Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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By RONI CARYN RABIN Women are more likely than men to die after a heart attack, and some researchers have suggested a reason: Doctors may be misdiagnosing women more often because their symptoms differ from those experienced by men. But a study published Monday indicates that too much has been made of gender differences in chest pain, the hallmark symptom of heart disease. Although the researchers found some distinctions, no pattern was clearly more characteristic of women or could be used to improve heart attack diagnosis in women, the authors concluded. “We should stop treating women differently at the emergency room when they present with chest pain and discomfort,” said Dr. Maria Rubini Gimenez, a cardiologist at University Hospital Basel and lead author of the new study, published in JAMA Internal Medicine. Instead, she said, all patients with acute chest pain must be evaluated for heart attack with appropriate diagnostics, including an electrocardiogram and blood tests. Roughly 80 percent of people who have chest pain and discomfort are suffering from indigestion, acid reflux or another relatively benign condition, said Dr. John G. Canto, director of the chest pain center at Lakeland Regional Medical Center in Lakeland, Fla., who has researched heart attack diagnosis. “The trick is, how do you figure out the 15 to 20 percent actually having a heart attack?” he said. The new research confirms “that there is a lot of overlap in symptoms between patients who are having a heart attack and those who aren’t, and there is a lot of overlap in symptoms between men and women.” The new study examined 2,475 patients, including 796 women, who reported to emergency rooms at nine hospitals in Switzerland, Spain and Italy complaining of acute chest pain between April 21, 2006, and Aug. 12, 2012. Copyright 2013 The New York Times Company
A whiff of oxytocin may help love not fade away. Researchers asked 20 unmarried men in multiyear relationships to rank the attractiveness of pictures of their partner, acquaintances, and strangers. When the men received a nasal spray of oxytocin—which is released by the body during sexual arousal—they rated their partners more highly but not the other women. MRI scans show that after an oxytocin dose, areas of the brain associated with rewards, which also drive drug addiction, were more active when the men saw pictures of their partner, the researchers report online today in the Proceedings of the National Academy of Sciences. The finding could help explain the biological roots of monogamy in humans: Being in a long-term relationship raises a person's oxytocin levels, which in turn increase the psychological reward of spending more time with that person. The cycle, the team concluded, could literally lead to an addiction to one’s lover. © 2013 American Association for the Advancement of Science
By NATASHA SINGER One afternoon a few months ago, a 45-year-old sales representative named Mike called “The Dr. Harry Fisch Show,” a weekly men’s health program on the Howard Stern channel on Sirius XM Radio, where no male medical or sexual issue goes unexplored. “I feel like a 70-year-old man in a 45-year-old body,” Mike, from Vancouver, British Columbia, told Dr. Fisch on the live broadcast. “I want to feel good. I don’t want to feel tired all day.” A regular listener, Mike had heard Dr. Fisch, a Park Avenue urologist and fertility specialist, talk about a phenomenon called “low testosterone” or “low T.” Dr. Fisch likes to say that a man’s testosterone level is “the dipstick” of his health; he regularly appears on programs like “CBS This Morning” to talk about the malaise that may coincide with low testosterone. He is also the medical expert featured on IsItLowT.com, an informational website sponsored by AbbVie, the drug maker behind AndroGel, the best-selling prescription testosterone gel. Like many men who have seen that site or commercials or online quizzes about “low T,” Mike suspected that diminished testosterone was the cause of his lethargy. And he hoped, as the marketing campaigns seem to suggest, that taking a prescription testosterone drug would make him feel more energetic. “I took your advice and I went and got my testosterone checked,” Mike told Dr. Fisch. Mike’s own physician, he related, told him that his testosterone “was a little low” and prescribed a testosterone medication. Mike also said he had diabetes and high blood pressure and was 40 pounds overweight. Dr. Fisch explained that conditions like obesity might be accompanied by decreased testosterone and energy, and he urged Mike to exercise more and to lose weight. But if Mike had trouble overhauling his diet and exercise habits, Dr. Fisch said, taking testosterone might give him the boost he needed to do so. “If it gives you more energy to exercise,” Dr. Fisch said of the testosterone drug, “I’m all for it.” © 2013 The New York Times Company
Erika Check Hayden Researchers have shown that just two genes from the Y chromosome — that genetic emblem of masculinity in most mammals — are all that is needed for a male mouse to conceive healthy offspring using assisted reproduction. The same team had previously reported1 that male mice missing only seven genes from their Y chromosomes could father healthy babies. The study brings researchers one step closer to creating mice that can be fathers without any contribution from the Y chromosome at all. The findings also have implications for human infertility, because the work suggests that the assisted-reproduction technique used in the mice might be safer for human use than is currently thought. “To me it is a further demonstration that there isn't much left on the poor old Y chromosome that is essential. Who needs a Y?” says Jennifer Marshall Graves, a geneticist at the La Trobe Institute of Molecular Science in Melbourne, Australia, who was not involved in the research. An embryo without a Y chromosome normally develops into a female, but biologists have long questioned whether the entire chromosome is necessary to produce a healthy male. A single gene from the Y chromosome, called Sry, is known to be sufficient to create an anatomically male mouse — albeit one that will be infertile because it will lack some of the genes involved in producing sperm — as researchers have shown by removing the Y chromosome and inserting Sry into other chromosomes. Why it takes two © 2013 Nature Publishing Group
