strange behaviors

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  • Richard Conniff writes about behavior, in humans and other animals, on two, four, six, and eight legs, plus the occasional slither.

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Mommy, Who’s for Dinner Tonight?

Posted by Richard Conniff on November 1, 2011

Natalie Angier writes today about animal cannibalism, starting with research  by Richard Shine at the University of Sydney in Australia  about cane toad tadpoles gobbling up cane toad eggs:

Significantly, the tadpoles weren’t simply hungry for a generic omelette. Reporting in the journal Animal Behaviour, Dr. Shine and his co-workers showed that when given a choice between cane toad eggs and the similar-looking egg masses of other frog species, Rhinella tadpoles overwhelmingly picked the cannibal option. Oh, little cane toads lacking legs, how greedily you snack on pre-toads packed in eggs!

Life after metamorphosis brought scant relief from fraternal threats. The scientists also demonstrated that midsize cane toads wriggle digits on their hind feet to lure younger cane toads, which the bigger toads then swallow whole. “A cane toad’s biggest enemy is another cane toad,” Dr. Shine said. “It’s a toad-eat-toad world out there.”

Rhinella’s brutal appetite is among a string of recent revelations of what might be called extreme or uncanny cannibalism, when one animal’s determination to feed on its fellows takes such a florid or subversive turn that scientists are left, as Mark Wilkinson of the Natural History Museum in London put it, “gobsmacked” by the sight.

There are males that demand to be cannibalized by their lovers and males that seek to avoid that fate by stopping midcourtship and hammily feigning rigor mortis. There are mother monkeys that act like hipster zombies, greeting unwanted offspring with a ghoulish demand for brains; and there are infant caecilians — limbless, soil-dwelling amphibians — that grow fat by repeatedly skinning their mother alive.

In the past, animal cannibalism was considered accidental or pathological: Walk in on a mother rabbit giving birth, and the shock will prod her to eat her bunnies. Now scientists realize that cannibalism can sometimes make good evolutionary sense, and for each new example they seek to trace the selective forces behind it.

Why do cane toad tadpoles cannibalize eggs? Researchers propose three motives. The practice speeds up maturation; it eliminates future rivals who, given a mother toad’s reproductive cycle, are almost certainly unrelated to you; and it means exploiting an abundant resource that others find toxic but to which you are immune.

“We’re talking about a tropical animal that was relocated to one of the driest places on earth,” Dr. Shine said. “Cannibalism is one of those clever tricks that makes it such a superb colonizer and a survival machine.”

You can read the full article, in which she describes male black widow spiders being eaten by the females after sex as “arachinirvana”  here.  I think it would be nerve-wracky-nirvana, no?

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