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A summer science fiction movie may have this plot: An organism gets its “superpower” from the food it eats. The only thing is that, this is real.
Some sea slugs ingest the photosynthetic organelles from the algae they eat, according to a recent study by biologists from Harvard University. During times of starvation, the organelles keep running the process of photosynthesis, which supplies their hosts with energy and nutrients.
This is a creature capable of stealing components from other creatures, incorporating them into its own cells, and then utilizing them. According to the researchers, that was the most bizarre form of biology they had ever encountered.
The research describes the process by which so-called “solar-powered” sea slugs sustain the organelles contained in “kleptosomes”—specialized membranes that serve as biological treasure troves. The findings were published in the Cell journal. There may be biomedical uses for the results of this study as well as new information on the history of eukaryotic cells.
The capacity to harness light energy from algae is the “wow” factor, according to the researchers. Sea slugs can effectively steal this ability. Some organisms acquire abilities, such as the capacity to glow in the dark or sting as a weapon. Plus, it’s awesome that they figured out how to keep these stolen abilities active for when they need them.
Several years ago, a researcher from the Bellono Lab started the study, which had been investigating endosymbiosis—the living organism inhabiting the host organism—for some time. Sea slugs utilize just components, the small organelles found inside their target cells, in contrast to corals that absorb entire algal cells.
The sea slug Elysia crispata, which is found in tropical waters of the western Atlantic and Caribbean, is described in the current research as being able to consume algae without completely digesting the chloroplasts.
The slugs, on the other hand, relocate these organelles to their intestines and encapsulate them in what scientists call a “kleptosome.” The organelles that have been stolen are preserved within this unusual slug structure so that photosynthesis can continue.
It seems that the slugs have figured out how to downregulate lysosomes, which are the cell organelles responsible for degrading waste products.
Slug proteins were found in the stolen chloroplasts, according to chemical analysis. It appears that the hosts were maintaining the viability of the stolen organelles. Organelles within the slugs were still actively producing algal proteins, indicating that they were still functioning.
The slugs stored the stolen organelles in what looked like leaves on top of their bodies (essentially a solar panel), and when they were fed enough, they turned greenish in color.
Another oddity was brought to the attention of the researchers when they found that starving slugs took on the color of fall leaves. Digesting the stolen organelles as a “last resort” energy source apparently destroyed the chlorophyll, the green substance within chloroplasts.
The researchers thinks photosynthesis isn’t enough to keep the slugs alive, contrary to what some of the existing scientific literature claims.
Their real purpose may involve considerably more intricacies than just solar panels. These features may function as concealment, food stores, or even to ward off predators. It’s likely a combination of all those factors.
Some significant events in life’s history may be revealed by these little slugs.
An important driver in the emergence of new forms of life has been endosymbiosis. As an example, the cellular organelles responsible for photosynthesis in plants and algae, the chloroplasts, and the energy-producing mitochondria were once free-living cells that were integrated into host cells.
Here is where endosymbiosis often began in systems such as mitochondria in humans and chloroplasts in plants: It was the incorporation of an ancient prokaryotic cell into the host. This is something the slug can accomplish in its lifespan.
Because endosymbiosis took place so long ago—billions of years ago—the proof is long since vanished. Scientists were able to study endosymbiosis in real time when they caught sea slugs stealing organelles.
Sea slugs that steal organelles are not limited to Elysia. The scientists are looking into a different family of sea slugs called Berghia that feeds on sea anemones, digests them, and then uses the venomous barbs as a weapon when they’re threatened.
Additionally, the slug hosts are capable of attaching these stolen organelles to their own neurological systems, allowing them to unleash a “bag full of spear guns.”
The results might have significant consequences, according to the researchers. Neurodegenerative diseases and lysosomal storage disorders are a group of metabolic illnesses characterized by an impaired ability to break down waste products. Understanding how the organelles are regulated may provide light on these disorders.
Lysosomes either fail to develop or don’t function correctly in certain instances, which is similar to how the slugs have evolved.
Sources:
Corey A.H. Allard et al. (2025). A host organelle integrates stolen chloroplasts for animal photosynthesis, Cell. DOI: 10.1016/j.cell.2025.06.003
Some sea slugs consume algae, incorporate photosynthetic parts into their own bodies to keep producing nutrients. https://phys.org/news/2025-06-sea-slugs-consume-algae-incorporate.html
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