Size does matter to sex-changing clownfish
Size does matter, especially if you are an aspiring clownfish: a U.S. researcher has discovered that male clownfish grow bigger and change sex if the breeding female is absent.
Clownfish, or Amphiprion percula, live in tropical waters worldwide. In the Madang Lagoon of Papua New Guinea, groups live among sea anemones, which help protect them from predators. Each group consists of a breeding pair and up to four non-breeders.
In these groups, the status of an individual is determined by its size. The largest of the group is the breeding female, followed in size by the breeding male, with the remaining non-breeders getting smaller as their rank decreases.
He removed the breeding female from one group to see what would happen. In the group, every fish grew and moved up a rank, with the male breeder - the second-largest - growing larger and then turning into a female. The largest of the non-breeders in turn grew, and then turned into the male breeder.
Buston suggests that the strategy may have evolved to prevent conflict between group members, because it ensures that subordinates do not become a threat to their dominants.
The group arrangement is advantageous to non-breeders, who have the chance of moving up the chain; but it is not so good for the breeding pair as the non-breeders can be a threat if they get too large. Breeders sometimes kill or evict non-breeders that have grown to a similar size as the breeders.
These results indicate that the growth rate and size adopted by animals that live in groups can be a strategic response to their social environment. By comparison, in other group situations, animals modify their behaviour within the group instead.