When Procreation Is a Matter of Real Estate

Sexual female rotifers, top, carrying resting eggs (the darker eggs) along with asexual females carrying lighter-shaded amictic eggs, and a single asexual female with an attached asexual egg.

The choice to have sex has everything to do with location, at least for tiny freshwater creatures called rotifers.

Rotifers can reproduce sexually or asexually, and the decision to go one way or another depends on the animals’ habitat, according to a new study in the journal Nature.

The researchers bred rotifers in three different environments: one in which the quality of available food was high, one in which it was low and one in which it was mixed. The rate of sexual reproduction remained the same where the food quality was consistently high or low, but it increased significantly in the mixed region over generations, the researchers found.

In the mixed environment, asexual females were more likely to produce sexually reproducing female offspring. In the two homogenous regions, females tended to produce asexual females — carbon copies of themselves.

The researchers believe that a more diverse set of genes is a useful survival tool in a heterogeneous environment.

“That would be the explanation as to why sex is beneficial and why the rate of sex goes up,” said Lutz Becks, an evolutionary ecologist at the University of Toronto and the study’s first author. “You are mixing your genes.”

After 12 weeks, or about 80 generations of rotifers, the researchers found that about 80 percent of the population in the heterogeneous group was sexual, compared with only about 40 percent of the homogenous groups.

“Nature is, of course, different from our simple laboratory environment, but this allows us to follow the rate of sex in real time,” Dr. Becks said.

Sindya N. Bhanoo, New York Times

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Full article and photo: http://www.nytimes.com/2010/10/19/science/19obrotifer.html

Caterpillars That Thrive in Water and on Land

Plenty of animals can live equally well in air or water. They don’t call frogs amphibians for nothing, after all. But insects — whoever heard of an amphibious insect?

Daniel Rubinoff, a biologist at the University of Hawaii, has. In a paper in The Proceedings of the National Academy of Sciences, he and a post-doctoral researcher, Patrick Schmitz, report on not one but a dozen very small caterpillars that can feed and breathe indefinitely both in and out of water. They are the first insects known to be truly amphibious.

The caterpillars are members of the moth genus Hyposmocoma that is endemic to Hawaii and has about 400 known species, almost all of which are strictly terrestrial. The amphibious ones live around rocks in Hawaii’s mountain streams. Dr. Rubinoff said he did not know why collectors had not noticed them before. “It’s almost like they closed their eyes when they crossed the streams,” he said.

The caterpillars, which build silk cases in different shapes according to the species, breathe in air like other insects, through small openings called spiracles. When under water, Dr. Rubinoff said, the caterpillars most likely obtain oxygen through diffusion across the skin.

The researchers performed genetic analyses of close to 90 Hyposmocoma species and discovered that the amphibious ones “pop up essentially unrelated to each other,” Dr. Rubinoff said. That suggests the amphibious trait evolved independently several times rather than once.

Dr. Rubinoff has an idea as to how that evolution occurred. Given Hawaii’s high rainfall, the water level in the streams these species inhabit fluctuates greatly. A caterpillar that spends its time on a river rock cannot move fast enough when the water level quickly rises and the rock becomes submerged. “If you’re a little caterpillar you’ve got to hunker down and hold on,” he said.

Henry Fountain, New York Times

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Full article: http://www.nytimes.com/2010/04/06/science/06obbugs.html

Evolving Sexual Tensions

male and female sage-grouse

 

The female sage-grouse, left, and her decorative male counterpart.

Males and females are different.

This is so obvious that, at first, it hardly seems worth pointing out. But in fact, it is remarkable. It is also the cause of a profound sexual tension.

The problem is, often, the pressures on males and females are not the same. In the fruit fly Drosophila melanogaster, for example, males must perform an elaborate song-and-dance routine to seduce each female; females, in contrast, must give off a certain smell to be attractive to a male. Females need to eat a high protein diet so as to be able to produce eggs; males can skimp on the proteins.

male sage-grouse

A strutting male sage-grouse.

