Posts By Dave
New kids in the growout tank
The slug colony is squeaking along toward full function. The next batch of plants arrived from KP Aquatics this week, so the broodstock and growout tanks are smorgasbords of macroalgae.
With the growout tank ready, I added the first youngsters from Box of Slugs 2. This batch consisted of two medium-sized and one small girl, and all seemed almost jubilant once they entered the tank.
The two largest could be twins.
New girls in growout tank, 4/18/15.
The little one is keeping an eye on big sister.
Big and little sister in growout tank, 4/18/15.
Moving the next generation into the system here should take a little pressure off the fodder in BoS 2. At some point I should get a better idea of the algae requirements on a per-slug basis.
Box of Slugs 1.0 upgrade!
After months of planning and anticipation, the new slug facility is up and running at Shady Grove. The original “system,” if you could call it that, was a 20 gallon long tank with an Evergrow LED fixture to supply light and a Hydor Ekip thermopump to provide heat and circulation. It worked fine in terms of egg production, and the adults seemed quite happy. The new system has a separate growout tank for baby slugs, a sump for equipment such as the heater and an automated topoff system to make up for evaporation. It will also have a hatchery tank, in which the eggs and veligers will have constant circulation of fresh, pest-free water.
After the shelf was built and painted, the system was set up in one of the lab spaces (no carpet, spill kits at the ready). For this test, only the 15 gallon broodstock tank and sump were used.
Preliminary test broodstock and sump
Then water was added…
Wet test, broodstock and sump
The plumbing and hardware appeared to function adequately, so it was ready to be set up in the office. The rack was moved into place and the sump was filled from the Bryopsis growout tank (photo below). For the final fill, I waited until I could get started first thing in the morning, so that I would have most of a day to keep an eye on it in case of unanticipated redirection of flow (i.e., flooding).
Box of Slugs 1.1, ready to be filled with water and livestock.
Then it was time to commit. Water, sand, plants, and slugs all had to be moved in an orderly way. In an hour or so, everyone was settled in their new homes. The seahorse had been moved to Box of Slugs 2 to minimize her stress, but all of the adult slugs, the broodstock, took their place in the 15 gallon tank on top.
Box of Slugs 1.1, up and running.
So there it is. The main slug tanks, for adult broodstock and growing youngsters, now have dividers to keep the Bryopsis from completely overwhelming the other algae. Heater, topoff valve, and pump are in the sump, where they can’t bother the slugs. Flow from the sump to the rest of the system passes through a reactor filled with activated carbon, to prevent possible inhibition of slug growth by secretions from the algae. It should also reduce any odors produced by a system packed with seaweed. Having a sump makes it easier to dose with calcium, bicarbonate, nitrate and phosphate without worrying that some is getting dumped on the slugs’ heads. As an added bonus, the tank is not taking up valuable real estate in the middle of my office.
The slugs seem happy in their new home. They are exploring, feeding, and starting their mornings by basking in the sun.
E. clarki in new home, checking temperature
Elysia clarki greeting the morning sun in new home
Now that phase 1 of B.o.S 1.1 is finished, I will be adding more macroalgae and move some of the the E. clarki youngsters from Box of Slugs 2 into the growout tank. The final phase will be to get the hatchery on line, to have more control of the timing and numbers of baby slugs.
Bonaire Photos: More
We are just about to post the photos of the setup process of the improved Box of Slugs 1.0, which will be known as BoS 1.1. It will have two broodstock tanks, a hatchery and a sump/Bryopsis storage tank. In the meantime, here are a few more photos from the January trip to Bonaire. Nothing to do with slugs, but the photos are at least of marine organisms. I hope you enjoy them. As always, click on the images to enlarge.
Longlure frogfish on Bari Reef, Bonaire.
Hawksbill and small green turtles on Bari Reef, Bonaire.
Brain coral, Bari Reef. Joanna in background.
Coney seabass on sponge, lobster antennae extending from hole in background. Bonaire.
Healthy colony of staghorn (Acropora cervicornis). Bonaire.
Sand diver lizardfish, Andrea I, Bonaire.
Lionfish, Bonaire
Foureye butterfly fish, Salt Pier,Bonaire.
Colorful Mussa coral, windward side of Bonaire.
Whitespotted filefish, Bari reef, Bonaire.
Balloonfish, Andrea I, Bonaire.
Jawfish near mooring buoy, Alice in Wonderland, Bonaire.
Gorgonian scene, Bonaire.
Longsnout seahorse (Hippocampus reidi), Salt Pier, Bonaire.
Voracious iguana, Slaagbaai National Park, Bonaire.
