GOOD VIBRATIONS HELP A FROG LOCATE TASTY PREY

GOOD VIBRATIONS HELP A FROG LOCATE TASTY PREY.  Living in southern
Africa, the aquatic frog Xenopus catches insects by detecting
critters' vibrations on the water surface.  Not able to see well in
a liquid environment, the frog gets a wealth of information from the
water waves that insects produce as they slosh around.  The waves
tell Xenopus the direction in which the insect is located. They even
give the frog a general idea of the type of insect that is making
the waves.  To detect the water waves on its skin, the frog has
about 180 receptors known as "lateral-line" organs, which are found
on the skin along both sides of the body, around the eyes, and also
on the head and neck.  Now, researchers in Germany (Leo van Hemmen,
TU Munich, [EMAIL PROTECTED], +49-89-289.12362) have developed a simple
model that explains how the lateral-line organs enable Xenopus to
locate and classify its prey.  Strikingly, the model suggests that
the frog can reconstruct the shape of the water wave (its
"waveform") from limited information, namely the movement of water
recorded by the 180 simple sensory organs.  In the frog, water gets
deflected by 4-8 flag-like structures (called "cupulae") in the
lateral line organs. Each deflection stimulates nearby hair cells to
generate electrical spikes that are synchronized in time with the
deflection.  The timed electrical spikes from the 180 sensory
organs, the researchers show, contain enough information for the
frog to "estimate" the shape of the water wave pretty accurately.
This is true even if some of the lateral-line organs are not
functioning properly. Furthermore, they show how the frog can
localize and distinguish between two different water waves coming
simultaneously from two insects in different directions.  This model
may also be applicable to the mechano-sensory systems of other
animals, such as crocodiles (Soares, Nature, 16 May 2002), which
have similar receptor organs (Franosch et al., Physical Review
Letters, upcoming).