Tag Archives: sea slug

Elysia chlorotica.

New species of sea slug steals algae chlorophyll to live a solar-powered lifestyle

Is it an animal? Is it a plant? Strangely, it’s a bit of both — one newly-discovered species of sea slug lives entirely on photosynthesis.

Elysia chlorotica.

Elysia chlorotica.
Image credits Karen N. Pelletreau / University of Maine.

Ever wished you could plaster your body with solar panels and just go about your day, feeding off sunlight in lieu of eating? Sorry to break it to you, then, but there’s one sea slug is living your dream right now. According to researchers from the Rutgers University-New Brunswick, the slug can suck raw material from algae to maintain its solar-powered lifestyle.

Light eating

“It’s a remarkable feat because it’s highly unusual for an animal to behave like a plant and survive solely on photosynthesis,” said Debashish Bhattacharya, senior author of the study.

“The broader implication is in the field of artificial photosynthesis. That is, if we can figure out how the slug maintains stolen, isolated plastids to fix carbon without the plant nucleus, then maybe we can also harness isolated plastids for eternity as green machines to create bioproducts or energy.”

Christened Elysia chlorotica, the mollusk can grow to about 2 inches long and lives in the intertidal zone between Nova Scotia, Canada and Martha’s Vineyard, Massachusetts, as well as in Florida, the team reports. As juveniles, the slugs munch on Vaucheria litorea, a non-toxic variety of brown algae, to appropriate their plastids — the algae’s photosynthetic organelles — and store them in their gut lining.

The team used RNA sequencing to see what the slug does with the plastids it ingests. Their results show that the animal’s body actively responds to the organelles, protecting them from digestion and turning on genes to utilize the photosynthetic products they synthesize. The team’s results resemble findings in corals — animals that maintain symbiotic dinoflagellates (algae) which perform photosynthesis to help feed the coral.

Bhattacharya explains that Vaucheria litorea is an ideal food source for the slug because it doesn’t have walls separating adjoining cells in its body — it’s essentially one long tube filled with nuclei and plastids. This means that the slug can suck out all the cellular contents through a single puncture, anywhere along the algae’s outer wall.

After gathering enough of the organelles (in the order of a few million), the slugs become photosynthetic. Just like a plant, they start using sunlight to create sugars (compounds that store chemical energy) in their bodies from carbon dioxide and water.

Previous research performed on other species of sea slugs suggested that the animals steal these plastids and store them as food for later use — similar to how our bodies store fat. So far, Elysia chlorotica seems to be the only species that actually uses them to carry out photosynthesis, Bhattacharya says.

“It has this remarkable ability to steal these algal plastids, stop feeding and survive off the photosynthesis from the algae for the next six to eight months,” he adds.

Finally, the team notes that, while the slugs store plastids, they don’t do the same for nuclei they ingest. They still don’t know how the slug’s body keeps the plastids healthy and operational for months, or how they operate the organelles without the algal nuclei — which normally control the plastids’ activity, Bhattacharya adds.

The paper “Active Host Response to Algal Symbionts in the Sea Slug Elysia chlorotica” has been published in the journal Molecular Biology and Evolution.

Slug P. californica.

‘Self-aware’, predatory, digital slug mimics the behavior of the animal it was modeled on

Upgrade, or the seeds of a robot uprising? U.S. researchers report they’ve constructed an artificially intelligent ocean predator that behaves a lot like the organism it was modeled on.

Slug P. californica.

Image credits Tracy Clark.

This frightening, completely digital predator — dubbed “Cyberslug” — reacts to food, threats, and members of its own ‘species’ much like the living animal that formed its blueprint: the sea slug Pleurobranchaea californica.

Slug in the machine

Cyberslug owes this remarkable resemblance to its biological counterpart to one rare trait among AIs — it is, albeit to a limited extent, self-aware. According to University of Illinois (UoI) at Urbana-Champaign professor Rhanor Gillette, who led the research efforts, this means that the simulated slug knows when it’s hungry or threatened, for example. The program has also learned through trial and error which other kinds of virtual critters it can eat, and which will fight back, in the simulated world the researchers pitted it against.

“[Cyberslug] relates its motivation and memories to its perception of the external world, and it reacts to information on the basis of how that information makes it feel,” Gillette said.

While slugs admittedly aren’t the most terrifying of ocean dwellers, they do have one quality that made them ideal for the team — they’re quite simple beings. Gillette goes on to explain that in the wild, sea slugs typically handle every interaction with other creatures by going through a three-item checklist: “Do I eat it? Do I mate with it? Or do I flee?”

