Colour drives hamlet speciation

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Researchers from Panama, Canada and the UK have demonstrated for the first time that colouration in coral reef fish can cause diversification in species.

The team of scientists from the Neotropical Environment Option (NEO), which comprises researchers from McGill University and the Smithsonian Tropical Research Institute (STRI), found that differences in behavioural patterns - spurred by the fishes colouration - can trigger the evolution of new species.

The NEO research team carried out their study on the serranid hamlet fish, Hypoplectrus spp., of which there are 13 distinct colour morphs.

Differences in the reproductive and feeding behaviour of these colour morphs, backed up by some genetic differentiation, has for the first time been used to show that they are actually separate species.

The hamlet fish were found to swim with non-predatory fish that had the same colouration as them. Because their prey would have no fear of these fish, it provided them with a guise through which they could approach prey - and consequently feed - without rousing suspicion.

The study, which involved diving across 94,000 square metres of reef in Panama, Belize and Barbados, also revealed that the Hamlet fish would reproduce with individuals of the same colouration.

Incipient speciation"Here, we demonstrate the potential for a single trait, colour pattern, to drive incipient speciation in the genus Hypoplectrus (Serranidae), coral reef fishes known for their striking colour polymorphism," the authors wrote in their paper in the Proceedings of the Royal Society.

"We provide data demonstrating that sympatric Hypoplectrus colour morphs mate assortatively and are genetically distinct."

"We identify ecological conditions conducive to disruptive selection on colour pattern by presenting behavioural evidence of aggressive mimicry, whereby predatory Hypoplectrus colour morphs mimic the colour patterns of non-predatory reef fish species to increase their success approaching and attacking prey.

"We propose that colour-based assortative mating, combined with disruptive selection on colour pattern, is driving speciation in Hypoplectrus coral reef fishes."

Environmental conditions"When investigating ecological selection, the first reflex is to look at the species' environmental conditions rather than at its behavioural traits", said Oscar Puebla, a PhD student at the NEO.

However, in the case of the hamlet fish, there "were no obvious ecological mechanisms" through which the researchers could classify the colour morphs as distinct species, says Dr. Frederic Guichard, assistant professor in the Department of Biology at McGill.

This resulted in the need to look at how the fishes colouration could affect their behaviour.

"We were at he frontier of our ability to detect new species and speciation."

For more information see the paper: Puebla O, Bermingham E, Guichard F and E Whiteman (2007) - Colour pattern as a single trait driving speciation in Hypoplectrus coral reef fishes. Proceedings of the Royal Society B Biological Sciences, Vol. 274, No. 1615, pp. 1265-1271.