ScienceWeek

SCIENCEWEEK

November 3, 2006

Vol. 10 - Number 44

--------------------------------

In any field find the strangest thing and then explore it.

-- John Archibald Wheeler

--------------------------------

Contents (full reports below):

1. Genomics: On the Genome of a Social Insect. The transformation of an insect species from a solitary lifestyle to advanced colonial existence requires alterations in every system of the body, coupled with sufficient plasticity in the traits prescribed by the genes to generate strong differences among the adult castes. A picture of this revolution at the genomic level appears in new work...

2. Paleoceanography: On the Ancient Hot Ocean. Reconstructing past ocean temperatures is an obsession for many Earth scientists. That's understandable -- such data provide insights into climate and its links to biogeochemical cycling, ocean circulation and tectonics, not to mention mass extinctions, evolutionary radiations, and other ups and downs of the biosphere. It is the isotopic and trace-element...

3. Evolutionary Biology: On Symbiosis. Microorganisms arose and diversified before the appearance of large multicellular organisms. The bodies of the latter provided new potential habitats for microbes -- habitats that were persistent, stable (from a microbial perspective), and nutrient-rich. As a result, large organisms, from oaks to humans, have been continuously enmeshed in complex...

4. Electromagnetism: Evidence for Rotational Doppler Effect. When an observer moves towards or away from a light source, the measured frequency of the light shifts in proportion to the source and observer's relative velocity. Perhaps the best-known example of this Doppler shift is the "redshift" -- a displacement towards lower frequencies -- of light emitted by receding galaxies. The Doppler shift also applies to...


--------------------------------

Also Noted:

Moral Minds. How Nature Designed Our Universal Sense of Right and Wrong. Marc D. Hauser. Ecco (HarperCollins), New York, 2006. Hardback: 511 pp. $27.95, C$35.95. ISBN 0060780703. More information at: http://www.amazon.com/exec/obidos/ASIN/0060780703/scienceweek

Relativity. The Special and General Theory. Albert Einstein. Plume (Penguin Group USA), New York, 2006. Hardback: 287 pp. $11. ISBN 0452287847. Translated by Roger W. Lawson. More information at: http://www.amazon.com/exec/obidos/ASIN/0452287847/scienceweek

The Triumph of the Fungi. A Rotten History. Nicholas P. Money. Oxford University Press, New York, 2006. Hardback: 213 pp., illus. $29.95. ISBN 019518971X. More information at: http://www.amazon.com/exec/obidos/ASIN/019518971X/scienceweek

An Introduction to Systems Biology. Design Principles of Biological Circuits. Uri Alon. Chapman and Hall/CRC, Boca Raton, FL, 2006. Paperback: 315 pp., illus. $49.95. ISBN 1584886420. More information at: http://www.amazon.com/exec/obidos/ASIN/1584886420/scienceweek

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Special Note: A New Book by the Editor of ScienceWeek:

JUNK SCIENCE. How Politicians, Corporations, and Other Hucksters Betray Us. Dan Agin. Thomas Dunne Books/St. Martin's Press, New York, 2006. Hardback: 336 pp., $24.95. ISBN 0312352417.

Question: What do the following have in common: George W. Bush, Leon Kass, Milton Friedman, Charles Krauthammer, Francis Fukuyama, William Kristol, Arthur R. Jensen, Steven Pinker, Dwight J. Ingle, William B. Shockley, Senator James M. Inhofe, Frederick Seitz, the food industry, the pharmaceutical industry, the longevity industry, the tobacco industry, creationism, racist psychology, chiropractics, and alternative medicine? Answer: They are all attacked by Dan Agin in his new book JUNK SCIENCE: How Politicians, Corporations, and Other Hucksters Betray Us.

