Pennywise, the dancing clown
The newest addition to our mantis shrimp family is a gorgeous green-black Gonodactylus smithii named Pennywise. The Gonodactylus genus has been my fourteen-year-old brother’s favorite genus ever since I told him that it essentially means scrotum fingers, as the two raptorial appendages held at the ready take on a somewhat humorous shape. For a review of mantis shrimp anatomy, see my last post here. The species name, smithii, is related to the word smithy, or blacksmith, presumably because blacksmiths and this mantis shrimp like to hammer things. Unlike the relatively tame Odontodactylus scyllarus (peacock) mantis, this species has significantly bigger hammers, and as such packs a bigger punch. I made the mistake of proffering my nail only once. When particularly aggravated, he will detach his dactyls from his propus and extend it toward me, revealing a cruel hook at the end that’s usually hidden, as though he’s flipping me the bird. A little high pitched voice in my head dubs him screaming “curse youuuu!!!” whenever he does this.
In my last post, I made up a thought experiment that would be useful once I started gathering data: What does it mean to the mantis shrimp that I put my finger near his burrow and then pull it back when he strikes every minute or so for a period of time?
You might predict that after a few intervals of striking, the mantis shrimp would no longer strike as readily. Perhaps it would strike every other time, and after a few more intervals, every five times, and then not at all. This kind of learning is called habituation, and can be a big confound in experiments involving behavior, and occurs because the mantis slowly realizes that I am not a real threat (after all, I’m not punching back and I retract my finger after one punch). But, the mantis shrimp does not have a perfect memory, so it there might be a longer interval than one minute where the rate of habituation would be so slow as to not happen at all. In other words, if I waited long enough between events of sticking my finger in the water, the mantis shrimp may not remember as clearly that I presented no real threat, and would probably punch with punctual predictably.
Houston, we have more than one.
I’ve been mulling over this thought experiment a lot because this past Friday, I got my first round of data! Pennywise was kind enough to lend his EMGs for several rounds of Q-tip-coated-in-shrimp-paste bashing. As soon as I put the Q-tip in front of him, he hit it with a vengeance. As with the second time; however, the third time, I had to prod him a little. The fourth time, he seemed disinterested. Evidently, Pennywise habituates very fast. I left him alone for a bit, hoping the habituation would wear off, and returned a few minutes later. After a mere 20 minutes or so, he was done for the day. Next time, I’ll try to space out my Q-tip presentations a bit more, otherwise Pennywise might become totally habituated to my stimuli.
I placed the probes in Pennywise’s extensor, the muscle that is responsible for building up the strike power, and here’s what we got! On the top in red is the audio trace. I’ve highlighted the sound of the pop from Pennywise striking a Q-tip. I don’t know if there would be observable cavitation here since the Q-tip is soft and held lightly, so this pop is probably just the sound of the dactyl heel hitting the target. The small green jagged spikes are the extensor’s activity, representing muscles twitches that are adding energy to the “spring”, or saddle. As I noted in my first post, this activity should represents the coactivation phase, where the flexor and the extensor both tense to build up energy in the saddle. Let’s compare the original paper with these data.
Obviously, my spikes aren’t as large as the ones in the journal article, but you can kind of tell that my trace is probably in the coactivation phase. I’m looking forward to collecting more data and starting to find patterns. Also, there’s another member of our mantis shrimp family coming in the next few days! Keep an eye out for my next and final post where I talk about results and the surprising namesake of the Squilla empusa, currently travelling in luxury by way of the US Postal Service.