As I was doing this project, the specter waiting for me as we started wrapping up our projects was the prospect of having to answer the question, “So what?” What is the point of this research? I spent most of my time working on the “methods,” the techniques (surgeries, soldering, coding) that became the experimental setup.
Everyone knows that you can’t do good science without a solid experimental setup, but before you design your experiment, you need a question to answer, a hypothesis. This imperative is known as hypothesis-driven research, and it’s the gold standard for doing science because it forces you to do novel work that will benefit the world. Sure, penicillin was discovered by accident, i.e., without being driven by a hypothesis, and a lot of good science is done by pursuing curiosity, but scientists usually strive for the traditional hypothesis-driven approach.
Well, for this ten-week program, you can’t do hypothesis-driven research; instead I had to formulate a valuable question while running experiments. These experiments, which I was designing on the fly, would in turn limit the kind of questions I could ask! For example, since I was making an EMG probe, I had to formulate a hypothesis related to mantis shrimp EMGs. I couldn’t all of a sudden decide that I actually wanted to see what neurotransmitters were involved in striking behavior, because you can’t measure neurotransmitters with EMG.
Well, “So what,” though? Mostly, it’s that no one has done this before, particularly in terms of making a backpack, comparing strike EMGs across mantis shrimp species, and, to a lesser degree, comparing power amplification across taxa.
Pennywise rocking his backpack.
Electrophysiology-focused mantis shrimp research has been purely acute and terminal, meaning that you only get one day’s worth of data from an animal before you are done with it. No one had ever made a chronic setup for EMGs in mantis shrimp. If you have a backpack that can be left on the animal for days or weeks at a time (i.e., chronic), you spend less money on getting new specimens, there is less loss of animal life, and you can have what’s called a within-subjects experimental design. Within-subjects designs have the advantage of allowing you to compare data from the same subject (i.e., each individual mantis shrimp) on different days in addition to comparing subjects to each other, making it easier to believe whatever you find. Surprisingly, no one has spent time making something like my backpack, so the methodology of my research is actually one of my biggest findings!
Also, if all goes well, the mantis sheds the backpack when it molts. I noticed today that Featherclown did exactly that, and is looking bigger and better than ever.
Different species of mantis shrimp might not punch in the same way
The phases of extensor activity leading up to the strike
As we all know, there are hundreds of species of mantis shrimp. However, no one has tried comparing EMGs of the strikes of two different species of mantis shrimp. What if you’re interested in studying a species besides those two? The Sheila Patek paper that I keep (post #1) on (post #2) referencing (post #3) examined twelve parameters of strike EMGs in Neogonodactylus bredini. Even though I recorded from three species, I was only able to get consistent strikes from one: Pennywise, the Gonodactylus smithii. The big question on my mind was about the difference between how Neogonodactylus and Gonodactylus build up energy to strike, visualized as above. From those twelve parameters in the Patek paper, I decided to replicate two: Duration of cocontraction phase, and number of extensor spikes in the cocontraction phase. I know. That’s a lot of explanation. Here are the graphs. Individual 0 is Pennywise, 1 through 6 are Patek’s Neogonodactylus-es.
Same number of spikes, but Pennywise is heads and shoulders above the Neogonodactylus-es vis-a-vis duration. At least, possibly. This is only one individual. Ideally I’d have at least as many Gonodactylus as Patek had Neogonodactylus, so I can’t say if Pennywise’s strikes are representative of his species’ entire population.
Power amplification across taxa
This is easily the least hypothesis-driven part of my project. The question I’m answering is, more or less, “how does mantis shrimp power amplification compare to that of crickets?”, and I’m using cockroaches as a sort of non-power-amplifying control group. Some speculative work has been done about the similarity in power amplification in crickets, so this part isn’t that new either. I’m not carefully measuring the behavior of crickets or cockroaches, so I can’t say a particular burst of EMG spiking produced a particular movement. I’m just comparing details about the bursting itself, which I selected in the cricket and cockroach data based solely on the bursts’ shape. It turns out that the power-amplifying species show an increase in the number of spikes (ie, average firing rate) from the first half of each spike burst to the second half, whereas the cockroach is a good control since it is all over the place and does not show a trend.
One analysis I wished I could have done involved the overall shape of the bursts itself. See how the cricket and mantis shrimp bursts seem to be hourglass shaped while the cockroach’s is more boxy? That is something I want to quantify eventually. Anyway, the rest of my poster can be found at danpollak.com/BYB.html.
Odds and ends
Looking back, I wish I could have done a few things differently, had I enough time. The backpack was plagued by water infiltrating its crevices, shorting it and rendering it useless until I could wick the moisture out with a rolled-up paper towel. This is why I had to revert to the Patek restraint, where the animal is held half-in, half-out of the water. If I could connect a waterproof plug to the backpack and release the mantis shrimp into its home tank, I could elicit striking behavior while the animal is actively defending its burrow against an “intruder” (i.e., my hand or a pen). That would open the door to research into how EMGs figure into mantis shrimp predation, social interaction, and myriad things I couldn’t speculate about. I hope that someday an intrepid marine biologist will see that chronic, modular EMG is possible and will simplify and waterproof it.
Slick graph huh? The highlight of my week was discovering a programming tool for visualizing statistics called Seaborn. I discovered that it is named after Sam Seaborn, Rob Lowe’s character on The West Wing, which, being my favorite TV television show, made me very happy. The kind of idealism I mentioned briefly at the top of this post, about how the research you do must benefit the people around you, is a theme on The West Wing, transposed onto policymaking. Sam Seaborn is a gifted speechwriter for the President, and is wont to expound on the value of integrity or honesty or some other embarrassingly bushy-tailed thing, except that after hearing him you really want to go around thwacking people on the head for being less than they ought to be. In figure 2 below, we see Sam Seaborn making the case for public education.
