The technical way to explain this odd-looking fowl is that it’s “gynandromorphous.” But if you just want to call it “one seriously confused chicken,” that works, too.
For a new study in Nature, Michael Clinton and colleagues investigated a few of these half-male, half-female chickens they obtained from chicken farms. Gynandropmorphs show up now and then not just in chickens, but also in parrots, pigeons, and some other kinds of animals. But scientists weren’t sure how the mix-up happens, since the standard idea for sex differentiation is that the sex hormones released by the gonads either masculinize or feminize the embryo. Clinton’s team discovered that bird cells don’t need to be programmed by hormones. Instead they are inherently male or female, and remain so even if they end up mixed together in the same chicken [BBC News].
The researchers had first assumed that the half-and-half chickens followed the hormone pattern, and that they were females with some sort of chromosomal problem on the male side (the lighter half of the bird in the image, which also sports a large wattle, sturdy breast musculature, and a leg spur on its male side). Instead, they found the chickens to be almost perfectly split between male and female. The hen half was, for the most part, made up of normal female cells with female chromosomes, whereas the cockerel side contained mostly normal male cells with male chromosomes [Nature News].
You are what you eat, and perhaps in some ways, what your mother ate. Back in 2003, Cheryl Rosenfeld’s team found that the diet they fed to pregnant mice caused a “striking variation” in the sex ratios of the offspring: High fat favored males, low fat favored females. Now Rosenfeld has a new study in the Proceedings of the National Academy of Sciences that says the mother’s diet can also affect the very way genes are expressed in the placenta.
To figure this out, Rosenfeld’s team studied the placentas attached to fetal mice 12 and a half days after conception, when the mice were midway through gestation but had yet to produce sex hormones like estrogen or testosterone (those can also alter gene expression, which would have confounded the study). They found that gene activity in the placentas differed significantly depending on whether the mom was fed a high- or low-fat diet. The biggest differences were found when comparing the high- and low-fat placentas linked to female fetal mice, suggesting that placentas nourishing females do a better job of responding to diet—and potentially protecting the fetus from harmful ingredients—than do those connected to males [ScienceNOW]. Specifically, of the 700 genes that they saw behave differently between the sexes, 651 were expressed more in females than males. In all, their study saw changes in the expression of nearly 2,000 genes.
Male animals often use their horns to fight over females, but at least one species’ females use their horns to fight over excrement.
The species, no surprise, is the dung beetle. Unlike many of the animals we usually associate with elaborate horns, antlers, or other head weaponry—in which the male has the most impressive set—dung beetle females have horns that put the male version to shame. The reason, says a new study in the Proceedings of the Royal Society B, is that females must battle one another for that precious manure. Nicola Watson and Leigh Simmons of the University of Western Australia, Perth, pitted female dung beetles (Onthophagus sagittarius) against each other in a race for dung – a valuable resource that provides nutrients for their eggs. Matched for body size, females with bigger horns managed to collect more dung and so provide better for their offspring [New Scientist].
Does your first- or second-grade daughter have trouble with math? Her anxiety could be stemming not just from a genuine fear of number crunching but also, a new study indicates, from an anxious female math teacher.
The study (pdf) published in the Proceedings of the National Academy of Sciences shows that if a female teacher is anxious about math, she tends to pass on that anxiety to her female students. This can make the female students believe they aren’t hard-wired for math like the boys, and cause them to shy away from fully flexing and developing their mathematical muscles.
The findings are the product of a year-long study on 17 first-and second-grade teachers and 52 boys and 65 girls who were their students [Science Daily]. Researchers recruited the female teachers from a Midwestern school district and assessed their level of math anxiety. They also gave math tests to 117 of these teachers’ students and jotted down their beliefs about math and gender at the beginning and end of the year. By the end of the year, the more anxious teachers were about their own math skills, the more likely their female students – but not the boys – were to agree that “boys are good at math and girls are good at reading” [AP].
Don’t count out the Y chromosome just yet. Far from being in a state of decay, as some studies have suggested, a new study in Nature says the male chromosome in humans is actually evolving at a furious pace.
Study leader David Page of MIT sequenced the human Y chromosome back in 2003, and in the new study his team compares it to the male chromosome of chimpanzees. The scientists expected the two sequences to look very similar. However, while human and chimp DNA generally differ by less than 2 per cent, more than 30 per cent of the Y chromosome differed between the two species [The Times].
We’ve heard (and written) plenty on the struggle of women to reach equal footing with men in the sciences. Now, two of the more prominent women in American science are talking up the issue before they accept their Nobel Prizes next week.
