Colour choice.

 

Fruits owe their rainbow of colors to the various animals that eat them. 

New evidence supports the idea that plants owe their rainbow of fruit colors to the different animals that eat them. Researchers first had to get past the fact that most animals don't see colors quite the way humans do.

Red plums. Green melons. Purple figs. Ripe fruits come in an array of greens, yellows, oranges, browns, reds and purples. Scientists say they have new evidence that plants owe their rainbow of fruit colors to the different animals that eat them.

That the bright red of a berry is a signal to hungry birds -- here I am, come eat me -- is not a new idea. Since the late 1800's researchers have speculated that the colors of fleshy fruits evolved to get the attention of certain animals, who carry them off and eventually drop their seeds on the forest floor.

But evidence to support the idea has been mixed at best, scientists say. Part of the problem is that many studies of fruit color assume we see color as other animals do, assigning fruits to a handful of color categories such as orange or yellow according to how humans perceive them.

There are good reasons to doubt whether red to us looks the same way it does to, say, a lemur. Humans have three types of color-sensing cone cells in the eyes, each one sensitive to different wavelengths of light. But most other mammals have only two types of cone cells. And birds have four, which helps them see a range of colors we can't see.

A fruit that looks blackish to us, for example, may actually reflect ultraviolet rays, which birds can see but humans can't.

"With the exception of a handful of other primates, no other animal on Earth sees color the way that we do," said study co-author Kim Valenta, assistant research professor of evolutionary anthropology at Duke University.

Many studies also neglect to consider other reasons why fruits develop their specific colors, the authors said. For example, some plant species may simply take after their closest genetic relatives, bearing fruits that are pink or brownish because their common ancestors did too. Or fruit color could be a product of environmental factors such as latitude, temperature, or properties of the soil.

Omer Nevo of the University of Ulm in Germany, Valenta and colleagues collected reflectance data on ripe fruits and leaves from 97 plant species in Uganda and Madagascar, such as yellow hackberries, bluish-black soapbush berries and whitish Weinmannia fruits.

The team found that the fruit colors of closely related species are no more similar than expected by random chance.

However, fruits that are mainly eaten by mammals such as monkeys and apes do indeed have higher reflectance in the green part of the spectrum, whereas fruits dispersed by birds reflect more in the red -- presumably because birds tend to rely more heavily on their keen color vision than many other animals, and reds are easier to spot against the green foliage.

The findings lend strong support to the idea that animal dispersers helped drive the evolution of fruit colors in tropical plants.

They also found that plants whose fruits reflected ultraviolet light also tended to have UV-reflecting leaves, suggesting that fruit color is at least partly a response to environmental factors that affect the whole plant -- such as protection from the sun's damaging rays.

Next they plan to analyze other fruit traits such as odor, size or texture. "It may be that visual conspicuousness -- often achieved using red -- entices birds, but scent is more important for luring animals whose sense of smell is keener than their sight," Nevo said.

Blue/ Purple:

Various Fruits and vegetables, like egg-plant, Blueberries, plums, and raisins can be found with a blue to purple hue. The colour Blue or Purple is due to phytonutrients known as anthocyanins, (which is a flavonoid) present in these items. Plants produce these phytonutrients to protect themselves against attacks from insects and damage from UV light. These phytonutrients also are advantageous to us in promoting health and preventing diseases. Studies have also found that they are effective in the control of obesity. This group also contains carotenoids, Vitamin C, Fibre and ellagic acid. All these are antioxidants, and anti-cancer agents

Green:

Spinach, Broccoli, Wheat grass, Kale and Brussel sprouts to name a few display their green colour, due to the presence of the green pigment Chlorophyll. This pigment is known to absorb light in the red and blue parts of the light spectrum and reflects the remaining which is mostly green. Thus these items appear green. Chlorophyll has been known for promoting human health and prevention of diseases. Also, there are two carotenoids present in green foods, which are Lutein and zeaxanthin. These carotenoids act as antioxidants in the human eyes and skin.

Red:

The red colour in certain fruits and vegetables are due to the presence of lycopene, which belongs to the carotenoids group. Thus, tomatoes, apples, strawberries, beet and pomegranates, display their red colour. Lycopene has been found to reduce the risk of cancers of the prostate, pancreas and to a certain extent, of the stomach. But further studies need to be done in this area. Lycopene is thought to protect against oxidation damage, especially due to ultraviolet light exposure and tobacco smoke.

Yellow/ Orange:

Yellow and Orange fruits and vegetables get their colour from lutein and zeaxanthin, carotenoids. These also contain antioxidants like Vitamin A and C. Oranges, mangoes, yellow peppers, lemons, pineapples, pumpkin have good quantities of these beneficial substances.

If we look at bell peppers (or Capsicum Annuum), they start out green and require more time on the plant itself to ripen to yellow, orange and red. Thus the red, orange and yellow variety are usually more expensive. Lutein and zeaxanthin carotenoids are known for their role in age-related macular degeneration (AMD for short, which is basically blurring of vision due to age) and cataracts. Vitamin C is known for its prevention of oxidation damage.

White:

Fruits and vegetables which are white in colour form an important part source of key nutrients (especially fibre, potassium and magnesium), and other micro constituents. The health benefits of white colour foods should not be underestimated and can increase shortfall of nutrients in our diet. Items in this category include potatoes, cauliflowers, turnips, corn, parsnips, mushrooms and onions, to name a few.

Fruits and vegetables have their distinctive colour due to presence of Phytochemical of varied nature. Various nutrients are present in different quantities in various foods. You should ensure that your daily diet compromises of as many coloured fruits and vegetables to get a combination of the health effects.

Benefits of colourful vegetables and fruits:

Lycopene: Reduction of cancer and oxidation damage

Chlorophyll: Prevention of deses healthy eyes and skin

Anthocyanin: control of obesity, antioxidant and anticancer agents

Carotenoids: eye health and reduction of oxidation damage