Why save what we love to kill?

Credit: John Kascht

From the AUG/SEP issue of Seed:
When the last surviving California condors were taken into captivity by the US Fish and Wildlife Service in the mid-1980s, they were transported to the San Diego Zoo’s Wild Animal Park and Los Angeles Zoo where, among other things, they were treated for parasites. Living within the feathers of the birds were Colpocephalum californici—an avian chewing louse that looks pretty much like all other lice: a bulbous head, stubby thorax, six hooked legs and a stout, hairy, segmented abdomen. But these lice lived only on California condors and were also facing extinction. More overlooked than willfully extinguished, the last C. californici vanished from the Earth in a puff of carbaryl-powder fumigation.

Its disappearance is an example of “coextinction,” or the extinction of one species because of the extinction or extreme rarity of a species on which it depends. Including the species at risk of coextinction would mean severe upward revisions to our estimates of endangered species. “They would absolutely skyrocket,” said Piotr Naskrecki, director of the Invertebrate Diversity Initiative at Conservation International. A 2004 study in Science estimated that 6,300 “affiliate” species—parasites, pollinators and mutualists—might be “coendangered” because their hosts are threatened. Rob Dunn, a zoologist at North Carolina State University and a coauthor of the study, said the figure is likely much higher. “It’s quite clear that we’re going to be losing species before they’re even described,” said Nigel Stork, an entomologist and CEO of the Rainforest Cooperative Research Center in northern Australia, who likely coined the term “coextinction” in a letter in Nature in 1993.

“Charismatic animals hog conservation dollars; the only ethic that makes the condor more important than its louse is its aesthetic value.”

It can be hard to see how the demise of a louse matters much. Though there is a general feeling that the extinction of anything—save a few lethal viruses, perhaps—is to be avoided, parasites are third-class citizens in the conservation world. Call it the “ick” factor. “It took long enough for people to care about wolves and things like that, so the idea that we would care about parasites is pretty far-fetched,” said Dunn. “On a daily basis we confront the issue that we can’t save everything,” said Oliver A. Ryder, a geneticist at Conservation and Research of Endangered Species at the Zoological Society of San Diego.

Nonetheless, there are many rationales for keeping a species from extinction. The most commonly cited are its intrinsic right to exist, its functional roles in ecosystems and the potential to provide some value to humans. By these criteria, the tiny, repulsive and multi-legged creatures are just as important as, if not more so than, tigers, condors or whales. But charismatic animals hog conservation dollars; the only ethic that makes the condor more important than its louse is its aesthetic value. “That’s a potentially justifiable reason to do conservation,” said Dunn, who belongs more to the intrinsic-value school, “but if that’s what we’re doing, we need to fess up to it.”

Noah Whiteman, a postdoc at the University of Missouri, St. Louis, has made the argument for parasite conservation based on their rich natural histories. In an article last year in the journal Animal Conservation, he wrote that if we don’t want to save parasites for their own sakes, we should save them for what they can teach us about their hosts.

To develop conservation plans and design reserves, wildlife managers consider how small populations of an endangered species interact or migrate. But genetic information can only go so far for a species with reduced genetic variability. In some cases, ectoparasites such as lice and ticks have greater variation, shorter generation times and higher rates of mutation than their hosts—meaning they evolve much faster, according to Whiteman. If researchers know enough about the parasites and how they move from host to host, the parasites’ genes can be used as proxies for the hosts’ or show interaction between populations that did not result in reproduction. “You can see the fingerprint much better of how these populations are related to one another in the lice than using the host data,” said Whiteman.

Such an approach has already been employed, although not as a conservation strategy. The bacteria that cause most peptic ulcers have been used to help trace human migrations, tiny crustaceans have been used to infer population dynamics of right whales, feline immunodeficiency virus revealed the demographics of cougars in the northern Rockies, and human head lice suggested that modern humans had contact with some unknown hominid lineage.

“You’re going to see more of these studies popping up,” said Whiteman, whose current research on the Galapagos hawk is the first use of the parasite-genes method on lice in a wild population, and the first to employ the method as a way to conserve some of nature’s ickiest creatures.

“Our thinking was that if conservation managers who just want to get rid of parasites would look at them in a different light, then maybe the host-specific louse of the California condor wouldn’t be extinct now,” he said. Because perhaps, in some sense, a California condor without its lice is not quite a California condor.

Originally published August 7, 2006


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