Geographic variation and ecological adaptation in Aurelia (Scyphozoa, Semaeostomeae): some implications from molecular phylogenetics

Mitochondrial and nuclear DNA sequence data indicate considerable phylogeographic structure and at least five sibling species of Aurelia in the Pacific Ocean. At least a sixth sibling species can be found in the northwest Atlantic Ocean. These data suggest long histories of geographic and ecological sub-division and divergence of populations, which are inconsistent with current descriptions of Aurelia as a tri-typic genus in which most populations belong to one almost ubiquitous ecological generalist, A. aurita Linnaeus. Existing ecological and systematic descriptions of Aurelia, therefore, should be re-evaluated in light of these molecular data. Reciprocally, such re-evaluations should facilitate interpretation of the molecular data. Here, we introduce new DNA sequence data from Pacific and Black Sea Aurelia and novel ecological data describing tropical Aurelia inhabiting a marine lake in Palau, Micronesia. Despite large genetic distances between temperate and tropical Aurelia and the different environments inhabited by these populations, their rates of feeding, growth, respiration and swimming are similar. We discuss this result in terms of geographic variation and ecological adaptation in Aurelia and also comment on population dynamics, blooms, exotic species and the systematics of Aurelia. Finally, we consider briefly the implications of these findings for other scyphozoan species.