Morphotype is not linked to mitochondrial haplogroups of Caribbean acroporid hybrids

The Caribbean Acropora corals, A. palmata and A. cervicornis form a hybrid with two broad morphotypes, bushy and palmate. These morphotypes were previously hypothesized to be linked to the hybrid’s maternal species. Here, we expand on this hypothesis by adding samples from across the range and by increasing genetic resolution. We reconstructed complete mitochondrial genomes as a proxy for maternal species. This yielded novel A. palmata haplogroups, only one of which was shared by all three taxa. Experts then evaluated photographs to classify corals to a taxon based on colony morphology. Expert classification revealed less accuracy and confidence in hybrid, and surprisingly A. palmata identification compared to A. cervicornis. No association between the bushy morph and mitochondrial haplogroups was found when mapping hybrid morphotypes to the mitogenome phylogeny. Therefore, mitochondrial haplogroup membership is not predictive of Caribbean acroporid hybrid morphology across the range. Additional work is needed to uncover determinants of colony morphology.