A bright green sea slug is that color because it has "stolen" a gene from the algae it feeds that lets it live more like a plant and get the energy it requires from sunlight, researchers say.
Like a leaf -- and very much not like a usual sea slug -- Elysia Chlorotica can absorb carbon dioxide, and go for months without food as long as there is sufficient light for the creature to get the energy it needs from photosynthesis, they say.
In addition to the hijacked gene, the slug takes in chloroplasts -- specialized cell parts involved in photosynthesis -- from its algae diet of Vaucheria litorea and then incorporates them into its own digestive cells.
The chloroplasts, seemingly unaware that they're not where they're supposed to be, keep performing their photosynthesis duties, helping feed the sea slug for as long as 9 months.
That's something that has puzzled scientist for a long time, because 9 months is longer than such choloplasts ever appear to function inside the algae they come from.
It's all down to that stolen gene, researchers have discovered; it plays a key role in sustaining photosynthesis by producing a vital enzyme that can repair damaged chloroplasts and keep them working.
And that theft is not a one-shot deal, they've found.
"The gene is incorporated into the slug chromosome and transmitted to the next generation of slugs," says study co-author Sidney K. Pierce, an emeritus professor at both the University of South Florida and the University of Maryland.
The next generation will still need to steal their own chloroplasts from the algae they eat, the researchers explain, but the passed-down gene is already present in the slug's genome and ready to go to work.
This strange connection between algae and sea slug comes as a surprise, the researchers report in the journal Biological Bulletin.
"There is no way on Earth that genes from an alga should work inside an animal cell," says Pierce. "And yet here, they do. They allow the animal to rely on sunshine for its nutrition. So if something happens to their food source, they have a way of not starving to death until they find more algae to eat."
This extremely rare example of genetic transfer between two multicellular species could have relevance to research into human gene therapy and could lead to better understanding of genetic diseases and potential treatments for them, the researchers say.
"Figuring out the mechanism of this naturally occurring gene transfer could be extremely instructive for future medical applications," Pierce says.