Keyword: Sexual Behavior
Link ID: 18956 - Posted: 11.23.2013
By Rahul K. Parikh, The message showed up on my desk one day while I was seeing a patient. Its choppy shorthand read: “Admits to injecting testosterone. Now decreased libido. Call back to discuss.” The caller was a 15-year-old lacrosse player who hadn’t been part of my practice long. Like many boys in his age group, he rarely came to the office. When I responded to his message later that afternoon, the young man carried his end of the conversation with the typical terseness of a teenager. “Where did you get the steroids?” I asked. “On the Internet.” “How long did you use them?” “A few months.” “And what are you experiencing now?” He told me his nipples were sore and swollen. “I’ve been more tired and moody as well.” My patient was experiencing classic side effects of steroid use. About 6 percent of teenagers admit to using performance-enhancing drugs, according to a recent survey, though it’s easy to assume that that number is low. How many teens would admit to using such drugs, even anonymously to a researcher? And yet here was one teen, forced by the drug’s side effect, having to make an embarrassing confession to me and his family. (Details of this case have been altered to protect patient privacy.) Despite my patient’s fear, I was confident that a young, healthy teenager who briefly used steroids would bounce back, though it might take some time — and patience — for his symptoms to dissipate. When I explained this to my patient, he told me that he wanted his testosterone level tested, to make sure there wasn’t something more seriously wrong. I got the sense that he thought there was some way I could magically undo the harm he had caused himself. I paused and considered his request, which came across more like an order. © 1996-2013 The Washington Post
Female mice that compete in promiscuous environments have sexier smelling sons, research has found. Scientists in Utah, US, studied the pheromones produced in the urine of male mice. They found that those whose mothers competed for mates were more sexually attractive to females. But this success was short-lived: their life spans were shorter than mice with monogamous parents. Adam Nelson from the University of Utah completed the study alongside senior author Prof Wayne Potts. It is published in the journal Proceedings of the National Academy of Sciences. "Only recently have we started to understand that environmental conditions experienced by parents can influence the characteristics of their offspring. This study is one of the first to show this kind of 'epigenetic' process working in a way that increases the mating success of sons," said Prof Potts. Epigenetics is the study of how differences in a parent's environment can influence how its offspring's genes are expressed. The researchers studied domestic mice which are usually paired in a cage and therefore breed with only one partner. To reintroduce the social competition wild mice experience, lab mice were kept in "mouse barns" which were large enclosures divided by mesh to create territories. The mice were able to climb over the mesh to access nest boxes, feeding stations and drinking water. BBC © 2013
By JOHN TIERNEY How aggressive is the human female? When the anthropologist Sarah B. Hrdy surveyed the research literature three decades ago, she concluded that “the competitive component in the nature of women remains anecdotal, intuitively sensed, but not confirmed by science.” Science has come a long way since then, as Dr. Hrdy notes in her introduction to a recent issue of Philosophical Transactions of the Royal Society devoted entirely to the topic of female aggression. She credits the “stunning” amount of new evidence partly to better research techniques and partly to the entry of so many women into scientific fields once dominated by men. The existence of female competition may seem obvious to anyone who has been in a high-school cafeteria or a singles bar, but analyzing it has been difficult because it tends be more subtle and indirect (and a lot less violent) than the male variety. Now that researchers have been looking more closely, they say that this “intrasexual competition” is the most important factor explaining the pressures that young women feel to meet standards of sexual conduct and physical appearance. The old doubts about female competitiveness derived partly from an evolutionary analysis of the reproductive odds in ancient polygynous societies in which some men were left single because dominant males had multiple wives. So men had to compete to have a chance of reproducing, whereas virtually all women were assured of it. But even in those societies, women were not passive trophies for victorious males. They had their own incentives to compete with one another for more desirable partners and more resources for their children. And now that most people live in monogamous societies, most women face the same odds as men. In fact, they face tougher odds in some places, like the many college campuses with more women than men. © 2013 The New York Times Company