Elizabeth Blackburn and Carol Greider, along with a third American, Jack W. Szostak, won this year’s award in medicine for showing how chromosomes protect themselves as cells divide. Speaking in Sweden in advance of the award ceremony, Blackburn said the setup of scientific careers prevents more women from reaching the upper echelon. “The career structure is very much a career structure that has worked for men. But many women, at the stage when they have done their training really want to think about family . . . and they just are very daunted by the career structure. Not by the science, in which they are doing really well” [AP].
Researchers have long sought an answer to burning question of why women live longer on average then men (you know, other than the fact that, as Harry Belafonte puts it, “man smart, woman smarter“). Now a new study in Human Reproduction by Japanese researchers reinforces the argument that the fault lies in men’s genes, a conclusion they reached by taking males completely out of the picture.
They studied mice created with genetic material from two mothers, but no father. This was achieved by manipulating DNA in mouse eggs so the genes behaved like those in sperm [BBC News]. The scientists then implanted those sperm-behaving eggs into female mice, creating 13 “bimaternal” mice. On average, these fatherless mice lived a third longer than those conceived in the usual manner, according to study leader Tomohiro Kono.
It’s been a bad month for chemicals and masculinity. Last week 80beats covered the discomforting link found between the chemical bisphenol A (BPA), which is found in any number of consumer products, and erectile dysfunction. Now the villains are phthalates, chemicals used to make plastics softer and more flexible. A new study in the International Journal of Andrology has raised a storm of concern that prenatal exposure to these chemicals could make boys less masculine in their play preferences.
Phthalates, which block the activity of male hormones such as androgens, could be altering masculine brain development, according to Shanna H. Swan, a professor of obstetrics and gynecology at the University of Rochester Medical Center and lead author of the new report [Los Angeles Times]. To test whether that link extended into behavior, Swan’s team tested women for phthalate levels midway through their pregnancy and then checked back in on the children four to seven years later.
The researchers asked parents to report their children’s patterns of play, but they knew they also had to separate any potential phthalate effect from the “nuture ” side of question. To determine how parental views might sway behavior, parents completed a survey that included questions such as, “What would you do if you had a boy who preferred toys that girls usually play with?” They were asked to respond with whether they would support or discourage such behavior, and how strongly [TIME].
By altering a female fruit fly’s pheromones, researchers have created an insect with so much sex appeal that it even attracts males of other species. But in a surprising twist, they didn’t boost the levels of some courtship chemical–instead they created flies that lacked all pheromones, which were then besieged suitors. The discovery suggests pheromones can be back-off rather than come-hither signals. The finding could lead to a better understanding of the chemical signals that help flies and other animals interpret the world, including how to select a mate and how to distinguish other species [Science News].
The study, published in Nature, also found that males who lacked all pheromones attracted unwelcome attention from other males, who attempted to copulate with their heads. Says lead researcher Joel Levine: “It’s amazing what you see…. There are some pretty crude movies” [Nature News].
To conduct their experiments, the researchers identified the cells on the inside of the fly’s exoskeleton (pictured in glowing green) that produce the pheromones, and inserted a gene into the fly genome to kill all these cells. The manipulated flies provided a sort of blank canvas to allow the scientists to test the role played by each chemical – and how the chemical signals interacted. “We found that one compound – one that males transfer on to females when they copulate – kept other males away,” said Dr Levine. “It’s the male’s way of sort of protecting his investment” [BBC News].
80beats: Fake Love Pheromone Lures Invasive Vampire Fish to Their Doom
80beats: Do Humans Communicate Via Pheromones? The Jury is Still Out
80beats: Ants That Illegally Procreate Are Revealed By Their Guilty Smell
Image: Jean-Christophe Billeter
Trouble is mounting for the South African athlete who was suspected of having an unfair advantage in women’s track events because of male characteristics. After 18-year-old Caster Semenya thumped the competition at an 800-meter race in Berlin, sports officials announced that Semenya would be subjected to a battery of tests to determine her gender. Now, unconfirmed sources have reported that the tests showed Semenya has both female and male reproductive organs, and her future in women’s sports is in doubt.
Newspapers in Australia reported that while Semenya’s external genitalia is female, she doesn’t have ovaries and instead has internal testes that produce the hormone testosterone. If the reports are accurate, Semenya probably benefited from that hormone boost by gaining muscle mass. But it now seems clear that there is no disciplinary action to be taken, because even if Semenya has high male hormone levels, it is not because of medical cheating. But that leaves a moral and ethical quandary and a medical issue which anyone else in the same position would be able to work out in private – for Semenya, it is all public [ABC Sport].
Experts says that based on the information reported, Semenya may have a condition called androgen insensitivity syndrome, in which the fetus develops functional testes, but then stops developing male characteristics. As a result, the baby develops down the “default” female route. The testes are there but usually do not descend and remain hidden in the body and the condition does not become apparent until adolescence when the girl does not start her period [BBC News]. Medical experts also note that internal testes can grow malignant tumors, and say that some doctors advise removing them as a precautionary measure.