More information about JUNK SCIENCE at: http://www.amazon.com/exec/obidos/ASIN/0312352417/scienceweek

A recent long review of this book appeared in the San Diego Union-Tribune, October 22, 2006. The review can be accessed at:

http://www.signonsandiego.com/uniontrib/20061022/news_lz1v22junk.html

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

1. GENOMICS: ON THE GENOME OF A SOCIAL INSECT

The following points are made by Edward O. Wilson (Nature 2006 443:919):

1) The transformation of an insect species from a solitary lifestyle to advanced colonial existence requires alterations in every system of the body, coupled with sufficient plasticity in the traits prescribed by the genes to generate strong differences among the adult castes. A picture of this revolution at the genomic level appears in new work (1).

2) If Earth's social organisms are scored by complexity of communication, division of labor, and intensity of group integration, three pinnacles of evolution stand out: humanity, the jellyfish-like siphonophores, and a select assemblage of social insect species (2,3). The honeybee, Apis mellifera, is a member of this insect group -- which also includes the spectacular leaf-cutting ants, army ants, and macrotermitine mound-building termites -- and no one can deny that it belongs in this front rank (4). As pointed out by the authors of the new work (1), the abiding mystery of A. mellifera is how creatures as tiny as worker bees, with brains containing only a millionth the number of neurons as do ours, are able to perform so many tasks and integrate them into a harmonious whole. Since the first publication on honeybees of the modern era, Charles Butler's Feminine Monarchie (1609), discoveries have flowed at the organism and colony levels, justifying Karl von Frisch's remark that, to scientists, "The life of bees is like a magic well. The more you draw from it, the more there is to draw."

3) The most celebrated characteristic of A. mellifera, next to its honey and pollination services, is, of course, the waggle dance. Foraging workers, on returning to the hive after successful searches for food sources or new nest sites, run figures-of-eight on the vertical comb surfaces, with the middle segment of their body symbolically representing the flight to be taken outward. This latter "waggle run" contains information about the direction of the target with reference to the Sun, as well as conveying distance from the hive. Timed buzzing and odor secretion enhance the message. Circular "round dances" supplant the full waggle dance to inform nestmates that the target is close to the nest.

4) Research in recent years has revealed other performances on the honeybee dance card. If the returning foragers discover many food handlers unemployed as they unload their harvest, they perform the "shaking dance" to bring more workers on to the dance floor and thence out to the field. If the reverse occurs, in other words if the foragers have trouble passing on their load, they engage in "tremble dances", to draft in more bees to act as food handlers. In addition to their terpsichorean program, honeybees employ pheromones. These substances, secreted from glands distributed over the body, variously alarm or recruit nestmates, distinguish them from alien bees, and classify them according to gender, caste and age (4,5). As workers pass through their natural adult lifespan of about 40 days, their socially active glands variously grow and shrink in programmed time sequences in concert with the labor roles they assume. The progression can be speeded up or reversed according to the needs of the colony. And as they shift among specialities, their receptiveness to particular signals rises or falls.

References (abridged):

1. The Honeybee Genome Sequencing Consortium Nature 443, 931-949 (2006).

2. Wilson, E. O. Sociobiology: The New Synthesis (Harvard Univ. Press, 1975).

3. Choe, J. C. & Crespi, B. J. (eds) The Evolution of Social Behavior in Insects and Arachnids (Cambridge Univ. Press, 1997).

4. Seeley, T. D. The Wisdom of the Hive (Harvard Univ. Press, 1995).

5. Michener, C. D. The Social Behavior of the Bees: A Comparative Study (Harvard Univ. Press, 1974).

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2. PALEOCEANOGRAPHY: ON THE ANCIENT HOT OCEAN

The following points are made by Christina L. De La Rocha (Nature 2006 443:920):

