Conch-L,
Today's New York Times has a short article which I will copy the best parts of. It may be availavble online.
Masaki Hoso of Kyoto University [et al] report that this directionality [in snails] has had an effect on snail eating snakes of the subfamily Pareatinae. In a paper in Biology Letters the researchers describe how the jaws of these snakes have evolved so the right mandible has more teeth than the left, and how the snakes have a much easier time eating a dextral snail than a sinistral one.
The researchers studied the feeding behavior of Isawaki's snail eating snake. It clamps onto the outside of the shell with its upper jaw, reaches in with its bottom jaw and alternately retracts the left and right mandibles to work the snail out.
With a dextral snail this all happens fairly easily. The snake approaches the snail from behind, turns its head so that the upper jaw clamps on the inner [??] side of the shell, reaches in with its bottom jaw and alternately retracts its mandibles for a couple of minutes, succesfully extracts the snail and swallows it.
But with a sinistral snail, the upper jaw tries to clamp down on the outer, spire side of the the shell [??] (which flares outward) and has a much more difficult time. The snake takes far longer to handle a sinistral snail, requiring more mandible retractions. And they often make a total hash of it, dropping the snail or otherwise failing to eat it.
The researchers suggest that evolutionary adaptationhas enabled the snake to find an ecological niche, consuming the snails that are more common. On the other hand the sinistral snails may take advantage as well: The rersearchers note that there is a remarkable diversity in sinistral snails in Southeast Asia and predation in snakes that favor the dextral variety may be a reason.
[I know at least a few birds eat snails (eg kite in Florida). And some birds that eat pine cones have assymetrical beaks to open the spiral sead covers of pine cones. Anyone know of any birds which have a similarly assymetric jaw for winkling out snails??]
Allen Aigen
Allen Aigen
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