“You come out of the water smelling like
rotten flower shop.” — AliSon S weeney
Blue twilight may trigger spawning
By Susan Milius
Sentimental songs aside,
maybe it’s an absence of moonlight that turns the bounding
main into a sea of love.
On nights after the full moon,
when the moon lags below the
horizon until after sunset, twilight takes on an especially
blue cast. That color shift
might cue the remarkably synchronized spawning of some
marine species, suggests Alison
Sweeney of the University of
California, Santa Barbara.
Corals may be the most famous of the
mass spawners. Sweeney recalls a coordinated spawning along miles of reef in
Palau that left a fragrant pink slick still
visible the next day: “You come out of the
water smelling like rotten flower shop.”
Corals don’t have central nervous
systems or actual eyes. Yet many corals manage to release their eggs and
sperm into the water on one or just a
few evenings of the year in the same few
Pink bundles of eggs and sperm poke out of coral
in Palau waiting for a signal to spawn. A new
study proposes blue-tinged twilight as the cue.
hours—sometimes just the same 20
minutes — as do neighbors of the same
species for miles around. Seasonal cues go
into this feat, but what interests Sweeney
and her colleagues is how species coordinate the fine-scale timing on a particular
evening. “This 20-minute precision is
pretty tough to explain,” she says.
In a first step to testing the notion of
a blue-twilight cue, Sweeney and her
colleagues floated sensors and a laptop
Fleas leap from
feet, not knees
study settles issue of how
impressive jumpers launch
By Daniel Strain
A decades-old debate about how the animal kingdom’s most renowned jumper
jumps appears to be settled.
Researchers with the University of
Cambridge in England have shown
that fleas take off from their tibiae and
tarsi — the insect equivalent of feet — and
not their trochantera, or knees. The
researchers report their conclusion in the
wedged into an inner tube out to corals
in the U.S. Virgin Islands. Measurements
showed that the blue shift can be detected
under water, the researchers report in the
March Journal of Experimental Biology.
Since the late 1960s, researchers
have known that fleas launch by storing energy in a naturally
springy protein called
resilin, then releasing the
pent-up energy in one big
bound. But where exactly
the spring power goes
wasn’t clear. One camp
said the force moves
down to the knees; the
other said the feet.
Gregory Sutton and
Malcolm Burrows were able to settle the
issue by collecting 51 slo-mo video clips of
leaping hedgehog fleas. The team
also drew up mathematical models to
simulate bug leaps and eyed flea anatomy
using a scanning electron microscope.
Flea knees never even touched the
ground in about 10 per-
cent of jumps, Sutton
says. With or without
knee contact, the fleas
still jumped with the
same speed and accelera-
tion. The team also found
long spikes on the flea tib-
iae and tarsi — good for
traction, perhaps — but
only short hairs on the
knees. The jumps Sutton and Burrows
watched on film also matched the
predictions of feet-jumping but not
knee-jumping mathematical models.
trochanter tibia tarsus
Jumping fleas take off
from their equivalent of
feet (the tibiae and tarsi).
