Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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Susan Milius Forget it, peacocks. Nice try, elk. Sure, sexy feathers and antlers are showy, but the sperm of a fruit fly could be the most over-the-top, exaggerated male ornamentation of all. In certain fruit fly species, such as Drosophila bifurca, males measuring just a few millimeters produce sperm with a tail as long as 5.8-centimeters, researchers report May 25 in Nature. Adjusted for body size, the disproportionately supersized sperm outdoes such exuberant body parts as pheasant display feathers, deer antlers, scarab beetle horns and the forward-grasping forceps of earwigs. Fruit flies’ giant sperm have been challenging to explain, says study coauthor Scott Pitnick of Syracuse University in New York. Now he and his colleagues propose that a complex interplay of male and female benefits has accelerated sperm length in a runaway-train scenario. Males with longer sperm deliver fewer sperm, bucking a more-is-better trend. Yet, they still manage to transfer a few dozen to a few hundred per mating. And as newly arrived sperm compete to displace those already waiting in a female’s storage organ, longer is better. Fewer sperm per mating means females tend to mate more often, intensifying the sperm-vs.-sperm competition. Females that have the longest storage organs, which favor the longest sperm, benefit too: Males producing megasperm, the researchers found, tend to be the ones with good genes likely to produce robust offspring. “Sex,” says Pitnick, “is a powerful force.” © Society for Science & the Public 2000 - 2016
By Christie Aschwanden When concussions make the news, it’s usually about football. But head injuries happen in other sports too, and not just to men. During a congressional hearing on concussions in youth sports on Friday, Dawn Comstock, an epidemiologist who studies sports injuries, told a House Energy and Commerce subcommittee that in sports like soccer and basketball in which girls and boys play by the same rules, with the same equipment and the same facilities, “girls have higher concussion rates than boys.” Comstock, a researcher at the Colorado School of Public Health, is the first author of a 2015 study published in JAMA Pediatrics that quantified concussions in high school soccer and found that they were about one and a half times more common in girls than in boys. When U.S. Rep. Diana DeGette, D-Colo., asked whether more data was needed to show that girls have higher concussion rates, Comstock replied, “We already have the data that’s consistently shown this gender difference.” What we don’t have, she said, is a proven explanation for the discrepancy. Some researchers have wondered whether women and girls are simply more likely to report their symptoms than men and boys are. “It’s a sexist way to say that they’re not as tough,” said Katherine Price Snedaker, executive director of Pink Concussions,1 an organization that is seeking answers to how concussions affect women and girls. The group recently held a summit on female concussion and traumatic brain injuries at Georgetown University, and one of the speakers was Shannon Bauman, a sports physician who presented data from 207 athletes — both male and female — who’d been evaluated at her specialty concussion clinic in Barrie, Ontario, between September 2014 and January 2016.
By Simon Oxenham The “cuddle chemical”. The “moral molecule”. Oxytocin has quite a reputation – but much of what we thought about the so-called “love hormone” may be wrong. Oxytocin is made by the hypothalamus and acts on the brain, playing a role in bonding, sex and pregnancy. But findings that a sniff of the hormone is enough to make people trust each other more are being called into question after a string of studies failed to replicate classic experiments. Paul Zak at the Centre for Neuroeconomic Studies in Claremont, California, made his moral molecule hypothesis famous in 2011 when he memorably squirted a syringe of the hormone into the air while delivering a TED talk. When people sniff oxytocin before playing a money-lending game, it increases how much they trust each other, he explained. But several teams have been unable to replicate his finding. Last November, Gideon Nave at the California Institute of Technology in Pasadena and his colleagues reviewed studies of oxytocin, and concluded that the effect of nasal squirts of the hormone on trust are not reliably different from zero. Nave’s team aren’t the only ones calling the moral molecule hypothesis into question. In 2012, Moïra Mikolajczak at the Catholic University of Louvain (UCL) in Belgium and her colleagues published their own seminal findings backing a link between trust and oxytocin. They found that when people filled out an anonymous questionnaire about their sex lives and fantasies, they were less likely to seal the envelopes they returned them in if given a nasal dose of oxytocin beforehand. © Copyright Reed Business Information Ltd.