Biologically simple, this process becomes quite complicated to handle successfully inside a computer program. That’s because, in order to make the right choice, an organism must be able to sense its internal state (i.e. whether it is hungry or not), obtain and process information from the environment (does this creature look tasty or threatening) and integrate past experience (i.e. ‘did this animal bite/sting me last time?’). In other words, picking the right choice involves the animal being aware of and understanding both its state, that of the environment, and the interaction between them — which is the basis of self-awareness.

Behavior chart slug.

Schematic of the approach-avoid behavior in the slug.
Image credits Jeffrey W. Brown et al., 2018, eNeuro.

Some of Gillette’s previous work focused on the brain circuits that allow sea slugs to operate these choices in the wild, mapping their function “down to individual neurons”. The next step was to test the accuracy of their models — and the best way to do this was to recreate the circuits of the animals’ brains and let them loose inside computer simulations. One of the earliest such circuit boards to represent the sea slug‘s brain, constructed by co-author Mikhail Voloshin, software engineer at the UoI, was housed in a plastic foam takeout container.

In the meantime, the duo have refined both their hardware and the code used to simulate the critters. Cyberslug’s decision-making is based on complex algorithms that estimate and weigh its individual goals, just like a real-life slug would.

“[P. californica‘s] default response is avoidance, but hunger, sensation and learning together form their ‘appetitive state,’ and if that is high enough the sea slug will attack,” Gillette explains. “When P. californica is super hungry, it will even attack a painful stimulus. And when the animal is not hungry, it usually will avoid even an appetitive stimulus. This is a cost-benefit decision.”

Cyberslug behaves the same way. The more it eats, for example, the more satiated it becomes and the less likely it will be to bother or attack something else (no matter its tastiness). Over time, it can also learn which critters to avoid, and which can be prayed upon with impunity. However, if hungry enough, Cyberslug will throw caution to the wind and even attack prey that’s adept at fighting back, if nothing less belligerent comes around for it to eat.

“I think the sea slug is a good model of the core ancient circuitry that is still there in our brains that is supporting all the higher cognitive qualities,” Gillette said. “Now we have a model that’s probably very much like the primitive ancestral brain. The next step is to add more circuitry to get enhanced sociality and cognition.”

This isn’t the first time we’ve seen researchers ‘digitizing’ the brains of simpler creatures — and this process holds one particular implication that I find fascinating.

Brains are, when you boil everything down, biological computers. Most scientists are pretty confident that we’ll eventually develop artificial intelligence, and sooner rather than later. But it also seems to me that there’s an unspoken agreement that the crux falls on the “artificial” part; that such constructs would always be lesser, compared to ‘true’, biological intelligence.

However, when researchers can quite successfully take a brain’s functionality and print it on a computer chip, doesn’t that distinction between artificial and biological intelligence look more like one of terminology rather than one of nature? If the computer can become the brain, doesn’t that make artificial life every bit as ‘true’ as our own, as worthy of recognition and safeguarding as our own?

I’d love to hear your opinion on that in the comments below.

The paper “Implementing Goal-Directed Foraging Decisions of a Simpler Nervous System in Simulation” has been published in the journal eNeuro.

A nudibranch, or sea slug, feeding on hydroid colonies. Credit: Gabriella Luongo.

A lazy seaslug hunts by ‘kleptopredation’, letting prey do half the work for it

A Mediterranean sea slug is an underwater pirate. British researchers found that the animal purposely targeted well-fed hydroids — distant relatives of coral — in order to consume the prey’s prey, so to speak. According to experiments, half of the sea slug’s diet is plankton, which is what the hydroids prey on.

A nudibranch, or sea slug, feeding on hydroid colonies. Credit: Gabriella Luongo.

A nudibranch, or sea slug, feeding on hydroid colonies. Credit: Gabriella Luongo.

Trevor Willis, a marine ecologist at the University of Portsmouth, UK, calls the intriguing behavior ‘kleptopredation’. The cunning and brutal feeding strategy belongs to Cratena peregrina, nudibranch species belonging to the sea slug family. It lives off the coast of Sicily where it likes to feed on the branched colonies of Eudendrium racemosum hydroids.

“This is very exciting, we have some great results here that rewrite the text book on the way these creatures forage and interact with their environment,” Willis said.

Secondhand grocery shopping

Hydroid colonies consist of individual polyps that feed on plankton and small crustaceans. After closely following Cratena p.‘s feeding patterns, the researchers found that the nudibranch preferred to eat polyps that had only recently fed. Specifically, the sea slug doubled its attack rate on prey that had just dined on zooplankton. The findings also explain why some biochemical signatures that distinguish predators from prey don’t work out clearly for nudibranchs and hydroids.

