Cannibalism just isn’t all it’s cracked up to be. Previously, scientists theorized that cannibalism is the most direct way for animals to get nutrients for growth and body maintenance. It also cuts down on competition for food and mates among members of the same species. But there are drawbacks to dining to close to home. For instance, cannibals put themselves at greater risk than other carnivores, because their prey is often equal in size and strength. Furthermore, cannibalism is counterproductive in evolutionary terms, says David Pfennig, assistant professor of biology at the University of North Carolina in Chapel Hill. If you’re trying to keep your traits alive in the gene pool, you should help your closest relatives instead of gobbling them down. Now Pfennig has uncovered a third reason to avoid cannibalism. In a recent paper in the journal Animal Behavior, he proposes that consuming your kin can actually make you sick. To prove this odd point, Pfennig and his associates collected the larvae of two closely related amphibians—the tiger salamander (Ambystoma tigrinum) and the small-mouthed salamander (A. texanum).
They exposed half the larvae to an infectious bacterial disease. Then they fed the whole lot to four groups of cannibalistic tiger salamanders, also in the larval stages.
One group of the cold-blooded cannibals was given healthy tiger salamander larvae, while a second group received diseased ones. The third group dined exclusively on healthy small-mouthed salamander larvae, and the remainder got—you guessed it—only diseased ones. The results? The larval salamanders that ate the diseased members of their own species fared poorly. Five of the 12 cannibals in this group died before reaching adulthood, and the ones that survived were permanently stunted—on average, about 10 percent smaller than the others. In a related experiment, Pfennig proved that tiger salamander larvae are much more likely to snack on the larvae of another species than on their own kind. The two experiments reinforce the notion that by shunning cannibalism, animals directly avoid certain diseases. “A potentially important cost of cannibalism is that this behavior may heighten the probability of acquiring deleterious parasites or pathogens above that experienced by non-cannibalistic predators,” concludes the article by Pfennig, S.G. Ho and E.A. Hoffman. “It’s an enigmatic behavior,” says Pfennig, who confesses to being fixated on cannibalism for much of his adult life. “Cannibalism may seem like a good way to make a living,” he says. “And yet it’s a behavior that in the animal kingdom is really rather rare.” David George Gordon’s latest book, The Eat-A-Bug Cookbook, is published by Ten Speed Press. |
