dramatically darker than mice getting a
neutral lotion.
Untreated mice exposed to UV rays for
24 hours had more than 20 times as much
DNA damage and sunburn as did mice
that had been treated with forskolin. After
20 weeks of exposure to UV rays for an
hour or so each day, untreated mice developed nearly twice as many skin tumors as
did the treated mice, the scientists report
in the Sept. 21 Nature.
The results show that “the reduced DNA
damage has a [positive] biological consequence,” says molecular biologist Richard A.
Sturm of the University of Queensland in
Brisbane, Australia. Increased melanin
reduced death among skin cells.
Studies had previously established that
people with dark skin are less likely to
become sunburned or get skin cancer than
fair-skinned people are. With the new work,
Sturm says, Fisher and his team “display
the tangible proof … for a photo-protective
role of melanin.”
Sturm is cautious about the possibility of
providing people with a forskolin-contain-ing cream. He notes that cyclic AMP can
stimulate cell growth, so increased amounts
of that molecule might pose a cancer risk.
Fisher is cautious too. “I am far from certain [that such a cream] would have activity in human skin,” he says. Still, the findings suggest that intervening in the
melanin-production process has potential
as a cancer preventive, he says.
“If [forskolin] turns out to be safe and
acceptable for human use, it can only be
helpful,” says dermatologist Barbara A.
Gilchrest of Boston University School of
Medicine. —N. SEPPA
Crickets
on Mute
Hush falls as killer fly
stalks singers
Within just 5 years, singing has nearly died
out among a population of cricket on a
Hawaiian island, researchers report.
A mutation for silence has spread so fast
because an invasion of deadly flies finds
male crickets to attack by following their
chirps, says Marlene Zuk of the University
of California, Riverside.
HOY AND G. HALDEMAN; LONGRICH
However, female crickets also listen for
chirps to find the males, so a guy who can’t
sing has a problem. The mute males seem
to be coping, at least temporarily, by clustering around the few remaining chirpers,
Zuk and her colleagues report in a Biology
Letters paper released online.
“What surprises me most is that the cricket
song went away so fast,” says Ron Hoy of Cornell University, who also studies crickets and
DON’T SING NOW Ormia ochracea flies
pinpoint the source of a cricket chirp, and
a female deposits larvae on the unlucky
songster. Consequently, male crickets
on Kauai are falling silent.
the song-tracking fly. “Natural selection is
coming down like a hammer,” he says.
The crickets (Teleogryllus oceanicus) that
are losing their songs came to Hawaii from
Australia and western Pacific islands. Their
nemesis, the Ormia ochracea fly, invaded the
Hawaiian Islands from North America.
These flies are about the size of houseflies
but have big red eyes and fly at dawn or dusk.
“You’ve never seen them,” says Zuk. “You
don’t have anything they want.”
In 1975, William Cade, now of the University of Lethbridge (Alberta), reported
that the female fly follows cricket chirps to
deposit larvae on a male. The larvae dig in
and eat the cricket from the inside.
Zuk and her colleagues found in the
1990s that Kauai had intense fly infestations, parasitizing one-third of the crickets. In her 2001 survey, she heard only
one male calling.
In 2003, Zuk didn’t hear anything in her
night searches. Then, she says, “suddenly, in
my headlamp, I start seeing crickets.” For
insect biologists, quiet, nighttime male crickets are shocking. “It’s like finding out that
peacocks dropped their tails,” Zuk says.
She found that the cricket population on
Kauai was higher than it had been for years,
but few males still had wings with functional
chirping equipment. When coauthor Robin
Tinghitella, also of Riverside, bred those
crickets, she concluded that the silence came
from changes in only a gene or two.
When the researchers broadcast recorded
cricket chirping, they found that the mutant
males hopped unusually close to the speakers. Lurking near a chirping male is probably their only way to meet females, says Zuk.
Once a female arrives, a male cricket normally produces a special, soft courtship
chirp to persuade her to mate. Theorists
have proposed that females of island species
tend not to be too choosy. As Zuk puts it, “If
there are only four guys and you don’t like
any of them, you die, and so do your genes.”
Zuk’s work gives “the most dramatic example yet of how flies have shaped communication in crickets,” says Cade. —S. MILIUS
Flying with
Their Legs
Hind feathers made
primitive bird nimble
The earliest-known bird may have soared
ancient skies on four wings. Feathers covered the legs of Archaeopteryx, a creature
that lived 150 million years ago and had
wings like modern birds but teeth and claws
like dinosaurs. A new report argues that
Archaeopteryx used these leg feathers to
improve its flight.
Scientists had assumed that the
Archaeopteryx’s leg feathers were for warmth and
streamlining. But when Nick Longrich of
the University of Calgary in Alberta reexamined a fossil of the creature, he found
that its leg feathers resembled the ones that
keep modern birds aloft. Thus, he argues in
the summer (September) issue of
Paleobiology, the legs functioned like small auxiliary wings, providing extra lift that made the
creature more nimble in the air.
Longrich became interested in
Archaeopteryx’s hind limbs 3 years ago, when a
primitive-bird fossil was discovered in
China. It had large feathers on its legs that
its discoverers argued played a role in flight
(SN: 1/25/03, p. 51). He wondered whether
the same was true for Archaeopteryx. “It
had never occurred to me to look at the
hind limbs,” he says.
An Archaeopteryx fossil found in 1877
FLYING FEATHERS Reexamination of a
fossilized Archaeopteryx reveals that the
creature had feathers on its legs that may
have helped it fly. Inset shows how the
Archaeopteryx may have looked with feathers.
