Why are American fruits so tasty
Evolution: why are fruits so colorful?
Fruits are often used by plants to spread: the seeds of the plant, hidden in fruits such as apples, cherries or plums, are supposed to be eaten by animals and then deposited elsewhere to germinate. It is therefore logical that fruit should look delicious, taste sweet, nutritious and be as easy to find in the tree as possible - and so fruits smell tempting and are often beautifully brightly colored. This hypothesis is anything but new, but it still has unexplored weaknesses: For example, are there fruit colors that only attract certain animals? And are different addressees the cause of the unmistakable spectrum from plum violet to cherry red? An international team of scientists led by Omer Nevo from the University of Ulm investigated this in the journal »Scientific Reports« and said: The colors of a fruit serve the sensory habits of suitable fruit eaters in the ecosystem.
This hypothesis is not easy to investigate. Just as not every typical super market orange looks like a natural orange, colors in the eyes of animals often look different than those of humans. This is not only due to fundamental anatomical differences in the construction of the eye or the tuning of the visual apparatus, which makes berries that appear black to us, shine bright for birds that can see in the UV range. Actually, one should now examine every fruit, record its reflective properties under natural light and compare it with the color perception of possible interested parties.
This article is included in Spectrum - The Week, 39/2018
Nevo and colleagues first tested a counter-hypothesis, according to which the fruits of many plants also get their colors from the stem line, i.e. through inheritance from the relatives. For this purpose, they collected the fruits and leaves of 97 plant species from different ecosystems in national parks in Uganda and Madagascar and determined the reflection values when irradiated with different wavelength ranges. It initially showed that the fruit colors of closely related species are no more similar than those of distant species.
It was noticeable, however, that fruits, which are mainly eaten by mammals such as monkeys, reflect in the green wavelength range, while typical bird meals reflect more red light components. This fits in with the well-known biology: Birds have superior color vision and can therefore see red berries or fruits in the forest of leaves more quickly. Primates, on the other hand, are more likely to rely on other senses - such as the sense of smell.
The UV reflection of some fruits could have other reasons for UV-seeing birds to notice it: It occurs mainly in plants where the leaves also reflect UV light more strongly. This is considered to be a protective reaction of plants that are exposed to particularly strong solar radiation: Anthocyanins are increasingly formed in their plant parts, which reflect UV light.
The researchers now want to look more closely for other conspicuous common features of the different fruits - in addition to typical odorous substances, for example, shapes, sizes and textures, which may also have been selected as a reaction to the preferences of fruit eaters over time.
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