Molecular phylogenetic evidence for the evolution of specialization in anemone®shes

Anemone¢shes (genera: Amphiprion and Premnas; family Pomacentridae) are a group of 28 species of coral reef ¢shes that are found in obligate symbiosis with large tropical sea anemones. A phylogenetic hypothesis based on morphological analyses of this group suggests that the ancestral anemone¢sh was a generalist with similar morphology to other pomacentrids, and that it gave rise to other anemone¢sh species that were more specialized for living with particular species of host anemones. To test this hypothesis we constructed a molecular phylogeny for the anemone¢shes by sequencing 1140 base pairs of the cytochrome b gene and 522 base pairs of the 16S rRNA gene for six species of anemone¢shes (representatives of all subgenera and species complexes) and two other pomacentrid species. Three methods of phylogenetic analysis all strongly supported the conclusion that anemone¢shes are a monophyletic group. The molecular phylogeny di¡ers from the tree based on morphological data in that the two species of specialized anemone¢shes (Premnas biaculeatus and Amphiprion ocellaris) were assigned to a basal position within the clade, and the extreme host generalist (Amphiprion clarkii) to a more derived position. Thus, the initial anemone¢sh ancestors were probably host specialists and subsequent speciation events led to a combination of generalist and specialist groups. Further phylogenetic studies of additional anemone¢sh species are required to substantiate this hypothesis.