Letters: Narwhal questions
May 05, 2014
I read with great interest about Dr. Martin Nweeia's discoveries surrounding the mysteries of the narwhal's unicorn tooth (April 7 ADA News). He has made truly marvelous discoveries that may explain behaviors in this curious species that has not been studied very much.
The most interesting discovery by far is that of an ability of the tusk to detect very small changes in sea water salinity by virtue of changes across a cellular gradient and communication to the brain via afferent nerve signals.
I had remembered that narwhals were the deep divers of the Arctic seas, routinely spending several hours of their day at 1,000 feet below the surface, where very little light is available. In addition to the crushing pressures, the salinity of the waters at depth is also much greater than at the surface. This makes the salinity gradient theory much more interesting, which may then link some kind of role in guiding the narwhal to the dark depths or across distances as salinity varies through the waters.
In terms of evolutionary development, acquiring a depth finder also makes sense if it led a hungry species to depths where it was easier to find food, such as squid. But it remains quite interesting how dental structures may have played into these changes. The narwhal is essentially edentulous, and except for its tusk-tooth, only retains remnant tooth buds or a few bits of dental tissues in early life. It is interesting to imagine how some particular behavior or anatomical parlay drove the shift of dental tissues to become purely sensory for some survival strategy.
Well, my congratulations to Dr. Nweeia for his discoveries that will certainly lead to a better understanding of the lives of these animals. The "tooth" does seem to matter.
Todd Morgan, D.M.D.