Meeting Abstract

16.4  Jan. 4  Host-Specificity of Sponge-Associated Unicellular Cyanobacteria, Candidatus Synechococcus spongiarum ERWIN, P. M.*; THACKER, R. W.; University of Alabama at Birmingham; University of Alabama at Birmingham erwin@uab.edu

Tropical and temperature marine sponges worldwide commonly associate with a unique lineage of symbiotic, unicellular cyanobacteria in the genus Synechococcus. These symbionts may benefit their host sponges through the provision of fixed carbon, the production of chemical defenses, and protection from UV radiation. Previous molecular analyses of these symbionts using 16S ribosomal RNA (rRNA) gene sequences suggested a generalist host-symbiont association with little genetic differentiation, despite evidence for vertical transmission. To further investigate the genetic diversity and host-specificity of these symbionts, we characterized partial 16S rRNA and entire internal transcribed spacer (ITS) rRNA gene sequences from cyanobacterial symbionts of 32 sponge individuals, representing 18 species from Caribbean, North Atlantic, Pacific, and Mediterranean reefs. ITS sequence data exhibited 4 to 5 times the variability of 16S sequence data and resulted in a well-resolved phylogenetic tree that revealed 12 distinct symbiont clades defined by reciprocal monophyly and >5% sequence divergence among sister clades. Most symbiont clades displayed a high degree of host-specificity at the genus and species level; however, some clades were associated with taxonomically distant but sympatric host species. In several host species, multiple symbiont clades were identified from a single individual. Our results show the phylogenetic utility of ITS rRNA sequence data in resolving the fine-scale relationships and host-specificity of sponge-associated cyanobacteria. Genetic differentiation of symbiont clades may be correlated with variable physiological capabilities and environmental preferences of the symbionts, and thus variable benefits to their host sponges.