SGER: Testing Opportunity of the Sensory Hypothesis in the Narwhal Tusk

Harvard University, Cambridge MA

Investigators

Abstract

Recent findings of microanatomy in the narwhal tusk (Nweeia et al., 2005) support a new hypothesis for function. Discovery of a dentinal tubule network that runs continuously from the inner pulpal wall through the dentin layer and extending to the outer cementum surface indicate that the tusk may have the ability to sense variables in its external environment. Such tubules have the capability to enable the detection of changes in pressure, temperature, osmotic or particle gradients and may also possibly enable tactile sensation as well. Evidence of these open tubules to the surface has not been observed in normal mammalian teeth, except in conditions of pathology and trauma. The existence of such tubules as a normal condition is extraordinary, especially given the exposure to harsh environmental conditions of cold water and pressure during dives of over 1500 meters. The study is a unique opportunity to test the overlying hypothesis that the tusk of the male narwhal is capable of sensory function, playing a role in female choice or male competition for reproduction in the species. The specific hypothesis is that exposing the tusk to water with widely varying salinity will result in changes in brain wave patterns. Water salinity has been chosen as the primary stimulus as it is relatively easy to control, and relates to one possible environmental stimulus that could be used in the navigation behaviors reported in the literature and by Inuit hunters and elders.. EEG signals will be recorded under conditions in which the water salinity is varied, and sound recordings from the narwhals will be simultaneously recorded.. Both systems are to be housed in portable, self sustaining, floating laboratory stations. The data will be analyzed to determine if measurable changes in EEG signals or acoustic signals correspond temporally with changes in the salinity of water introduced to the tusk water jacket. Should the hypothesis that the narwwhal tusk have a sensory function prove to be correct, it will have a broad impact on our understanding of a new sensory system in a unique animal, and the work also should have a positive impact on the public understanding of science.