08 January 2013

SICB 2013, day 4

On Sunday, I saw biologists making do with lab tape, sunscreen, and “Wet and wild black matte fingernail polish.” There is still a lot of room for McGyver-style low tech equipment in biology.

I spent a good chunk of Sunday morning at SICB in a session on digging and burrowing. This is a subject near and dear to my heart, as it’s been one of the topics I've published on most consistently during my career.

Sarah Sharpe had a fun talk on how sandfish lizards bury themselves. Their lab had built a robot that could successfully mimic the lizard’s ability to travel through sand, but failed miserably at getting into sand in the first place. Through a series of simple experiments, Sarah showed that the sandfish lizards are hopeless if they cannot use their limbs. She showed a video of a lizard trying to submerge into sand with its limbs restrained, and it was just sad.

If they have just one pair available, the lizards can get into the sand, but they are very bad at it, particularly if they have only their back legs to work with.

Dwight Springthorpe did work that was probably closest to the stuff I had done in the past, looking at ghost crab burrow construction. He showed some very cool x-ray videos of crabs with tiny little lead strips glued to them so they would be visible in the x-rays. Ghost crabs definitely have a preferred side that they dig with, using their walking legs to hook and pull sand towards them. He also showed that crabs are much faster to burrow when they are burrowing horizontally rather than vertically.

Kelly Dorgan had my favourite quote of the day, during her talk on digging by polychete worms: “I did what I often do when worms don’t cooperate, which is turn to theory.” Haven’t we all thought that at one time or another? She had a rich talk that tied how worms dig to the path of meandering rivers, among other things.

Kelly Mead Vetter did some fairly qualitative descriptions of mantis shrimp burrowing, Her work was more interesting because much of the ecological and behavioural work on stomatopods suggested the their burrows were hard to build, but she showed they were much more dynamic and changing over time.

At the end of the digging session, I was completely jealous of all the work that is being done in this field. It would be nice to get back to it, but other people are much better equipped to do much of it than I am.

After the digging was done, I focused mainly on sensory biology in the afternoon.

Trevor Rivers showed that sea creatures that fluoresce when attacked benefit from glowing. Worms that are able to glow when predators attack have about a 40% survival rate. This may sound like a losing strategy, except that if you consider that their survival drops to almost nothing when their predators can’t see them.

Nicolas Lessios, a former conference roommate, showed that Triops, sometimes marketed as a "prehistoric" crustacean, use their vision to maintain the position in the very bottom on the shallow, short-lived pools they often live in.

Michael Bok, author of the Arthropoda blog, demonstrated a neat partly trick of stomatopod crustacean eyes. Along a central band of their eyes, mantis shrimp have two visual pigments that absorb ultraviolet light. But using filters in the lenses of the eyes, the animals are able to differentiate the ultraviolet spectrum with much more precision. The only problem now is that it is not at all clear why stomatopods have these highly specialized eyes. Why do they care about ultraviolet light so much? Still unknown.

Ashlee Rowe, one of my partners-in-crime on a nociception symposium last year for Neuroethology, ended off the day, not with a bang, but with a sting.

She has been studying the relationship between grasshopper mice and their scorpion prey. The sting of the Arizona bark scorpion is nasty: strong enough to kill a human. It’s also incredibly painful, Ashlee related one description from a sting victim, who said it was like “being burned with a cigarette, then having a nail driven through it.”

The scorpion toxin is painful because it causes a sodium channel in neurons to become more likely to open, and stay open. The practical upshot is that neurons start firing action potentials, wildly out of control.

The grasshopper mice feel the pain. Young mice in particular will drop a scorpion they’re attacking if they are stung, but they never learn to stop attacking the scorpion. This suggests that the stings aren’t particularly painful or aversive. (At this point, Ashlee showed a video of a young, cute mouse getting nailed in the face repeatedly by a scorpion, prompting an audible reaction from the audience in sympathy with the mouse.)

Surprisingly, the scorpion venom works on the sodium channels of the grasshopper mice exactly the same way as it does on regular mice (which are not resistant). The grasshopper mice have evolved changes in a second, separate sodium channel that works a little differently. The scorpion venom binds to a channel that sets the threshold for a neuron, but those channels cannot start action potentials. A second sodium channel does that. And that’s the one that is mutated in grasshopper mice. As a result, the grasshopper mouse neurons don’t start the crazy, out of control spiking that the scorpion causes in other mammals.

Scorpion thrusts. Grasshopper mouse parries. A beautiful story in evolution and neuroethology.

(Oh, those items I mentioned at the start of the article? The tape was used to restrain sandfish lizard legs; the sunscreen was used to stop the eggs of brownheaded cowbirds reflecting ultraviolet light; and the nail polish was used to blindfold lobsters attacking fluorescing prey.)

Grasshopper mouse and scorpion picture from here.


Bora Zivkovic said...

Ha! Ashlee Rowe and I were in grad school together!

Kyle said...

I missed that grasshopper mouse talk, but it sounds fun!