Washington, Jan 8 : A new study has demystified the annual migration of millions of monarch butterflies from the eastern North American to a cluster of pine groves in central Mexico.
Steven M. Reppert, MD, a University of Massachusetts Medical School Professor and Chair of Neurobiology, has said that the journey is driven by a complex molecular mechanism in a tiny cluster of cells in the butterfly brain.
Reppert's earlier research had stated that the butterflies use a time-compensated sun compass and daylight cues to help them navigate to the pine groves.
His studies have revealed that time compensation is provided by the butterfly's circadian clock, which allows the monarch to continually correct its flight direction to maintain a fixed flight bearing even as the sun moves across the sky.
Now, in the latest study, researchers have described the monarch butterfly circadian clock, and identified an entirely new clock gene. The new clock gene provides insight into the biology of the butterfly and its migration.
With the new study the researchers reveal that the circadian clock of the monarch uses a novel molecular mechanism, which has not been found in any other insect or mammal.
Through the study of fruitfly and mouse in a bid to understand the insect clock and the mammalian clock, scientists had described a clock mechanism that is essentially a loop where proteins are made and destroyed over a cycle, which takes approximately 24 hours to complete. Further, investigators identified those factors that work together to drive this process.
The researchers were interested in one of these factors, called CRY, a cryptochrome protein that was initially discovered in plants and was subsequently found in the fly and the mouse.
In the fly, CRY functions as a blue light photoreceptor, allowing light access to clock-containing cells enabling the resetting of the clock by the light-dark cycle. In the mouse, CRY does not function to absorb light.
Genetic studies revealed that the monarch had not only the fly-like CRY, but also another cryptochrome that further tests identified as a new clock molecule in the butterfly.
The scientists also found that the core components of the monarch clock resembled those of the mammalian clock. As in the mouse, CRY2 functions in the butterfly to maintain the feedback loop, while CRY1 still allows light to access the cells, as in the fly.
"This is a very interesting realignment of how one thinks about insect clock models. There was no reason to suspect that the butterfly clock would be different from that of Drosophila. That it is different has already told us something about how circadian clocks have evolved. What we have in the butterfly is an astounding clock mechanism, one that is more similar to our own circadian clock and less similar to the clock of the fly! The presence and function of two distinct CRYs suggest that the monarch's is an ancestral clock; a clock that, over the course of evolution, has changed differently in other insects and mammals," Reppert said.
The study "Cryptochromes Define a Novel Circadian Clock Mechanism in Monarch Butterflies That May Underlie Sun Compass Navigation" is published in PLoS Biology.