1) Reconstructing past ocean temperatures is an obsession for many Earth scientists. That's understandable -- such data provide insights into climate and its links to biogeochemical cycling, ocean circulation and tectonics, not to mention mass extinctions, evolutionary radiations, and other ups and downs of the biosphere. It is the isotopic and trace-element compositions of sedimentary materials that provide the necessary information to quantitatively infer past temperatures. But that task is not straightforward, even for the past few hundred million years for which we have relatively pristine sediments to analyse. Go back to the Precambrian -- roughly 4.5 billion to 0.5 billion years ago -- and the job is even more daunting. Not only are there few sedimentary materials of that age left to work with, but all of those that do remain have been altered since they were laid down. Thus, for decades we have not known what to make of geochemical estimates (1-3) indicating that between 3.5 billion and 1.2 billion years ago the ocean was as hot as 55-85 C. Those estimates have been especially difficult to believe given the geological evidence for glaciations during this time (4). Robert and Chaussidon (5), however, have now used the silicon-isotopic composition of ancient rock samples to support the earlier, intriguing results (1-3).

2) Deducing the environmental conditions of the Precambrian ocean would be a stunning achievement. This is, after all, the setting for the origin of life and the evolution of the great microbial diversity that led to and still supports plant and animal life today. The previous estimates of Precambrian ocean temperatures (1-3) are based on the oxygen-isotopic composition of chert, a siliceous rock that is formed when silica precipitates from sea water. Precipitated silica will have an 18O to 16O ratio that is higher than the fluid from which it formed, and the extent to which the 18O to 16O ratio is higher is inversely related to temperature. For a given fluid composition, then, the higher the temperature, the lower the resulting 18O to 16O ratio of the silica (reported as delta-18O when normalized to a standard). Thus, the remarkably low delta-18O values of Precambrian chert, and their increase towards the Precambrian-Cambrian boundary, could indicate an ancient ocean that was scores of degrees warmer than the modern one and that cooled gradually. But caution dictates ascribing the strikingly low delta-18O values of ancient chert to other factors, such as the hydrothermal, metamorphic or other alteration of those rocks over billions of years, and not to superwarm Precambrian sea water.

3) But the low delta-18O values may indicate high temperatures after all. Robert and Chaussidon (5) point out that the Precambrian chert samples with the highest delta-18O values (that is, those least likely to have been altered) have delta-18O values that correlate strongly with their silicon-isotopic composition (30Si/28Si, reported as delta-30Si). It is unlikely that such a relationship would have been maintained during alteration, suggesting that the isotopic signal of these particular chert samples is primary and robust. This evidence alone supports the contention that the Precambrian ocean was quite warm. But Robert and Chaussidon (5) have taken things a step further by using the silicon isotopes on their own to make an alternative temperature estimate.

4) The delta30Si values of chert older than 1 billion years can be high (5) relative to the siliceous sediments and ocean waters of the modern day. Precambrian concentrations of dissolved silicon were extreme, not far from the point of saturation, and were controlled largely by abiotic reactions. Robert and Chaussidon assume that seawater delta-30Si was steady over time, and argue that the delta-30Si of chert and that of the silica precipitated during the circulation of hydrothermal fluids through ocean crust must have together equalled the delta-30Si of the mantle, the ultimate source of silicon to the system. Because precipitates have a lower delta-30Si than the dissolved silicon from which they formed, an increase in the proportion of hydrothermal silicon precipitated should be reflected in an increase in the delta-30Si of chert. And if the temperature of sea water controlled the extent of the hydrothermal silicification, the delta30Si of Precambrian chert should reveal the temperature of the ocean at that time.

References (abridged):

1. Knauth, L. P. & Lowe, D. R. Earth Planet. Sci. Lett. 41, 209-222 (1978).

2. Knauth, L. P. & Lowe, D. R. Geol. Soc. Am. Bull. 115, 566-580 (2003).

3. Knauth, L. P. Palaeogeogr. Palaeoclimatol. Palaeoecol. 219, 53-69 (2005).

4. Kopp, R. E., Kirschvink, J. L., Hilburn, I. A. & Nash, C. Z. Proc. Natl Acad. Sci. USA 102, 11131-11136 (2005).

5. Robert, F. & Chaussidon, M. Nature 443, 969-972 (2006).

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

3. EVOLUTIONARY BIOLOGY: ON SYMBIOSIS

The following points are made by Nancy A. Moran (Current Biology 2006 16:R866):

