USF finds sea slugs can live on sunlight, like plants

Part animal, part plant! This may sound like a tabloid headline, but scientists at the University of South Florida showed this month 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 handful of slugs, including the leaf-shaped Elysia chlorotica, could eat algae but save the algae's chloroplasts from digestion, and feed off of the remaining energy from the chloroplasts. Chloroplasts are where photosynthesis occurs - that is, the plant process of turning light into energy.

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

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

USF scientists 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 University of California, 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 the salt marshes of New England and Canada, passes these genes on to its offspring. Upon hatching, the babies need one last ingredient to make the whole system work: chloroplasts (the slugs don't have the genetic instructions to produce the chloroplasts on their own). All a young slug has to do to get such instructions, however, is have a big meal of algae.

Once the chloroplasts are in the green sea slug's system, the slug is capable of making its own food out of light. It might never have to forage for algae again, said Sidney K. Pierce, a USF biology professor who presented the findings Jan. 7 at the annual meeting for the Society for Integrative and Comparative Biology.

The slugs' success at grabbing genes from another species - and incorporating them biologically - without waiting for evolutionary providence could help unlock key advancements in genetic technology, Pierce said.

"Probably no one cares about slug biology except me and a few other people in the whole world," Pierce said. "But this whole idea of gene transfer is enormously important. If we can figure this out, it may help with not only genetic engineering, but gene therapy down the road."