Mitogenomics reveals low variation within a trigeneric complex of black corals from the North Pacific Ocean

A 2013 study revealed that three morphologically distinct antipatharian genera ( Dendrobathypathes , Lillipathes , Parantipathes ) from the eastern North Pacific (ENP) are genetically indistinguishable using three mitochondrial and four nuclear markers (7,203 bp). To investigate whether this lack of molecular variability extends beyond three mitochondrial genes, we sequenced the complete mitogenome of a single representative within each genus. Dendrobathypathes was the only specimen from the 2013 study containing high molecular weight (HMW) DNA. In terms of geographic proximity to the ENP, the closest Lillipathes and Parantipathes yielding HMW DNA were from the central North Pacific near Hawai'i. Based on cox3 -IGR- cox1 , Lillipathes and Parantipathes each contained two variable sites and thus were not equivalent substitutes for specimens from the ENP. Nonetheless, variation was extremely low when comparing the mitogenomes, with 32 variable positions across 17,687 bp. Pairwise comparisons revealed 18 ( Dendrobathypathes and Parantipathes ) and 23 ( Lillipathes and Parantipathes; Lillipathes and Dendrobathypathes ) variable sites. An ML-based phylogenetic reconstruction using 13 protein-coding genes and two rRNAs revealed that the three North Pacific genera grouped in a clade with Atlantic Dendrobathypathes , while Atlantic Parantipathes spp. formed a sister clade. Previous research hypothesized that hybridization with subsequent introgression was responsible for the lack of variability among genera. Due to uniparental inheritance and lack of recombination, mtDNA cannot identify hybrids; however, finding Pacific Parantipathes grouping with Dendrobathypathes and Lillipathes rather than Atlantic Parantipathes suggests that the trigeneric complex has a unique evolutionary history. If high-resolution nuclear markers support hybridization, it will be important to elucidate the molecular mechanism that maintains three distinct morphological forms occurring in sympatry.