School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia.
Anat Rec (Hoboken). 2011 Mar;294(3):373-8. doi: 10.1002/ar.21338. Epub 2011 Jan 31.
Previous studies have suggested that the inner ear of some benthic species of elasmobranchs contain only exogenous material within their otoconial organs, a unique feature within vertebrates. However, these examinations have not accounted for the possibility of otoconial degeneration or used modern experimental methods to identify the materials present. Both of these issues are addressed in this study using inner ear samples from the adult Port Jackson shark, Heterodontus portusjacksoni. A comparison of the otoconial mass in fixed specimens over short and medium time scales reveals that over those timescales the degeneration of calcium carbonate-based otoconia does not occur and confirms that calcium carbonate-based otoconia are not found within the otoconial organs of H. portusjacksoni. Additionally, microanalysis of the chemical composition and ultrastructure of the otoconial mass using energy dispersive X-ray microanalysis and scanning electron microscopy confirms that the entire otoconial mass is comprised of exogenous silicon dioxide particles, bound within a carbon matrix. This exogenous material is suggested to play an equivalent role to the otoconia found in other species of elasmobranchs, and allows both hearing and vestibular control to occur in benthic sharks that spend their lives foraging within a sandy substrate.
先前的研究表明，一些底栖鲨鱼物种的内耳中耳石器官内仅含有外源性物质，这是脊椎动物中的一个独特特征。然而，这些检查并未考虑到耳石退化的可能性，也没有使用现代实验方法来确定存在的物质。本研究使用成年杰克逊港鲨鱼（Heterodontus portusjacksoni）的内耳样本解决了这两个问题。在短时间和长时间尺度上比较固定标本中的耳石质量表明，在这些时间尺度上，碳酸钙基耳石不会退化，并证实杰克逊港鲨鱼的耳石器官中不存在碳酸钙基耳石。此外，使用能量色散 X 射线微分析和扫描电子显微镜对耳石质量的化学成分和超微结构进行的微观分析证实，整个耳石质量由外源性二氧化硅颗粒组成，这些颗粒被束缚在碳基质内。这种外源性物质被认为在其他鲨鱼物种的耳石中发挥等效作用，并允许在一生都在沙质基质中觅食的底栖鲨鱼中发生听觉和前庭控制。
