Scientists from Spain and the USA have found that clownfish groups living in a single anemone are not close relatives.
Publishing their results in a recent issue of the journal Molecular Ecology, Peter Buston, Steven Bogdanowicz, Alex Wong and Richard Harrison studied a population of the clown anemonefish, Amphiprion percula, in Madang Lagoon in Papua New Guinea.
Amphiprion percula lives in groups composed of a breeding pair and zero to four non-breeders.
The scientists analyzed the relatedness of 32 individuals from nine groups using seven polymorphic microsatellite DNA loci, and found that the members within a group were not closely related at all (the probability that two individuals from the same group share an allele is the same as that of two individuals from the same reef sharing the allele).
Although it is logical to assume that both breeders and non-breeders stand to gain by associating with relatives (breeders might prefer to tolerate non-breeders that are relatives because there is little chance that relatives will survive to breed elsewhere; non-breeders might prefer to associate with breeders that are relatives because of the potential to accrue indirect genetic benefits by enhancing anemone and, consequently, breeder fitness), the results indicate otherwise.
There are two possible explanations for this discrepancy: one is that the deleterious effects of inbreeding makes it difficult to initiate such a breeding system, especially when there is no lack of recruits from other sources; the other, more important, explanation is that the high cost associated with searching for a new anemone to colonise selects against young fish leaving their natal anemone to return to it (i.e. settlers probably do best to remain at the first anemone they encounter, regardless of the number or identity of residents).
For more information, see the paper: Buston, PM, SM Bogdanowicz, A Wong and RG Harrison (2007). Are clownfish groups composed of close relatives? An analysis of microsatellite DNA variation in Amphiprion percula. Molecular Ecology 16, pp. 3671"3678.