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A Tapeworm To Call My Own

The Loom
By Carl Zimmer
Jul 9, 2009 2:32 AMNov 5, 2019 12:24 AM


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Long after I'm dead, there will be stingrays swimming the Arafura Sea infested with tapeworms that bear my name. There are about 1.8 million species with names, out of an estimated 8 to 9 million species in total. In 2007 alone, scientists named 18516 new species. Naming a species is actually the final step in a long, slow journey. It starts with the discovery of an organism that looks like it just might not belong to any known species. Scientists then search the scientific literature to see if it is indeed new to science. If it is, they inspect it in painstaking detail, observing all the information one might be able to use to identify another organism as belonging to the same species. This is not the sort of work a gene-sequencing robot can do for you on your lunch break. This is natural history, old school. This tapeworm was discovered in 1999. Janine Caira of the University of Connecticut and Kirsten Jensen of the University of Kansas were traveling aboard the Ocean Harvest, a commercial trawling ship sailing the Arafura Sea off the north coast of Australia. The fisherman pulled up a massive whip-ray belonging to a species never seen before (shown below). Caira and Jensen were particularly interested in what lurked inside the fish: its tapeworms.

There are some 6000 species of tapeworms named so far. Some species live inside people. Others live inside beetles. Others live inside frogs. Not only do tapeworms live in a huge range of animal hosts, but the life cycle of a single species may take it through several different species--a shrimp, a fish, a sea bird, and back to the shrimp, for example. Scientists know a lot about a few species of tapeworms, but most of them live in familiar hosts like ourselves. But unfamiliar hosts have tapeworms too. Caira and her colleagues have traveled the world over to cut open sting rays, sharks, and other cartilaginous fishes to search for new species of tapeworms. And more often than not, they find them. The tapeworms they found that day in 1999, belonged to a genus called Ancanthobothirum. They were small, measuring less than an inch long. Caira and Jensen dropped some of them into alcohol so that they could extract DNA later, and dropped the rest into formalin, which preserved the parasites so that they could be studied under a microscope without decaying. That task fell to Carrie Fyler, who was writing her dissertation on Acanthobothrium, which contains 165 known species. After studying the tapeworms Caira and Jensen brought back, Fyler determined that there were at least five new species among them, all gathered from a single fish. Last year Fyler asked me to come to the annual meeting of the American Society of Parasitologists, where she had organized an entertaining session on parasites in popular culture. There were talks on parasites in the movies, in art, and in poetry. Fyler asked me to give a talk based on my own experience writing blogs, articles, and an entire book,

Parasite Rex

, on these marvelous beasts. At the meeting, Fyler told the audience how the book had helped propel her into parasitology. What she didn't tell them was that she was working on a paper describing the five whip-ray tapeworms, and that she was doing me the honor of naming one of them for me. Now, at last, the paper has come out in the journal Folia Parasitologica. Meet Acanthobothrium zimmeri.

I'm happy to report that A. zimmeri is an excellent parasite. It has the bizarre anatomy that you'd expect from a tapeworm--an animal that has abandoned brains, eyes, and mouth, and has turned its skin into inside-out intestines. Its head is festooned with a distinctive set of suckers, hooks, and muscular pads, which it presumably uses to clamp onto the gut of its host. Like other tapeworms, the rest of its tiny body (1.5 to 3.1 millimeters long) is made up mostly of segments, each of which carries both testes and ovaries. (I note, without comment, that each segment's vagina is described as "thick-walled, sinuous.") When I first discovered I was going to have a species named for me, I was overwhelmed by delusions of grandeur. But at the parasitology meeting, I was quickly brought back down to Earth. Fyler mentioned to another tapeworm expert that she was naming a species for me, and he said, "Yeah, I guess that makes sense. Acanthrobothrium is kind of tall and thin like you." Apparently naming species was not the hallowed ritual I imagined. It is actually rather routine, because biologists have so many species to name. In fact, species can be named for all sorts of odd reasons. Carl Linneaus, who first invented the whole two-part Latin name system we still use today, liked to name weeds for his scientific enemies. Fyler named the other four tapeworms found in the whip-ray for (1) the ship that Caira and Jensen were on (A. oceanharvestae), (2) her grandfather "Pop" (A. popi), (3) James Rodman at the National Science Foundation (A. rodmani), and (4) Jim Romanow, who took care of the microscopes Fyler used (A. romanowi). I'm still grateful for Fyler's gesture, and I still can't help feeling some vaguely paternal pleasure at seeing how A. zimmeri helps scientists learn a little bit more about the diversity of life and how that diversity evolved. Fyler and her colleagues compared its DNA to other Acanthobothrium species and discovered something interesting: the five species that live in the one fish are not closely related to each other. Instead, their closest relatives live in other whip-rays. Somehow their ancestors must have made the leap from one host to another, and somehow they must have made a place for themselves in the crowded ecosystem that is the inside of a whip-ray's gut. For now, that leap remains almost entirely a mystery. Scientists have no idea what sort of life cycle A. zimmeri and its relatives have--what happens to the eggs that are released from the whip-rays, or what other hosts they may have to invade first before finally ending up in another whip-ray. Like its whip-ray host, A. zimmeri's intermediate hosts probably have yet to get a name of their own. I hope some day scientists do figure out my namesake's lifecycle, but I also worry that their time may be running out. Whip-rays, like many other rays and sharks, are in serious trouble these days thanks to reckless overfishing. And whenever one species becomes extinct, it can take other species with it. Switching host species is an exquisitely rare event, and so it's likely that A. zimmeri can only live in one species of whip-ray. When its host goes, it may disappear as well. Extinction is inevitable in the grand scheme of history: all species disappear after several million years, give or take. I just hope that A. zimmeri, along with the rest of the world's diversity, doesn't go sooner rather than later.

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