The Opposing Thumb

An opinionated digit leafs through the biological literature

Visitors: Fred Nijhout

Friday’s seminar kicked off with a Donnie Darko moment, as Duke University’s Fred Nijhout introduced his work with a photo (sadly not reproduced here) of himself struggling to hold on to a calf-sized, somewhat menacing rabbit. Nijhout’s work centers on one of those deceptively simple questions: how do you know when to stop growing? Freaky rabbit illustrated a key point: size determination is both highly plastic and very responsive to selection. So why don’t we run into giants & dwarves all over the place? Or, as he put it, “mice and elephants start out the same size, and they never make a mistake”.

Nijhout and his group have described a variety of control mechanisms in insects. The milkweed bug stops growing when it is literally too full, responding to signals from abdominal stretch receptors. The ever-popular dung beetle is limited by how much crap their parents accumulate- the amount of fecal matter rolled up into balls to feed the larvae determines how big they’ll be. The problem is more tractable in insects because their exoskeleton limits growth to discrete periods. It also means that developing insects must determine when they are ready for a new stage, in molting or at metamorphosis.

The diversity of experimental models and approaches at one point seemed to be heading out of this world, as Nijhout setup the hypothesis that gravity was a key factor in determining size. An informal poll of the audience clearly indicated that I was not alone in expecting bugs in space. Maybe the space shuttle science payload was overbooked. The solution? ” I built a centrifuge. At 4 Gs they (the larvae) were just plastered against the side of the cage.” The solution in this particular case seem to lay in the ability to deliver oxygen to the growing Manduca.

A great seminar complete with inspirational quote. Remember kids, you’re “better off being small animal than a dead animal”.

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