Dynamic Similarity or Size Proportionality? Adaptations of a Polar Copepod.

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This project explores the feasibility of applying fluid physical analyses to evaluate the importance of viscous forces over compensatory temperature adaptations in a polar copepod. The water of the Southern Ocean is 20 Celsius colder and nearly twice as viscous as subtropical seas, and the increased viscosity has significant implications for swimming zooplankton. In each of these warm and cold aquatic environments have evolved abundant carnivorous copepods in the family Euchaetidae. In this exploratory study, two species from the extremes of the natural temperature range (0 and 23C) will be compared to test two alternate hypotheses concerning how Antarctic plankton adapt to the low temperature-high viscosity realm of the Antarctic and to evaluate the importance of viscous forces in the evolution of plankton. How do stronger viscous forces and lower temperature affect the behavior of the Antarctic species? If the Antarctic congener is dynamically similar to its tropical relative, it will operate at the same Reynolds number (Re) as its tropical congener. Alternatively, if the adaptations of the Antarctic congener are proportional to size, they should occupy a higher Re regime, which suggests that the allometry of various processes is not constrained by having to occupy a transitional fluid regime. The experiments are designed with clearly defined outcomes regarding a number of copepod characteristics, such as swimming speed, propulsive force, and size of the sensory field. These characteristics determine not only how copepods relate to the physical world, but also structure their biological interactions. The results of this study will provide insights on major evolutionary forces affecting plankton and provide a means to evaluate the importance of the fluid physical conditions relative to compensatory measures for temperature. Fluid physical, biomechanical, and neurophysiological techniques have not been previously applied to these polar plankton. However, these approaches, if productive and feasible, will provide ways to explore the sensory ecology of polar plankton and the role of small-scale biological-physical-chemical interactions in a polar environment. Experimental evidence validating the importance of viscous effects will also justify further research using latitudinal comparisons of other congeners along a temperature gradient in the world ocean.