Among greater sage-grouse, Centrocercus urophasianus, females are smaller than males and have straw-colored feathers. Males have flamboyant feathers and strut and cavort and puff themselves up to seduce females. Needless to say, in this species females do all the childcare: they choose a nest site, sit on the eggs, then feed and protect the chicks.

In sum, the traits that make a “good” male are often different from those that make a “good” female. (Note: I’m only talking about “good” in evolutionary terms. That means a trait that improves your chance of having surviving offspring.) Since many of these traits have a genetic underpinning, male and female genes are thus being sculpted by different forces.
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Working as a Team, Bacteria Spin Gears

One bacterium, working alone, can’t accomplish much. But put a bunch of them together, and they can move mountains.

Researchers harnessed the collective swimming behavior of bacteria to turn these tiny gears.

Well, maybe not mountains. But how about a tiny gear?

Researchers at Argonne National Laboratory, Northwestern and Princeton have shown that the collective swimming behavior of bacteria can be harnessed for work. While the process is not very efficient, it is a promising step toward the development of hybrid biological and micromechanical machines.

In some respects, bacterial swimming resembles Brownian motion, the random movement of particles or molecules in a medium. But Igor S. Aranson, an Argonne researcher who is the senior author of a paper describing the work in The Proceedings of the National Academy of Sciences, said that in equilibrium conditions, it was impossible to extract useful energy from Brownian motion — the laws of thermodynamics did not allow it.

“But bacteria, they don’t know about this law,” Dr. Aranson said.

The researchers used tiny polymer gears with asymmetric teeth floating in a thin film teeming with Bacillus subtilis, a bacterial species known for its swimming ability. Above a concentration of about 10 billion bacteria per cubic centimeter, the gear would rotate. Dr. Aranson said that unlike molecules in Brownian motion, which reflect off whatever they strike, when the bacteria hit a tooth, “they just keep pushing.” They slide along the edge of the tooth until they reach the “V” junction where the next tooth starts. Since one edge of each tooth is longer than the other, more bacteria slide along the long edges, transferring more momentum to them and rotating the gear in one direction.

One of the limitations of the process, Dr. Aranson said, is that the bacteria eventually run out of nutrients. But they can stop pushing even before that. “Bacteria behave too much like people,” he said. “They start to do something else.”

Henry Fountain, New York Times

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Full article and photo: http://www.nytimes.com/2009/12/22/science/22obgear.html

Cell Death Occurs In Same Way In Plants And Animals

celldeathIn both plant and animal cells that undergo programmed cell death, the protein TUDOR-SN is broken down. In pollen, from the model plant mouse-ear cress, a reduction in TUDOR-SN leads to fragmentation of DNA (red signal) and premature cell death.

Research has previously assumed that animals and plants developed different genetic programs for cell death. Now an international collaboration of research teams, including one at the Swedish University of Agricultural Sciences, has shown that parts of the genetic programs that determine programmed cell death in plants and animals are actually evolutionarily related and moreover function in a similar way.

The findings were published in Nature Cell Biology October 11.

For plants and animals, and for humans as well, it is important that cells both can develop and die under controlled forms. The process where cells die under such forms is called programmed cell death. Disruptions of this process can lead to various diseases such as cancer, when too few cells die, or neurological disorders such as Parkinson’s, when too many cell die.

The findings are published jointly by research teams at SLU (Swedish University of Agricultural Sciences) and the Karolinska Institute, the universities of Durham (UK), Tampere (Finland), and Malaga (Spain) under the direction of Peter Bozhkov, who works at SLU in Uppsala, Sweden. The scientists have performed comparative studies of an evolutionarily conserved protein called TUDOR-SN in cell lines from mice and humans and in the plants norway spruce and mouse-ear cress. In both plant and animal cells that undergo programmed cell death, TUDOR-SN is degraded by specific proteins, so-called proteases.

