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的交界处，这是一种尚未被很好理解的流体环境。它不像滑雪船后面隆隆作响的尾流那样动荡。它不是可预测的层流，就像光滑的石头上的稳定流动一样。在这种过渡环境中，即使是水的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感受。极地水域的粘度是亚热带水域的两倍。除了粘度，还有对生理的热效应和生物体大小的差异。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。这项研究的目的是测量神经冲动传导速度、呼吸频率、游泳和逃逸速度以及肌肉质量，以确定是否正在发生代谢补偿，以及为了保持这种动态相似性，正在发生什么代谢补偿。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，使其能够跨STEM学科工作。从本科生到博士后水平的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，正在学习指导其他学生。外展的重点是将该项目的成果纳入佐治亚州亚特兰大设计博物馆的展品中，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，以改进解决问题的方式。在中等雷诺数下的流动状态表现为粘性区域和惯性区域之间的转变。浮游动物和桡足类动物一样，在这个界面内活动。这些小型生物通过感知周围液体的微小变化来发现猎物、捕食者和配偶。然而，流体粘度改变了有机体产生和感知的流体信号，这如何影响个体的桡足类动物的表现还知之甚少。该项目的目标是研究粘度作为一种进化力量所起的作用，从而导致身体尺寸、流场体积、传感器长度和神经功能、游泳速度和肌肉质量的适应。本研究的模式系统是真毛虫属的三个种。目标物种进化成生活在温度从0摄氏度到23摄氏度，粘度从1.84到1厘米斯托克的流体状态的梯度中。这种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毫米每秒。在一定粘度范围内对神经冲动传导速度、呼吸频率、游泳和逃逸速度以及肌肉质量进行了实验测量，以阐明维持从亚热带到极地的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种自然的实验，以检验生活在中等雷诺数的有机体中粘度的影响，在这种情况下，粘性力是重要的。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.