Cryptochrome and Magnetic Sensing

Magnetic sensing is a type of sensory perception that has long been studied. Over the past 50 years, scientific studies have shown that a wide variety of living organisms have the ability to perceive magnetic fields and can use information from the Earth’s magnetic field in orientation behavior. Examples abound: salmon, sea turtles, spotted newts, lobsters, honeybees and perhaps us humans can all perceive and utilize geomagnetic field information.

cryptochrome

But perhaps the most well-studied example of animal magnetoreception is the case of migratory birds (e.g. European robins (Erithacus rubecula), silvereyes (Zosterops l. lateralis), garden warblers (Sylvia borin)), who use the Earth’s magnetic field, as well as a variety of other environmental cues, to find their way during migration.

The avian magnetic compass is a complex entity with many surprising properties. The basis for the magnetic sense is located in the eye of the bird, and furthermore, it is light-dependent, i.e., a bird can only sense the magnetic field if certain wavelengths of light are available. Specifically, many studies have shown that birds can only orient if blue light is present. The avian compass is also an inclination-only compass, meaning that it can sense changes in the inclination of magnetic field lines but is not sensitive to the polarity of the field lines. Under normal conditions, birds are sensitive to only a narrow band of magnetic field strengths around the geomagnetic field strength, but can orient at higher or lower magnetic field strengths given accommodation time.

A Radical-Pair-Based Avian Compass

Despite decades of study, the physical basis of the avian magnetic sense remains elusive. The two main models for avian magnetoreception are a magnetite-based model and a radical-pair-based model (for review see, e.g., Solov’yov, Schulten, Greiner, 2010). The former suggests that the compass has its foundation in small particles of magnetite located in the head of the bird. The latter idea is that the avian compass may be produced in a chemical reaction in the eye of the bird, involving the production of a radical pair. A radical pair, most generally, is a pair of molecules, each of which have an unpaired electron. If the radical pair is formed so that the spins on the two unpaired electrons in the system are entangled (i.e. they begin in a singlet or triplet state), and the reaction products are spin-dependent (i.e., there are distinct products for the cases where the radical pair system is in an overall singlet vs. triplet state), then there is an opportunity for an external magnetic field to affect the reaction by modulating the relative orientation of the electron spins.

How could a radical pair reaction lead to a magnetic compass sense? Suppose that the products of a radical pair reaction in the retina of a bird could in some way affect the sensitivity of light receptors in the eye, so that modulation of the reaction products by a magnetic field would lead to modulation of the bird’s visual sense, producing brighter or darker regions in the bird’s field of view. (The last supposition must be understood to be speculative; the particular way in which the radical pair mechanism interfaces with the bird’s perception is not well understood.)

When the bird moves its head, changing the angle between its head and the Earth’s magnetic field, the pattern of dark spots would move across its field of vision and it could use that pattern to orient itself with respect to the magnetic field. This idea is explored in detail by Ritz et al (see below). Interestingly, studies have shown that migratory birds exhibit a head-scanning behavior when using the magnetic field to orient that would be consistent with such a picture. Such a vision-based radical-pair-based model would explain several of the unique characteristics of the avian compass, e.g., that it is light-dependent, inclination-only, and linked with the eye of the bird. It is also consistent with experiments involving the effects of low-intensity radio frequency radiation on bird orientation, as suggested by Canfield et al.

The question remains as to where, physically, this radical pair reaction would take place. It has been suggested that the radical pair reaction linked to the avian compass arises in the protein cryptochrome. Cryptochrome is a signaling protein found in a wide variety of plants and animals, and is highly homologous to DNA photolyase. There is some evidence that retinal cryptochromes may be involved in the avian magnetic sense. Detailed analysis of cryptochrome as a transducer for the avian compass would require an atomic-resolution structure of the protein, and unfortunately, no structure of avian cryptochrome is currently available.

However, the structure of cryptochrome from a plant (Arabidopsis thaliana) is available, and the cryptochromes of plants and birds are structurally very similar. Recent experiments by Ahmad et al. (Ahmad, Galland, Ritz, Wiltschko and Wiltschko. Magnetic intensity affects cryptochrome-dependent responses in Arabidopsis thaliana. Planta 225, 615-624 (2007)) have shown that Arabidopsis seedlings exhibit a magnetic field effect. Processes involved with cryptochrome signaling (such as hypocotyl growth inhibition) are enhanced under a magnetic field of 5 G (as compared with an Earth-strength 0.5 G magnetic field).

Both photolyase and cryptochrome internally bind the chromophore flavin adenine dinucleotide (FAD). In photolyase, the protein is brought to its active state via a light-induced photoreduction pathway involving a chain of three tryptophans. Studies suggest that cryptochrome also is activated by a similar photoreduction pathway.

