CLOWNFISH EVOLUTION · Molecular phylogeny and evolution of specialization in anemonefishes and in their host sea anemones

Final Activity Report Summary - CLOWNFISH EVOLUTION (Molecular phylogeny and evolution of specialization in anemonefishes and in their host sea anemones)

We focussed on a widely speciating group of marine fishes, the so-called anemonefishes, which belonged to the family pomacentridae. All anemonefishes belonged to only two genera, namely amphiprion, with 27 species, and premnas, with one species. The two genera comprised only anemonefishes. These groups of fishes and the tropical sea anemones that hosted them were an astonishing example of extreme specialisation resulting in the evolution of a symbiotic behaviour involving two animal species. Some anemonefishes were specialised to cooperate with a single or few species of sea anemone, being immune to their poisonous tentacles but sensible to those of other species of sea anemones, while other anemonefishes were more generalist and able to live together with a number of different kind of anemones. It would be expectable that the species of anemonefishes most diffuse in terms of space and location were those that were able to be hosted by the widest number of sea anemones. Nevertheless, our results showed that there was not a similar relationship. We analysed the nucleotide sequences for three mitochondrial products, namely the 12S ribosomal deoxyribonucleic acid (DNA), 16S ribosomal DNA and cytochrome B. We found strong support for the monophyly of anemonefish, but not for the separation of the subfamily amphiprioninae, into two subgenera, i.e. premnas and amphiprion. In fact, p. biaculeatus and a. ocellaris and percula had sister taxa in a clade quite basal to, and relatively well separated from, most of the other anemonefish. The most interesting feature was the very well supported basal position of a. latezonatus. This species was only diffused in a very restricted range in Lord Howe Island off eastern Australia. The classic adaptive radiation theory assumed that additional information might be found as the number of species increased. This trend was claimed as being a general evolutionary trend that could be found in virtually every taxon. On the basis of the phylogenetic reconstruction, based on mitochondrial DNA (mtDNA), we investigated the evolution of specialisation in anemonefishes. Contrary to the classic adaptive radiation theory, the reconstructions suggested a specialist as the ancestor of amphiprioninae. The most diffused species was a. clarkii, which was able to live in 10 different species of anemones. In fact, a. clarkii was a very aggressive fish, particularly efficient in defending the anemone from fish that fed on its tentacles, therefore increasing its own possibility of survival and reproductive success. The generalist a. clarkii seemed to be a derived species, while the ancestral anemonefish might have looked like and shared the life style of the extant species a. ocellaris/percula, p. biaculeatus or a. latezonatus.

Data: CORDIS, © European Union