SPONGE MUTUALISM IN THE FACE OF CLIMATE CHANGE
Hill, Russell T
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Three epizoic symbioses between new sponge species of the genera Plakortis, Haliclona, and Xestospongia deweerdtae are reported here. Barcoding of the cytochrome oxidase subunit 1, 28S rRNA and 18S rRNA genes allowed me to formally describe the Plakortis spp. as P. deweerdtaephila and P. symbiotica. Both Plakortis spp. are obligate hosts of the sponge X. deweerdtae. Unlike Plakortis spp., X. deweerdtae can have a free-living lifestyle. This discovery motivated me to: 1) Use next-generation sequencing to ask whether microbial symbionts are playing a role in shaping these sponge associations; 2) Evaluate how top-down factors influence these associations by analyzing crude extracts of each species by LCMS and determine their palatability to fish to test if chemical defenses from Plakortis spp. translocate into the Xestospongia tissue, and protect it from predation, and 3) Test whether the X. deweerdtae and P. deweerdtaephila sponge pairs in Panama are more resilient than free-living X. deweerdtae in the face of climate change. My results on bacterial and sponge cell counts revealed that Plakortis spp. are high microbial abundance sponges and that X. deweerdtae and H. plakophila are low microbial abundance sponges. Diversity indices showed no differences in microbial richness but a higher Simpson’s index (D) for Plakortis spp. than both epibionts. Microbial community shifts in X. deweerdtae epibionts not observed in the free-living lifestyle were a consequence of the presence of microbial phyla found in the Plakortis spp. basibiont, suggesting the possibility of horizontal transfer of symbionts from the basibiont to the epibiont. Crude extracts from tissues of both free-living and associated lifestyles of X. deweerdtae confer chemical defense. These results suggest that top-down predation pressures from reef fish do not influence the associated life-style of X. deweerdtae. Exposure to high pCO2 and warmer temperature revealed that acidification had an ameliorating effect against necrosis caused by high temperatures in free-living and associated individuals of X. deweerdtae as well as their P. deweerdtaephila basibiont. The X. deweerdtae epibiont was more resistant to temperature increments than P. deweerdtaephila. I performed a similar experiment on an invasive Hawaiian sponge Mycale grandis and discovered that neither acidification nor temperature affect skeleton synthesis. Taken together these findings suggest that these symbioses are mutualistic in nature and that sponges are likely to survive the predicted temperature and pCO2 conditions for the end of the century.