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Coronavirus 2020: Breeding In Isolation

Along with most of the working world, the Solar Slug team was summarily ejected from the lab on March 19, 2020.  I have been allowed to return occasionally to perform maintenance on the tanks, but was otherwise expected to stay home and continue teaching and other work remotely.  The next generation of slugs had been laying eggs, but I would not be able to devote any form of loving attention to the offspring.

As a devoted follower of the blog, you will remember that it took several years to work out conditions for rearing baby slugs.  The hatchlings need to be protected from pathogens and predators, and must have access to a clean supply of Bryopsis plumosa in order to take their first meals.

Some of the baby slugs did not get the memo.  A few weeks after we began isolation, I saw a few tiny slugs in one of the tanks.  It was a bit of a relief, because I had begun to wonder if I would be able to rear the next generation before the adults became too old to produce eggs.  

Baby slug, reared without effort. Note the large cluster of Valonia at the right of the photo.  4/14/20

The photo below gives a better sense of scale. The youngster, probably already a few weeks old, is less than a centimeter, and is dwarfed by one of the parents. It is impossible to be certain whether it is feeding on the red, filamentous algae, or finding green algae in there somewhere. Their overall color makes it clear that they are both full of green chloroplasts.

Two generations of slug in 10 gallon tank. 4/14/20.

As I mentioned above, hatchling Elysia can be delicate, and are very particular about their first meals. If Bryopsis plumosa is not available, then they will starve. During the period of neglect, Bryopsis pennata (excellent food for the adults) has been growing well. Other algae, such as Ulva and Valonia (bubble algae) have also been thriving, along with the unidentified filamentous red algae. Although I have not seen it, there very well may be adequate growth of B. plumosa hidden among the other algae.

Bryopsis and other algae in 10 gallon tank. 6/3/20

Early mortality must have been pretty high, because there are a few dozen youngsters (rather than hundreds) cruising the tank. That is more than enough slugs to keep the colony going for the year, but would not be adequate for experiments. Fortunately/unfortunately the campus is unlikely to return to normal by the fall, so student Slug Club will probably be postponed. Meantime, the new kids will grow into the next generation of parents.

Bahia Adventures. Part 3: The Late Middle

Elysia diomedea in field station tank. 6/30/18

Having the permits meant that we could get straight to work.  The first order of business was to get the tanks ready and find some slugs.  As a happy coincidence, the tides were very low, allowing us to explore the tide pools for interesting organisms.  Even better, we could collect rocks and plants for the slugs tanks by simply picking them up and putting them into a bucket, rather than having to dive down to get them.  We quickly had the tanks ready for sluggy inhabitants.

Tanks ready for slugs. Each contains a small collection of rocks and algae. The tank on the right is illuminated by a high-output LED fixture, while the one on the left is shaded by black felt, resulting in a 100-fold difference in intensity. 6/30/18.

The tanks were also ready for experiments.  One of the hypotheses we wanted to test was that photosynthesis by the slugs’ kleptoplasts contributes to the presence of bad tasting compounds in their mucus and/or tissues.  To test this hypothesis, half of the slugs would be kept in the dark for a week, while the others would be live under lighting adequate for photosynthesis.  For the experiment, one tank would be lit by strong LED lighting, with photosynthetically active radiation (PAR) above 100 µmol photons per square meter per second (plenty for photosynthesis), while the other received less than 1% of that amount.  The tanks were connected to the same life support system and had similar amounts of algae and rocks, so the conditions in the two tanks were nearly identical.

The plants and rocks were an excellent start, but our luck was even better.  We managed to find seven relatively large Elysia in the tide pools just in front of the station.  Even though I have not found Elysia in the same locations during hundreds of hours of snorkeling, they were present in abundance during low tide. It looked as thought the forces controlling the bay were smiling upon us after thumbing their noses at us for a week.

The slugs settled in well, exploring their new habitat and lounging on the algae.

Elysia diomedea in tank at BLA station. 6/30/18.

Elysia diomedea exploring rocks in new home. 6/30/18.

There was even reproductive activity.  As can be seen below, slugs appeared to court each other.

Elysia diomedea courting in a tank at the BLA station. 7/2/18.

They deposited multiple egg masses.  The masses contained thousands of tiny white eggs without extra-embryonic yolk, which is consistent with what others have observed for the species (see e.g., the Sea Slug Forum) .   

Egg mass of Elysia diomedea. 7/4/18.

 

Egg mass of Elysia diomedea in BLA station tank. 7/3/18.

