Washington: Scientists claim to have
identified for the first time an insect, known as aphids, that
can make their own essential nutrients called carotenoids.
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.