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

最近对独角鲸象牙的显微解剖发现（Nweeia et al., 2005）支持了一种新的功能假说。牙本质小管网络的发现表明，象牙可能具有感知外部环境变化的能力，该网络从牙髓内壁连续穿过牙本质层并延伸到牙骨质外表面。这种小管具有检测压力、温度、渗透或颗粒梯度变化的能力，也可能实现触觉感觉。在正常哺乳动物的牙齿中，除了在病理和创伤的情况下，没有观察到这些通向表面的开放小管的证据。在正常情况下，这种小管的存在是非同寻常的，特别是在潜水超过1500米时，暴露在冷水和压力的恶劣环境条件下。这项研究是一个独特的机会，可以检验一个重要的假设，即雄性独角鲸的象牙具有感觉功能，在雌性选择或雄性竞争繁殖方面发挥作用。具体的假设是，将象牙暴露在盐度变化很大的水中会导致脑电波模式的变化。水的盐度被选择为主要刺激，因为它相对容易控制，并且与一种可能的环境刺激有关，这种刺激可以用于文献报道的导航行为以及因纽特猎人和老年人。在不同盐度的条件下记录脑电图信号，同时记录独角鲸的录音。这两个系统都将被安置在便携式、自给自足的浮动实验室站中。将对这些数据进行分析，以确定脑电图信号或声学信号的可测量变化是否与引入象牙水套的水的盐度变化在时间上对应。如果独角鲸长牙具有感觉功能的假设被证明是正确的，它将对我们对一种独特动物的新感觉系统的理解产生广泛的影响，这项工作也应该对公众对科学的理解产生积极的影响。

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.