Current models predict the demise of reefs in the next 200 years due to increasing sea surface temperatures and ocean acidification. It is thus essential to identify habitats, taxa and evolutionary mechanisms that will allow some coral species to maintain their role as foundation fauna. The merging of two genomes through hybridization produces a unique combination of traits and phenotypic variation in the hybrids. This phenotypic variation may promote hybrid adaptation to habitats not accessible to the parent species. While hybridization is common in corals, evidence for adaptation to new habitats due to morphological innovation in coral hybrids is missing. In the past, hybridization between Caribbean Acropora palmata (elkhorn) and A. cervicornis (staghorn) corals was rare and restricted to the F1 generation.
Results/Conclusions
New genetic data indicates that hybrids are now mating with each other and are capable of mating with A. palmata and A. cervicornis. In parallel, a variety of intermediate morphologies to the arborescent staghorn and elkhorn shaped parental species are now observed. Here, we conducted morphometric analyses using high-resolution 3D scans and scanning electron microscopy on Caribbean acroporid colonies representing the continuum of phenotypes between A. cervicornis and A. palmata and correlated the data with the genetic origin of the hybrid (i.e. F1, F2 or backcross). Our preliminary results suggest that intermediate morphologies are not restricted to F1 hybrids and putative parental species can be backcross individuals. These data together with recent field observations of higher disease resistance, higher thermal tolerance, higher hybrid abundance, and hybrid habitat expansion suggests that the hybrids’ ecological role and evolutionary potential is changing. Thus, coral hybrids are a possible and probable mechanism for coral adaptation to changing environmental conditions.