Laura Glynn, Pregnancy brain typically refers to lapses in attention and memory. About 80 percent of new mothers report difficulties remembering things that once came naturally, and although not all studies support this, the weight of the evidence shows that during pregnancy, women exhibit measurable declines in important cognitive skills. But it's not all bad news. The maternal brain also features important enhancements. Mother rats score higher in tests of attention, foraging and planning than peers who have never given birth. These gains most likely render them better able to defend and provide for their pups. The benefits for human moms are less clear, but data are emerging that suggest human pregnancies initiate neural restructuring. A 2010 study found that in the first few months after giving birth, human females show changes in several key brain regions. Specifically, they often exhibit increased volume in the hypothalamus, striatum and amygdala—areas essential for emotional regulation and parental motivation—as well as in regions governing decision making and protective instincts. We can glean further evidence from behavioral changes during pregnancy. Many women exhibit blunted physiological and psychological responses to stress, which may afford mother and fetus protection from the potentially adverse effects of taxing situations. And in the postpartum period, the hormones that sustain breast-feeding maintain these dampened stress responses. © 2016 Scientific American
Sara Reardon As a medical student in Paris in the 1980s, Eric Vilain found himself pondering the differences between men and women. What causes them to develop differently, and what happens when the process goes awry? At the time, he was encountering babies that defied simple classification as a boy or girl. Born with disorders of sex development (DSDs), many had intermediate genitalia — an overlarge clitoris, an undersized penis or features of both sexes. Then, as now, the usual practice was to operate. And the decision of whether a child would be left with male or female genitalia was often made not on scientific evidence, says Vilain, but on practicality: an oft-repeated, if insensitive, line has it that “it's easier to dig a hole than build a pole”. Vilain found the approach disturbing. “I was fascinated and shocked by how the medical team was making decisions.” Vilain has spent the better part of his career studying the ambiguities of sex. Now a paediatrician and geneticist at the University of California, Los Angeles (UCLA), he is one of the world's foremost experts on the genetic determinants of DSDs. He has worked closely with intersex advocacy groups that campaign for recognition and better medical treatment — a movement that has recently gained momentum. And in 2011, he established a major longitudinal study to track the psychological and medical well-being of hundreds of children with DSDs. © 2016 Nature Publishing Group
By David Shultz Did you sleep well? The answer may depend on your age, location and gender. A survey of 5000 sleepers from across the world has revealed that women get the most sleep, particularly those under the age of 25. Daniel Forger at the University of Michigan in Ann Arbor and his team were able to get their huge dataset thanks to Entrain, a smartphone app that people use to track their sleep. With their consent, Forger’s team accessed users’ data on their wake time, bed time, time zone and how much light they were exposed to during the day. Analysing this information, they found that middle-aged men sleep the least, while women under the age of 25 sleep the most. As a whole, women appear to sleep on average for 30 minutes longer than men, thanks to going to bed slightly earlier and waking up slightly later. For an individual, the time they woke up had the strongest link to how much sleep they got, suggesting that having a job that starts early every day can mean that you get less sleep than someone who starts work at a later hour. There were also differences between countries. People in Singapore, for example, sleep for an average of 7.5 hours a night, while Australians get 8.1 hours. Late bedtimes seem to be to blame – people in Singapore tended to stay up until after 11.45 pm each night, while people in Australia were likely to hit the hay closer to 10.45 pm. The team found that, in general, national wake-up times were linked more to daylight hours than bedtimes. This could be because bedtimes are more affected by social factors. © Copyright Reed Business Information Ltd.
By Virginia Morell After defeating other males in boxing matches and winning a territorial roost—and a bevy of females—a male Seba’s short-tailed bat (Carollia perspicillata, pictured) might think his battles for reproductive rights are over. But the defeated males of this neotropical species have a trick up their sleeve: clandestine matings with willing females. The tactic works, and now researchers know why. Scientists studied bats in a captive colony in Switzerland, removing alpha males from their harems for 3 days, and examining their sperm—as well as that of their rivals. A previous study showed that the sneaky males have faster, longer lived sperm, which gives them a leg-up on the alpha male. Researchers had suspected this was because the sneakers produced this supersperm to compete. But the new study finds that after the 3 days of abstinence, the alpha male’s sperm is as agile and vigorous as that of his rivals. Thus, the team reports today in the Journal of Experimental Biology, the sneaky males aren’t generating special sperm—they just mate less, so their sperm is in better shape when it comes time to race to the egg. © 2016 American Association for the Advancement of Science.
