Einstein Science Reporting for Kids
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29-Apr-2010

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Chance encounter with fungus made aphids colorful



Pea aphids with genetically based differences in carotenoid content. Green and red individuals represent a naturally occurring polymorphism; yellow‑green individuals are mutants derived from a red parental line.
Image courtesy of Charles Hedgcock, R.B.P

Tiny insects called pea aphids are the first animals known to make their own pigments, called "carotenoids," scientists have discovered. Other animals, including humans, don't make our own carotenoids. We have to get them from the food we eat.

Carotenoids provide color and play other important roles in our cells, such as detecting light, and disarming harmful molecules called free radicals. They're usually found in plants, as well as some algae, fungi and bacteria.

Pea aphids are either red (and these tend to get eaten by ladybugs) or green (and these tend to be preyed upon by parasitic wasps). Curious about the difference, Nancy Moran and Tyler Jarvik of the University of Arizona looked for clues in the pea-aphid genome which has recently been sequenced.



Samples of three pea aphid clones that differ in genes for carotenoid production.
Image courtesy of Charles Hedgcock, R.B.P

Unexpectedly, they found that the aphid genome includes instructions for making enzymes for producing carotenoids. And, these "homemade" carotenoids are responsible for the pea aphids' colors.

The researchers think that an ancestor of the aphids must have once gained carotenoid-producing genes from a fungus. Their study appears in the 30 April issue of the journal Science.

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