Journal Club: A Sea Slug’s Guide to Plastid Symbiosis
The Elysia literature is rich, varied, and growing constantly. From time to time, I will highlight a recent paper that strikes my fancy.
The paper of the moment is a recent review by de Vries and his colleagues that, from my point of view, demonstrates how the field of kleptoplasty in sacoglossans is maturing as a growing number of researchers apply diverse methods and approaches. Although I will summarize some of the highlights below, it is worth reading this short, nicely written paper for yourself (de Vries et al., 2014, Acta Soc Bot Pol 83: 415-421)
This paper illustrates a larger point that I have had to learn repeatedly during my career: as much as possible, one needs to look at the data and the biology, unfiltered by the way you think it should work. Almost invariably, one generates a mental model to organize one’s observations about a biological system. This model forms the basis for additional experiments, which can potentially support the model, but which almost always show you how naïve and simple your initial model was. The model is essential to focus one’s thinking, but any biological system is more complex (and therefore more interesting) than your limited human mind can imagine. So, there comes a time to listen to what the biology is telling you, and to think very hard about the next generation of models.
The paper by deVries and colleagues highlights that the field is at a point where researchers can, and must, think more deeply about the mechanisms and functions of kleptoplasty. They lay out a series of fundamental unanswered questions regarding the biology of solar sacoglossans.
- How do the slugs sort the kleptoplasts from the stuff that gets digested? When sacoglossans feed, they pierce the wall of an algal cell with a specialized radullar tooth, and suck out the contents. The extracted material contains mostly stuff the slugs will digest immediately (e.g., cytoplasm, nuclei, mitochondria), but also chloroplasts. How does a slug’s digestive system handle the material, with chloroplasts segregated and moved from digestive organelles to the cytoplasm, where photosynthesis can continue?
- How are stolen plastids maintained? Despite initial reports of horizontal transfer of genes from the genomes of the plants to those of the slugs, more recent experiments indicate that this is not the case. So how are the kleptoplasts maintained in a functional state without an algal genome (remember, the nucleus was digested) to direct the synthesis of the structural proteins and enzymes needed to replace those that are constantly degraded? Perhaps the kleptoplasts carry the capability with them, but the details remain mysterious.
- What is special about the biology of slug and algal species that participate in long-term retention (LTR) of chloroplasts for up to months at a time. There are seven species of sacoglossans known to be LTR slugs. These seven slugs are not monophyletic (i.e., are not derived from a common ancestor), and vary in the details of their diets. Some, like E. chlorotica, specialize on a single food plant, whereas others (e.g., E. clarki) feed on multiple species. In some cases, LTR species feed on the same food plants as short-term retention (STR) species, which maintain plastids for only a few days or weeks (e.g., E. clarki vs. E. papillosa). The slugs themselves, therefore must have some specializations to enable LTR. However, in a given LTR species, retention times vary for kleptoplasts of different algal species. These observations indicate that both the slugs and the algae have specializations, completely unknown at this point, that enable long-term survival of chloroplasts inside LTR slugs’ cells.
- Possibly the most fundamental question regards the functions of stolen chloroplasts: what good are kleptoplasts anyway? Multiple experiments have demonstrated that photosynthesis alone cannot support slug survival in the long term, and it is currently unclear whether starch produced by photosynthesizing kleptoplasts even enters the slugs’ cytoplasm. One hypothesis is that the plastids serve as “living larders,” being digested as needed by the slugs during periods of starvation. Kleptoplasts may also produce biochemicals needed by the slugs. For example it has been suggested that juveniles may depend on kleptoplast-derived lipids during their development. It is surprising that the function of long-term kleptoplasty remains mysterious so many years after its discovery.
- I wanted to end with an issue that the authors touched on briefly, that of photobehavior. Experiments have been performed examining phototaxis and parapodial extension in response to light, with the interpretation of the data being strongly influenced by the assumption that the behaviors support photosynthesis in some way. This issue is of particular interest to me, and, although a full discussion of the literature must await a future post, a lot of the data are not really consistent with the behaviors serving to optimize photosynthesis. Like, why aren’t slugs most active in mid-day, or why do they seem to be most affected by wavelengths in the middle part of the spectrum that are nearly useless for photosynthesis? From my point of view, some hard thinking about experimental design and interpretation are in order.
The paper ends with a quote from Ed Yong that echoes my introduction to this blog post, but is much more eloquent: “Science is about resisting the easy pull of conclusions. It’s about testing stories that seem like they should be right to see if they actually are right.”