Willis says that, effectively, the colorful sea slug is using another species as a fishing rod so it can easily gain access to food it otherwise wouldn’t have. What’s more, the sea slug’s prey does all the work for it.

“People may have heard of kleptoparasitic behaviour – when one species takes food killed by another, like a pack of hyenas driving a lion from its kill for example. This is something else, where the predator consumes both its own prey and that which the prey has captured,” Willis explained.

The researchers first realized that they were dealing with a novel predation pattern after they looked at nitrogen isotope levels in the nudibranchs, hydroid polyps, and zooplankton, discovering that the sea slugs had much lower levels than expected if polyps were their only prey. This investigation suggested that the hydroid polyp represent a fraction of the total mass ingested by the sea slugs.

Oddly, this behavior might actually benefit the hydroid colony in the long-run. By increasing its energy intake from their prey’s plankton diet, the sea slugs effectively consume fewer polyps than they would have otherwise. As such, the nudibranch’s novel predation extends the life of the hydroid colony.

It’s not clear at this point how widespread the behavior is. This is something which Willis and colleagues are investigating.

“Our ability to understand and predict ecosystems in the face of environmental change is impeded by a lack of understanding of trophic linkages,” said Dr Willis, but he added there was still a lot to learn from research. “While we have some great results, like any science worth its salt, it raises more questions than it answers.”

Scientific reference: Kleptopredation: a mechanism to facilitate planktivory in a benthic mollusc, Biology Letters (2017).

Sea Slug boasts disposable penis

Well we all use disposable tissues, dishes, I’ve heard of disposable tails of even limbs, but a disposable penis? Talk about taking things to the next level… But that’s exactly what this sea slug has. After mating, it simply discards its penis, grows a new one, and can even have sex again the same day.

sea slug

Chromodoris reticulata, is a type of soft-bodied marine mollusk, and as for the penis disposing process, researchers explain that it simply just falls off. Lead author Ayami Sekizawa from the Osaka City University and his team watched the species copulate 31 times and found that the animals are “simultaneous hermaphrodites” – meaning that both members are both the “man” and the “woman”, impregnating each other.

A typical mating episode involves two individuals touching each other with their genital orifices, then starting the copulation. After a while, one of them backs off, then the other backs off, then they walk for a while with elongated penises, and then the genitalia just sever from their bodies and float away.

“The sea slug sheds 1/3 of the internal penis length after each copulation,” Sekizawa said. “The sea slug is able to grow the penis gradually to its original length.”

But this loss doesn’t seem to hamper the sea slug’s life:

“In one case,” the researchers wrote, “we observed three successive copulations each separated by approximately 24 hours.”

There still isn’t a good explanation for why this happens, but there are a handful of other animals that exhibit a similar behavior. Argonauta, a type of octopus and some orb-weaving spiders have the same type of behavior.

“Little is known about mating behavior in simultaneously hermaphroditic animals,” Sekizawa said. “The disposable penis in our nudibranch (sea slug) study is merely one case of peculiar mating behavior” in these animals.”

Heh, and here I was thinking that squirrels who masturbate to avoid STDs were weird.

The July Awesome Animal Award goes to: The Sea Swallow

A while ago, we started this animal award, giving the first one to the mimic octopus, and the second one to the amazing Siberian salamander, which can survive after being frozen in temperatures as low as -45 degrees Celsius. Each month, we’ll highlight an animal so special and unique it just makes you go ‘Wow!’. This month it’s the living pokemon, the sea swallow, the blue sea slug: Glaucus atlanticus.

The strange beauty of its animal is enough to make it spectacular on its own, but this creature is more remarkable than it seems at a first glance. It is a marine gastropod mollusk, much like clams and oysters, but unlike them, it doesn’t have a solid shell. It is the only member of its family, although it is closely related to Glaucilla marginata, to which it bears quite a resemblance. It typically eats plankton or other microscopic algae, but what’s truly interesting is that it can eat Portuguese Man O’ War (Physalia physalis), a poisonous jellyfish-like creature; but not only does it eat it, but it also consumes the entire organism, storing the venomous nematocysts for its own use, in the thin feather-like “fingers” on its body. Because it can store the venom from several Portuguese Man O’ War, it can be much more poisonous than the creatures it devours.

But Glaucus atlanticus gets even more awesome: it actually floats on its back, due to a gas-filled sac in its stomach. The dorsal side, which is actually the foot and underside, is blue or somewhere between blue and white, while the true dorsal surface is completely silver-grey. This is a remarkable adaptation called counter shading, which helps trick predators.

Glaucus is also a hermaphrodite a hermaphrodite, containing both male and female reproductive organs, and even more interesting, after the mate, both animals produce eggs.