1) Microorganisms arose and diversified before the appearance of large multicellular organisms. The bodies of the latter provided new potential habitats for microbes -- habitats that were persistent, stable (from a microbial perspective), and nutrient-rich. As a result, large organisms, from oaks to humans, have been continuously enmeshed in complex interactions with microorganisms during their evolution. Biologists have paid most attention to associations with microbes that are pathogenic; typically, microbial infection has been viewed as deleterious, or at best irrelevant, to vigor and reproduction. But the last 15 years have witnessed increased appreciation of interactions that benefit the host as well as the microbe. These interactions are loosely grouped under the term "symbiosis" and the microbial partners called "symbionts". Although the term "symbiont" is typically applied to mutualistic microorganisms, it is often used to include associates for which the full spectrum of effects on hosts is not known.

2) Symbiosis is ubiquitous in terrestrial, freshwater, and marine communities. It has played a key role in the emergence of major life forms on Earth and in the generation of biological diversity. Numerous authors have pointed out that Darwin did not emphasize symbiosis as an evolutionary mechanism; its role is, of course, not inconsistent with Darwin's main ideas, but appreciation of symbiosis as a source of evolutionary novelty has developed relatively recently. Its importance is perhaps most strikingly illustrated by the symbiotic events that led to the evolution of eukaryotic organelles -- plastids and mitochondria -- from cyanobacterial and alpha-Proteobacterial ancestors, respectively.

3) For plants, associations with fungi and bacteria were key innovations in the colonization of land and of specific habitats. Eukaryote-associated microbes act as metabolic partners for accessing limiting nutrients and also as protectors, producing toxins that ward off herbivores or pathogens. Similar associations have arisen with animals, allowing colonization of diverse niches, such as the specialized feeding on plant or animal tissues, and the use of deep ocean hydrothermal vent habitats. Often, the associations are persistent for the hosts, frequently being transmitted vertically across generations, from mother to progeny. The organisms involved in a symbiosis may be sufficiently fused that they cannot live apart or be recognized as distinct entities without close scrutiny.

4) Before biological research became focused on genetic model organisms, greater attention was paid to the study of symbiosis. Microscopy was used extensively to discover and elucidate symbioses before the middle of the 20th century. The reasons for a period of relative neglect, until about 1990, are complex. One contributing factor has been the unsuitability of most symbiotic partners as models for laboratory studies of genetics and development. The organisms that are easiest to grow and study in the laboratory, such as Escherichia coli, Arabidopsis thaliana, Drosophila melanogaster and Mus domesticus, are weedy species adapted to show fast growth in temporary niches. These species have lifestyles relatively free of complex interdependencies with other species. But most microorganisms in natural communities are likely to have obligate dependencies on other species (often other microbes), explaining why 99% of microorganisms are difficult or impossible to culture. Similarly, most symbionts of plants and animals cannot be readily cultured independently of hosts, precluding most conventional microbiological analyses.(1-5)

References (abridged):

1. Arnold, A.E., Mejia, L.C., Kyllo, D., Rojas, E.I., Maynard, Z., Robbins, N., and Herre, E.A. (2003). Fungal endophytes limit pathogen damage in a tropical tree. Proc. Natl. Acad. Sci. USA 100, 15649-15654.

2. Baumann, P. (2005). Biology of bacteriocyte-associated endosymbionts of plant sap-sucking insects. Annu. Rev. Microbiol. 59, 155-189.

3. Brownlie, J.C., and O'Neill, S.L. (2005). Wolbachia genomes: insights into an intracellular lifestyle. Curr. Biol. 15, 507-509.

4. Ley, R.E., Peterson, D.A., and Gordon, J.I. (2006). Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell 124, 837-848.

5. McFall-Ngai, M.J., and Gordon, J.I. (2006). Experimental models of symbiotic host-microbial relationships: understanding the underpinnings of beneficence and the origins of pathogenesis. In: Seifert, H.S., Dirita, V.J. (Eds.), Evolution of Microbial Pathogens. (2006). ASM Press, Washington, D.C.

