The Colorful Secret Of The Pea Aphid

Red and green aphids climb on a plant. i i

hide captionRed and green aphids get their different colors by producing carotenoids, or color compounds.

Courtesy of Charles Hedgcock, R.B.P.
Red and green aphids climb on a plant.

Red and green aphids get their different colors by producing carotenoids, or color compounds.

Courtesy of Charles Hedgcock, R.B.P.

Normally, animals get their DNA from their parents. But a new study shows that they can also get genes from another species. In fact, animals can even take genes from creatures outside of the animal kingdom — like from fungi. And that's pretty surprising.

"The idea that animals picked up DNA from microbes — until recently that was thought to be nonexistent," says John Werren, an evolutionary geneticist from the University of Rochester.

But new research shows that it can happen. Researchers found evidence in a tiny insect called the pea aphid.

"They're sort of pear-shaped with big hind ends and smaller heads and long spindly legs and antennae," says Nancy Moran, a geneticist at the University of Arizona. "And the interesting thing about them that's related to this work is that they come in two colors — red and green."

The Importance Of Color

Coloring is important for aphids because it helps them foil their predators. Many animals, including pea aphids, get their coloring from molecules called carotenoids. Lutein is one that's a bright yellow. And lycopene is the carotenoid that makes tomatoes red.

"Basically, these little red aphids are like little tomatoes," says Moran. While they don't have lycopene, they're full of a red carotenoid.

Red, green and yellow-green pea aphids. i i

hide captionRed, green and yellow-green pea aphids. Scientists recently found that, unlike other animals, pea aphids create their own color compounds. Other animals have to eat theirs — usually in the form of plants, berries and tomatoes.

Courtesy of Charles Hedgcock, R.B.P.
Red, green and yellow-green pea aphids.

Red, green and yellow-green pea aphids. Scientists recently found that, unlike other animals, pea aphids create their own color compounds. Other animals have to eat theirs — usually in the form of plants, berries and tomatoes.

Courtesy of Charles Hedgcock, R.B.P.

The thing is, animals don't make their own carotenoids. Aninals get carotenoids by eating plants and berries and fungi that make carotenoids. And yes, aphids are animals. They're small ones, but they're animals.

An Unusual Insect

But Moran wondered if aphids were an exception to the rule.

"And the big thing that made a difference in the ability to find that out was the genome sequence of the aphid was completed recently," she says.

Surely you've heard about the Aphid Genome Project. Anyway, Moran sat down at her computer and looked through the aphid genome for the genes that are responsible for carotenoids. And to her surprise, there they were.

"It's totally unexpected," she says. "But once the genome sequence is there, it's also extremely simple to look. It's a five-minute job."

So the next question was, where did the aphids get the genes? Because remember, animals don't make carotenoids. Moran says that took a bit longer to track down, but now, as she reports in the journal Science, she believes she has the answer.

Gene-Stealing

"Well, the evidence is pretty clear-cut for this case," she says, "that they actually picked them up, believe it or not, from fungi." Fungi include things such as yeast and mushrooms.

"The DNA from a fungus went into the aphid somehow," Moran says, "and then stayed there and continued to function."

The aphids essentially stole the fungi's microbial genes. It's what scientists call lateral gene transfer.

Could humans also be stealing genes from bacteria or fungi? Julie Dunning Hotopp from the University of Maryland says it doesn't appear so.

"The human genome project has shown that there is not lateral gene transfer," she says, "at least that's inherited."

But Dunning Hotopp is not done looking. She believes it may just be possible that humans occasionally pinch a gene or two from bacteria or fungi.

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