| Coral reefs harbor some of the most diverse communities in the world and provide benefits to human societies. Their success has been attributed to the symbiosis of the holobiont (scleractinian corals, Symbiodinium or zooxanthellae, and a prokaryotic community). Projects improving our knowledge of the different players are crucial to preserve this globally-threatened ecosystem. The use of molecular techniques has aided in the identification of the enormous genetic diversity of Symbiodinium. I evaluated the use of an alternative technique, high-resolution melting (HRM), to genotype Symbiodinium types based on ITS region 2 (ITS2). Results showed successful genotyping using HRM analysis. HRM is advantageous because no expertise in molecular methods is required. Another important area of research in coral reef biology is the study of free-living Symbiodinium. More than 80% of reef corals that engage in symbiosis have to acquire Symbiodinium de novo each generation from an environmental pool of the symbiont. Different habitats were sampled in Curacao during three sampling periods to identify free-living Symbiodinium populations. Clades A- C, F- H were identified using the chloroplast marker 23S-HVR. Log-linear modeling and non-metric multidimensional scaling showed the importance of habitat and, to a lesser degree season to explain the observed patterns. I also investigated the evolutionary relationships between members of the genus Symbiodinium. Phylogenetic inferences have been mainly carried out using ribosomal DNA (rDNA), which may result in incorrect reconstructions. I used partial sequences of the 70 kDa heat shock protein (hsp70) to infer phylogenetic relationships among Symbiodinium types. Hsp70 phylogenetic inference resulted in a new evolutionary hypothesis. The contrasting results may reflect a complicated evolutionary history of Symbiodinium. Finally, survival of corals also depends on their ability to respond to different stressors. One way corals may persist is by exhibiting transcriptional variation upon which natural selection can act. I analyzed gene expression variation under natural conditions in the reef-coral Acropora millepora. After controlling for environmental factors, a large proportion of genes were differentially expressed between colonies. However, whether these genetic variations combined with epigenetic modifications will allow corals to cope with the rapid pace of global change remains unknown. |