By Sarah Kaplan The ancient Greeks spoke of a mythological society composed entirely of warrior women. The medieval traveler John Mandeville wrote of a place whose female rulers "never would suffer man to dwell amongst them." "Paradise Island," home of Wonder Woman, was a feminist utopia where no one with a Y chromosome was allowed. Sadly, those places only exist in fiction. But something like them does exist in the real world. It's in a wetland in rural Ohio. And it's full of salamanders. "They’re pretty incredible," said Robert Denton, a biologist at Ohio State who studies an unusual group of salamander species that literally don't need men. These creatures – all female – reproduce by cloning themselves. To keep their gene pool diverse, they sometimes "steal" sperm left behind on trees and leaves by male salamanders of other species and incorporate that DNA into their offspring. Most sexually reproducing organisms have two sets of chromosomes to make up their genome – one from each parent. But one of these strange salamanders can have between two and five times that much genetic material lying in wait within her cells. It's as if they have multiple genomes to fall back on, and that's made them incredibly successful. "Polyploid" salamanders have been around some 6 million years, Denton said — far longer than most other animal species that reproduce asexually. Since a lack of diversity means having a smaller arsenal of genetic variation to fall back on when living conditions change, these groups usually go extinct relatively quickly. © 1996-2016 The Washington Post
by Susan Milius There’s nothing like a guy doing all the child care to win female favor, even among giant water bugs. Thumbnail-sized Appasus water bugs have become an exemplar species for studying paternal care. After mating, females lay eggs on a male’s back and leave him to swim around for weeks tending his glued-on load. For an A. major water bug, lab tests show an egg burden can have the sweet side of attracting more females, researchers in Japan report May 4 in Royal Society Open Science. Given a choice of two males, females strongly favored, and laid more eggs on, the one already hauling around 10 eggs rather than the male that researchers had scraped eggless. Females still favored a well-egged male even when researchers offered two males that a female had already considered, but with their egg-carrying roles switched from the previous encounter. That formerly spurned suitor this time triumphed. A similar preference, though not as clear-cut, showed up in the slightly smaller and lighter A. japonicus giant water bug. “We conclude that sexual selection plays an important role in the maintenance of elaborate paternal care,” says study coauthor Shin-ya Ohba of Nagasaki University. © Society for Science & the Public 2000 - 2016
Nicola Davis Benedict Cumberbatch’s deep and booming voice might have made him a hit among women, but a low pitch is more likely to have evolved to intimidate other men, new research suggests. When both heterosexual men and women were played recordings of male voices, the deeper tones were hailed by men as sounding more dominant. While the deeper voices were judged to be more attractive by female listeners, the effect was weaker, the researchers report. “If you look at what men’s traits look like they are designed for, they look much better designed for intimidating other males than for attracting females,” said David Puts of Pennsylvania State University, who led the study. Published in Proceedings of the Royal Society B: Biological Sciences, the three-part study by an international team of scientists explored the links between voice pitch and mating systems, attractiveness and, for males only, perceived dominance. A formula for the perfect voice? Read more In the first leg of the research, the scientists turned their attention to primates encompassing Old and New World monkeys, as well as humans and other apes, to explore differences in “fundamental frequency” between males and females of each species - the aspect of the voice that is perceived as pitch. After selecting 1721 recordings, they found large differences were more common in polygynous species - where males mate with more than one female - than monogamous ones. That, they say, could be because in polygynous species, competition between males is greater - hence a male with a lower-pitched voice deemed to be intimidating could have the edge in securing a mate. Intriguingly, the researchers found that among the apes humans showed the greatest difference in pitch between the sexes, suggesting our ancestors were not searching for “the one” but were polygynous - a situation Puts still believes to be the case. © 2016 Guardian News and Media Limited
