Meeting Abstract

P3.189  Friday, Jan. 6  Examination of genetic regulation of Symbiodinium uptake and the morphological development of the zooxanthella-dense pinadocerm in the sponge Cliona varians. STREHLOW, B*; MCCAULEY, M; RICHARDSON, C; PETERSON, K; COTMAN, C; HILL, A; HILL, M; Univ. Richmond; Univ. Mississippi; Univ. Viriginia; Univ. Richmond; Univ. Richmond; Univ. Richmond; Univ. Richmond mhill2@richmond.edu

Several species of sponge harbor intracellular populations of zooxanthellae. The dinoflagellates are primarily located in pinacoderm exposed to light. The processes that produce this spatial distribution are unknown. We used Cliona varians forma varians to examine the establishment and spatial development of zooxanthella populations under natural field conditions. To create aposymbiotic tissue, pinacoderm was removed from C. varians, and the choanosome was placed in a light-tight container for 2 months. Explants of the aposymbiotic sponges were attached to CaCO₃ blocks, allowed to heal in the dark for another week, and were then placed in 1 m of water in the flats on the ocean side of Summerland Key. Tissue was sampled every other day for approximately 120 days to examine natural reinfection dynamics. Cryosectioned replicates indicated that sponges remained nearly devoid of zooxanthellae for nearly two weeks, but at some point after 12 days, the zooxanthella populations began to increase rapidly within the sponge. We examined parameters including symbiont density, symbiont position within the sponge, cladal identity of zooxanthellae, and chlorophyll concentration. We also experimentally reinfected aposymbiotic tissue to elucidate patterns in gene expression during the initiation and maintenance of the symbiosis. We used suppressive subtractive hybridization techniques to identify genes involved in zooxanthalla uptake by aposymbiotic C. varians. Our work shows that genes involved in phagocytosis, the immune system, and various cell-signaling pathways are regulated during reinfection of sponge tissue. This system provides opportunities to identify commonalities in the pathways that zooxanthellae utilize to gain entry into host cells.