionary divergence time estimation. (For a primer of phylogenetics see this post.)

The venereal affliction known as “crabs” is an infestation of lice that specifically reside in the pubic region of humans. Pubic lice, Pthirus pubis, are of a genetically and morphologically distinct genera of lice from the head louse, Pediculus humanus. If you compare the evolutionary history of primates with the history of the lice that parasitize them, an interesting picture emerges.


Phylogenetic cladograms, assembled from morphological and genetic characters, for primates and parasitic lice. Dotted lines indicate parasite-host relationships. Figure from Weiss, 2009; after Reed et al., 2007.

Continue reading ‘We contracted crabs from gorillas’

Three parisitoid wasp genomes published

Last week I talked a bit about parisitoid fly larvae. Now, the genomes have has been published for three species of parisitoid wasps in Science. These guys are every bit as brutal as the flies, and then some. They forcibly inject their eggs into their insect hosts, often caterpillars. Some species inject multiple eggs while other inject a single egg that later divides into many cloned larvae that form a colonial social hierarchy within their host. Once they mature, the larvae burst out the side of their host. However, even this insult isn’t the end of the torture for the unfortunate caterpillar. The larvae employ mind controlling chemicals to force the caterpillar to use its silk to build them a cocoon, and then watch over its pupating murderers until it keels over dead.

Parisitoid wasp larvae from National Geographic’s, “In the Womb.” Watch in high quality for maximum revulsion.

Nature, you are one psychotic bitch.

Read this review for a wider overview of parasitoid wasps and their contributions to pest control and biological sciences, including discoveries made in the recent genomics work.

One interesting point jumped out at me. The parisitoid wasps are insanely diverse, with species estimates exceeding 600,000. Entomologist Michael Strand even posits that,

There’s a really compelling argument that these parasitoid wasps may be more diverse than beetles[.] Virtually every arthropod on Earth is attacked by one or more of these parasitoid wasps.

This extreme diversity seems to be tied to rapid evolvability (a concept that I have noted before in regards to arthropods) and rigid host specificity. While some wasps are generalists, laying eggs in a variety of arthropods, the vast majority parisitize a specific host species. This specificity is the result of evolutionarily optimized venoms and mind-controlling toxins, tailor made for their host species, and leading to rapid divergence of parisitoid wasp populations as they discover new host animals. This is not unlike the algal specificity of the sea slug I discussed last week. Its biology is ideally suited for maintaining chloroplasts taken up from a single species of algae.

Researchers hope to develop parisitoid wasps as a research model and exploit their prey specificity for pest control that will benefit agriculture. With bio-engineered parisitoid wasp terminators coming soon to a pasture near you, aphids and caterpillars should just cut their losses and run for their lives.

References:
The Nasonia Genome Working Group, 2010. Functional and Evolutionary Insights from the Genomes of Three Parasitoid Nasonia Species. Science, 327(5963), 343-348.


I have moved.
Arthropoda can now be found here.

Michael Bok is a graduate student studying the visual system of mantis shrimp.

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