Insects that make their own essential nutrients 'spotted'

No other animals are known to make the potent antioxidants. Until now researchers thought that the only way animals could obtain the orangey-red compounds was from their diet. But, an Arizona University team has found otherwise.

In their research, the scientists have also figured out how the aphids they studied, known as pea aphids, acquired the ability to make carotenoids which are building blocks for molecules crucial for vision, healthy skin, bone growth and other key physiological functions.

"What happened is a fungal gene got into an aphid and was copied. Although gene transfers between microorganisms are common, finding a functional fungus gene as part of an animal's DNA is a first.

"Animals have a lot of requirements that reflect ancestral gene loss. This is why we require so many amino acids and vitamins in the diet.
"Until now it has been thought that there is simply no way to regain these lost capabilities. But this case in aphids shows that it is indeed possible to acquire the capacity to make needed compounds.

"Possibly this will be an extraordinarily rare case. But so far in genomic studies, a single initial case usually turns out to be only an example of something more widespread," Nancy Moran, who led the team, said.

In fact, an accident in the laboratory plus the recent sequencing of the pea aphid genome made their latest discovery possible, the scientists say.
Pea aphids, known to scientists as Acyrthosiphon pisum, are either red or green. Aphids are clonal -- the mothers give birth to daughters that are genetically identical to their mothers.

So when an aphid in the lab's red 5A strain began giving birth to yellowish-green babies, the scientists knew they were looking at the results of a mutation.
"We named it 5AY for yellowish. That yellowish mutant happened in 2007. We just kept the strain as a sort of pet in the lab. I figured that one day we'd figure out how that happened," she said.
Symbiotic bacteria live within aphids in specialised cells. The bacteria, which are passed from mother to babies, supply the insects with crucial nutrition. If their bacteria die, the aphids die.

The scientists, who have been studying the pea aphid-bacteria system for decades, already knew the three main species of symbiotic bacteria did not make carotenoids. They also were pretty sure the aphids didn't get their carotenoids from their diet.
Aphids eat by sucking the phloem sap from plants, but the sap is carotenoid-poor. In addition, the carotenoids in the aphids were different from those usually found in plants, the scientists say.