However cryptochrome’s signalling state has a limited lifetime. Under aerobic conditions, the stable FADH molecule slowly reverts back to the initial FAD state as illustrated in Fig. 3. This process is not well understood and occurs on the millisecond time scale. The cryptochrome back-reaction attracted considerable attention recently due to indications that it may be the key link to avian magnetoreception. In the course of the back-reaction a radical pair is formed between flavin and an oxygen molecule.

 

James Hansen (Inventor of Global Warming) Embarrasses NASA

WASHINGTON (AP) – Exactly 20 years after warning America about global warming, a top NASA scientist said the situation has gotten so bad that the world’s only hope is drastic action.

James Hansen told Congress on Monday that the world has long passed the “dangerous level” for greenhouse gases in the atmosphere and needs to get back to 1988 levels. He said Earth’s atmosphere can only stay this loaded with man-made carbon dioxide for a couple more decades without changes such as mass extinction, ecosystem collapse and dramatic sea level rises.

“We’re toast if we don’t get on a very different path,” Hansen, director of the Goddard Institute of Space Sciences who is sometimes called the godfather of global warming science, told The Associated Press. “This is the last chance.”

Hansen brought global warming home to the public in June 1988 during a Washington heat wave, telling a Senate hearing that global warming was already here. To mark the anniversary, he testified before the House Select Committee on Energy Independence and Global Warming where he was called a prophet, and addressed a luncheon at the National Press Club where he was called a hero by former Sen. Tim Wirth, D-Colo., who headed the 1988 hearing.

To cut emissions, Hansen said coal-fired power plants that don’t capture carbon dioxide emissions shouldn’t be used in the United States after 2025, and should be eliminated in the rest of the world by 2030. That carbon capture technology is still being developed and not yet cost efficient for power plants.

Burning fossil fuels like coal is the chief cause of man-made greenhouse gases. Hansen said the Earth’s atmosphere has got to get back to a level of 350 parts of carbon dioxide per million. Last month, it was 10% higher: 386.7 parts per million.

Hansen said he’ll testify on behalf of British protesters against new coal-fired power plants. Protesters have chained themselves to gates and equipment at sites of several proposed coal plants in England.

“The thing that I think is most important is to block coal-fired power plants,” Hansen told the luncheon. “I’m not yet at the point of chaining myself but we somehow have to draw attention to this.”

Frank Maisano, a spokesman for many U.S. utilities, including those trying to build new coal plants, said while Hansen has shown foresight as a scientist, his “stop them all approach is very simplistic” and shows that he is beyond his level of expertise.

The year of Hansen’s original testimony was the world’s hottest year on record. Since then, 14 years have been hotter, according to the National Oceanic and Atmospheric Administration.
Two decades later, Hansen spent his time on the question of whether it’s too late to do anything about it. His answer: There’s still time to stop the worst, but not much time.
“We see a tipping point occurring right before our eyes,” Hansen told the AP before the luncheon. “The Arctic is the first tipping point and it’s occurring exactly the way we said it would.”

Hansen, echoing work by other scientists, said that in five to 10 years, the Arctic will be free of sea ice in the summer.

Longtime global warming skeptic Sen. James Inhofe, R-Okla., citing a recent poll, said in a statement, “Hansen, (former Vice President) Gore and the media have been trumpeting man-made climate doom since the 1980s. But Americans are not buying it.”

But Rep. Ed Markey, D-Mass., committee chairman, said, “Dr. Hansen was right. Twenty years later, we recognize him as a climate prophet.”

Tom C. Van Flandern (1940 – 2009) “Exploded Planet Hypothesis” 

Dr. Thomas Charles Van Flandern, an expert in celestial mechanics and cosmology, died January 9, 2009 in Seattle, Washington, of colon cancer. He was 68. Van Flandern was an astronomer at the U.S. Naval Observatory from 1963 to 1983. He developed software to predict and analyze lunar occultations to improve lunar orbital and fundamental star catalog data. In later years he championed increasingly controversial theories. But his 1978 prediction that some asteroids have natural satellites, which was almost universally rejected, was verified when the Galileo spacecraft photographed Dactyl, a satellite of (243) Ida, during its flyby in 1993. Besides astronomy and computers, he had strong interests in biochemistry and nutrition, and he ran a business selling personal computers in the 1980s.

Tom Van Flandern was born June 26, 1940 in Cleveland, Ohio, the first child of Robert F. Van Flandern and Anna Mary Haley. His father, a police officer, left the family when Tom Van Flandern was 5. His mother died when he was 16; he and his siblings then lived with their grandmother, Margery Jobe, until he went to college.

