Doctor of Philosophy (PhD)
Reef-building corals are long-lived and may take many centuries to adapt, making them especially susceptible to climate change. However, corals host microbial symbionts that can change quickly, potentially speeding acclimation. My dissertation aimed to determine the degree of coevolution and flexibility between corals and their microbiomes among hosts, across space, and in response to stress.
Microbial communities are usually surveyed by sequencing the 16S rRNA gene, however the PCR primers used also amplify coral DNA, thereby limiting prokaryotic read coverage. To mitigate this contamination, I designed a peptide nucleic acid clamp that increased the recovery of bacterial reads by 2-11x without introducing biases. Next, I examined the co-evolution and plasticity of the microbiomes of two gorgonian hosts with differing levels of genetic subdivision. Within species, the microbiomes were inherited and co-evolved with the host. Some microbes had species-specific lineages, suggesting the potential for co-evolution. However, within species, microbiome flexibility was constrained by the genetic differentiation of the host, mirroring patterns in microalgal symbionts. Lastly, I explored coral microbiomes from near hydrothermal vents, where conditions emulate those predicted under climate change. On- and off-vent coral microbiomes were compositionally and functionally distinct. On-vent microbiomes did not display symptoms typical of microbiomes of stressed corals, suggesting they may have helped acclimate their hosts to the extreme conditions.
My work sheds light on how the compositional and functional flexibility of the coral microbiome can facilitate the adaptation of the coral holobiont to natural and anthropogenically-induced environmental stressors. My findings support the potential for adaptation of coral via their microbial symbionts, but this potential is constrained by the level of genetic differentiation in the host, which directly impacts their flexibility in acquiring a locally-adapted microbiome. However, with successful symbiont shuffling, corals can persist, and even thrive, beyond their typical thresholds presenting a beacon of hope for the resilience of coral reefs under continued climate change.
Parker, Alicia Marie Riegel, "The Roles of Host Species, Geographic Scale and Environmental Stressors in Shaping the Composition of Coral Microbiomes" (2020). LSU Doctoral Dissertations. 5358.
Hellberg, Michael E.