Butterfly 'GPS' found in antennae
By Judith Burns
Science and environment reporter, BBC News

* North America's Monarch butterflies use a 24-hour "clock" in their
antennae to help navigate the 4,000km to overwinter in Mexico, say
scientists. *

Every autumn about 100 million Monarch butterflies migrate to the south.

The insects navigate according to the position of the Sun, adjusting their
calculations as it appears to move across the sky.

A paper in the journal Science shows the location of the clock is the
antennae rather than the brain.

Scientists say the finding is a surprise as it has always been thought that
the butterflies used a 24-hour clock in their brains in conjunction with
their "Sun compass" when they migrated.

But some observations from 50 years ago indicated that when the butterflies'
antennae were removed the insects no longer flew in the right direction.

A research team from University of Massachusetts Medical School, US, was
also interested in studying the role of the antennae in butterfly social
reactions as Monarchs are extremely gregarious when they migrate.

* Flight Simulator *

They removed the antennae from a group of butterflies and compared the way
they flew with a control population in a flight simulator.

The intact butterflies all flew southwest, as normal, but the insects
without antennae, although they flew strongly, headed off in random

Co-author, Dr Steven Reppert, told BBC News: "This then perked up our
interest more and set up a whole series of experiments, which essentially
led us to discovering that the antennae, really we think, are the major site
of the circadian clock that compensates for the movement of the Sun."

The researchers tested the molecular cycles of the circadian clock in the
brains of the insects without antennae and discovered that they were still
functioning normally.

Dr Reppert said: "So this suggested that: Wow! Maybe there's a clock in the
antennae that's more important for the time compensated component of the
insects' Sun compass orientation... It was a total surprise."

What they did next was to show that the molecular control of the clock in
the antennae is identical to the way it is in the brain. They also showed
that the antennal clock can sense light independently from the brain and can
function independently.

Dr Reppert said: "What's so cool about what we did is it suggests that these
clocks have a function that is directly related to the brain itself, that it
is really regulating a central brain process."

In order to prove that the antennae contain both a light sensor and a clock,
the scientists painted the antennae of one group of insects with black
enamel paint and compared their behaviour with that of a group whose
antennae were coated with transparent paint.

* Skewed orientation *

The group with the black painted antennae all flew together in the wrong
direction, while those with the transparent paint were unaffected.

According to Dr Reppert: "This strongly suggested that the timing of the
clocks was still apparent but since the antennae were painted black the
internal clocks couldn't adjust their 24-hour oscillation to the prevailing
light-dark cycle.

"So that's why their orientation was skewed. This brought everything
together and really pointed towards the antennae as the major source of this
time compensation mechanism."

"I think the take home message is that this really emphasises the importance
of this appendage, the antenna of the butterfly.

"I think it's becoming more and more clear that the antennae have a number
of functions that are independent from being odour detectors. They can
function as ears, sensing sound and changes in barometric pressure, and now
we can add to the list this function as a timepiece."

The paper also suggests that other insects such as foraging honeybees and
ants may use their antennae in a similar way.
Story from BBC NEWS:

Published: 2009/09/25 00:00:40 GMT