Plastid Turn Over in Sacoglossan Sea Slug, Elysia timida

Undergraduate #7
Discipline: Biological Sciences
Subcategory: Cell and Molecular Biology

Thien Crisanto - Humboldt State University

Photosynthetic symbiosis exists in several underwater organisms including sacoglossans, or sap-sucking, sea slugs. These sea slugs are capable of stealing the chloroplasts, or plastids, from the algae that they eat in a process called kleptoplasty. The slugs contain the only animal cells known to house functional plastids, and can store them in their digestive epithelial cells for many months.

Elysia timida is a sacoglossan from the Mediterranean Sea near Italy. It is one of the few species of sacoglossans known to eat two different algal species, Acetabulum acetabularia and Acetabulum peniculus. Elysia timida was used to test the hypothesis that the turnover of A. acetabularia to A. peniculus within the slug would occur in the first few hours after feeding. At 5 different time points, E. timida was fed exclusively A. acetabularia and then A. peniculus. PCR (Polymerase Chain Reaction) was used to amplify primers AaChi1 for A.
acetabularia, and Aprbcl_2 for A. peniculus, in order to observe the presence of algal DNA within the slug. The fluorescence intensity of the gels were measured using ImageJ. The findings indicated that the presence of A. acetabularia fades from the slugs’ DNA, and is replaced by A. peniculus within the first few hours after feeding. A. acetabularia continued to fade over the 10 day time frame. By studying the slugs, we will be able to learn about the evolutionary benefits of the slug-plastid symbiosis and examine the symbiotic interaction on a molecular level. Further investigation will include designing new primers for the PCR, quantifying the results using qPCR (Quantitative Polymerase Chain Reaction), and conducting the feeding experiment over a longer period of time.

Funder Acknowledgement(s): This study was supported by a travel scholarship from HSU-LSAMP (grant #HRD-1302873) awarded to Thien Crisanto. I would like to thank C. Rauch, J. De Vries, Dr. S. Gould, and Dr. B. Martin, of the Institute for Molecular Evolution in Düsseldorf, Germany, for allowing me to work in their lab and join in their study of sacoglossans.

Faculty Advisor: Bruce O'Gara.,