70.1 Friday, Jan. 6 Determining the benefits of symbiosis: tracing the products of symbiont nitrogen and carbon metabolism to host sponges using incubations with enriched stable isotopes FREEMAN, Christopher/J*; THACKER, Robert/W; BAKER, David/M; FOGEL , Marilyn; Univ. of Alabama, Birmingham; Univ. of Alabama, Birmingham; Carnegie Institution of Washington; Carnegie Institution of Washington email@example.com
While some marine sponges host microbial communities that might confer supplemental nutrition crucial to host survival,our understanding of how these interactions benefit the host is still limited. To assess the transfer of symbiont nitrogen and carbon across the species Aplysina cauliformis, Aplysina fulva, Chondrilla nucula, Neopetrosia subtriangularis, and Xestospongia bocatorensis, which host abundant microbial populations, and Niphates erecta, which lacks symbionts, we conducted light-dark bottle incubations using seawater laced with inorganic compounds enriched in 15N and 13C followed by the isolation of sponge and microbial cell fractions from bulk sponge tissue prior to isotope analysis. Since these compounds can only be taken up by microbial symbionts, 15N and 13C enrichment of the sponge fraction is due to the transfer of enriched biomolecules produced by the symbiont. Enrichment of 15N and 13C was highest in sponges hosting dense communities of microbial symbionts and was directly related to the photosynthesis / respiration ratio of each species, suggesting that nutrient uptake and transfer is dependent on the productivity of the symbiosis. In a second experiment, we incubated Aplysina cauliformis in 4 treatments (full light, low shade, high shade, and dark) with enriched 13C tracer. While the 13C enrichment of microbial and sponge cell fractions was highest in the full light treatment, the nutritional interaction between symbiont and host remained stable across all treatments. Together these studies provide compelling evidence supporting the contention that hosting dense communities of microbial symbionts provides the host with access to products of novel microbial metabolic pathways.