By Leonard Sax, M.D., Ph.D Why is it that girls tend to be more anxious than boys? It may start with how they feel about how they look. Some research has shown that in adolescence, girls tend to become more dissatisfied with their bodies, whereas boys tend to become more satisfied with their bodies. Another factor has to do with differences in how girls and boys use social media. A girl is much more likely than a boy to post a photo of herself wearing a swimsuit, while the boy is more likely to post a photo where the emphasis is on something he has done rather than on how he looks. If you don’t like Jake’s selfie showing off his big trophy, he may not care. But if you don’t like Sonya’s photo of herself wearing her bikini, she’s more likely to take it personally. Imagine another girl sitting in her bedroom, alone. She’s scrolling through other girls’ Instagram and Snapchat feeds. She sees Sonya showing off her new bikini; Sonya looks awesome. She sees Madison at a party, having a blast. She sees Vanessa with her adorable new puppy. And she thinks: I’m just sitting here in my bedroom, not doing anything. My life sucks. Boys are at lower risk for the toxic effects of social media than girls are, for at least three reasons. First, boys are less likely to be heavily invested in what you think of their selfies. “Does this swimsuit make me look fat?” is a question asked by girls more often than by boys. Second, boys tend to overestimate how interesting their own life is. Third, the average boy is likely to spend more time playing video games than Photoshopping his selfie for Instagram. And in video games, unlike social media, everybody truly can be a winner, eventually. If you play Grand Theft Auto or Call of Duty long enough, you will, sooner or later, complete all the missions, if you just keep at it. © 2016 The New York Times Company
By Patrick Monahan You might have seen a video from David Attenborough’s The Life of Birds series where a male superb lyrebird (Menura novaehollandiae) attempts to lure a mate by imitating a smorgasbord of bird calls and even chainsaws. As nature’s show-offs, male animals tend to have more elaborate colors and courtship behaviors than their female counterparts, so it’s typical that the male would get the public’s attention. The same is true in science: Plenty of female birds sing songs, but researchers have in the past often dismissed them as simply being evolutionary tag-alongs of the males’ “come hither” calls. Now, by recording the calls of female superb lyrebirds, researchers have found that they can keep up with the boys just fine. According to a study published this week in Frontiers in Ecology and Evolution, the females collectively imitated 19 other species of birds, and also sang lyrebird-specific songs. And they changed their songs depending on context, using more lyrebird-specific “whistle” calls when out foraging and vying for territory, but more mimicking calls when defending their nests (as in the audio file below). The fact that the females change their type of call depending on the context makes it likely that these songs evolved in their own right—and the males’ calls aren’t so special after all. Plus, that part about the chainsaw? It probably doesn’t even happen in the wild. © 2016 American Association for the Advancement of Science
Medical research and new drugs to treat human illness usually start with studies on mice and rats. But that type of research has been traditionally sexist — using far more male than female rodents. Scientists warn that has already led to drugs and treatments that are potentially dangerous for women and say the approach slows down the development of treatments and drugs that are safe and effective for everyone. Cara Tannenbaum, scientific director of the Institute of Gender and Health at the Canadian Institutes of Health Research, cited a couple of examples on CBC's The Current of cases where drug side-effects turned out to be far more harmful in women: A stomach drug called cisapride that was sold in the 1990s under the name Prepulsid was withdrawn by Health Canada in 2000 because it sometimes caused irregular heartbeat and sudden death "in women only," Tannenbaum said. Among the victims was the 15-year-old daughter of former Ontario MP Terence Young. "It's not clear that the drug was ever tested in female animals or minors," Tannenbaum added. Health Canada has issued a warning about sleeping pills containing the drug zolpiclone, also known as Ambien, Tannenbaum said. Women are recommended to take half the dose that is prescribed to men. "It was recently discovered that the level of the drug was 45 per cent higher in women the next day, which can lead to car accidents," Tannenbaum said. Jeffrey Mogil, a neuroscientist and pain specialist at McGill University, said there are lots of reasons to suspect men and women respond differently to many different kinds of drugs, but very little actual data. "We actually don't know the scope of the problem," he told The Current. ©2016 CBC/Radio-Canada.
