PARENT SESSION
OOS 1: Genetic Explorations of the Seascape: Using Molecules and Experiments to Understand Marine Biodiversity.
Organized by: E Sotka and R Thacker
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 141 .
Relationships between host-specificity and the strength of mutualisms: Molecular and ecological approaches to sponge-cyanobacteria symbioses.
Thacker, Robert*,1, 1 University of Alabama at Birmingham, Birmingham, AL
ABSTRACT- Cyanobacterial symbionts of marine sponges have only recently been investigated using molecular techniques. These investigations have revealed that these symbionts can be specialists restricted to a single host species or generalists found in multiple host species. For example, each sponge species in the Lamellodysidea/Dysidea complex hosts a genetically distinct clade of the filamentous cyanobacterium Oscillatoria spongeliae. In contrast, a single clade of the unicellular cyanobacterium Synechococcus spongiarum has been reported from a broadly diverse group of sponges, including Xestospongia exigua. Cyanobacteria may benefit their hosts by fixing carbon or nitrogen that is subsequently acquired by the host sponge. The impacts of symbiotic cyanobacteria on host sponge metabolism can be manipulated by shading, which reduces cyanobacterial photosynthesis. During field experiments in Guam and Palau, shaded L. herbacea and L. chlorea dramatically lost mass. These results suggest that Oscillatoria symbionts benefit their host sponges, with the host sponge gaining more nutrition from photosynthesis than by feeding from the water column. Despite the large mass loss, cyanobacterial abundance did not change, indicating that these symbiont do not disperse and are not consumed. In contrast, shaded X. exigua did not change in mass, but showed decreased cyanobacterial abundance. Synechococcus symbionts may be commensals that exploit the resources provided by their sponge hosts without affecting sponge growth; these symbionts may disperse or may be consumed under adverse environmental conditions. These results agree with co-evolutionary theories that predict specialist symbionts to have stronger effects on their hosts than generalists, particularly if specialists have limited dispersal abilities.
Key words: cyanobacteria, coevolution, sponge, mutualism