Brooding in the Antarctic: Östergren had it nearly right

The majority of south polar asteroids have nonpelagic development. Nonpelagic development is unusually frequent in the subantarctic islands, where endemism is high. However, species with nonpelagic development are no more frequent at localized sites on the antarctic continental shelf than at most other places in the world. Other groups of south polar echinoderms follow similar patterns. We conclude, in agreement with Ostergren (1912), that neither harsh polar conditions nor poor food conditions are responsible for the high incidence of nonpelagic development in the southern seas. Rather, species with nonpelagic development may be generated by the strong circumantarctic current that flows through the Drake Passage, separating the Magellanic and the Scotia Arc regions. Species with nonpelagic development could be infrequently rafted to adjacent sites in the Scotia Arc, as well as to more distant subantarctic islands and the antarctic continental coastline. Once in a new locality they could speciate in relative isolation. Such a possibility should be tested using molecular and cladistic approaches to follow phylogenetic lineages among selected clades of brooders.