Monday, June 09, 2008

Rotifer fluid mechanics

One of my best students, NN, has become fascinated with the ways in which rotifers use their cilia, and wants to do a senior honors thesis on the fluid mechanics of rotifer cilia. She is interested in issues of scaling, how they use their cilia in feeding and locomotion, and the differences in the cilia between males and females. Males use their cilia only for locomotion, while females use them for both locomotion and feeding, leading to some fascinating questions about the trade-offs females make to have their cilia serve these two very different, and very important roles.

I very much want to encourage her in this, but started by explaining to her that as an evolutionary demographer, I know squat, make that squat/2 about biomechanics. And of all the parts of biomechanics I don't understand, Low Reynolds Number Fluid Mechanics may just be the part I understand least. I understand it so little I don't even know what it means. The Reynolds number has something to do with the ratio of the size of the object to the viscosity of the fluid, or something like that. This helpful Wikipedia article describes it in terms I only vaguely understand. What I understand it to mean is that the smaller an organism or piece of an organisms is, the more viscous the fluid effectively is. A whale moving through water experiences an environment in which viscosity is much less important than a rotifer moving through the same, equally viscous water. The rotifer has a very low Reynolds number, and its cilia have even lower Reynolds numbers. The viscosity of the water they move is so high, it is like a human arm through tar. Or something like that.
But don't quote me on any of that because it is probably wrong.

So I told NN that I was glad to work with her on that, but she would need an adviser from a biomechanics lab, like that of Mimi Koehl. Luckily, one of my best friends in my department is one of Mimi's students, and is interested in ciliary feeding. And this morning we went to the grocery store together, and by the time the groceries were in the fridge, my friend had agreed to meet with my student and help her figure out how to frame and answer her question. My only claims on the project will be that I helped generate the questions, am brining the collaboration together, and am providing the study organisms. In other words, I may end up co-advising a senior thesis on a topic I know nothing about. Hopefully by the end I will at least know what a Reynold's number is.

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