Butterfly ears suggest Bat influence

[Rcjohnsen]

Butterfly ears suggest a bat influence
S. Milius
Sci. News 157:54
Jan.22,00
   Hungry bats whipping through the blackness to gulp down insects may have
driven moths into daylight—creating what we know as butterflies—suggest
Canadian researchers.
The idea springs from their discovery of butterflies that have ultrasonic ears,
explains Jayne E. Yack of Carleton University in Ottawa. Night-flying, tropical
butterflies of the superfamily Hedyloidea have on their wings ears sensitive to
high frequencies, Yack and James H. Fullard of  the University of Toronto
report in the Jan. 20 NATURE.
    Such ears can detect an incoming bat's echolocation pulses in time for the
insect to try zigzagging out of death's way. Many moths have evolved such
ultrasonic hearing, but researchers hadn't detected it in butterflies, Yack
notes.
    She and Fullard hypothesize that bats' evolution of echolocation more than
50 million years ago drove moths to protect themselves. Some developed ears
that could detect bat ultrasound pulses; others adopted the daylight lifestyle
of the butterfly.
"In a sense, bats may have invented butterflies," Yack suggests.
Malcolm J. Scoble of the Natural History Museum in London deems the suggestion
"a very interesting idea" and "a reasonable speculation."
    Hedylids—a little mothy and a bit butterflyish—were long considered moths
and placed in the inchworm group. In 1986, Scoble reclassified the 40 hedylid
species as a superfamily of butterflies. "It caused a little bit of excitement
among my colleagues," he recalls, but has since  won converts.
    When Yack examined the hedylids in Canada's national insect collection,
some wing structures caught her attention. She had done her dissertation on
moth ears and immediately recognized an ear. "It was one of those amazing
moments when you see something that no one has seen before," she remembers.
    Microscopic views revealed a mothlike ear, about half a millimeter across,
with a delicate drum membrane as transparent as cellophane, she says. Each wing
has one ear.
    To see how the ears work in living butterflies, Yack scoured Panama in
search of hedylid populations that hadn't vanished. Her first circuit, "a
miserable trip," was unsuccessful.
    When she finally located enough butterflies to test, she played pulses of
high frequency sound at night. "They would go into these wild, crazy loops and
spins and dives," resembling a moth's evasive flight, she says. When Yack
interfered with hearing—by clogging the ears with Vaseline, for instance—the
butterflies no longer responded.
    "I'm quite convinced that they've found an ear," comments William E. Conner
of Wake Forest University in Winston Salem, N.C. However, he cautions that it's
too early to say whether the ears remain from moth ancestors or have arisen
more recently.
    Both he and Ronald R. Hoy of Cornell University find it plausible that
night-flying butterflies like the hedylids would evolve ultrasonic hearing to
evade bats. "If you're an insect and you fly at night, in principle you have a
bat problem," Hoy says.
     Insects can solve that problem in a variety of ways such as lurking in
plants, being too tiny a mouthful to be worth chasing, or growing large enough
to look formidable. Still, Hoy has found bat detectors in a wide range of
night-fliers, such as crickets, katydids, locusts, praying mantises, green
lacewings, and beetles. He says that metallic squeaks made by jingling keys
under street lamps or porch lights will often send insects into a bat-avoiding
plop.
    Conner wonders whether the hedylids can make noises in the frequencies that
they hear. The tiger moths he studies make ultrasonic clicks in response to the
sound of a bat's approach. Debate flourishes over whether the clicks jam the
bat's echolocation system or advertise that tiger moths taste awful, the sonic
equivalent of warning colors that unpalatable day-flying insects flash at
birds.
    If hedylids make ultrasonic noises, Conner asks, do they squeak as they
flirt? He discovered that his tiger moths click to each other, their sounds
outweighing pheromones in courtship. "They're like acoustic fireflies," Conner
says.
   Biologists generally agree that moths gave rise to butterflies, although the
path that they  took remains "a tantalizing enigma," as Scoble puts it.
S. Milius