Chinese Academy of Sciences, Beijing

A palaeontologist considers the evolution of birds’ mechanism of breathing.

During both inhalation and exhalation, the air in birds’ lungs moves in just one direction, through small tubes. This is unusual: most animals move air tidally, in and out of dead-end gas-exchange structures. The question of when and how the avian breathing mechanism evolved is interesting to palaeontologists like me who study these unusual features.

Traditionally, the avian pattern of one-way breathing has been thought to depend on special accessory air sacs that work similarly to bellows. Largely because they don’t have these air sacs, alligators have always been presumed to be tidal breathers. However, this has now been questioned by Colleen Farmer and Kent Sanders at the University of Utah in Salt Lake City, who suggest that alligators actually breathe like birds (C. G. Farmer & K. Sanders Science 327, 338–340; 2010).

By measuring air and water flows in the lungs of anaesthetized and dead alligators, respectively, the authors demonstrate unidirectional flow. They draw the reasonable inference that this bird-like breathing is characteristic of the archosaurs, a broad group that includes both alligators and birds.

The finding is leading to changes in the direction of palaeontological research. Farmer and Sanders’ results imply that air sacs are not essential for unidirectional breathing. The function of these sacs in extinct ancestors of birds — dinosaurs such as theropods — should thus be reconsidered.

Unidirectional breathing probably appeared among ancestral archosaurs during the Early Triassic period, some 250 million years ago, a time of low oxygen levels that might have encouraged evolutionary experimentation with improved ventilation. This raises the question of whether the drastic conditions led to other notable changes in Triassic animals.

University of Graz, Austria

A chemist muses on the technique of microwaving flowing chemical reactions.

A hot topic in synthetic chemistry is continuous-flow processing involving ‘microreactors’ or related devices. Making molecules using a continuous-flow process has several advantages over the more conventional batch approach: for example, reaction conditions can be easily scaled up to production capacities without the need for further optimization.

Chao-Jun Li at McGill University in Montreal and Michael Organ at York University in Toronto, both in Canada, and their colleagues combined continuous-flow processing, using standard glass capillaries, with microwave irradiation to perform extremely fast chemical reactions (G. Shore et al. Chem. Eur. J. 16, 126–133; 2010). The team generated propargyl amines, which are important synthetic intermediates, using a three-component reaction.

To achieve efficient microwave heating, the researchers coated the insides of the flow tubes with thin films of metals such as gold and copper. Analysis by scanning electron microscopy showed that these metal films typically consisted of clusters of metal nanoparticles, which have been shown to catalyse a variety of valuable synthetic transformations.

What struck me in this study was the achievement of such high reaction temperatures — in excess of 900 °C on the outer surface of the glass tube — with comparatively low levels of 2.45-gigahertz microwave irradiation.

Reactions at such high temperatures are extremely fast. One could speculate that, in these conditions, some chemical transformations might occur in the gas phase, as seen in flash vacuum thermolysis, a technique that is used to perform high-temperature organic reactions in the gas phase. This could potentially open up an easy way to perform high-temperature gas- or liquid-phase reactions in a scalable manner.

Karolinska Institute, Stockholm, Sweden

A human geneticist explores genetic diversity in Asia.

We often imagine that the heterogeneity of human populations is a reflection of thousands of years of human migration, but there is little evidence to support this. DNA may provide a source of such evidence, particularly that of the people of Asia, which has a population of 3.9 billion and a diverse set of ethnic groups.

Previous studies of Asian migration history and genetic diversity included only a limited number of protein markers and relatively few individuals from each ethnic group. So it was no surprise that the HUGO Pan-Asian SNP Consortium launched an effort to scrutinize Asian genetic variation in more detail. The consortium, made up of dozens of researchers spread predominantly across Asia, analysed the genomes of nearly 2,000 people from 75 ethnic groups. What was surprising was that most of the East Asian haplotypes — patterns of gene variants that co-occur on a single chromosome — were found in either South East Asia or South Central Asia. Moreover, half of these haplotypes were found in South East Asia alone (HUGO Pan-Asian SNP Consortium Science 326, 1541–1545; 2009).

This suggests that this area of the continent was the most probable source of migration to other parts of Asia early in human history. The haplotype diversity is strongly correlated with latitude, and the northward gradient of haplotype distribution points to a possible direction of migration of ancient Asians.

Although the data do not disprove the direction of a second wave of migration that is presumed to have occurred from Africa to Asia, they do indicate substantial dominance of population migration from South East Asia towards other Asian territories. This is an exciting example of genetics providing solid evidence of migration paths, filling in the gaps of human history.

University of Liverpool, UK

An evolutionary biologist marvels at how species evolve to help each other out.

Mutualistic interactions between species underpin much of nature’s biodiversity. These associations range from prolonged and intimate, such as those between nitrogen-fixing bacteria and leguminous plants, to fleeting — visits of pollinating animals to flowers, for example. Despite the wide-ranging importance of mutualisms, there have been few experimental studies on their origins or evolution.

In a fascinating experiment, Kristina Hillesland and David Stahl at the University of Washington in Seattle watched a novel two-species interaction develop from teetering baby steps to a stable, robust mutualism over just 300 generations (K. L. Hillesland and D. A. Stahl Proc. Natl Acad. Sci. USA 107, 2124–2129; 2010).

Grown in the lab with lactate as the sole nutrient source, the bacterium Desulfovibrio vulgaris and the archaeon Methanococcus maripaludis, which never interact in nature, had to collaborate to survive. D. vulgaris fermented lactate to produce acetate, carbon dioxide and hydrogen — a reaction that sustains growth only if the hydrogen concentration is kept low. M. maripaludis fulfilled this requirement by consuming hydrogen to reduce carbon dioxide to methane.

Communities were initially poorly adapted to do this, and underwent drastic fluctuations in population size, with some even going extinct. In other communities, however, natural selection ensured that the two processes were optimized, thereby jointly increasing the fitness of both species. Co-evolved communities outperformed their evolutionary ancestors by growing 80% faster and producing 30% more biomass.

The work demonstrates the evolution of a stable multispecies mutualism, enhancing our understanding of how such interactions, so important for biodiversity, come about in nature.

Weizmann Institute of Science, Rehovot, Israel

A computational biologist looks at how identical cells come to differ.

My main interest is in understanding how complex biological behaviours are encoded by DNA. An example of such behaviour is the ability of genetically identical cells to generate diversity in their phenotypes, or observable traits, by changing how genes are expressed from one cell to the next. How expression variability occurs over short timescales (for example, during a cell cycle) has been well studied; much less is known about it over longer timescales.

So I was excited by work from Narendra Maheshri of the Massachusetts Institute of Technology in Cambridge and his colleagues. They demonstrate that slow expression fluctuations of a yeast gene are regulated locally, or in cis, by that gene’s promoter — a nearby stretch of DNA that regulates the gene’s expression (L. M. Octavio et al. PLoS Genet. 5, e1000673; 2009).

They studied the yeast protein FLO11, placing two copies of the protein’s promoter in the same cell, each in front of an engineered fluorescent ‘reporter’ gene. The reporters switched expression slowly and independently, implying that the expression fluctuations were locally encoded. The authors further identified global, or trans, regulators that affect the fast and slow expression fluctuations of FLO11. The type of expression effect that a regulator exerts seems to depend on several factors, including the location of the regulator relative to the site at which transcription, or reading of the DNA, begins, and relative to sites for other regulators.

Although the mechanistic details of this encoding are still unclear, applying similar approaches to many more promoters should bring us closer to understanding how other complex phenomena are encoded by DNA. This will hopefully allow us to one day predict the phenotypic effects of human genetic variation.