Guppies and the fruits of orange

21 05 2012

Why does a lure work? What makes prey move towards a predator?  How does a predator know what would make a good lure?  All these questions were answered for one circle of life in the streams of Trinidad.  An Australian Research team found prawns with orange dots at the center point of their pincers, and found them lying in wait rather than moving as they usually would. The researchers also found the prey of these prawns, Trinidadian guppies, to be coloured with specks and splashes of the same orange colouring. Female guppies mated on a regular basis with the most orange guppies, and less as the orange diminished. Guppies were also found to be less afraid of those prawns with orange pincers. What created this obvious bias for the colour orange?

Let’s back track a bit to a time before this preference. There are Orange trees which drop the odd orange fruit into the stream, and when they do so, the guppies fastest to react to the colour reap the most benefits. Over evolutionary time these guppies gained a preference to the colour orange. Those males with orange colouring were preferred by females, and mated more often generating an increase in orange male guppies. This explains the colouration of guppies found by the researchers.

The pre-existing prawns in the stream hunted the guppies, but the prawns with some orange in their pincers began to get better results. The prawns with orange coloured pincers were better fed, and gradually more prawns had orange spots on their pincers. Guppies still knew to stay away from prawns if attacked even if there was orange, so prawns that sat and weighted gained the advantage of camouflage, so the guppies only saw the orange colouring, but not the full prawn until it was too late.

The study that was done to confirm all of this was first to look at other streams with guppies and model prawns some with the orange coloured pincers others without. The difference was profound, as the fish stayed well away from the non coloured prawns, but swam very closely around the orange prawns. The same test was done with guppies from other streams not associating orange with food or mates, and the guppies stayed away from all prawns regardless of colour.

This shows that one change in life style can lead a web of changes branching off through other species, all traceable back to the original source, in this case orange fruit falling from trees on the banks of Trinidadian streams.

I am curious to know if guppies will come to associate orange with danger, as the prawns will only get more successful, though, everything may just become so orange that it holds no preference at all. I hope more examples of this action/reaction event are discovered and studied in the future to give us an even more complete understanding of evolution and all the macroscopic effects involved.

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