As the study of kleptoplasty evolves from “gosh, wow, a photosynthetic slug” to a more complex and interesting view of the animals’ biology, the questions become more focused and more sophisticated. It will be fun to watch, and with a little time and effort, participate in the process.
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.
Howard Nash, pushing flies
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.
Nematostella vectensis, May 2011.
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.
Sea Lions Basking in Bahia de los Angeles
Plus, the islands themselves were spectacular, and it was invigorating just to be on them.
Ocean Discovery Students on the Island of Flecha, summer 2014. Jorobado island in Background.
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.
Elysia diomedea, Bahia de los Angeles
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.
Elysia on orange LED.
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).
Very Odd Sacoglossan
In the previous post, I mentioned that there are at least five species of slugs in Box of Slugs 2.0. Four Elysia species were described in that post, but the one in the picture below is odd enough to warrant its own spotlight. This tiny beauty was clearly different from the Elysia, having branched rhinophores, and being adorned with cerata, outgrowths from the dorsal surface. It is more reclusive than the others, rarely making its presence known except for the occasional appearance in the early morning before lights-on. It is also very quick to become scarce, diving behind or into a clump of algae, if the lights come on when it is out and about. These behaviors, combined with my limitations as a photographer, explains the quality of the images so far.
Mystery slug with cerata in Box of Slugs 2
When I first saw this creature, with its frilly cerata, I believed it to be a nudibranch. In general, marine aquarists are not pleased about seeing nudibranchs in their tanks. They tend to be specialist predators, focusing on one or a few species of prey items. Prey can be sponges, bryozoans, corals, or even other molluscs. As a result, nudibranchs can either be pests, destroying prized species, or, more likely, will starve to death in the absence of preferred foods
I had removed the slug to a small container, and was debating its fate, when Joanna made it clear that killing the slug was the less preferred option. Realizing that I did not yet know what I was dealing with, I took a few macro shots and started to go through field guides. Looking more closely, I realized that it was not a nudibranch, but a sacoglossan like Elysia. The lack of external gills on the posterior end (see photo below) mean that this animal is not a nudibranch, and the combination of cerata and branched rhinophores suggest that it is a species of Cyerce. Cyerce antillensis comes from the right part of the world to have ridden in on some macroalgae, and it lives on Penicillus, so it is a promising candidate. It is a variable species, and is the closest match I have found so far, but I have not yet seen a photo of Cyerce antillensis that is convincingly similar to our slug. In any case, the slug was returned to the Box of Slugs as a harmless curiosity.
Sacoglossan with cerata, dorsal
The photos above and below show a body filled with green stuff, presumably chloroplasts removed from its food plant(s). According to the literature, however, Cyerce is not kleptoplastic.
With time and luck, opportunities for better photographs will present themselves. Who knows, there may even be enough of them to start seeing young ones.
Sacoglossan with cerata, ventral
Sacoglossan, possibly Cyerce, B.o.S 2.0, 3/7/15
When two species turn into five
An interesting exercise in how parsimony and preconceptions can mislead.
As the most recent posts suggest, slugs have been added, and have appeared, in Box of Slugs 2.0. Here is a streamlined sequence of events from my point of view.
The tank was set up, and slugs (E. clarki) & macroalgae (Penicillus, Udotea and Avrainvillea) were purchased from a collector. A few days after the new organisms settled in, we left for a little over a week. After we got back (as described here), not only were there some E. clarki eggs masses (one of which I watched being deposited), but also some tiny sluglets. Logical conclusion: the small slugs were baby E. clarki. The timing seemed a bit off, because the youngsters appeared a little too soon based on the incubation times observed for E. clarki in Box of Slugs 1.0 (about 16-17 days), but [mutter about temperature or previously deposited eggs or something].
As the little guys grew, they looked like they might be more than one species (see this post), and the one that looked most closely like E. clarki stilll did not look quite right. Maybe the big, ruffly parapodia develop as they mature? Are they really laying eggs at such a small size? Although I did not know what baby E. clarki looked like, suspicions were becoming aroused.
It all came into focus over the past week, as a sizable cohort of baby slugs appeared and started to grow quickly on a diet of Bryopsis. What do baby E. clarki look like? It turns out that they look like little teeny versions of their parents, complete with broad, ruffly parapodia and loosely rolled rhinophores.
Very small E. clarki in Box of Slugs 2.0. 2/24/15
Baby E. clarki, dorsal view
Baby Elysia clarki, ventral view. 2/27/15
Baby E. clarki on Derbesia, dorsal view.
No doubt, they look like tiny versions of the adults lumbering around the tank. They may have hatched from eggs laid by one of the residents, or from a clutch of almost fully developed eggs that I added a week or so back.