The proteases in animal cells belong to a family of proteins called caspases, which are enzymes. Plants do not have caspases – instead TUDOR-SN is broken down by so-called meta-caspases, which are assumed to be ancestral to the caspases found in animal cells. For the first time, these scientists have been able to demonstrate that a protein, TUDOR-SN, is degraded by similar proteases in both plant and animal cells and that the cleavage of TUDOR-SN abrogate its pro-survival function. The scientists have thereby discovered a further connection between the plant and animal kingdoms. The results now in print will therefore play a major role in future studies of this important protein family.

Cells that lack TUDOR-SN often experience premature programmed cell death. Furthermore, functional studies at the organism level in the model plant mouse-ear cress show that TUDOR-SN is necessary for the development of embryos and pollen. The researchers interpret the results to mean that TUDOR-SN is important in preventing programmed cell death from being activated in cells that are to remain alive.

The research teams maintain that the findings indicate that programmed cell death was established early on in evolution, even before the line that led to the earth’s multicellular organisms divided into plants and animals. The work also shows the importance of comparative studies across different species to enhance our understanding of how fundamental mechanisms function at the cellular level in both the plant and animal kingdoms, and by extension in humans.

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Full article and photo: http://www.sciencedaily.com/releases/2009/10/091013105335.htm

Seeing Blue: Fish Vision Discovery Makes Waves In Evolutionary Biology

fish ss

The scabbardfish (Lepidopus fitchi) is now the only fish known to have switched from ultraviolet to violet vision, or the ability to see blue light.

Emory University researchers have identified the first fish known to have switched from ultraviolet vision to violet vision, or the ability to see blue light. The discovery is also the first example of an animal deleting a molecule to change its visual spectrum.

Their findings on scabbardfish, linking molecular evolution to functional changes and the possible environmental factors driving them, were published Oct. 13 in the Proceedings of the National Academy of Sciences.

“This multi-dimensional approach strengthens the case for the importance of adaptive evolution,” says evolutionary geneticist Shozo Yokoyama, who led the study. “Building on this framework will take studies of natural selection to the next level.”

The research team included Takashi Tada, a post-doctoral fellow in biology, and Ahmet Altun, a post-doctoral fellow in biology and computational chemistry.

Vision ‘like a painting’

For two decades, Yokoyama has done groundbreaking work on the adaptive evolution of vision in vertebrates. Vision serves as a good study model, since it is the simplest of the sensory systems. For example, only four genes are involved in human vision.

“It’s amazing, but you can mix together this small number of genes and detect a whole color spectrum,” Yokoyama says. “It’s just like a painting.”

The common vertebrate ancestor possessed UV vision. However, many species, including humans, have switched from UV to violet vision, or the ability to sense the blue color spectrum.

From the ocean depths

Fish provide clues for how environmental factors can lead to such vision changes, since the available light at various ocean depths is well quantified. All fish previously studied have retained UV vision, but the Emory researchers found that the scabbardfish has not. To tease out the molecular basis for this difference, they used genetic engineering, quantum chemistry and theoretical computation to compare vision proteins and pigments from scabbardfish and another species, lampfish. The results indicated that scabbardfish shifted from UV to violet vision by deleting the molecule at site 86 in the chain of amino acids in the opsin protein.

“Normally, amino acid changes cause small structure changes, but in this case, a critical amino acid was deleted,” Yokoyama says.

More examples likely

“The finding implies that we can find more examples of a similar switch to violet vision in different fish lineages,” he adds. “Comparing violet and UV pigments in fish living in different habitats will open an unprecedented opportunity to clarify the molecular basis of phenotypic adaptations, along with the genetics of UV and violet vision.”

Scabbardfish spend much of their life at depths of 25 to 100 meters, where UV light is less intense than violet light, which could explain why they made the vision shift, Yokoyama theorizes. Lampfish also spend much of their time in deep water. But they may have retained UV vision because they feed near the surface at twilight on tiny, translucent crustaceans that are easier to see in UV light.

A framework for evolutionary biology

Last year, Yokoyama and collaborators completed a comprehensive project to track changes in the dim-light vision protein opsin in nine fish species, chameleons, dolphins and elephants, as the animals spread into new environments and diversified over time. The researchers found that adaptive changes occur by a small number of amino acid substitutions, but most substitutions do not lead to functional changes.

