Collaborative Research: Dynamic similarity or size proportionality? Sensory ecological adaptations of Euchaeta to viscosity

像桡足类这样的小型浮游生物生活在层流和湍流状态的界面，这是一种流体环境，目前还没有得到很好的理解。它不像滑雪船后面隆隆的尾流那样动荡。它不是可预测的层流，就像平稳的水流从光滑的石头上缓缓流过。在这种过渡环境中，即使是水粘度的微小变化也会以意想不到的方式影响生物体的行为和感官知觉。极地水域的粘度是亚热带水域的两倍。除了粘度，还有热对生理的影响和生物大小的差异。然而，初步研究表明，极地物种在动态上与亚热带物种相似。这表明，从极地到亚热带，它们与周围环境的流体物体相互作用非常相似。本研究的目的是测量神经冲动传导速度、呼吸速率、游泳和逃逸速度以及肌肉质量，以确定是否以及发生了何种代谢补偿来维持这种动态相似性。更广泛的影响包括培训处于不同教育阶段的早期职业科学家跨STEM学科工作。从本科到博士后水平的8名学员正在流体动力学、海洋生物学和神经生理学领域工作，以解决围绕海洋中关键生物进化的问题。通过在实验室中创建一个教育阶梯，学生们在学习科学方法的同时学会指导其他学生。外展的重点是将这个项目的成果纳入佐治亚州亚特兰大设计博物馆的展览中，以分享浮游生物如何利用自然的解决方案成为创新设计的一部分，以改善解决问题的方式。在中间雷诺数的流动形式的特点是粘滞和惯性主导之间的过渡。桡足类等浮游动物就在这个界面内活动。这些小生物通过感知周围液体的微小变化来探测猎物、捕食者和配偶。然而，流体粘度改变了生物体产生和感知的流体信号，而这是如何影响个体桡足类动物的表现的，人们知之甚少。这个项目的目标是研究粘度作为一种进化力量在身体大小、流场体积、传感器长度和神经功能、游泳速度和肌肉质量方面的适应中所起的作用。本研究的模型系统是真毛藻属的一个由三个物种组成的群。目标物种已经进化到可以生活在温度从0到23摄氏度，粘度从1.84到1摄氏度的梯度流体状态中。该物种的长度相差三倍，游泳速度从每秒不到1毫米到超过103毫米不等。神经冲动传导速度、呼吸速率、游泳和逃逸速度以及肌肉质量正在实验中测量，以阐明从亚热带到极地维持动态相似性所涉及的代谢补偿的潜在机制。对同系物的关注提供了一个自然的实验来检验粘度对生活在中间雷诺数的生物体的影响，其中粘性力是重要的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Small planktonic organisms like copepods live at the interface of laminar and turbulent regimes, which is a fluid environment that is not well understood. It is not turbulent, like the rumbly wake behind a ski boat. It is not predictable laminar flow, like the steady flow creeping by a smooth stone. In this transitional environment, even small changes in the viscosity of the water can impact an organism’s behavior and sensory perception in unexpected ways. Waters in the polar regions have twice the viscosity as that in the subtropics. In addition to viscosity there are thermal effects on physiology and differences in organism size. Nevertheless, pilot studies indicate that polar species are dynamically similar to the subtropical ones. This suggests their fluid-object interactions with their surrounding environment is very similar from the poles to the subtropics. The goal of this study is to measure nerve impulse conduction velocities, respiration rates, swimming and escape speeds, and muscle mass to determine whether and what metabolic compensation is occurring to maintain this dynamic similarity. The broader impacts include training early career scientists at different stages of their education to work across STEM disciplines. Eight trainees ranging from undergraduate to post-doctoral levels are working within the fields of fluid dynamics, marine biology and neurophysiology to address questions surrounding the evolution of key organisms in the ocean. By creating an educational ladder in the lab, students are learning to mentor other students as they learn the scientific method. Outreach is focused on incorporating results from this project into exhibits at the Museum of Design Atlanta, Georgia to share how planktonic organisms can become part of innovative design using solutions from nature to improve the way problems are solved. Flow regimes at intermediate Reynolds number are characterized by the transition between viscous and inertia-dominated realms. Zooplankton like copepods operate within this interface. These small organisms detect prey, predators and mates by sensing small changes in the fluid that surrounds them. However, fluid viscosity alters the fluid signals that are created and perceived by the organisms and how this affects the performance of individual copepods is poorly understood. The goal of this project is to investigate the role viscosity plays as an evolutionary force leading to adaptations in body size, volume of flow field, sensor length and neural function, swimming speeds and muscle mass. The model system for this study is a group of three species in the genus Euchaeta. The target species have evolved to live in a gradient of fluid regimes spanning temperatures from 0 to 23ºC and viscosities from 1.84 to 1 Centistokes. The species vary in length by three-fold and swim at speeds from less than 1 to over 103 millimeters per second. Nerve impulse conduction velocities, respiration rates, swimming and escape speeds, and muscle mass are being measured experimentally under a range of viscosities to elucidate underlying mechanisms of metabolic compensation involved in the maintenance of dynamic similarity from the subtropics to the poles. The focus on the congeners offers a natural experiment to examine the effects of viscosity in an organism that lives at intermediate Reynolds number where viscous forces are important.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.