Assisted Gene Flow Yields Physiologically Robust Acropora palmata With Novel Allelic and Transcriptomic Profiles

Assisted gene flow (AGF) is a conservation approach that facilitates the spread of alleles and may accelerate the recovery of genetically depauperate populations. The threatened Caribbean coral Acropora palmata is approaching regional extinction within the western Atlantic partly due to increasing water temperatures associated with global climate change. Previously, AGF was conducted by crossing gametes collected from three regions (Curaçao-CU, Florida-FL, and Puerto Rico-PR) characterized by contrasting temperature regimes and low gene flow among them. Here, we compared the physiology of these AGF cohorts in comparison to purebred Florida and Curaçao cohorts under ambient and high temperature conditions. Exposure to high temperatures resulted in few physiological changes, likely because the corals hosted the thermally tolerant algal symbiont, Durusdinium trenchii. However, the purebred cohorts grew significantly faster than both AGF cohorts. Like the phenotypic responses, gene expression changes in response to heat stress were muted overall. However, AGF cohorts deviated from the expected mid-parent value across dozens of genes, representing novel gene expression patterns. Importantly, AGF crosses harbored 879 private alleles that were previously not recovered in representative genets from Florida. These findings suggest that corals created using AGF have similar physiology to purebreds, carry novel alleles, and represent novel gene expression patterns that carry important conservation values which could be integrated into the functionally extinct A. palmata population in Florida.