Sunday, August 15, 2010

YPM ICH 8403: Electric elephantfish with big brains

So apparently when you've got a long schnoz, intelligence is something that comes along with the territory. Or so it would seem if elephants and elephantfishes were your only two data points. Elephantfishes comprise the family Mormyridae, and they parallel elephants not only in nasal appearance, but in high intelligence as well, with a brain size to body mass ratio equaled only by our own!

Here are two Mormyrids, species Gnathonemus longibarbis, from YPM ICH 8403, collected in 1956 in Uganda's Lake Kyoga:


Why the long proboscis? Mormyrids live in Africa and tend to inhabit murky lakes and swamps; the proboscis is thought to be a touch organ that helps them locate the mud-dwelling invertebrates that they like to feed on. As far as I can tell though, it's not like an elephant's trunk-- elephantfishes can't suck anything into their proboscis since, as I found on our specimens, as there are no openings at the end. All it does is help find food. In fact, the mouth is actually above the proboscis, not below it! Here is a shot where you can see this:


Why such a big brain? To meet the demands of being electric. That's right, they are electric, and their cerebellum is so specialized and large that it even has its own special name, the "mormyrocerebellum". This mormyrocerebellum is the neural center for coordinating their electricity.

You might be thinking about electric eels right now, which use their electricity to stun prey, but Mormyrids actually use their electricity quite differently, in a dizzying number of ways! Because they live in murky lakes and have poor eyesight, they use it for orientation and navigation. The electric field is continuous and envelops them, so when they swim near an object, the field is interrupted and they are alerted to the object's proximity. They also use their electricity for various means of communication, including territorial interactions, species recognition, individual recognition, courtship, and communicating social status. This is possible because the elephantfish can both output and receive very specific electrical signals--signals that vary by only fractions of a millisecond. Most fish rely on visual and other types of signals for communication, but given their turbid habitat, the Mormyrids' unique electrical system works better for them.


Sources:

Helfman, Gene S., B.B. Collette, D.E. Facey, and B.W. Bowen. 2009. The Diversity of Fishes, 2nd ed. Wiley-Blackwell, Hoboken.

Paxton, John R., and W.N. Eschmeyer. 1994. Encyclopedia of Fishes. Academic Press, San Diego.

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