By David Dobbs
For years the story on rat sex has been this: the male seeks above all else to ejaculate quickly, and once he has done it with one female, he is eager to move on to new partners. The female, meanwhile, seeks to extend the sex encounter through "pacing." A new study finds that if pacing is slow enough, the male will prefer that familiar partner to someone new. The wait, it seems, makes the female more attractive.
"It's an awful lot like what we were taught in high school," says Concordia University psychologist James Pfaus, who co-authored the study with Nafissa Ismail, the graduate student who conceived it.
The experiment made innovative use of standard research devices called pacing chambers, which are cages with dividers having either one or four holes big enough to let a female rat through but too small for the larger male. Thus, the female can join or leave the male, allowing her to significantly lengthen her arousal and, studies have shown, her chance of pregnancy. But the mating rituals last longer in the one-hole chambers, because the male, eager to get at the female, often sticks his big head in the hole, blocking her only passage back to his side and delaying her return.
The researchers let 20 couples mate in one-hole chambers and 20 in four-hole chambers. Then they placed each couple, along with a novel female, in a larger, open area. Among males from four-hole chambers, about half preferred their familiar mates. Among males who mated more slowly in the one-hole chambers, 80 percent preferred the familiar partner.
Driving this behavioral dynamic is, as always with rat sex, some neurochemical reward. Boston University biologist Mary Erskine notes that "sexual preferences come from chemical rewards, and we can be sure there are some here." Sexual climax, in fact, unleashes a flood of pleasure-producing hormones and neurotransmitters, such as testosterone and dopamine. Pfaus speculates that the higher level of arousal created by the longer wait generates a stronger release, and a more substantial reward, thereby enforcing the preference.
"Whether it's simply a stronger dose of the usual chemical rewards or some in addition, we don't know," Pfaus says. "But something is making this sort of mating more rewarding to the male or rewarding in a different way."
2007-02-07
2007-01-24
Brilliant Whiteness of Strange Beetle Explained
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| Forget bleach: this bug may be the key to whiter whites | |
| By JR Minkel | |
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The beetle might not stand out against the brilliant blue of a butterfly, but "in terms of sheer design ingenuity, for me this is my favorite," says optical physicist Pete Vukusic of Exeter University in England, who has studied the bright coloring of dragonflies and butterflies. | ||||||
Vukusic knew he was on to something when he saw Cyphochilus on an insect collector's Web site. "Something this amazingly bright and white had to be coming from something very thin," meaning its thin coat of scales, he says. "That in itself is quite interesting. Any industry can make something very white that's thick." The more layers a material has, he says, the stronger it can scatter light and the brighter its color can be. In this week's Science Vukusic and his colleagues report that the bug's five-micrometer-thick scales were whiter than a child's baby tooth, which is encased in a millimeter-thick layer of white enamel. They used an international standard to assess the beetle's relative whiteness. Electron microscopy revealed the scales are made of a tangle of seemingly randomly oriented filaments, each about 250 nanometers wide. A random microscopic structure is key to producing a white color, which results when all wavelengths of light scatter equally from a surface. If the surface contains any repeating pattern, it will reflect light of the wavelengths that match that pattern. | ||||||
Vukusic says the brightness of the color results from gaps of air between the filaments. Light scatters every time it passes between two materials that differ greatly in the speed of light through them, also called their refractive index. Like facets in a diamond, the more places light can scatter, the brighter the ultimate color. "If you separate the scattering centers, but not by too much, then you actually improve the efficiency at which the whole light spectrum is scattered," Vukusic says. If manufacturers can learn how to harness this effect, he says, they might be able to whiten just about anything that's white. | ||||||
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The Incredible, Medical Egg
| Genetically modified chickens that produce medicines in their eggs may be the drug factories of the future | |
By David Biello |
Helen Sang of the Roslin Institute in Edinburgh, Scotland, and her colleagues used lentivirus to introduce a gene into freshly fertilized chicken embryos that trigger the production of various drugs rather than the protein ovalbumin, which normally makes up roughly 54 percent of egg whites. The researchers screened the resultant cockerels for one that produced the new gene in its semen. They then bred him with normal hens to produce a flock of chickens that carried the inserted gene thereby producing medicines in their egg's whites. | ||||||
Tests of the flocks' eggs showed that they could produce either miR24--a monoclonal antibody used in treating melanoma--or interferon b-1a--an immune system protein used against multiple sclerosis, among other things--depending on which gene was inserted. The chickens produce 15 to 50 micrograms per milliliter of egg white, the researchers found, and though this is not as efficient as the expression of ovalbumin, it is efficient enough to allow for subsequent purification into therapeutic drugs. "We would expect the transgene not to be as efficient as the endogenous gene it was based on as only some of the regulatory elements were used and the transgene may be inserted in the chromosome at a position that does not favor anywhere near maximal expression," notes Roslin's Adrian Sherman, who also participated in the research. "I'm sure there is potential for improvement." | ||||||
| Chicken eggs may prove a better way to producepharmaceuticals than other genetically modified products (such as goat milk) that have been previously explored. Chickens are easy to raise, produce numerous eggs, and are cheap to keep. And, after raising five generations of the modified birds, the researchers have observed no adverse health effects, according to the paper published online January 15 in Proceedings of the National Academy of Sciences USA. Even though the therapeutic proteins worked as intended during in vitro assays, it will be years before the process is ready to be used to produce drugs for human consumption, researchers say. Roslin's chickens join a similar effort using stem cells developed by Origen Therapeutics. Regardless of which "biofactory" delivers drugs first, a new medicinal use for the venerable egg is now apparent. | ||||||
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| Chicken Eggs Made to Produce Human Antibodies | ||||||
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| Egg Beaters |
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