SAN DIEGO, CALIFORNIA—Compulsive gamblers aren’t necessarily greedier than the rest of us—their brains may just be wired to favor money over sex. That’s the conclusion of a study presented here today at the Society for Neuroscience conference. This tendency to prioritize money over more basic desires resembles other addictions like alcoholism, researchers say, and could point toward new therapies. Of the millions of people who gamble for fun or profit, about 1% to 2% qualify as pathological gamblers. They can't quit despite encountering serious negative consequences—going into debt, damaging relationships, and even smashing up slot machines and getting arrested when the habit gets out of control. This inability to stop even after sustained loss is one reason gambling recently became the first behavioral addiction to be recognized by psychiatry's most frequently used diagnostic manual, the DSM-5, says Guillaume Sescousse, a neuroscientist at the Radboud University Nijmegen in the Netherlands who led the new study. After all, he says, professional poker players can play for 10 hours a day and not be considered addicts—so long as they can stop when their luck runs out. Researchers have long hypothesized that the basis for gambling addiction might be hypersensitivity to the highs of winning money, caused by dysfunctional wiring in neural circuits that process reward. Studies have produced conflicting results, however, so Sescousse decided to investigate an alternative hypothesis. He wondered if instead of being overly sensitive to monetary reward, compulsive gamblers were less sensitive to other rewarding things, like alcohol and sex. © 2013 American Association for the Advancement of Science
Brian Owens The hordes of microbes that inhabit every nook and cranny of every animal are not just passive hitchhikers: they actively shape their hosts’ well-being and even behaviour. Now, researchers have found evidence that bacteria living in the scent glands of hyenas help to produce the smells that the animals use to identify group members and tell when females are ready to mate. Kevin Theis, a microbial ecologist at Michigan State University in East Lansing, had been studying hyena scent communication for several years when, after he gave a talk on the subject, someone asked him what part the bacteria might play. “I just said, ‘I don’t know’,” he says. He started investigating. He found that for 40 years, scientists had wondered whether smelly bacteria were involved in animals' chemical communication. But experiments to determine which bacteria were present had been inconclusive, because the microbes had to be grown in culture, which is not possible with all bacteria. However, next-generation genetic sequencing would enable Theis to identify the microbes in a sample without having to grow them in a dish. Using this technique, Theis and his colleagues last year published a study1 that identified more types of bacterium living in the hyenas’ scent glands than the 15 previous studies of mammal scent glands combined. In both spotted hyenas (Crocuta crocuta) and striped hyenas (Hyaena hyaena), most of the bacteria were of a kind that ferments nutrients exuded by the skin and produces odours. “The diversity of the bacteria is enough to potentially explain the origin of these signals,” says Theis. Now, they have found that the structure of the bacterial communities varied depending on the scent profiles of the sour, musky-smelling 'pastes' that the animals left on grass stalks to communicate with members of their clan. In addition, in the spotted hyenas, both the bacterial and scent profiles varied between males and females, and with the reproductive state of females — all attributes that hyenas are known to be able to infer from scent pastes. The work is published this week in Proceedings of the National Academy of Sciences. © 2013 Nature Publishing Group
Anjan Chatterjee Before I realized what was happening, the patient reached down between my legs and grabbed my genitals. It was 1985, in the middle of the night during my medicine internship. I was working about 110 hours a week. Every third night I was on call and felt lucky if I got a couple of hours of sleep. That night, I was taking care of this patient for another intern. On my endless “to do” list was the task of placing an intravenous line. When I got to her room it was dark. I didn’t know what her medical condition was. I was focused on starting her IV and then moving on to my next task. I turned on the soft light over her hospital bed and gently woke her. She seemed calm. I loosened her restrained arm to look for a good vein. That was when she grabbed me. Even in my sleep-, food-, and sex-deprived state, I recognized that my charms were not the reason for her attention. She acted indiscriminately. She grabbed nurse’s breasts and students’ buttocks with the same enthusiasm. I had not yet started my neurology residency and did not know that she was suffering from a human version of Klüver-Bucy syndrome. The syndrome is named after Heinrich Klüver, a psychologist, and Paul Bucy, a neurosurgeon, who observed that rhesus monkeys changed profoundly when their anterior-medial temporal lobes were removed. They became placid. They were no longer fearful of objects they would normally avoid. They became “hyper-oral,” meaning they would put anything and everything in their mouth. They also became hypersexual. A similar syndrome occurs in humans. The patient I encountered that night had an infection affecting parts of her brain analogous to those parts in monkeys that Paul Bucy removed. All the cultural and neural machinery that puts a check on such behavior was dissolved by her infection. She displayed sexual desire, the deep-rooted instinct that ensures the survival of our species, in its most uninhibited form. © 2013 Salon Media Group, Inc.
