Green sea slugs use plant genes to live on sunlight

Part animal, part plant! This may sound like a tabloid headline, but scientists say that a green sea slug has managed to incorporate enough algae parts to easily live off of sunlight, just as a plant does.

Scientists already knew that a few slugs could eat algae but save the algae’s chloroplasts from digestion and feed off of their energy. Chloroplasts are where the photosynthesis process of turning light into energy occurs.

But this was not a self-sustaining system, since most slugs cannot make their own chlorophyll, a green pigment that fuels the chloroplasts. To get more chlorophyll, the slugs would have to eat more algae.

The green sea slug, however, can make its own chlorophyll.

Scientists at the University of South Florida have identified several algae genes within the slug’s body that are crucial to photosynthesis.

“This is the ultimate in horizontal gene transfer,” said Terry Gaasterland, a UC San Diego professor and director of the Scripps Genome Center, who was not involved in the study.

Once it incorporates algae genes into its system, the green sea slug, which lives in salt marshes in New England and Canada, passes the genes on to its offspring. The babies need chloroplasts to make the system work (the slugs don’t have the genetic instructions to produce them on their own). But all a young slug has to do to acquire such instructions is have a big meal of algae. Once the chloroplasts are in its system, the slug can make food out of light. It might never have to forage for algae again, said Sidney K. Pierce, a University of South Florida biology professor.

The slugs’ success at biologically incorporating another species’ genes could help unlock key advancements in genetic technology, Pierce said.

“This whole idea of gene transfer is enormously important,” said Pierce, who presented the findings Jan. 7 at a meeting of the Society for Integrative and Comparative Biology.

“If we can figure this out, it may help with not only genetic engineering, but gene therapy.”