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No left turn
Natural History, June, 2007 by Stephen Reebs
With their slender, drab-colored bodies, snakes of the genus Pareas seem quite ordinary--until you look them in the mouth. When they open wide, many Pareas species display a remarkable asymmetry: in P. iwasakii, for example, about twenty-five teeth line the right side of the jaw, whereas only about seventeen line the left. The asymmetry was recently discovered by Masaki Hoso; his graduate advisor, Michio Hori, an ecologist at Kyoto University in Japan; and a colleague.
The investigators suggested that the reason for the snakes' "right-mouthedness" might be traceable to their diet of snails. The snakes pull snails from their shells by alternately retracting the left and right sides of their jaws. Snail shells usually coil to the right, or dextrally, so having more teeth on the right side could be helpful for the snakes.
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To test that idea, the investigators obtained snails whose shells coiled to the left, or sinistrally, then measured the predation success of four P. iwasakii snakes on sinistral and dextral snails. The snakes took about twice as long to handle the sinistral snails, retracted their jaws about one-third more frequently, and still succeeded a quarter less often, compared with their attacks on dextral prey.
Sinistral snails tend to be scarce worldwide, but in Southeast Asia and Japan--where the right-mouthed snakes live--they're present in more species. Having evolved a particular jaw dentition to handle the more abundant dextral shells, the snakes may now be exerting selective pressure on snails for more sinistral shells. (Biology Letters)
COPYRIGHT 2007 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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