Some animals will go to extraordinary lengths to scale the social ladder, remaining small until an opportunity arises and then changing size and sex to move up a rung, reveal US scientists.
A study of clownfish, an anemone-dwelling marine fish known for its bright orange and white patterning, has found that hierarchical boundaries are so entrenched in their 鈥渃ulture鈥� that subordinates control their size and growth rate to the millimetre. When the position at the top of a group becomes vacant, social climbers will go as far as changing sex.
Clownfish reside in discrete groups dominated by the top- ranking female breeder. Her lower-status male partner is next, followed by up to four progressively smaller and lower- ranking, non-breeding subordinates.
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鈥淲e found that as you go down the social rank, each fish maintains its size at 80 per cent that of the one immediately above it 鈥� if a fish ever grew too close to the size of its superior, it was immediately rejected,鈥� said Peter Buston, who led the research at Cornell University in Ithaca, New York.
When the dominant breeder in a group dies, all the fish move up a social level. The top male changes sex to become the primary female, the top-ranking non-breeding subordinate becomes a sexually active male and all the other subordinates shift up a rank.
Access to food
Buston suggests an evolutionary reason for why the fish stick to their prescribed size: 鈥淚t鈥檚 in order to avoid conflict between a very close-knit social group. Individuals remain together for very long periods of time (tens of years) and this way they can survive in harmony,鈥� he told New 女生小视频.
But Steve Matchett, assistant curator at the National Marine Aquarium in Plymouth, UK, says individual size is linked to food availability.
鈥淚t鈥檚 common sense that a fish lower down in the pecking- order will be more stressed and have less access to food than a dominant one 鈥� that鈥檚 why it is smaller,鈥� he argues.
But Buston insists: 鈥淚f it was simply down to food availability, the fish would not adhere to such a strict 80 per cent size rule between hierarchies. This research shows that modification of size and growth rates can be used as a strategy to resolve conflict within animal societies.鈥�
Journal reference: Nature (vol 424, p 145).
