CURTIS*, N. E.; MASSEY, S. E.; PIERCE, S. K.; Univ. of South Florida; Univ. of South Florida; Univ. of South Florida: The algal source of symbiotic chloroplasts in Elysia crispata is not Caulerpa

The sacoglossan sea slug, Elysia crispata, sequesters chloroplasts from algal food sources in cells that line the digestive diverticula. The captured chloroplasts can photosynthesize for up to four months. Both plastid-encoded and nuclear-encoded chloroplast proteins are synthesized while the plastids reside in the slug cell, and at least one algal gene is present in the slug genomic DNA. One difficulty in identifying other transferred algal genes is that the algal source of the plastids is unknown. While literature indicates that E. crispata feeds on several species of Caulerpa, our own observations indicate that is almost certainly wrong. In the laboratory, both adult and juvenile E. crispata did not feed on any of several species of Caulerpa. We have identified the source of the symbiotic chloroplasts by PCR amplification of the chloroplast rbcL gene from E. crispata. These results indicate that E. crispata sequesters chloroplasts from the chlorophytic algae Penicillus capitatus and Halimeda incrassata. Thus, the symbiosis is less specific than may be the case in most other kleptoplastic slugs. In addition, since other species of Elysia are being considered as bio-control agents for Caulerpa infestations in the Mediterranean and elsewhere, our results suggest that testing the slugs for chloroplast origins with molecular markers is necessary to definitively identify algal food sources. (NSF grant # IBN 0315227)