Origin Myth, Part 2
At the end of Part 1, I had discovered Elysia diomedea, and the seed was planted about diverting possible future research toward marine organisms.
A lot of changes were occurring before and during 2012. The event that probably had the most impact was the death of my long-time mentor and Lab Chief, Howard Nash, in 2011. Aside from the emotional consequences of such a loss, there were also the practical details associated with the closure of the lab. Papers needed to be finished, and I needed to chart the next stage of my career.
In retrospect, it was a great opportunity to ask myself what I would do if I could do anything I wanted. Well, almost anything. Astronaut or dinosaur hunter, for example, were pretty much off the table. In the end, the direction that most excited me was teaching at the university level, hopefully with the possibility of sneaking in a little research with the undergraduates.
As luck would have it, a lecturer position in physiology and neurobiology (my two areas of expertise) opened at the Universities at Shady Grove campus of the University of Maryland College Park. I was pleased, relieved, and amazed to be offered the position, and then overwhelmed with the amount of work that it took to do a credible job teaching undergraduate lecture and lab courses. In the back of my mind, though, I continued thinking about involve students in studying an interesting and relevant question.
One of the first questions regarded which organism to study. I had spent the previous 20 years or so studying Drosophila, which is a marvelous organism with an enormous experimental toolkit. It is also extremely small (not so good for most aspects of neurophysiology) and is being studied by close to a gazillion people. Hard to find a niche for a shoestring operation in that melee.
I had become excited about Nematostella, a little mud-dwelling anemone that is becoming an increasingly popular model organism for the study of development, genetics, and evolution of cnidarians. These animals have a simple nervous system that may resemble that of our earliest multicellular ancestors. It seemed like studying the activity and connections in the nervous system could provide fundamental insight into how nervous systems evolved. They are easy to keep, and the Nematostella community is very enthusiastic and supportive. Recording electrical activity from the teeny neurons in the Nematostella nervous system, however, was somewhat more ambitious than was practical with the available resources.
Elysia should have been the obvious choice from the beginning. They are sizable molluscs, and molluscs are known for large, easily identifiable neurons that are accessible to relatively simple recording techniques. There was even a small literature regarding neurobiology of E. chlorotica. Furthermore, E. chlorotica had been reported in the Chesapeake Bay, so it seemed like an excellent way of making a connection between work in the lab on campus and the local ecology.
A plan was forming: Behavior and ecology with E. diomedea in Bahia, physiology and ecology with E. chlorotica in Maryland.
After finishing the 2014 spring semester at UM, I was again lucky enough to be able to join Ocean Discovery at Bahia de los Angeles. Professional and personal obligations left me with less time for planning than I would have liked, but I had developed two questions for the trip. First, is E. diomedea attracted to light, as one might expect of a photosynthetic organism? This would lay the groundwork for more detailed experiments on spectral preference and neural circuitry. Second, what does the slug eat? Surprisingly, that was not (and is still not) known. Almost all other Elysia species eat green macroalgae, but E. diomedea was rumored to feed upon Padina, a brown alga with which the slug is commonly associated.
The plan was simple: collect a small group of E. diomedea as soon as possible, and perform behavioral assays. This was to be followed by a workshop in which I would enlist the students to help extract the chlorophylls from the slugs and perform paper chromatography to separate the pigments and compare them to those of local algae species. I brought my electrophysiology kit, along with some LEDs and a controller for phototaxis assays, and managed (with a lot of help from Dr Talley and several trips to Dixieline Hardware), to collect the solvents, tubes, paper and other items required for chromatography.
Sadly, Drew was unable to travel down to Bahia that year. That cost me the opportunity to spend time with a friend and colleague, and it meant that he would not be able to supervise the students studying the movement of energy from the sea to the islands (“spatial subsidy,” a.k.a. “Energy Transfer”). Although I was far from a perfect substitute, I had spent a few summers observing, and had an adequate theoretical overview of the project, so I offered to help out with the students and staff for the few weeks I was there. (Be patient, this will eventually be relevant to the slug project.)
