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Prey, predator make same poison
By Rachel Ehrenberg
There’s a patent war pending over the
invention of the cyanide bomb.
Zygaena caterpillars, which deter hungry birds by storing the poison in their
flesh, make cyanide using the exact same
cellular machinery as their host plants,
scientists report April 12 in Nature Communications. It still isn’t clear which
one came up with the recipe first, but
the researchers say the discovery is the
first known example of organisms from
entirely different kingdoms evolving the
same biochemical treachery.
Some plants, such as bird’s-foot trefoil,
concoct cyanide bombs that are trip-wired
to blow up in the mouths of nibbling animals. When a slug or insect chews a leaf,
ingredients that are kept in different compartments in the plant’s cells combine to
form cyanide, poisoning the animal.
Scientists knew that some caterpillars
could eat cyanide-laced plants and store
the poison in their bodies. But researchers only recently discovered that when
host plants are cyanide-poor, the caterpillars can make the poison themselves as
a means of deterring their own predators.
“We had no clue how they were making it,” says study coauthor Birger Møller
of the University of Copenhagen.
The researchers first speculated that
sometime in the evolutionary past, the
caterpillars stole the genetic instructions for making cyanide from the plants.
But the plants’ and caterpillars’ cyanide
genes look nothing alike, Møller and his
colleagues discovered. Strangely though,
the plants and caterpillars both use genes
that are found in pretty much all living
things (humans use genes of this type to
break down toxins in the liver).
Not only do both organisms record
their cyanide-concocting instructions in
three similar but very distantly related
genes, they also build the poison with
the same cookware. The enzymes work-
ing the molecular assembly line leading to
cyanide are the same, modifying the same
molecular ingredients in both creatures,
the researchers report.
Zygaena caterpillars, which deter preda-
tors by secreting droplets of cyanide
(circled), get the poison either from eat-
ing poison-laced plants or by making it.
to safely sequester the toxic compound.
Conversely, if the caterpillars already
made cyanide and they chanced upon
plants that did too, the insects could have
saved energy and resources by getting the
poison from the plant. s
By Tina Hesman Saey
The molecular mechanics behind an
example of evolution dating back to
Darwin’s time may soon be revealed.
As soot from coal-fired
factories blackened trees
and buildings in 19th century England, naturalists
noted that peppered moths
in polluted regions blended
in by sporting a sleek, all-black look known as the
carbonaria form instead of
the usual lightly speckled
wings. Within a few decades
the black moths made up 90
percent or more of the population in urban areas.
Now, researchers led by
Ilik Saccheri, a geneticist at
the University of Liverpool in England,
report online April 14 in Science that they
have traced the mutation responsible
for the funereal look to one region of a
chromosome that in butterflies contains
genetic instructions for creating color
patterns. This region is an adaptation
hot spot, where mutations produce hun-
dreds of different wing color patterns in
“Presumably it takes hundreds of
genes to make a wing pattern,” says
Robert D. Reed of the University of Cali-
fornia, Irvine. “So why does this [relatively
small] region appear over and over again?”
No one has found the pre-
cise DNA changes that lead
to the many different color
patterns, but scientists are
scouring the region.
Likewise, Saccheri and
his colleagues don’t yet
know the exact nature of the
carbonaria mutation. They
do know that black moths
collected from 80 sites in
the United Kingdom share
some key genetic signposts,
suggesting that the carbon-
aria mutation involves only
one spot in the genome and
happened just once, probably shortly
before the first reported sightings in
1848 near Manchester.
A black peppered
moth (left) nearly
replaced the original
type during England’s
How the moth
lost its speckles
Tracing the genetic roots of
a classic evolutionary tale
May 7, 2011 | SCIENCE NEWS | 11