Ian Sample Science editor The subtle impact of genetics on the age at which people lose their virginity has been teased apart by scientists and shown to have an effect on how well people fare at school. Though mostly driven by upbringing and peer behaviour, a person’s age when they first have sex is also shaped by biological factors where genes have a role to play. Researchers found that differences in DNA could account for a quarter of the variation in the age at which people lost their virginity, with other factors, among them religious beliefs, family background and peer pressure, making up the rest. Genes influence academic ability across all subjects, latest study shows Read more “We were able to calculate for the first time that there is a heritable component to age at first sex, and the heritability is about 25%, so one quarter nature, three quarters nurture,” said John Perry, an expert in reproductive ageing and related health conditions at Cambridge University. Among 38 sections of DNA found to affect the age at which people first had sex were genes that drive reproductive biology, such as the release of sex hormones and the age of puberty. Still others were found that appear to affect behaviour, personality and appearance. A variant of one of the genes, named CADM2, linked an early start to one’s sex life with risk-taking behaviour and having a large number of children. A version of another gene, MSRA, found in people who lost their virginity later than average, was linked to irritability. © 2016 Guardian News and Media Limited
Scientists have outwitted the crafty rat with a stimulating new formula that puts sex on the brain. A team at Simon Fraser University in Burnaby, B.C., has developed a rat trap that combines synthetic sex pheromones, food scents and baby rat sounds to lure rodents to their deaths. The bait has proven 10 times more powerful than traditional traps and could be commercialized in about two years, said principal investigator Gerhard Gries. "Rats are really intelligent, and in order to manipulate them you have to be intelligent as well, and do that in a way that addresses their needs," said Gries, a communication ecologist in the department of biological sciences. "It smells delicious, it smells like rat and it sounds like rat." Research outlining the pheromone component of the control tactic was published last week in the international edition of the German peer-reviewed online journal Angewandte Chemie, which translates to "Applied Chemistry." The research on the use of baby rat sounds was published recently in the journal Pest Management Science. Gries worked for several years with research associates Stephen Takacs and Regine Gries, his wife, to develop the three-pronged extermination technique. Humans have waged war against the pests for more than 10,000 years, said Gerhard Gries, noting they spread disease, reduce agricultural crop yields and threaten endangered animal species. But rats are quick learners that have evolved to avoid traps, a behaviour called "neophobia," he said. ©2016 CBC/Radio-Canada.
By Nicholas Bakalar Hormone therapy for prostate cancer may increase the risk for depression, a new analysis has found. Hormone therapy, or androgen deprivation therapy, a widely used prostate cancer treatment, aims to reduce levels of testosterone and other male hormones, which helps limit the spread of prostate cancer cells. From 1992 to 2006, researchers studied 78,552 prostate cancer patients older than 65, of whom 33,382 had hormone therapy. Compared with those treated with other therapies, men who received androgen deprivation therapy were 23 percent more likely to receive a diagnosis of depression, and they had a 29 percent increased risk of having inpatient psychiatric treatment. Longer hormone treatment increased the risk: Researchers found a 12 percent increased relative risk with six or fewer months of treatment, a 26 percent increased risk with seven to 11 months, and a 37 percent increased risk with a year or more. The study, in The Journal of Clinical Oncology, is observational, and does not prove causation. The senior author, Dr. Paul L. Nguyen, of Brigham and Women’s Hospital, said that research is finding “almost an avalanche of side effects” with hormone therapy. Still, for some patients, especially those with severe disease, it can be a life saver. “You have to know what the potential upside is. For some guys it will still be worth it, but for some not.” © 2016 The New York Times Company
Carl Zimmer Five days a week, you can tune into “Paternity Court,” a television show featuring couples embroiled in disputes over fatherhood. It’s entertainment with a very old theme: Uncertainty over paternity goes back a long way in literature. Even Shakespeare and Chaucer cracked wise about cuckolds, who were often depicted wearing horns. But in a number of recent studies, researchers have found that our obsession with cuckolded fathers is seriously overblown. A number of recent genetic studies challenge the notion that mistaken paternity is commonplace. “It’s absolutely ridiculous,” said Maarten H.D. Larmuseau, a geneticist at the University of Leuven in Belgium who has led much of this new research. The term cuckold traditionally refers to the husband of an adulteress, but Dr. Larmuseau and other researchers focus on those cases that produce a child, which scientists politely call “extra-pair paternity.” Until