Study shows 'solar powered' sea slugs can survive long term in the dark

Nov 20, 2013 by Bob Yirka report
Exemplary images of P. ocellatus specimens. Image (i) shows a slug kept in the light and which was regularly fed, hence best representing natural conditions. Image (ii) shows a slug after 55 days of starvation in the dark. Credit: Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098/rspb.2013.2493

(Phys.org) —A team of researchers from Germany and the Netherlands has found that at least two species of sea slug thought to be able to endure long periods of starvation by gleaning energy from the sun has found that the slugs can live for long periods of time without food and with or without sunlight. In their paper published in Proceedings of the Royal Society B: Biological Sciences, the team describes experiments they conducted with the slugs and then outline their findings.

The two types of sea (Plakobranchus ocellatus and Elysia timida) survive by eating algae, but prior research has shown that the creature can survive very long periods of starvation. Because the slugs do not digest—at least right away—a specialized subunit of known as an organelle, that in the algae is responsible for photosynthesis, scientists have believed that the slugs were somehow gaining energy from the sun using the cells from the algae.

To test this theory, the researchers subjected several of the sea slugs to long periods of starvation under three different conditions. One group of the slugs was kept in the dark without food—another group was kept in a sunlit enclosure but was also not given any food. A third group was given a chemical that inhibits photosynthesis and was then kept in a lighted enclosure, but was not given any food either.

After 55 days the researchers pulled the slugs from their enclosures and studied them to learn if there were any differences among them. Surprisingly, the researchers could not find any. All the members of all three groups survived and all lost approximately the same amount of weight. A subsequent test showed just how durable the slugs really are—the researchers put six of them in a dark enclosure and didn't feed them for 88 days—all of the slugs survived and even appeared healthy.

The results of the study disprove the idea that the slugs somehow derive energy from the photosynthesizing cells they keep alive for long periods in their bodies. The researchers suggest that the slugs may instead be allowing the cells to remain alive for long periods of time, simply to eat them slowly as time passes. This means that the cells are apparently kept alive by the sun while in the slugs body—sort of an internal farming system, allowing the slugs to survive long starvation periods, which because they move so slowly, appears a necessary adaption to ensure survival.

Explore further: Researchers discover sea slugs that stab each other in the head after copulation (w/ Video)

More information: Plastid-bearing sea slugs fix CO2 in the light but do not require photosynthesis to survive, Published 20 November 2013 DOI: 10.1098/rspb.2013.2493

Abstract
Several sacoglossan sea slugs (Plakobranchoidea) feed upon plastids of large unicellular algae. Four species—called long-term retention (LtR) species—are known to sequester ingested plastids within specialized cells of the digestive gland. There, the stolen plastids (kleptoplasts) remain photosynthetically active for several months, during which time LtR species can survive without additional food uptake. Kleptoplast longevity has long been puzzling, because the slugs do not sequester algal nuclei that could support photosystem maintenance. It is widely assumed that the slugs survive starvation by means of kleptoplast photosynthesis, yet direct evidence to support that view is lacking. We show that two LtR plakobranchids, Elysia timida and Plakobranchus ocellatus, incorporate 14CO2 into acid-stable products 60- and 64-fold more rapidly in the light than in the dark, respectively. Despite this light-dependent CO2 fixation ability, light is, surprisingly, not essential for the slugs to survive starvation. LtR animals survived several months of starvation (i) in complete darkness and (ii) in the light in the presence of the photosynthesis inhibitor monolinuron, all while not losing weight faster than the control animals. Contrary to current views, sacoglossan kleptoplasts seem to be slowly digested food reserves, not a source of solar power.

Related Stories

Invasion of the slugs—halted by worms...

May 12, 2013

The gardener's best friend, the earthworm, is great at protecting leaves from being chomped by slugs, suggests research in BioMed Central's open access journal BMC Ecology. Although they lurk in the soil, they seem to pro ...

Green sea slug makes chlorophyll like a plant

Jan 12, 2010

(PhysOrg.com) -- Scientists from the University of South Florida in Tampa have found a green sea slug is able to synthesize chlorophyll like a plant, which makes it the first animal known to be capable of ...

African black slug serves as healthy reminder

Jun 19, 2013

A new, invasive species of slug found recently in South Texas serves as a good reminder to thoroughly wash fruits and vegetables before eating them, according to an expert with the Texas A&M AgriLife Extension ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Egleton
1 / 5 (1) Nov 20, 2013
More evidence that Rupert Sheldrake is right.
The law of conservation of energy/matter is a dogma.

More news stories

Atom probe assisted dating of oldest piece of earth

(Phys.org) —It's a scientific axiom: big claims require extra-solid evidence. So there were skeptics in 2001 when University of Wisconsin-Madison geoscience professor John Valley dated an ancient crystal ...

ISEE-3 comes to visit Earth

(Phys.org) —It launched in 1978. It was the first satellite to study the constant flow of solar wind streaming toward Earth from a stable orbit point between our planet and the sun known as the Lagrangian ...