Their results provided a reference framework for further research, and helped bring to light the limitations of studies that rely on statistical analysis of gene sequences alone to identify adaptive mutations in proteins.

“Evolutionary biology is filled with arguments that are misleading, at best,” Yokoyama says. “To make a strong case for the mechanisms of natural selection, you have to connect changes in specific molecules with changes in phenotypes, and then you have to connect these changes to the living environment.”

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Full article and photo: http://www.sciencedaily.com/releases/2009/10/091016121827.htm

The Wonderful World of the Teeny-Tiny

Microscopic Photography

There are millions of photo competitions. But very few of them deal with objects that are normally invisible to the naked eye. SPIEGEL ONLINE brings you the winners of this year’s microscopic photo competition.

It isn’t uncommon for scientists to spend countless hours staring into a microscope. Only rarely, however, do they take pictures of what they see. And even then the images tend to be gray and amorphous, depicting malignant tissue or the activity of a particular protein inside a cell.

 

For the uninitiated, such images are impenetrable. Yet the micro-world can also be a beautiful place, full of splendour that normally remains hidden to the naked eye. Capturing that beauty is the aspiration of micro-photographers, those who magnify the miniature and take pictures of the tiny. The images that result are often full of unfamiliar shapes and forms — and surprisingly colorful. Only rarely is it possible to identify the subject being photographed.

Since 1974, though, depictions of the diminutive have been the subject of an annual photo contest, called the Nikon Small World Competition. A jury of photographers, science journalists and researchers choose the best of the best among microscopic photos.

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micro 1

First place in this year’s Nikon Small World Competition went to Heiti Paves of Estonia. The image shows the anther of a thale cress (arabidopsis thaliana) magnified 20 times. The plants pollinate themselves and reproduce quickly, making them a favorite for genetics researchers.

micro 2

Second place, Gerd Günther of Germany. The spiny sow thistle (sonchus asper) can be found in Austria and Germany. This image is part of the plant’s flower stem magnified 150 times.

micro 3

Third place, Pedro Barrios-Perez of Canada. The image shows a wrinkled photoresist, a light-sensitive material used in a number of industrial processes, such as micro-electronics. The image was magnified 200 times.

micro 4

Fourth place, James Hayden of the US. This image is the result of viewing the ovary of an anglerfish through a special fluorescent microscope. Magnified four times.

micro 5

Fifth place, Bruno Vellutini of Brazil. A researcher at the University of Sao Paolo, Vellutini’s picture shows a young sea star magnified 40 times.

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Eleventh place, Dominik Paquet of Germany. Zebra fish are often used in the study of genetic Alzheimer’s. In this image, magnified 10 times, the nerve cells are stained green while the Alzheimer’s genes are colored blue and red.

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One of those honored this year, Dominik Paquet of the Adolf Butenandt Institute in Munich, is a prime example as to how many of the images in the contest come into existence. His image, which came in 11th place, sprang from his research into the cellular processes related to Alzheimer’s disease. Zebra fish are often used to make the death of nerve cells visible. Tiny fish larvae are injected with an Alzheimer’s-causing gene, which is then colored using an antibody to make it easily perceptible. His laser microscope does the rest.

A Simple Sow Thistle

Paquet entered one of the resulting images to the photo contest. “Compelling images are important for research,” Paquet, 29, says. “And they help communicate what we are doing to the broader public.”

Some 2,000 photographers sent in their work to the contest, and the subject matter varies widely. Some photographers took pictures of magnified chemical compounds, others show details from the world of microbiology. And not all those who submitted photographs come from the world of science. Anyone with a microscope can participate in the contest. Although standard instruments are enough, many of the images were taken with highly specialized microscopes that can cost hundreds of thousands of euros.

But even the simplest of microscopes can result in impressive photos. An image submitted by photographer Gerd Günther from Düsseldorf took second place in this year’s contest — and was created using a simple, store-bought device. His subject? A simple sow thistle.

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Full article and photos: http://www.spiegel.de/international/zeitgeist/0,1518,654690,00.html