Keyword: Sexual Behavior
Link ID: 18904 - Posted: 11.10.2013
Where, exactly, does the sand flea have sex? On the dusty ground, where it spends the first half of its life? Or already nestled snugly in its host—such as in a human foot—where it can suck the blood it needs to nourish its eggs? The answer to this question, which has long puzzled entomologists and tropical health experts, seems to be the latter. A new study, in which a researcher let a sand flea grow inside her skin, concludes that the parasites most likely copulate when the females are already inside their hosts. Tunga penetrans, also known as the chigger flea, sand flea, chigoe, jigger, nigua, pique, or bicho de pé, is widespread in the Caribbean, South America, and sub-Saharan Africa. The immature female burrows permanently into the skin of a warm-blooded host—it also attacks dogs, rats, cattle, and other mammals—where over 2 weeks it swells up to many times its original size, reaching a diameter of up to 10 mm. Through a small opening at the end of its abdominal cone, the insect breathes, defecates, and expels eggs. The female usually dies after 4 to 6 weeks, still embedded in the skin. Native to the Caribbean, sand fleas infected crewmen sailing with Columbus on the Santa Maria after they were shipwrecked on Haiti. They and others brought the parasite back to the Old World, where it eventually became endemic across sub-Saharan Africa. Even today it is an occasional stowaway, showing up in European and North American travel clinics in the feet of tourists who have gone barefoot on tropical beaches. For people living in infested regions, however, the flea is a serious public health issue. What starts as a pale circle in the skin turns red and then black, becoming painful, itchy—and often infected, a condition called tungiasis. One flea seems to attract others, and people can be infested with dozens at once. © 2013 American Association for the Advancement of Science
By Brian Switek I’m going to ruin sea otters for you. Or at least I’m going to tarnish their reputation as some of the most charming little beasties in the seas. For as cute as they are while intertwining paws at an aquarium, frolicking among the wafting fronds of California kelp forests, or smashing sea urchins open with stones, some sea otters have developed the disturbing habit of humping and drowning baby seals. When I first heard about the behavior from a marine biologist friend of mine, I didn’t quite believe sea otters could be so diabolical. Maybe the bad behavior was just a rumor. But no, the strange sea otter attacks on baby seals are a reality and have even made their way into the technical literature. In 2010, California Department of Fish and Game biologist Heather Harris and colleagues reported 19 individual cases of male sea otters trying to mate with, and often fatally injuring, harbor seal pups in the Monterey Bay, Calif. area between 2000 and 2002 alone. Delivered in the scientific deadpan required of such papers, the Aquatic Mammals report attributes the incidents to three male sea otters “observed harassing, dragging, guarding, and copulating with harbor seals,” persisting for up to seven days after the otters killed the objects of their misguided advances. The ordeal must have been horrific for the seals. The victims that were necropsied by veterinarians had lesions around the nose, eyes, flippers, and genitals, including perforations in the vaginal and rectal tracts. A painful and confusing end for the poor pups. © 2013 The Slate Group, LLC.
Guest post by Bruce Bower Among 16- to 22-year-old U.S. males, 7.6 percent report taking various potentially dangerous substances at least monthly to counteract what they regard as an alarming lack of muscularity. Young men whose insecurities inspire them to use growth hormones, steroids and other body-altering chemicals represent the male counterpart of females whose idealization of thinness prompts them to induce vomiting and otherwise purge their bodies of food, proposes a team led by epidemiologist Alison Field of Boston Children’s Hospital. Purging and other eating disorders occur mainly in girls and women. Boys and men so obsessed with muscles that they take substances prohibited in competitive sports are more numerous than researchers and clinicians realized, and have been overlooked, Field and her colleagues conclude November 4 in JAMA Pediatrics. The researchers examined questionnaires that each of 5,527 males completed eight times between 1999 — at ages 12 to 18 — and 2010. Most participants were white and from middle-class families. No information on sports team participation was available. © Society for Science & the Public 2000 - 2013.
