Patiriella pseudoexigua (Asteroidea: Asterinidae): a cryptic species complex revealed by molecular and embryological analyses

Abstract

Cryptic lineages were identified within a morphologically uniform group of sea stars distributed from Australia to Japan. Among eight populations, all of which have been referred to Patiriella pseudoexigua, we found seven unique mitochondrial DNA sequences clustered into four distinct lineages. These four lineages formed a monophyletic group in which sister clades were separated by small genetic distances but could be differentiated from each other on the basis of reproductive differences. The four lineages thus appear to be separate but very closely related species. Examination of reproduction in several Queensland populations revealed that one population (Statue Bay) consisted of hermaphroditic intragonadal brooders with live-born offspring while other populations (Townsville, Bowen, Airlie Beach) consisted of dioecious free-spawners with a planktonic larva. The brooded larvae from central Queensland populations closely resembled brooded embryos and larvae of a Japanese lineage, while the planktonic larvae from northern Queensland were similar to the original description of planktonic larvae from a Taiwan population. However, each of the viviparous lineages was more closely related to a lineage with planktonic larval development than the viviparous lineages were to each other. Patiriella pseudoexigua thus comprises at least four species with different reproductive phenotypes in which viviparous brooding appears to have evolved in parallel. Based on previous taxonomic work we propose the following names for these four lineages: the dioecious free-spawner from northern Queensland (including the P. pseudoexigua type locality) is P. pseudoexiguasensu stricto; the viviparous brooder from central Queensland is undescribed and here referred to as Patiriella sp. nov; the dioecious free-spawner from Taiwan is temporarily referred to as Patiriella sp. (a senior name for this species may be P. pentagonus); and the hermaphrodite brooder from Japan should be raised to specific status and referred to by the new combination P. pacifica.