Ever wondered why certain fruits are red and some green? Well, you are not alone. This question has puzzled scientists for many years and now a team of researchers from Germany, Canada and Madagascar have a simple answer — to attract animals. The colour of the fruit depends primarily on the visual capacity of the local seed dispersing animals.
This was shown by a study published in Biology Letters that looked at the colours of fruits and the animals that disperse their seeds, in Uganda and Madagascar. More specifically, they did not just look at colour alone, but rather at the difference between the colour of fruit and leaves.
In Uganda, monkeys, apes and birds are the primary seed dispersers. While Old-World monkeys and apes have a colour vision similar to that of humans, birds are one step higher and can see even more colours than us. The researchers found that fruits in Uganda take advantage of this colour vision of animals, and colour fruits in shades that make them stick out in the eyes of animals which can distinguish between red and green.
But in Madagascar, the main seed-dispersing animals are lemurs amongst whom most or all the animals are unfortunately red-green colourblind. So, fruits and leaves have acquired shades that make them stick out to colourblind animals.
Other driving forces
To fully understand the forces driving fruit colour, the authors conducted another study, which was published this week in Scientific Reports . They tested whether closely related species tend to be similar, whether abiotic factors such as solar radiation can affect fruit color and the colour of the fruits dispersed by different animals.
While ancestors and closely related species did not affect fruit colour, abiotic factors did play a role. Though fruit and leaf colour did not correlate in the visible light spectrum, they did show similarities at the UV light part of the spectrum. “The fruit and the leaf reflected UV light in a similar way. This could be due to some defense system. Ultraviolet light can be harmful to both fruits and leaves, so species that defend their leaves by reflecting UV light do the same in the fruits,” explains Dr. Kim Valenta, a research assistant professor at the University of Duke, USA, and first author of the paper.
The researchers also found that in both Uganda and Madagascar, fruit species that rely on bird seed dispersal tend to be redder while those which specialise on primate seed dispersal are greener. “This may be explained by the fact that primates possess an excellent sense of smell and their heavier reliance on fruit scent means that, on an average, fruits need to invest less in visual signals,” explains Dr. Omer Nevo, a post-doctoral researcher at the University of Ulm, Germany, and one of the authors of the paper.