Study shows why some wrasses clean

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The evolution of cleaning in wrasses is not linked to their size as previously suggested.

According to the results of a new study, which has just been published in the Journal of Evolutionary Biology, the reason why some wrasses evolve to become cleaner fishes is related to colour, not to size.

Previous studies have hypothesised that small size and colour pattern might be prerequisites for cleaning the parasites off other fish species.

To test the theory, Arnal, Verneau and Desdevises sequenced parts of the ribosomal RNA gene sequences of 32 different species of labrid found across the Indo Pacific, Atlantic and Mediterranean, to try and look for clues in their genetics.

In order to link the molecular data with the phenotypic characteristics of the fish, they also recorded the size and shape of the fishes' bodies, and used a sophisticated computational analysis to try and identify links between the two.

The results show that there is no link between either body size or shape, but there is a correlation between the presence of cleaning behaviour and the presence of a dark lateral stripe in wrasses, such as the Cleaner wrasse, Labroides dimidiatus.

The team believes that it is the presence of this distinctive stripe that determines the evolution of cleaning behaviour in these fish.

For more information see the paper: Arnal C, Verneau O and Y Desdevises (2006) - Phylogenetic relationships and evolution of cleaning behaviour in the family Labridae: importance of body colour pattern. Journal of Evolutionary Biology 19: 755-763.