Disentangling genetics and environment to optimize reef restoration in a changing climate

Background/Question/Methods

Genotype-by-environment interactions (GxE) indicate that variation in organismal traits cannot be explained by fixed effects of genetics or site-specific plastic responses alone. For tropical coral reefs experiencing dramatic environmental change, identifying the contributions of genotype, environment, and GxE on coral performance will be vital for both predicting persistence and developing restoration strategies. We quantified the impacts of G, E, and GxE on the morphology and survival of the endangered coral, A. cervicornis, through an in situ transplant experiment exposing common garden (nursery) raised clones of ten genotypes to nine reef sites in the Florida Keys. Outplants were fate-tracked over one year with colony-level 3D photogrammetry to measure changes in growth, morphology, and survival. Coral mucus was sampled in the nursery prior to outplanting (T12) and again one year later from surviving ramets (T12). 16S rRNA amplicon sequencing was used to assess changes in epibiotic microbial composition, richness, and beta-diversity.

Results/Conclusions

We uncovered significant GxE on coral size and survivorship indicating that no universal winner exists in terms of colony performance. Moreover, the presence of GxE also implies the existence of intraspecific variation in phenotypic plasticity. Rather than differences in mean trait values, we find that individual-level morphological plasticity is adaptive in that the most plastic individuals also exhibited the fastest growth and highest survival. This indicates that adaptive morphological plasticity may continue to evolve, influencing the success of A. cervicornis and resulting reef communities in a changing climate. The relative abundances of two dominant bacterial taxa Midichloriaceae (MD3-55 genus) and Cyanobacteria (Synechococccus) varied consistently between host genotypes, whereas neither the composition nor taxonomic relative abundance were significantly different among field sites. Several high MD3-55 hosting genotypes showed rapid diversification and an increase in MD3-55 following transplantation. Results indicate healthy A. cervicornis genotypes retain distinct epibiome signatures through time. As focal reefs are active restoration sites, this knowledge can be directly applied to restoration planning. Taken together, these results establish A. cervicornis as a system for studying the eco-evolutionary dynamics of phenotypic plasticity that also can inform genetic- and environment-based strategies for coral restoration.