the 20th century, it was difficult to prove that a particular man was the biological father of a particular child. In 1304 a British husband went to court to dispute the paternity of his wife’s child, born while he was abroad for three years. Despite the obvious logistical challenges, the court rejected the husband’s objection. “The privity between a man and his wife cannot be known,” the judge ruled. Modern biology lifted the veil from this mystery, albeit slowly. In the early 1900s, researchers discovered that people have distinct blood types inherited from their parents. In a 1943 lawsuit, Charlie Chaplin relied on blood-type testing to prove that he was not the father of the actress Joan Barry’s child. (The court refused to accept the evidence and forced Chaplin to pay child support anyway.) © 2016 The New York Times Company
Keyword: Sexual Behavior
Link ID: 22089 - Posted: 04.09.2016
Modern humans diverged from Neanderthals some 600,000 years ago – and a new study shows the Y chromosome might be what kept the two species separate. It seems we were genetically incompatible with our ancient relatives – and male fetuses conceived through sex with Neanderthal males would have miscarried. We knew that some cross-breeding between us and Neanderthals happened more recently – around 100,000 to 60,000 years ago. Neanderthal genes have been found in our genomes, on X chromosomes, and have been linked to traits such as skin colour, fertility and even depression and addiction. Now, an analysis of a Y chromosome from a 49,000-year-old male Neanderthal found in El Sidrón, Spain, suggests the chromosome has gone extinct seemingly without leaving any trace in modern humans. This could simply be because it drifted out of the human gene pool or, as the new study suggests, it could be because genetic differences meant that hybrid offspring who had this chromosome were infertile – a genetic dead end. Fernando Mendez of Stanford University, and his colleagues compared the Neanderthal Y chromosome with that of chimps, and ancient and modern humans. They found mutations in four genes that could have prevented the passage of Y chromosome down the paternal line to the hybrid children. “Some of these mutations could have played a role in the loss of Neanderthal Y chromosomes in human populations,” says Mendez. © Copyright Reed Business Information Ltd.
by Sarah Zielinski Spring has finally arrived, and birds’ nests all over the country will soon be filling up with eggs and then nestlings. Watch a nest long enough (the Science News staff is partial to the DC Eagle Cam) and you’ll see itty bitty baby birds begging for a meal. But mama birds don’t always reward that begging with food. In some species, like the tree swallow, birds that beg more will get more food. But in others, like the hoopoe, mom ignores who is begging and gives more food to the biggest chicks, researchers have found. This lack of an overall pattern has confounded ornithologists, but it seems that they may have been missing a key piece of the puzzle. A new study finds that the quality of the birds’ environment determines whether a mama bird can afford to feed all of her kids or if she has to ignore some to make sure the others survive. The study appears March 29 in Nature Communications. Stuart West of the University of Oxford and colleagues compiled data from 306 studies that looked at 143 bird species. When the birds were living in a good environment — one that had plenty of resources or a high amount of predictability — then mom would feed the chicks that beg the most, which were often the ones that needed the most help. But when the environment was poor in quality or unpredictable, then mama bird responded less to begging. |© Society for Science & the Public 2000 - 2016.
Keyword: Sexual Behavior
Link ID: 22079 - Posted: 04.07.2016
By Elizabeth Pennisi The “brrreeet” you hear in the video above is not coming from this broadbill’s beak, but rather from its wings. Charles Darwin marveled at “instrumental music” of birds—from the rattled quills of peacocks to the wing-drumming of grouse and the wing “booming” of night-jars. But those percussive noises are no match for the definitive tones generated by the three Smithornis broadbills (S. rufolateralis, S. capensis, and S. sharpei) that live in remote forests in sub-Saharan Africa. One bird acoustics specialist was so intrigued in 1986 by a recording of this “song,” that he vowed to hear it for himself. More than 2 years ago, he and his colleagues tracked two of these species down in the wild. Synchronized high-speed video and acoustic recordings revealed the downstroke of the wings produces the tones as the bird flies in a meter-wide oval from its perch and back again. At first the researchers thought the outermost flight feathers flutter to make the sounds, but studies of a wing and of the feathers themselves in a wind tunnel showed that the inner flight feathers are “singing” the most, the team reports today in the Journal of Experimental Biology. The tones may scale with the species’ body and feather size, with the bigger ones producing deeper tones, the researchers suggest. The wing tones seemed to have replaced vocal singing, they note, and are likely unique to this group of birds. Audible 100 meters away in dense forest, they represent yet another innovation for communicating with one’s peers. © 2016 American Association for the Advancement of Science