The Velige People

One of the great pleasures of working with really talented undergraduates is that they know stuff I don't and make me learn stuff I would never otherwise have gotten to learn. Take NN. I met NN when I went to the Invertebrate Zoology class she was taking to ask if any of the students wanted to help me with my rotifer experiments. A couple of days later I got a resume from NN, and quickly realized that in addition to being a great assistant, she knows enormously more about aquatic invertebrates, and a bunch of other biological topics, than I do. A good start.

One of the topics she knows and I don't is biomechanics. She quickly developed an interest in rotifer fluid mechanics. So yesterday afternoon NN and I went up to the lab of Dr. Mimi Koehl, aquatic invertebrate biomechanician extraordinar and talked to her grad-student and my friend, Lindsay.

It turned out Lindsay and NN have a lot in common. They both are fascinated by aquatic invertebrates, biomechanics, fluids, and the interactions of these concepts. And they both know what a veliger is. In fact, they had quite a long discussion about veligers of different types, and how many of them have a range of similarities to rotifers. I, throughout this entire conversation, played the game of trying to take part in the discussion while also attempting to deduce what a veliger was.

I figured out this much: veligers are a subset of the larvae of aquatic invertebrates. They are motile plankton whose motive force and/or feeding is supplied by rings of compoud cilia, the same as one would find in a rotifer. They often grow up into forms that are not moved by cilia, like muscles and snails. When said quickly, veligers sounds a lot like villagers, which renders funny any conversation about what sorts of creatures eat veligers.

Today I looked up what a veliger actually is. I wasn't too far off the mark. A veliger is a young mollusk in a developmental stage provided with a velum, a membrane edged with clilia used for locomotion and feeding. Cilia are only a reasonable way to get around if one is small (a couple of millimeters at most) so once a veliger grows that big it generally moves on to other means of locomotion, losing its velum and thereby its veliger status. Veligers are found in the bivalves (clams, muscles etc) and the marine gastropods (snails and sea-slugs).

Lindsay says that several people have wanted to study how veligers use their cilia to feed and move, but that little progress has been made because of the difficulty of finding and keeping them. They die, they grow up, they don't reproduce quickly. So since I know how to provide a large number of the animals that most closely resemble veligers in their use of cilia, rotifers, and Nicole and Lindsay know about biomechanics and veligers and all that, it seems we have a good collaboration.

P.S. Here is a photo of a Fusitriton veliger that Lindsay sent me. I Photoshopped it to increase the contrast, to make the cilia more visible.

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.