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Guppies lust after killer orange prawn

Posted on behalf of Alice Lighton.

The model prawn used in the experiment, with female guppy at bottom left.

A. De Serrano

A murky-brown prawn that lives off the coast of Trinidad has evolved orange spots on its pincers to tempt local guppies. The fish mistake the markings for both food and a potential mate, and unwittingly become the prawn’s next meal.

Researchers placed a model of a Macrobrachium crenulatum prawn into a tank with female Trinidadian guppies, who were understandably wary of its head and claw areaa. But when the prawn’s pincers were decorated with orange spots, as they are in the wild, the fish couldn’t resist taking a closer look.

The experiment, published today in Proceedings of the Royal Society B, didn’t show whether the fish mistook the prawn for food or a male guppy. Trinidadian guppies originally evolved orange markings to attract mates, because of the resemblance to nutritious orange fruits that fall into the coastal waters. The prawns appear to have latched onto the same trick, and are now convincing enough that they can catch the guppies’ attention.

“The guppies pecked at the prawn, suggesting they thought it was a food source, but then it’s all linked back together,” says Cameron Weadick, a member of the research team at the University of Toronto in Ontario.

This sort of trickery is seen throughout the animal kingdom. The larvae of one species of North American mussel are parasitic and must be eaten to survive. They therefore group together into the shape of a minnow until they are ingested by a larger fish. Similarly, female Photuris fireflies use their light to attract males of a different genus, which they then eat. However, the authors of the guppy paper believe that M. crenulatum is the only species that takes advantage of both foraging and sexual desire.

The researchers were unable to transport a live M. crenulatum from Trinidad to Canada, so as well as using a model of a prawn, they attempted to disguise a crayfish using orange nail varnish. The crayfish acted as a predator, and grabbed at the fish with its pincers, but the guppies were not fooled. “Guppies are probably clued into a lot of things — movement patterns, smells, not just colour,” says Weadick.

There is no guarantee the prawn’s disguise will continue to work. M. crenulatum’s colouring may one day provide enough evolutionary pressure that female guppies associate orange with danger, rather than desire.

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