It turns out that, rather than the two species of slugs that were purchased from KP Aquatics, we have five. The adult clarki and crispata that I purchased are the real deal. Both species have the same general shape, with ruffly parapodia and loosely rolled rhinophores. Both are very fond of Bryopsis, at least in captivity.
E. clarki are uniformly green with white spots, and seem to grow and thrive better than the other species in their captive algal world.
E. clarki in Box of Slugs 1.0
E. crispata may be the the glamour slug of the tank. The bluish hue and large white spots make these slugs very eye-catching.
Elysia crispata in Box of Slugs 2.0.
After looking at a lot of photos, especially at the Sea Slug Forum, I have identified the other species with some confidence. What I had originally identified as E. clarki is most likely E. papillosa. Looking at it side by side with E. clarki in the photo below, it is clearly not the same species. The parapodia of E. papillosa are much smaller and simpler, the rhinophores are pinkish and more tightly rolled, and the spots are smaller and more sparse. Unlike clarki and crispata, papillosa does not appear particularly fond of Bryopsis, preferring to hang out and feed on Penicillus most of the time. Another interesting difference is that E. papillosa uses its parapodia to swim from time to time. Despite hundreds of hours of observations of E. clarki, including the slugs floating in the water column, I have never seen them use their parapodia for propulsion. Maybe the less elaborate parapodia are more useful for swimming (think using a square dancing skirt vs a wedding dress).
Large adult E. clarki (left) with presumed E. papillosa (right).
The final Elysia species, which has very small parapodia, is presumed to be E. tuca. The bright green coloration, the white rhinophores and the white areas on the head, along with the small parapodia, are anatomical features of E. tuca. Combined with the species tendency to spend its time on Halimeda and its common occurrence in the Florida Keys, where I assume the algae were collected by KP Aquatics, and it’s a pretty good bet that these are E. tuca, and that they rode in with the first shipment of macroalgae. They show no interest in Bryopsis, spending most of their time associated with Halimeda, and making the occasional trip to Penicillus or Avrainvillea.
Elysia tuca (left) and E. papillosa (right) on Penicillus that has been overgrazed and overgrown.
The different species wander around the tank constantly, but tend to focus on their food plants.
A trio of Elysia: papillosa (left), crispata(top), and tuca (bottom right)
As far as I can tell, they do not interact socially. In the photo below, E. tuca crawls over E. crispata as it would any other obstacle.
E. papillosa, crispata and tuca, making a dogpile.
So, rather than the two species of Elysia I purchased, there are four species. On top of that, at least a few of them are reproducing successfully. Not bad.
But didn’t I mention five species? There is one more sacoglossan species in the tank that has not been discussed. Although the species above are interesting enough in their own right, the final species warrants a post of its own.
Stay tuned.
Growing Like…..Weeds!
Things have been going quite well in the in-line refugium known as Box of Slugs 2.0. Although it might not be considered a plus in most aquaria, algae have been very successful in the new tank. A less sophisticated aquarist might dare to call the tank an eyesore, yet the slugs could not be happier. Here are a few of the youngsters grazing on what I think is Derbesia.
Trio of Youngsters, Box of Slugs 2.0
Indeed, it has been a great time for the little guys, and they have been growing like the little slug-weed chimeras that they are. Many have gone beyond the twiggy little worm stage to looking and behaving like proper small slugs.
At this size, I am still unsure that they are all E. clarki. The one below is most likely E. tuca almost looks like E. chlorotica, or maybe E. subornata, and does not have much in the way of parapodia.
tuca chlorotica not clarki?
The small slugs below look more convincingly like the adults in the tank. Rolled rhinophores, parapodia starting to ruffle, chloroplasts throughout the body, including the foot, all point to the little guys being the common lettuce slug of the Keys.
Young E. papillosa clarki, 2/8/15
Baby slug exploring
Will they get spots and ruffles like the purported parents? Time will tell. [note added later: these are not young E. clarki, as a few of the edits above indicate]
Adult E. clarki 2/5/15
They still have a long way to go to get to full size, as can be seen in this photo of the adult from the photo above grazing on Bryopsis while a youngster wanders about.
Growing baby and parent 2/13/15
One of the more interesting developments is the appearance of very small, dense egg masses in Box of Slugs 2. At first, I attributed them to the small herd of E. crispata that arrived a few weeks ago, since I have no idea of the size or appearance of their egg masses. I need to start putting a ruler or something in the photo for scale, but this clutch is about the size of the first coil of the a standard E. Clarki mass from Box of Slugs 1 (shown here, for example), and the little embryos are packed much more tightly.
