How monarch butterflies are wired for navigation

May 04, 2005

In their extraordinary annual migration from North America to Mexico, monarch butterflies are known to use the angle of polarized sunlight as a celestial guide to help them keep to a straight and true path southward. But details of their navigational machinery have remained a mystery.

Now, researchers, led by Steven Reppert of University of Massachusetts Medical School, Ivo Sauman of the Czech Academy of Sciences and Adriana Briscoe of the University of California at Irvine, have explored the infinitesimal butterfly brain to uncover new insights into that machinery. Their findings show that the same ultraviolet light that has become an anathema to cancer-wary humans is critical for butterfly navigation. Also, the researchers were surprised to discover a key wiring connection between the light-detecting navigation sensors in the butterfly's eye and the creature's circadian clock--a critical link if the butterflies are to compensate for the time of day in using their "sun compass."

The researchers' techniques include molecular analysis of butterfly brain proteins, as well as flight tests in which the scientists manipulated the light reaching their insect subjects and measured the navigational response.

In their studies, the researchers discovered that ultraviolet photoreceptors dominated in the region of the butterfly visual system known to specialize in polarized light detection. To confirm that the butterflies, indeed, required ultraviolet polarized light to navigate, the researchers tested the insects in a "flight simulator," in which they could control the light polarization and thus influence the butterflies' direction of flight. The researchers found that when they placed a UV-interference filter over the polarized light source, the butterflies lost their orientation response.

The researchers also pinpointed the location of the circadian clock in the butterfly brain. Such circadian clocks govern the approximately 24 hour activity and metabolic cycles of animals from the simplest insects to humans. Reppert and his colleagues found that key genes responsible for the clock's molecular "ticks" were expressed in a brain region called the dorsolateral protocerebrum. Using tracer molecules, they were surprised to discover tiny neural fibers containing a key clock protein that connected with the polarization photoreceptors in the butterfly eye.

"This pathway has not been described in any other insect, and it may be a hallmark feature of butterflies that use a time-compensated sun compass," wrote the researchers. They also speculated that another such clock-related pathway of fibers they detected between two regions of the butterfly brain may play a role in regulating the insects' hormonal system, to induce the longevity that enables the butterfly to extend its survival in its overwintering grounds in Mexico.

Source: Cell Press

Explore further: Dinosaur footprints set for public display in Utah

add to favorites email to friend print save as pdf

Related Stories

Butterflies switch lifestyles using hormones

Aug 15, 2014

Many habitats on Earth change dramatically with the seasons, profoundly affecting food availability, predation pressure and reproductive opportunities for animals living in these seasonal habitats. To survive ...

Mustard plants have double defence against insect pests

Aug 14, 2014

Mustard plants have a double line of defence against foraging insects. The plants can release odours to attract miniscule wasps, which parasitise insect pest eggs. However, mustard plants also react by allowing cells to die, ...

Recommended for you

Dinosaur footprints set for public display in Utah

11 hours ago

A dry wash full of 112-million-year-old dinosaur tracks that include an ankylosaurus, dromaeosaurus and a menacing ancestor of the Tyrannosaurus rex, is set to open to the public this fall in Utah.

Fossil arthropod went on the hunt for its prey

22 hours ago

A new species of carnivorous crustacean has been identified, which roamed the seas 435 million years ago, grasping its prey with spiny limbs before devouring it. The fossil is described and details of its lifestyle are published ...

User comments : 0