Meeting Abstract
Broadcast-spawning coral species have wide geographic ranges, spanning strong environmental gradients, but it is unclear how much spatially varying selection these gradients actually impose. Strong divergent selection might present a considerable barrier for demographic exchange between disparate reef habitats. We investigated whether the cross-shelf gradient (nearshore – offshore – deep) is associated with spatially varying selection in two common coral species, Montastraea cavernosa and Siderastrea siderea, in the Florida Keys. We used 2bRAD to genotype 20 juveniles and 20 adults from each of the three reef zones across two cross-shelf transects to identify signatures of selection occurring within a single generation. Preliminary results from the first transect revealed unexpected results. Each species was found to be composed of four to five genetically distinct subpopulations, with gene flow between them highly reduced in 30-50% of the genome. Each species includes two sympatric populations that are only found in the deep (20 m) habitat, while the other populations are found almost exclusively on the shallower reefs (3-7 m). Here, we compare these initial findings with data from a second cross-shelf transect to investigate possible along-shore variability in the patterns environmental specialization and to establish whether cryptic genetic subdivision in these two coral species may be a general feature throughout the Florida Keys. Siderastrea siderea and M. cavernosa have emerged as two of the most ecologically successful species on the degraded Florida Keys Reef Tract, and this work offers important insight on the genomic background of divergent selection and speciation that may in part explain their broad environmental range in this ecosystem.
