Arthropod Roundup: Amphipods under the ice, high octane isopods, and the pea aphid genome

Quick blurbs about arthropod research and news:

• NASA climate researchers have discovered animal life deep below the Pine Island Glacier Ice Shelf in Antarctica. The researchers drilled a hole six-hundred feet deep and eight inches wide into the glacial ice sheet about twelve miles from the open ocean. When they lowered a camera below the ice sheet, the scientists were surprised to see a Lyssianasid amphipod crustacean swim up and park on the cable. The researchers were only expecting to find microbial life under the ice sheet this far in from the open ocean. It is unknown what the primary energy source for animals living here could be. The presence of a three-inch amphipod, however, suggests a much more elaborate and dynamic ecosystem than hypothesized in this poorly understood habitat. (DSN has a video of the amphipod)
• Limnoriid isopods, commonly called gribble worms for some reason (they neither are, nor resemble worms), have a ravenous appetite for wood. This is not unusual among arthropods; many diverse groups including termites, millipedes, and squat lobsters are capable of digesting woody plant matter. However, all these creatures process the wood with the aid of gut-dwelling symbiotic bacteria. A new study finds that the Limnoriid isopod, Limnoria quadripunctata is special in that it doesn’t rely on bacteria-produced catalysts to break down wood, but rather has the necessary glycosyl hydrolase enzymes incorporated into its genome. These enzymes are evolutionarily related to similar proteins found in arthropods, but their derived function for wood digestion in Limnoriid isopods is completely novel. The researchers, or their over-excitable university PR department, think the study of these enzymes could aid in bio fuel synthesis.
• The gemone of the pea aphid, Acyrthosiphon pisum, has been sequenced. This is the first Hemipteran (true bug) genome and will provide clues about the evolutionary history of certain hexapod groups. This new genome could also help agriculturalists develop new techniques to control aphid pests and the spread of aphid-borne plant viruses. Researchers are also interested in the pea aphid’s, apparently, scaled down immune response system and their ability to easily switch specialization from one plant species to another.

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

Deep-sea crustaceans on film and near-bottom ampipod swarms

The BBC is presenting an article and series of films from a recent University of Aberdeen research expedition. The films are shot between 5.5 kilometers and 10 kilometers in depth and feature snailfish, decapod shrimp, isopods, and amphipods as they scavenge on a bait bag. The videos are narrated by Dr. Alan Jamieson, and he shares some neat insights about deep sea life.

I am personally surprised at the ridiculous swarms of amphipods in the 9 km and 10 km videos. I did not think deep sea life was that dense except around vents and seeps. They don’t say how long the bait bag was there before the film starts, and it could have been down there for hours attracting every amphipod in a 100 m radius. However, a quick check of the literature reveals that these near-bottom deep-sea amphipod swarms have been observed near vents as well as in open abyssal plains. Pelagic swarming is not typically a characteristic attributed to deep sea crustaceans and its ecological significance is unknown.

A swarm of undescribed paradaliscid amphipods, photographed from the submersible Alvin near a deep sea vent in the East Pacific Rise (Dover et al., 1992).

References:
Dover, C.L.V. et al., 1992. Deep-sea amphipod swarms. Nature, 358(6381), 25-26.

Rock me Bathynomus

At first I thought this was a joke, but it’s real. Gloriously real.

Musician and blogger Pagan Wanderer Lu commissioned a music album centered around the giant isopod, Bathynomus giganteus, as a sort of creative experiment. Seventeen musicians contributed to the project, composing songs about life, love, and giant deep-sea crustaceans. Get the whole album, “Songs About Giant Isopods”, here.

More awesome crustaceans from Antarctica

As I mentioned previously, the antarctic is home to a startling, and poorly surveyed, preponderance of marine life. Now, the British Antarctic Survey has released some excellent photographs of some of these animals. Here are the arthropod highlights (click the photos to embiggen):

Serolid sp. – Wait, yesterday didn’t I say that trilobites are extinct? Well, that is still true. This animal  is actually an isopod crustacean, related to terrestrial pill bugs. The flattened body shape of this animal is an adaptation that makes it easier to burrow into sediment.

Antarcturus sp. – Despite the apparent morphological disparity, this is also a member of the isopod order. This animal is a member of the Antarcturidae family. Unlike Serolids, which are bottom-dwelling scavengers, these isopods live on the branches of coral and sponges. They reach their long frontal appendages out in the water column to catch planktonic prey.

These two isopods nicely demonstrate the tremendous amount of morphological diversity that similar animals can evolve in order to best suit their lifestyle. Furthermore, Serolid sp. is a great example of convergent evolution between isopods and trilobites. These two arthropod groups are unrelated, yet species within them have evolved a similar body shape in order to best suit their shared bottom-dwelling lifestyles.

Photos by: Peter Bucktrout