http://www.msnbc.msn.com/id/11368151/

Toxic toads evolve to aid Australian invasion
Longer legs helped cane toads hop all over in just a few short decades

By Ker Than

LiveScience

Updated: 1:49 p.m. ET Feb. 15, 2006

Toxic toads bound across the northern tropics of Australia faster than
ever, thanks to the evolution of longer legs in the few short decades
since humans introduced them to their own little paradise.

Cane toads (Bufo marinus) were first brought in from Hawaii in 1935 to
control the spread of beetles that were ravaging Australia's sugar cane
crop. But instead of controlling the pests, the toads have become pests
themselves. A deadly chemical defense system disposes quickly of
potential predators.

The toads have expanded their range to cover more than a third of
Australia's total land area.

From the 1940s through the 1960s, the toads were invading at a rate of
about 6 miles per year; now they're taking over at a rate of about 30
miles a year.

To find out why the toads are spreading so fast, researchers stationed
themselves about 40 miles east of Australia's port city of Darwin, in a
region where the cane toads had not yet spread.

When the toads arrived, the researchers found that those in the vanguard
of the invasion had legs that were up to 6 percent longer than average;
shorter-legged stragglers followed. The study showed that newer
populations of toads tended to have longer legs than those in
long-established populations.

A top pest
It should come as no surprise that cane toads are among the world's top
100 invasive species. They are the world's most introduced amphibian.
They mate year-round and females lay up to 30,000 eggs at a time.

The toads can grow as large as dinner plates and weigh up to 4.5 pounds.
Their heads and backsides are studded with rows of warts that secrete a
milky white toxin called bufotoxin.

Because Australia has no native toads, many native predators such as
snakes, lizards and mammals are very sensitive to the toxin. So when the
toads spread, they immediately kill off many of the region's top
predators.

"We don't know what effect it may have to remove so many top predators
from a complex tropical ecosystem, but it's likely to be bad news," said
study team member Richard Shine of the University of Sydney.

When an invasive species is first introduced, the population remains low
for a few generations before exploding, Shine said.

"It's likely that such lags reflect, at least in part, adaptive changes
in the invader to suit it to the new environment," Shine told
LiveScience.

Shine and his colleagues warn in the February 16 issue of the journal
Nature that Australia could face an "ecological nightmare" if the spread
isn't controlled soon.

Australian scientists have tried for decades to eradicate the toads, but
with limited success. Last year, researchers announced they had
successfully lured and trapped the toads using ultraviolet lights like
those used in disco clubs.

© 2006 LiveScience.com

http://www.msnbc.msn.com/id/11368151/

Toxic toads evolve to aid Australian invasion
Longer legs helped cane toads hop all over in just a few short decades

By Ker Than

LiveScience

Updated: 1:49 p.m. ET Feb. 15, 2006

Toxic toads bound across the northern tropics of Australia faster than
ever, thanks to the evolution of longer legs in the few short decades
since humans introduced them to their own little paradise.