You might see why Seaborn is an apt name for a tool that tries to turn statistics into persuasive visual arguments, clear and careful communication that enables the best in us.
It’s been a blast to be a part of BYB’s program this summer, and I am grateful to those of you who took the time to skim even one of my posts. Thank you and sorry to Toothfinger and Beastie Boy for giving your lives to my incompetence with animal care. It’s a comfort to imagine you two in shrimp heaven now, burrowing to your hearts’ content. Please Daniel we can’t keep doing this.
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.
Pennywise on our makeshift operating table with his backpack affixed to his carapace. Wires have yet to be cut and inserted into his merus.
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.
Featherclown is pictured on the right, photogenically showing off said Patek restraint, though he didn’t feel like punching that day.
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.
I want you to do me a favor. I want you to hit me as hard as you can.
What’s that? You want more background?
Folks, things have started to pick up. Perhaps the most important development since June 11th has been the christening of our two mantis shrimp, which will give me an excuse to talk about mantis shrimp anatomy. We have two mantis shrimp living in our humble makerspace, All Hands Active: Toothfinger and Featherclown.
Toothfinger’s name comes from his scientific name, Odontodactylus scyllarus. To break that down, “Odonto” means relating to a tooth or teeth (think dentist), and “dactylus” is related to a greek word for finger. Featherclown’s name comes from two common names for Odontodactylus scyllarus, the peacock mantis shrimp (peacocks having those big colorful feathers), and the harlequin mantis shrimp (harlequin meaning clown, not the Joker’s love interest).
Anyway, let’s get into the anatomy that gave Toothfinger his name: the second raptorial maxillipeds, or as scientists in the field call them, his raps. The raps are 4-part “fingers,” composed of a the merus (the “femur”), the carpus (think the carpal bones of the hand), the propus (the “tibia”), and finally the dactyl. I briefly mentioned the concept of power amplification in my first post. It’s the way mantis shrimp are able to store up and quickly release an immense amount of energy that a single muscle twitch cannot accomplish by itself. This energy is stored in a sort of “spring” embedded in its rap called the saddle.
The seminal work on this spring action, as well as the EMG work I cited in my last post, was done by Professor Sheila Patek. In addition to being a true science badass (podcast) and an alumnus of my school, UMass Amherst, she discovered the mechanism of power amplification in mantis shrimp. The saddle shape on the merus is known as a hyperbolic paraboloid, a shape that shows up in architecture and origami. Here’s a gif of my Starbucks paper bag—turned saddle, resisting deformation. This should give you a sense of how the saddle stores and releases energy. By using multiple twitches, the extensor muscle in the merus compresses the saddle further and further, twitch by twitch, until the energy is released by the flexor.
Facing the 3-inch long beasts
Having done recordings in several insects, I felt that I had enough data for a preliminary cross-species analysis of EMGs between insects and the mantis shrimp. Meaning that I had to face the prospect of touching Toothfinger and Featherclown, those murderous bastards. However, it turned out that the challenge wasn’t in keeping my fingers intact, but in getting the stomatopods to punch at all.
The juicy bits of mantis shrimp behavior happens inside of and around their burrow: they grab whatever comes too close to the opening, recede into their lair, and get to work opening up the shell with intermittent audible clicks. Some of the first work on mantis shrimp from the ‘60s detailed their territoriality. Most social interactions involve burrow eviction/defense, where one stomatopod has to demonstrate dominance over another individual who wants its to steal its digs, no pun intended.
So their striking is closely tied to their burrow. My first attempt to get them to punch involved making a behavioral chamber that simulated a burrow. No dice. Featherclown just sat there. Then, I tried copying Sheila Patek’s restraint paradigm from her EMG paper, and again we encountered a distinct lack of dice. Odds are I’d have to invest a lot of time in habituating the animals to a restraint setup, plus it’s not burrow-like at all.
Left: my attempt at a simulated burrow
Right:Sheila Patek’s restraint design
I was feeling a bit lost, and then I noticed another paper from the Patek lab had come out on this year with a methodological stroke of genius: just use the actual burrow! In the lab, a mantis shrimp burrow is usually an ~6-inch long PVC pipe. Why not open a window lengthwise along the pipe, and place the window against the glass?
All that was left was to see if they’d strike from their new burrow, so I stuck my hand into the tank.
Holy reliability, Batman! If spaced out by a minute or two, I can pretty much elicit a strike every time. Here’s a fun thought experiment: what does it mean to the mantis shrimp that I put my finger near his burrow and the pull it back when he strikes every minute or so for a period of time?
To hear more about how Professor Sheila Patek’s scientific badassery, check out this podcast, and to hear about how she ended up making this discovery, check out her TED talk.
Crane, R. L., Cox, S. M., Kisare, S. A., & Patek, S. N. (2018). Smashing mantis shrimp strategically impact shells. The Journal of Experimental Biology, 221(Pt 11), jeb176099. https://doi.org/10.1242/jeb.176099
Dingle, H., & Caldwell, R. L. (1969). The Aggressive and Territorial Behaviour of the Mantis Shrimp Gonodactylus Bredini Manning (Crustacea: Stomatopoda). Behaviour, 33(1–2), 115–136. https://doi.org/10.1163/156853969X00341
Patek, S. N., Korff, W. L., & Caldwell, R. L. (2004). Biomechanics: Deadly strike mechanism of a mantis shrimp. Nature, 428(6985), 819–820. https://doi.org/10.1038/428819a
Kagaya, K., & Patek, S. N. (2016). Feed-forward motor control of ultrafast, ballistic movements. Journal of Experimental Biology, 219(3), 319–333. https://doi.org/10.1242/jeb.130518