Tom Van Flandern became interested in astronomy as a child. He used his first telescope, purchased with newspaper delivery earnings, to observe lunar occultations, and then learned how to predict them, sparking a life-long passion for dynamical astronomy. While attending St. Ignatius High School, Van Flandern and fellow student Thomas Petrie organized the Cleveland Moonwatch team to observe the first artificial satellites, the only team without an adult organizer.

In 1958, Tom Van Flandern entered Xavier University where he led the Cincinnati Moonwatch team. He learned computer programming at a summer job with General Electric and wrote software to calculate “look angles” from orbital elements. The Cincinnati team became a top producer of observations using these predictions. Tom obtained a B.S. in mathematics from Xavier in 1962. He spent the next year at Georgetown University studying astronomy.

On July 6, 1963, Tom Van Flandern married Barbara Ann Weber in Kentucky. They remained together until his passing 46 years later. They had four children, Michael, Constance, Brian, and Kevin. Also in 1963, Tom began work in the Nautical Almanac Office of the U.S. Naval Observatory in Washington, DC. He became an expert on refining the lunar orbit from timings of lunar occultations, then the best observations for that purpose. He encouraged observations by providing observers with predictions of occultations for their locations. He designed a cable system connecting all observers timing a grazing occultation, to record their observations at a central station. After a 1964 success, four amateur astronomical societies built similar cable systems.

Tom Van Flandern relished efforts to simplify computer calculations. He and Henry Fliegel developed an algorithm to calculate a Julian date from a Gregorian date that would fit on a single IBM card. They published this in a paper, “A machine algorithm for processing calendar dates” in 1968 in the Communications of the Association for Computing Machinery. This was used in countless business applications worldwide. With Kenneth Pulkkinen, he published “Low precision formulae for planetary positions”, in Ap. J. Supp. in 1979. The paper set a record for the number of reprints requested from that journal.

Tom Van Flandern earned a PhD in astronomy from Yale University in 1969. His thesis was “A discussion of 1950-1968 occultations of stars by the Moon”, advised by Prof. G. M. Clemence. In 1976 Van Flandern asserted that the orbits of 60 long-period comets traced to a common origin, supporting Michael Ovenden’s exploded planet hypothesis.

He founded the non-profit Meta Research, Inc. in 1990 to provide support for alternative theories in astronomy. The Meta Research Bulletin reported the newest discoveries and how they presented difficulties to accepted astronomical theories, such as the Big Bang and planetary formation. The Bulletin claimed mainstream scientists preferred making ad hoc corrections to the theories rather than acknowledge fundamental difficulties that might jeopardize their funding.

Tom Van Flandern’s advocacy of an artificial origin for the “face on Mars”, especially after higher-resolution images were taken in 2001, antagonized many. His questioning of the speed of gravity, first published in a 1998 paper in Physics Letters A, provoked additional attacks from relativists. He showed the same persistence with these controversies that had enabled him to solve complex programming and celestial mechanics problems.

Tom Van Flandern did not reject General Relativity as some have asserted, but rather rejected its geometrical interpretation. He said: “General relativity has a geometric and a field interpretation. If angular momentum conservation is invoked in the geometric interpretation to explain experiments, the causality principle is violated. The field interpretation avoids this problem by allowing faster-than-light propagation in forward time.” Tom Van Flandern strongly attacked some alternative theories, such as Velikovsky’s ideas of recent planetary close approaches, turning one of Velikovsky’s supporters, C. L. Ellenberger, into a strong critic.

If not for these antagonisms, the “mainstream” part of Tom Van Flandern’s work in later years might be better acknowledged, including his “Eclipse Edge” company that organized expeditions to several solar eclipses, and his work with E. Lyytinen on the passage of Earth through cometary debris trails. Their prediction was closest to the observed time of the Leonid storm maximum of November 2001.

Tom Van Flandern held memberships in the International Astronomical Union, the American Astronomical Society (and in its Divisions on Dynamical Astronomy and Planetary Sciences), and several other scientific organizations. He received second prize from the Gravity Research Foundation in 1974 and the Astronomy Award from the Washington Academy of Sciences in 2000. An asteroid, (52266) 1986 AD, was named “Van Flandern” in his memory on February 9, 2009.

Tom Van Flandern’s survivors include his wife, Barbara; his brother William; and his four children. He was buried in Sequim, Washington, near his last home. His inquisitive mind, unshakable integrity, and boundless enthusiasm are remembered fondly by his friends and colleagues. He left behind a valuable legacy of astronomical work.