The silver lining was that I was able to spend every morning out on the islands with the students. On the trip out, there was something exciting to see almost every morning. Dolphins, whales, sea lions and whale sharks all greeted us at one time or another.
Plus, the islands themselves were spectacular, and it was invigorating just to be on them.
So I got to spend mornings pretending to be a biological oceanographer. Afternoons were filled with a variety of tasks, but I tried to spend as much time as possible snorkeling in pursuit of Elysia. (See, I told you we would return to sea slugs.). Based on how quickly I had found them the previous summer, I fully expected to have a small pile of them in short order. Strangely, though, there seemed to be none to be found. I combed areas heavily grown with Padina (the potential food plant mentioned above), other areas with Codium (“dead man’s fingers,” another potential food plant), rocky areas with turf algae, but found no slugs. I looked in the shallows, and as deep as was practical with a snorkel and a few weights. Nothing.
After almost a week, it became rather distressing. Reviewing Hans Bertsch’s work on the distribution of opisthobranchs in Bahia de los Angeles, I noticed that there had been a steady decline during the years of his study, which worried me a bit. Were conditions deteriorating in some way, so that E. diomedea was increasingly scarce in the bay? Also, he had not mentioned collecting as far south as we were, so maybe conditions were not as good at our field station. But I had found them the previous year…
The breakthrough came on a day when the students were working at the station, so we did not have to get on a boat to the islands first thing in the morning. With a little free time, it seemed like a great opportunity for more slug hunting, even if my optimism was starting to fade. I was pleasantly surprised to find one of the little guys within a relatively short period. So surprised, in fact, that I had forgotten to bring any sort of container, which led to a comical juggling act of carrying a small, squishy creature back to shore in large clumsy hands. Given their apparent rarity, the little gal was extremely valuable, and losing her would have been a huge blow. She made it back to shore, and got her own spacious plastic tub with an airstone for circulation. For good measure, I added a small rock with a collection of possible food plants. Below is a photo of her, with a ruler to provide the appearance of scientific rigor.
The following morning was also available for snorkeling, and I promptly collected three more Elysia. Although it might have been coincidence, finding four animals during a relatively short period of collecting in the morning, compared to finding zero after several hours of hunting in the exact same area during afternoons, suggests that it was the time of day, rather than the location or long-term trends, that was the important factor in success.
In retrospect, it makes sense that the slugs were most exposed in the morning. My working model when I started the project was that “solar sea slugs” would be strongly dependent on light, and maximize their exposure by lolling about in the afternoon sun. Recent work indicates that, despite the presence of kleptoplasts, the slugs depend almost entirely on feeding for their energy and nutrition. My captive slugs seem to be (note that this is fully anecdotal at the moment) at their most active, especially regarding egg laying and general exploration, in the evening and early morning. The rest of their time is mostly spent face down in their food plants, like so many squishy, aquatic cows.
The remaining time allowed for a few experiments, including a quick and dirty look at phototaxis and spectral preference. Unsurprisingly, they are attracted to light, and appear to prefer the long wavelengths, such as the orange shown below. The experiment was pretty crude, but the results match what had previously been shown for other species.
This almost closes the genesis of the Elysia project, and gets us just about to the beginning of the Solar Sea Slug Blog. I left Bahia knowing much more about the behavior and anatomy of Elysia than when I had arrived, and realized that the little slugs were much more complex than would be expected of “crawling leaves.”
Back in Maryland, I was ready to start hunting for local E. chlorotica in the Chesapeake. An email exchange with Dr. Sidney Pierce, now Professor Emeritus at the University of South Florida quickly disabused me of the idea. In his opinion, reports of that species, and its food plant, here are dubious.
Perhaps it was just as well. E. clarki is easily available and easy to fatten up on nuisance algae, and E. papillosa may be smaller, but appears to have similarly broad preferences and a rapid generation time (which will be the subject of a future post).