PNAS highlights for the week of April 25-29

April 25, 2005

Songbird Color Vision: Attracting Mates, Avoiding Predators

Differences in color vision allow songbirds to be less obvious to predators yet maintain their attractiveness to other songbirds, according to newly released research.

In some bird species, males attract mates with bright, elaborate plumage, but such conspicuous traits can draw the attention of predators. Birds can see ultraviolet (UV) light, but mammalian predators cannot, suggesting that UV-reflecting feathers may act as a private communication signal between birds. Such a signal, however, would not protect small birds from larger birds of prey.

Previous studies indicate that songbirds, such as sparrows, see shorter UV wavelengths compared with avian predators, such as hawks. To determine if differences in UV perception could influence detection in the wild, Anders Ödeen and colleagues measured UV reflections from the plumage of Swedish songbirds within their natural habitats. Using mathematical models, the authors calculated how songbird plumage would be seen from the perspective of birds of prey versus other songbirds.

The researchers found that the songbirds' feathers were more conspicuous to other songbirds than to their avian predators, suggesting the evolution of a private signaling system. These results emphasize the importance of accounting for differently tuned sensory systems when studying animal behavior and evolution.

Chestnut Tree Clock Stops for Winter

The circadian rhythms of the chestnut tree go silent during cold winter months, according to researchers.

Winter dormancy is an important adaptive strategy that enables plants to persist during periods of stressful environmental conditions. Dormancy is induced by the short days and cold temperatures of winter.

Isabel Allona and colleagues investigated the role of the chestnut's circadian clock genes in regulating this period of dormancy. The researchers grew chestnut seedlings under controlled conditions in the laboratory and then analyzed the expression of two genes, CsTOC1 and CsLHY.

These genes are similar in sequence to the clock components in the well-studied plant Arabidopsis. The researchers found that, like their counterparts in Arabidopsis, the genes' expression levels fluctuated in a clock-fashion during simulated summer days. During winter days, however, expression levels ceased to oscillate and remained high. The researchers encountered the same effect when they lowered the temperature to just above freezing even though the day length remained long.The oscillation resumed as temperatures rose.

These results suggest that woody and herbaceous plants have differing methods for responding to cold.

Fungus Borrows Energy Tool from Bacteria

One fungus, Leptosphaeria maculans, appears to have an energy-generating mechanism never before seen outside of prokaryotes (microorganisms without nuclei) and may be the first eukaryote (microorganisms with nuclei) found to possess a rhodopsin protein with proton-pumping energy capabilities.

Respiration and chlorophyll-based photosynthesis are classically thought of as the two methods used by eukaryotes to create a proton gradient for energy. Leonid Brown and colleagues, however, have found that L. maculans possesses a gradient builder seen only in prokaryotes before.

Bacteriorhodopsins are proteins embedded in cell membranes. In response to specific wavelengths of light, the bacteriorhodopsins undergo a chemical reaction that effectively pumps ions across the membrane, setting up a charge differential.

The researchers found that L. maculans possesses a rhodopsin similar to bacteriorhodopsin. To test the ability of the rhodopsin to function as a protein pump, the researchers embedded the protein in tiny spheres. In the presence of light, the researchers noted a change of pH between the inside and outside of the sphere, indicating proton movement across the membrane.

The results suggest that some eukaryotes may share the prokaryotic ability to use light-sensitive retinal proteins as electrical gradient generators.

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Geographic and Genetic Differences in Barbary Monkeys

DNA analysis of the threatened Barbary macaque in Morocco and Algeria shows genetic differences between the populations.

Rice Plant Gene Protects Against Fungus

One gene in rice plants may control resistance to fungus disease and environmental stressors.
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The Proceedings of the National Academy of Sciences (PNAS) is the multi-disciplinary, peer-reviewed journal of the National Academy of Sciences. Founded in 1914, PNAS publishes daily online and weekly in print. The preceding highlights are not intended to substitute for articles as sources of information. The articles in PNAS report original research by independent authors and do not necessarily represent the views of the National Academy of Sciences or the National Research Council.

Proceedings of the National Academy of Sciences

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