Although, I did not have a camera with sufficient resolution to show the details of the masses,  I would agree with others that E. diomedea embryos are smaller than those of E. clarki and E. crispata. The relatively small size of the embryos, and resulting smaller amount of yolk, means that E. diomedea are probably “planktotrophic,” hatching earlier and feeding on plankton in order to finish development.  Larger embryos, such as those of E. clarki and E. crispata, are “lecithotrophic” living on plentiful yolk stores  until it is time for the veligers to settle and start feeding on Bryopsis.

Having slugs and algae also gave us the chance to do some DNA extraction.  The students took small samples from a couple of slugs, and some local algae, then extracted the DNA using the DNeasy Plant kit from Qiagen.

Codium specimen. A small sample was removed for DNA extraction and amplification. 7/3/18.

 

Unidentified green alga. DNA was sampled for identification. 7/3/18.

After a few rounds of incubations and separations, the students had generated tubes of clear liquid that presumably held DNA.

Elizabeth, Maria, Keyla, and Lily holding tubes of DNA extracts. 7/3/18.

Meantime, there was lots of other stuff going on.  Ric had been leading the other half of the group in troubleshooting and starting the feeding experiments.  Because we wanted to test the palatability of the tissues from slugs kept in the dark, we needed to modify the feeding assay we used in tanks at USG for use with fish in the bay.  It seemed simple enough to hang food cubes on fishing line that is anchored by lead weights at one end and held in the water column by a float at the other.  Figuring out the right thickness of fishing line, and how best to secure the lines to the weights and floats, required a good bit of trial and error.

The students were also working on their scientific presentation skills.  In one exercise, Ric had them give short summaries of the work while standing in the bay, in order to have them project their voices in a noisy, distracting environment.

Students giving talks while standing in the bay. 
7/2/18.

Unfortunately, two weeks had passed, which meant that it was time for me to leave the students, the great people from Ocean Discovery, my friend Drew, the bay, and the slugs, and return to Maryland.  The students were doing great, the assays had started to work (although the first round of PCR amplification of the DNA extracts was not successful), Ric had everything well in hand, and there would be a real molecular biologist arriving in a few days to act as my substitute.

I watched my last sunrise at Bahia for the season.

Sunrise over the bay.

I grabbed some of the DNA, packed my things, said my goodbyes, and headed north to San Diego.

Slug Life! The Photobiology group on my last morning. From left: Keyla, Bennie, Zaira, Me, Maria, Ric, Lily, Diana, Melanie, Elizabeth.  7/6/18.

At this point, we were about halfway through the field season.  After all the hard work and adaptive management, will there be results?

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.

Longlure frogfish on Bari Reef, Bonaire.

Hawksbill and small green turtles on Bari Reef, Bonaire.

Hawksbill and small green turtles on Bari Reef, Bonaire.

Brain coral, Bari Reef. Joanna in background.

Brain coral, Bari Reef. Joanna in background.

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Coney seabass on sponge, lobster antennae extending from hole in background. Bonaire.

Healthy colony of staghorn (Acropora cervicornis). Bonaire.

Healthy colony of staghorn (Acropora cervicornis). Bonaire.

Sand diverlizardfish, Andrea I, Bonaire.

Sand diver lizardfish, Andrea I, Bonaire.

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Lionfish, Bonaire

Foureye butterfly fish, Salt Pier,Bonaire.

Foureye butterfly fish, Salt Pier,Bonaire.

Colorful Mussa coral, windward side of Bonaire.

Colorful Mussa coral, windward side of Bonaire.

 

Whitespotted filefish, Bari reef, Bonaire.

Whitespotted filefish, Bari reef, Bonaire.

Balloonfish, Andrea I, Bonaire.

Balloonfish, Andrea I, Bonaire.

Jawfish near mooring buoy, Alice in Wonderland, Bonaire.

Jawfish near mooring buoy, Alice in Wonderland, Bonaire.

Gorgonian scene, Bonaire.

Gorgonian scene, Bonaire.

Longsnout seahorse (Hippocampus reidi), Salt Pier, Bonaire.

Longsnout seahorse (Hippocampus reidi), Salt Pier, Bonaire.

Voracious iguana, Slaagbaai National Park, Bonaire.

Voracious iguana, Slaagbaai National Park, Bonaire.

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.”

Seahorse Sculpture

Although there is activity behind the scenes, it continues to be quiet on the front page here.  For the moment, enjoy a photo of a seahorse sculpture on Bainbridge Island, courtesy of Ann and Hans.

Seahorse Scupture on Bainbridge Island

Seahorse Sculpture on Bainbridge Island