Meeting Abstract
In many freshwater habitats, Chlorella spp. form intracellular symbioses with a variety of heterotrophic host taxa including several species of freshwater sponge. The facultative nature of the sponge:Chlorella association offers opportunities to identify factors that permit long-term residency within organelles, and to discern pathways that allow the algae to avoid the host’s digestive response. Freshwater sponges also offer many tractable qualities of a model system to study features of intracellular occupancy. Here, we describe how we isolated, cultured, and cared for sponge-derived Chlorella, and how we obtained, curated, and grew Ephydatia gemmules. We also describe how we used the emergent sponges in experiments to test hypotheses about Chlorella symbioses. The fate of Chlorella populations was followed after inoculating algae-free E. mülleri and E. fluviatilis under different experimental conditions. Furthermore, we present RNASeq data on differential gene expression observed in E. mülleri exposed to bacteria, heat-killed Chlorella, and live Chlorella. We discuss this work in light of growing interest in the evolution of specificity between hosts and symbionts, the stability of algal populations in heterotrophic hosts, and the fundamental and realized niche of phototrohpic algae.
