Dynamics of Cnidarian-Algal Symbioses

Symbioses between cnidarians and dinoflagellates in the genus Symbiodinium are widespread in the marine environment. Their importance to reef-building corals and reef nutrient cycles is well documented and loss of these symbionts (termed coral bleaching) can lead to reef degradation and coral death. A growing body of research shows that these symbionts are genetically diverse and vary in their response to environmental perturbations. A comparison of symbiont diversity across multiple host taxa and a determination of how flexible symbioses are in response to environmental perturbation are essential to understanding host and symbiont distribution patterns and to identifying the processes critical to maintaining a viable symbiosis. The objective of this project is to examine how Symbiodinium diversity is established and the processes that control the distribution of different taxa of Symbiodinium. This work will identify and compare symbioses characterized by host-symbiont specificity with symbioses that change with environmental conditions. Molecular techniques (microsatellite polymorphic loci, length variation in chloroplast 23S rDNA and sequence analysis of nuclear ribosomal internal transcribed spacer regions) will be used to characterize Symbiodinium diversity in the initial symbionts colonizing planulae as well as diversity of the symbiont complement within single host colonies and within and among host populations and species. Specifically, the "baseline" diversity of Symbiodinium will be determined through population scale surveys of each host species over a range of habitats and the manner in which the symbiont community varies among hosts and across environments assessed. Phylogenetic comparisons of symbionts from closely related hosts will test for co-speciation and population genetic analyses will examine connectivity between Symbiodinium populations. A series of manipulative experiments examining the processes maintaining the variation (or lack there of) observed in the baseline diversity surveys will then be conducted to test the importance of host genotype vs. environment (GxE) in determining the complement of symbiont in the adult host and to characterize the fidelity of symbiont-host partnerships (i.e., specificity vs. flexibility of the symbiosis). Quantitative real-time PCR will be used to quantify the abundance of different symbiont taxa within hosts over time. These data will help to determine if changes in symbiont populations can be induced and if symbionts within a given host reflect host-symbiont specificity, environmental selection among symbionts or stochastic, founder effects. Understanding the dynamics of Symbiodinium has important ramifications for understanding how the symbiosis responds to environmental changes and thus the short and long term responses of reef taxa to climate change. Symbiodinium is a diverse group and if this diversity is widespread within single host colonies or if the association is in a state of continual flux, then changes in host algal community structure can generate changes in functional and physiologic traits of the host-symbiont system. Alternatively host taxa with fixed complements of symbionts would be less able to acclimatize to changing environmental conditions. Broader Impacts: This work will result in the training of at least 2-3 graduate students and at least 8 undergraduates. Through this project these students will have the opportunity to participate in research in both a lab and field setting, learning a range of molecular and algal culturing techniques. Projects based on this proposal will also be introduced in a field course enabling groups of students to design and carry out field studies based on this project. The extensive culture collection housed at the University at Buffalo is an important resource that is available to researchers worldwide. The funding will enable the collection to be maintained and enhanced.