Current Biology http://www.current-biology.com

ScienceWeek http://scienceweek.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

4. ELECTROMAGNETISM: EVIDENCE FOR ROTATIONAL DOPPLER EFFECT

The following points are made by Miles Padgett (Nature 2006 443:924):

1) When an observer moves towards or away from a light source, the measured frequency of the light shifts in proportion to the source and observer's relative velocity. Perhaps the best-known example of this Doppler shift is the "redshift" -- a displacement towards lower frequencies -- of light emitted by receding galaxies. The Doppler shift also applies to sound waves, causing the characteristic rise and fall in the pitch of a passing police siren. New work (1) has now measured the broadening of a spectral line caused by an effect analogous to the conventional Doppler effect. In this case, however, the shift in frequency arises not from linear motion, but from rotation -- the rarely encountered rotational Doppler effect.

2) Place a watch at the center of a rotating turntable, and, viewed from above, its hands will seem to rotate more quickly. This classical effect applies to all rotating vectors, for example to the spatial pattern of the electric field of any light beam carrying angular momentum. The electric-field vector rotates at the frequency of the light, but an additional rotation of the beam about its axis of propagation will speed up or slow down the field rotation, resulting in a frequency shift proportional to the rate of rotation of the beam. The rotational Doppler effect is seen by looking at a rotating body along or parallel to its axis of rotation. It is therefore distinct from the linear Doppler shift that arises from viewing the edges of an extended body -- a galaxy, say -- in a direction perpendicular to its rotation axis. The effect was originally observed and analysed in terms of Jones polarization matrices, which describe the effect of a medium on the orientation of the electric-field vector (2). The effect has also been cited as an example of a geometric, or Berry, phase shift that occurs in a system whose parameters are progressively changed before it is brought back to its initial state (3).

3) At a more subtle level, the angular momentum of light can be divided into spin and orbital components (4). The spin angular momentum is associated with the rotation of the electric-field vector. This corresponds to circular polarization, meaning that the tip of the vector traces a circular pattern in space as it rotates. The orbital angular momentum, on the other hand, is associated with a rotation of the light wave's phase. Whereas the spin angular momentum can take only two independent states (clockwise or anticlockwise, according to the sense of the field vector's rotation), the orbital angular momentum can take any number of states with different values of angular momentum. In all cases, for a given field rotation speed, the Doppler frequency shift is proportional to the total angular momentum. This shift has been directly quantified for the rotation of electromagnetic beams at millimeter wavelengths (5).

4) Barreiro et al (1) examined the spectrum of transitions between energy levels in rubidium gas, using as probes two light beams carrying different values of orbital angular momentum. The rotational Doppler effect is easily masked by larger frequency shifts, such as the normal linear Doppler shift. The authors used a geometry in which all these unwanted frequency shifts balanced to zero, and chose an intricate rubidium transition that needs two photons and a magnetic field to be activated. The transition had an initial line-width of 52 kilohertz, but when orbital angular momentum was introduced to the light beams, this broadened to 300 kHz -- a clear signal of the rotational Doppler effect.

References (abridged):

1. Barreiro, S., Tabosa, J. W. R., Failache, H. & Lezama, A. Phys. Rev. Lett. 97, 113601 (2006).

2. Garetz, B. A. & Arnold, S. Opt. Commun. 31, 1 (1979).

3. Simon, R., Kimble, H. J. & Sundarshan, E. C. G. Phys. Rev. Lett. 61, 19-22 (1988).

4. Allen, L., Beijersbergen, M. W., Spreeuw, R. J. C. & Woerdman, J. P. Phys. Rev. A 45, 8185-8189 (1992).

5. Courtial, J., Robertson, D. A., Dholakia, K., Allen, L. & Padgett, M. J. Phys. Rev. Lett. 81, 4828-4830 (1998).

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=