Egg Mass 2/13/15
As mentioned above, I thought these were eggs from crispata, but was thrown for a bit of a loop when I saw one of the youngsters curved around the mass as if laying them. Can they really be mature enough to lay eggs? I collected the mass below, and am documenting the embryos’ development. They are definitely fertile, as indicated by the classic circling movements inside their eggs, and maybe this time I can get a brood to mature in a controlled environment and find out which species they turn into. Stay tuned.
Slugs on NPR!
Terry Gosliner of the California Academy of Sciences was on NPR’s Science Friday this afternoon, talking about…SEA SLUGS!
Mostly he talked about the northward movement of the Hopkins Rose nudibranch (below), and what that tells us about warming temperatures in the Pacific.
Photo by Gary McDonald, posted on FeaturedCreature.com
Of course, he could not help but mention Solar Sea slugs and kleptoplasty. I mean, who can spend an entire interview talking about a spiky pink abomination when you can talk about green beauties like Elysia? It was a bit disappointing that he referred to Elysia as a nudibranch (we all know that they are not), and implied that they derived as much benefit from their chloroplasts as corals do from their zooxanthellae. Nevertheless, any radio show about sea slugs is a good radio show.
More information and audio can be found on the Science Friday web site.
Ten Interesting Factoids About Solar Slugs
Not surprisingly, many of the comments that have been posted by others on the blog are spam, and many of these are helpful people with names like “Central Air Conditioning,” and offer assistance in increasing traffic on the site.
To be honest, although I would like for the site to be useful to all of the denizens of the InterWeb, the site is mainly a way for me to keep track of my progress, along with helping me organize the links and literature comprising the world of slugs. So, I am not particularly interested in increasing traffic for the time being.
Nonetheless, maybe it’s time to generate a little click bait. While not to the high standards of “10 things Kim Kardashian will eat today” or “11 things your dog hates,” there are plenty of catchy lists to be made with all the fascinating information from the world of sacoglossan biology.
Here are ten things you should know about Elysia, in no particular order.
1. They suck sap. Like other sacoglossans, they pierce the cell walls of their food plants with rasping mouthparts, the radulla, and suck out the contents.
2. Larvae are lecithotrophic, meaning they live off of stored yolk while they are in the brief free swimming, or veliger, stage. This means that they do not have to find food during this period.
3. Larvae metamorphose rapidly. With some exceptions, the veliger stage lasts only a few days, and the juvenile slugs settle onto their food plants and begin their benthic (bottom dwelling) lives.
4. They like to float randomly. Although this may not apply to all species, captive E. clarki and E. crispata like to release their hold on the substrate from time to time. They often skim the surface layer, and also float around in the water column. This may not be a natural behavior, but I have observed wild E. crispata “going for a float” when launched by the current generated by a passing fish. Whether this behavior aids dispersal or is simply a byproduct of being the same density as seawater is unclear.
5. They are hermaphrodites. Adult Elysia produce both eggs and sperm at the same time. They cannot fertilize themselves, but can mate with anyone of the same species that they encounter. Was it Woody Allen who said it doubles your chance of finding a date on Saturday night?
6. They steal chloroplasts. When they suck the sap from their food plants, the chloroplasts (photosynthetic subcellular structures) are taken and moved to digestive diverticula, which are special outpouchings of the digestive system. The chloroplasts can be maintained for many months, and produce measurable amounts of energy for the slugs. Contrary to earlier reports, however, photosynthesis by these stolen chloroplasts (“kleptoplasts”) is not enough to stave off starvation.
7. Several Elysia species are being studied as sources of potential therapeutics. As can be found in the Natural Products page, the slugs contain chemicals derived from their food plants that may be useful in treatment of cancer and other disorders.
8. Elysia species often eat a variety of food plants. Many slugs, such as nudibranchs, are highly specialized to feed on a single kind of animal or plant. Although this may be the case for some species of Elysia, many will accept multiple plant species. Further, there have been reports that juveniles prefer different plants from adults.
9. They have adapted to many climates and conditions. For example, on the east coast of North America, Elysia species range from Nova Scotia to the Caribbean. As an example of the range of ecological adaptations, Elysia crispata is commonly found on corals reefs, while E. catulus is restricted to seagrass beds.
10. Elysia do not have gills. The large surface area generated by their parapodia allows them to perform gas exchange through their skin, obviating the need for gills. They are frequently, and erroneously referred to as nudibranchs because of their superficial similarity to this group, but nudibranchs have prominent gills, as illustrated by the fact that their name means “naked gills.”
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