Literature

"People who need to consult maps, radio traffic reports, or the Global Positioning System to navigate from one city to another should stand in awe of monarch butterflies. They migrate thousands of kilometers to a small winter retreat in Mexico. These intrepid travelers use the sun as a guide, but exactly how has been a mystery. Now researchers demonstrate that monarchs depend on an internal clock to determine their course. [. . .] Without a clock, the sun would prove an unreliable landmark as it moves across the horizon; a clock allows animals to compensate for this apparent motion and maintain a direct course."

So wrote Elizabeth Pennisi in 2003, commenting on a research paper dealing with monarch migration skills. Having established that there is a solar compass and an internal clock, the researchers have been concerned with the genetic components of the clock. This work has appeared recently in PLOS Biology.

The monarch butterfly (Danaus plexippus)

Robinson summarises the genetic clock mechanism that has been elucidated for Drosophila:

"In fruit flies, five proteins are central to the operation of the clock. Clock (Clk) and Cycle (Cyc) bind together to form a transcriptional complex, which drives production of Period (Per) and Timeless (Tim). Per and Tim then link up to repress the production of Clk and Cyc, thus creating a negative-feedback loop controlling the concentrations of Per and Tim - the essence of the clock mechanism. The fifth protein, Cryptochrome (Cry), is light sensitive, and when it absorbs blue light, it disrupts the Per-Tim complex, thereby resetting the periodic oscillations, which keeps the molecular clock and it output rhythms in tune with the ambient light-dark cycle."

It is found that the mouse (thought to be representative of mammals in general) has a modified clock:

"The mammalian clock uses Clk and a Cyc-like protein, but it has no Tim. Instead of a single cryptochrome, it has two, neither of which is light sensitive, but both of which are the major repressors of the mammalian clock feedback loop."

The significance of the above is that the monarch butterfly has both of these molecular mechanisms. The authors describe their research findings in this way:

"The circadian clock plays a critical role in monarch butterfly migration by providing the timing component to time-compensated sun compass orientation. Here we characterize a novel molecular clock mechanism in monarchs by focusing on the functions of two CRYPTOCHROME (CRY) proteins. In the monarch clock, CRY1, a Drosophila-like protein, functions as a blue-light photoreceptor for photic entrainment, whereas CRY2, a vertebrate-like protein, functions within the clockwork as the major transcriptional repressor of the self-sustaining feedback loop. An oscillating CRY2-positive neural pathway was also discovered in the monarch brain that may communicate circadian information directly from the circadian clock to the central complex, which is the likely site of the sun compass."

Robinson concludes: "the results in this study suggest that part of the remarkable navigational ability of the butterfly relies on its ability to integrate temporal information from the clock with spatial information from its visual system. This allows the monarch to correct its course as light shifts across the sky over the course of the day." These are fascinating findings. These sophisticated systems are exciting to study and lead to many avenues of further research. At very least, evidence is here in abundance for complex specified information, which is the hallmark of intelligent design.
There are interesting questions too for evolutionists. This quote comes from a report by Faye Flam:

"CRY1 and CRY2 likely started as a single ancestral clock gene, said Adriana Briscoe a biologist at the University of California, Irvine, who was involved with some of the earlier work identifying the two genes. They would have been duplicated by accident in some early life form - probably something that predated the separation of animals from the other kingdoms of life. Over the course of time the two duplicates evolved slightly different functions. The CRY1 gene's proteins respond directly to the blue wavelength of light, while CRY2 uses indirect input from other light-sensing cells, usually located in the eye. Eventually, most organisms lost one form and kept the other."

What we have here is the quest for a plausible story, with some things being likely, other things occurring by accident, and the proposed scenario regarded as probable. We appear to be at the beginning of this particular line of enquiry, so comment is premature. However, the ancestral starting point requires there to have been homologues of both cry1 and cry2, which makes subsequent evolution a form of degeneration. The authors refer to the monarch butterfly having "an ancestral clock in which both cry1 and cry2 are expressed". Evolution by differential gene loss appears to be invoked quite frequently, but it is not the kind of evolutionary change that builds complex specified information.

Cryptochromes Define a Novel Circadian Clock Mechanism in Monarch Butterflies That May Underlie Sun Compass Navigation
Haisun Zhu, Ivo Sauman, Quan Yuan, Amy Casselman, Myai Emery-Le, Patrick Emery, Steven M. Reppert.
PLoS Biology, 8 January 2008, 6(1), e4 doi:10.1371/journal.pbio.0060004

Abstract: The circadian clock plays a vital role in monarch butterfly (Danaus plexippus) migration by providing the timing component of time-compensated sun compass orientation, a process that is important for successful navigation. We therefore evaluated the monarch clockwork by focusing on the functions of a Drosophila-like cryptochrome (cry), designated cry1, and a vertebrate-like cry, designated cry2, that are both expressed in the butterfly and by placing these genes in the context of other relevant clock genes in vivo. [. . .] The results define a novel, CRY-centric clock mechanism in the monarch in which CRY1 likely functions as a blue-light photoreceptor for entrainment, whereas CRY2 functions within the clockwork as the transcriptional repressor of a negative transcriptional feedback loop. Our data further suggest that CRY2 may have a dual role in the monarch butterfly's brain - as a core clock element and as an output that regulates circadian activity in the central complex, the likely site of the sun compass.

See also:

Robinson, R. In Monarchs, Cry2 is King of the Clock, PLoS Biology, January 8, 2008 6(1): e12 doi:10.1371/journal.pbio.0060012

Flam, F. Amazing journey of the monarch butterfly, The Philadelphia Inquirer, 21 January 2008.

Pennisi, E. Monarchs Check Clock to Chart Migration Route, Science, 300, May 23 2003: 1216-1217.