JoNel Aleccia NBC News Obesity may be a factor in early puberty in U.S. girls, a new study finds. About 17 percent of American kids ages 2 to 17 are obese, according to the CDC. There’s yet another reason to worry about the obesity epidemic among America’s kids: Extra weight may be sending U.S. girls into puberty earlier than ever. Researchers have found that girls with higher body mass index, a ratio of height and weight, may start developing breasts more than a year before their thinner friends — perhaps as early as second grade. The change is spawning a whole new market of child-sized sanitary pads — decorated with hearts and stars — and deodorants aimed at 8- to 10-year-olds, according to a new study and an editorial published Monday in the journal Pediatrics. “The girls who are obese are clearly maturing earlier,” said Dr. Frank Biro, a pediatrics professor at Cincinnati Children’s Hospital Medical Center. “BMI is, we found, the biggest single factor for the onset of puberty.” In addition, white girls are maturing about four months earlier than in a landmark 1997 study that shocked parents with the news that their daughters who played with My Little Pony could be entering puberty. Biro’s team followed more than 1,200 girls ages 6 to 8 in three cities — San Francisco, Cincinnati and New York — from 2004 to 2011, carefully documenting their BMI and their maturation process.
By JAN HOFFMAN There are activities common to most humans that we enjoy immensely, without much thought, and as frequently as opportunity and instinct provide. On occasion, researchers feel they need to know why. Recently, experimental psychologists at Oxford University explored the function of kissing in romantic relationships. Surprise! It’s complicated. After conducting an online survey with 308 men and 594 women, mostly from North America and Europe, who ranged in age from 18 to 63, the researchers have concluded that kissing may help people assess potential mates and then maintain those relationships. “The repurposing of the behavior is very efficient,” said Rafael Wlodarski, a doctoral candidate and lead author of the study, published in Archives of Sexual Behavior. But another hypothesis about kissing — that its function is to elevate sexual arousal and ready a couple for coitus — didn’t hold up. While that might be an outcome, researchers did not find sexual arousal to be the primary driver for kissing. Participants in the survey were asked about their attitudes toward kissing in different phases of romantic relationships. They were then asked about their sexual history: for example, whether they had been more inclined toward casual encounters or long-term, committed relationships. They also had to define their “mate value” by assessing their own attractiveness. Later, during data analysis, the researchers looked at how individual differences affected a person’s thoughts on kissing. Copyright 2013 The New York Times Company
Keyword: Sexual Behavior
Link ID: 18845 - Posted: 10.29.2013
by Bethany Brookshire There are many animal species out there that exhibit same-sex mating behavior. This can take the form of courtship behaviors, solicitation, all the way through to mounting and trading off sperm). In some species, it’s clear that some of this behavior is because the animals involved have pair bonded. But what about insects? Many insects mate quickly, a one and done approach, with very little bonding involved beyond what’s needed to protect against other potential suitors. When it comes to bugs, is it intentional same-sex behavior? Or is it all a mistake? Hypotheses are out there, but in the end, we need science. A new study in the November Behavioral Ecology and Sociobiology wants to answer these questions. The authors did a meta-analysis of papers looking at same-sex sexual activity in male insects and arachnids. They tried to tease out why same-sex sexual behavior might occur in insects. What are the benefits? The potential downsides? And from that, to hypothesize why it might occur. Some of it, it turns out, could be due to context. A lot of observed same-sex mating behavior in insects is observed, for example, when the males are all housed together, away from the females. Partially because of this (but possibly for other reasons as well), same-sex sexual behavior in insects tends to occur much more frequently in the lab than in the wild. But it’s still often documented in the field. Why does it happen? Some say that by mating with a “passive” male and transferring sperm, that sperm then gets passed over to the female when the passive male mates. Sneaky. But does it really happen? And if it does, is it effective? So far, it doesn’t appear that it is; less than 0.5% of the offspring resulted from the transfer of sperm when these cases were documented. © Society for Science & the Public 2000 - 2013
