Phenotypic and mtDNA variation in Philippine Kappaphycus cottonii (Gigartinales, Rhodophyta)

Members of the carrageenan-producing seaweeds of the genus Kappapphycus have a complicated taxonomic history particularly with regard to species identification. Many taxonomic challenges in this group have been currently addressed with the use of mtDNA sequences. The phylogenetic status and genetic diversity of one of the lesser known species, Kappaphycus cottonii, have repeatedly come into question. This study explored the genetic variation in Philippine K. cottonii using the mtDNA COI-5P gene and cox2-3 spacer sequences. The six phenotypic forms in K. cottonii did not correspond to the observed genetic variability; hinting at the greater involvement of environmental factors in determining changes to the morphology of this alga. Our results revealed that the Philippine K. cottonii has the richest number of haplotypes that have been detected, so far, for any Kappaphycus species. Our inferred phylogenetic trees suggested two lineages: a lineage, which exclusively includes K. cottonii and another lineage comprising the four known Kappaphycus species: K. alvarezii, K. inermis, K. malesianus, and K. striatus. The dichotomy supports the apparent synamorphy for each of these lineages (the strictly terete thalli, lack of protuberances, and the presence of a hyphal central core in the latter group, while the opposite of these morphologies in K. cottonii). These findings shed new light on understanding the evolutionary history of the genus. Assessing the breadth of the phenotypic and genetic variation in K. cottonii has implications for the conservation and management of the overall Kappaphycus genetic resources, especially in the Philippines.