Biomechanics and biophysics of anti-predator defence in hagfishes

盲鳗是一种古老的类似鳗鱼的底栖海洋动物，据信出现在5亿多年前。盲鳗进化的持久力的一个可能的解释是，它们有能力通过在几分之一秒内分泌大量纤维粘液来保护自己免受捕食者的攻击。在我最近两次获得探索项目资助的过程中，我的实验室已经阐明了黏液功能背后的几种机制。我们已经证明，除了海水，黏液由两种主要成分组成，黏液和丝状物，它们的浓度非常低。我们还表明，粘液腺的渗出物的部署包括卷曲的粘液线的解开，粘液囊的肿胀，以及这两种成分之间复杂的相互作用。我们已经证明，黏液纤维成分的展开涉及到海水溶解胶的溶解和储存在盘绕螺纹中的应变能的释放。我们最近阐明了产生它们的特殊细胞内粘液线的三维结构，这启发了我们研究这些细胞内粘液线产生的生物物理机制。我们发现黏液囊主要有两种，它们对钙离子破裂的要求不同。我们还表明，囊泡膜上的水通道蛋白在海水中加速了它们的膨胀。这里提出的研究将试图回答以下问题，关于盲鳗黏液是如何发挥作用的，以及它是如何在黏液腺中产生的：腺线细胞如何在细胞质中产生一种精巧的盘绕和非常强的黏液线，这种黏液线的长度是其宽度的15万倍？是什么促使海水中的粘液囊膨胀，又是什么使它们在粘液腺内凝结？我们已经证明盲鳗黏液非常善于堵塞捕食者的鳃，直到最近，我们还认为这种黏液能有效地防止捕食者的攻击。然而，最近公布的盲鳗深海视频显示，只有在被捕食者咬伤后，粘液才会释放出来。这一观察结果引出了一个有趣的问题：盲鳗是如何在最初的咬伤中幸存下来的，尤其是当它被鲨鱼这样可怕的捕食者咬伤时。为了回答这个问题，我们将测试关于盲鳗如何避免这些最初咬伤的生物力学假设。总的来说，本文提出的研究将阐明盲鳗保护自己免受捕食者攻击的机制，并可能导致在抗穿刺和高性能材料制造领域的新型仿生技术。它也可以帮助我们了解这些独特的动物是如何在这个星球上存活这么久的。

Hagfishes are an ancient group of eel-like, benthic, marine animals that are believed to have appeared over half a billion years ago. One possible explanation for the evolutionary staying power of hagfishes has to do with their ability to defend themselves from predators by secreting large volumes of fibrous slime in a fraction of a second. Over the course of my last two Discovery grants, my lab has elucidated several mechanisms underlying the function of the slime. We have shown that, in addition to seawater, the slime consists of two main components, mucus and threads, which are present in very low concentrations. We have also shown that the deployment of exudate from the slime glands involves the unraveling of coiled slime threads, the swelling of mucus vesicles, and a complex interplay among these two components. We have shown that the deployment of the fibrous component of the slime involves the dissolution of a seawater soluble glue and the release of strain energy stored in the coiled thread. We recently elucidated the three dimensional structure of slime threads within the specialized cells that produce them, which has inspired us to investigate the biophysical mechanisms by which the thread is produced within these cells. We have found that there are two main kinds of mucous vesicles, and they differ in their requirement for calcium ions to rupture. We have also shown that aquaporins in the vesicle membrane accelerate their swelling in seawater. The research proposed here will attempt to answer the following questions about how hagfish slime functions and how it is produced in the slime glands: How do gland thread cells produce an exquisitely coiled and remarkably strong slime thread in their cytoplasm that is 150,000 times longer than it is wide? What drives the swelling of the mucus vesicles in seawater and what keeps them condensed within the slime gland? We have shown that hagfish slime is remarkably good at clogging the gills of fish predators, and until recently, we assumed that the slime was effective at preventing attacks from predators. However, recently published deep-sea videos of hagfishes show that the slime is released only after it is bitten by a predator. This observation leads to the intriguing question of how a hagfish survives the initial bite, especially when that bite comes from a formidable predator like a shark. To answer this question, we will test biomechanical hypotheses about how hagfishes avoid injury from these initial bites. Overall, the research proposed here will illuminate the mechanisms by which hagfishes defend themselves from predators, and may lead to novel biomimetic technologies in the areas of puncture resistance and the manufacture of high performance materials. It may also help us understand how these unique animals have survived on this planet for so long.