by Susan Milius Your calamari, it turns out, may have come from a temporary transvestite with rainbows in its armpits. Well, not armpits, but spots just below where the fins flare out. “Finpits,” cell biologist Daniel DeMartini nicknamed them. He and his colleagues have documented unusual color-change displays in female California market squid, popular in restaurants. Squids, octopuses and cuttlefishes are nature’s iPads, changing their living pixels at will. DeMartini, of the University of California, Santa Barbara, saw so many sunset shimmers, blink-of-an-eye blackouts and other marvels in California’s Doryteuthis opalescens that it took him a while to notice that only females shimmered the finpit stripe. It shows up now and then during life, and reliably for about 24 hours after decapitation, DeMartini found. The squid are color-blind, and what prompts their display is known only to them. But the researchers have figured out how it works. The squid make rainbows when color-change cells called iridocytes lose water. Other kinds of color-change cells work their magic via pigments, but not iridocytes. “If you take a bunch of iridocyte cells in red, blue, green or yellow and you grind them up, then you wouldn’t see any color,” DeMartini says. Instead, little stacks of protein plates inside the cells turn colorful only when water rushes out of the stack. How closely the plates snug together determines whether the stack looks blue, scarlet or anything in between. © Society for Science & the Public 2000 - 2013
By ELISABETH ROSENTHAL The barrage of advertisements targets older men. “Have you noticed a recent deterioration of your ability to play sports?” “Do you have a decrease in sex drive?” “Do you have a lack of energy?” If so, the ads warn, you should “talk to your doctor about whether you have low testosterone” — “Low T,” as they put it. In the view of many physicians, that is in large part an invented condition. Last year, drug makers in the United States spent $3.47 billion on advertising directly to consumers, according to FiercePharma.com. And while ever-present ads like those from AbbVie Pharmaceuticals have buoyed sales of testosterone gels, that may be bad for patients as well as the United States’ $2.7 trillion annual health care bill, experts say. Sales of prescription testosterone gels that are absorbed through the skin generated over $2 billion in American sales last year, a number that is expected to more than double by 2017. Abbott Laboratories — which owned AbbVie until Jan. 1 — spent $80 million advertising its version, AndroGel, last year. Once a niche treatment for people suffering from hormonal deficiencies caused by medical problems like endocrine tumors or the disruptive effects of chemotherapy, the prescription gels are increasingly being sold as lifestyle products, to raise dipping levels of the male sex hormone as men age. “The market for testosterone gels evolved because there is an appetite among men and because there is advertising,” said Dr. Joel Finkelstein, an associate professor at Harvard Medical School who is studying male hormone changes with aging. “The problem is that no one has proved that it works and we don’t know the risks.” © 2013 The New York Times Company
By Scicurious When most of us hear birds twittering away in the trees, we hear it as background noise. It’s often hard to separate out one bird from another. But when you can, you begin to hear just how complex birdsong can be, a complex way of male signaling to a female how THEY are the best, and THEY are the one they should clearly pick. You hear ups and downs and trills and repeating themes. We used to think that birdsong was a relatively simple gene by environment interaction. The big males with the big songs get the best females, and then it’s a matter of also getting the best food, and the then healthy bird teaches its offspring to sing, and the health offspring goes on to display the best song. The song is therefore an “honest signal” of the bird’s fitness, it’s got good genes and good food and it is ready to MATE, baby! But how much of it is really training and how much is genetic? To find out, we go to what may possibly be the cutest of research subjects…the zebra finch. To look at the relationship between genes and environment in song learning, the authors turned to the zebra finch. Many other studies have also looked at the zebra finch and how it learns song, and how environmental pressures (like say, not enough food) change the way the song is displayed. But those experiments usually bred the birds and looked at the environment…they didn’t look at the teachers. The father birds, who were “teaching” their offspring to sing. © 2013 Scientific American
by Colin Barras Male marsupial mice just don't know when to stop. For Antechinus stuartii, their debut breeding season is so frenetic and stressful that they drop dead at the end of it from exhaustion or disease. It may be the females of the species that are driving this self-destructive behaviour. Suicidal breeding, known as semelparity, is seen in several marsupials. This is likely linked to short breeding seasons and the fact that the marsupial mice only breed once a year. It is not clear why this is, but it may be that females can only breed when the population of their insect prey reaches its peak. A year is a long and dangerous time for a small animal, so under these circumstances males might do best to pump all their resources into a single breeding season. To test this idea, Diana Fisher of the University of Queensland in St Lucia, Australia, and her colleagues tracked how insect abundance changed with the seasons in the marsupials' home forests. Sure enough, they found that the marsupials' breeding seasons were shortest where insect abundance followed a predictable annual pattern. But the insects are not the whole explanation. It turns out that females do sometimes survive the year and breed again. So why do the males always die? The key factor is that the females are highly promiscuous, says Fisher. Coupled with the short breeding season, this leads to intense competition between males. "Males that exert extreme effort in this short time are at an advantage." © Copyright Reed Business Information Ltd.