Chapter 8. Hormones and Sex
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by Ed Yong In the image above, all the eggs in the top row are laid by cuckoos and those in the bottom row belong to their victims. These uncanny similarities help cuckoos to fob off their parental duties by laying their eggs in the nests of other species. If the hosts can’t tell the difference between their eggs and the foreign ones, they’ll end up raising the cuckoo chick as their own. And they pay a hefty price for their gullibility, since cuckoo chicks often kill or outcompete their foster siblings. The relationship between cuckoos and their hosts is a classic example of an evolutionary arms race. Cuckoos, should evolve eggs that more closely match those of their hosts, while the hosts should evolve keener senses to discriminate between their own eggs and a cuckoo’s. The greater honeyguide isn’t a cuckoo but uses the same tactics—it parasitises the nests of little bee-eaters by laying eggs of the same size and shape. But this mimicry doesn’t help it to fool the bee-eaters, which seem to accept any old egg no matter how different it looks. Instead, Claire Spottiswoode from the University of Cambridge has found that the parasitic honeyguides are fighting an evolutionary arms race against… each other. Bee-eaters build their nests underground, usually within abandoned aardvark burrows. When honeyguides invade, they’ll puncture the bee-eater’s eggs before laying their own. This kills some of the eggs outright and weakens others. If any chicks survive to hatching, they’re finished off by the honeyguide chick, which stabs its foster siblings to death with a vicious hooked bill.
Louis Herman The mournful, curiously repetitious yet ever-changing songs of male humpback whales have long puzzled scientists. The tunes are part of the males’ mating displays, but researchers don’t know their exact function, or which males in a population are doing the singing. Now, scientists who’ve been studying the giant marine mammals in Hawaii for almost 40 years report that even sexually immature males join older males in singing, apparently as a way to learn the music and to amplify the song. The beefed-up, all-male choruses may attract more females to the areas where the songsters hang out. Scientists generally thought that only adult male humpbacks (Megaptera novaeangliae) sing, says Louis Herman, a marine mammal biologist emeritus at the University of Hawaii, Manoa, and the lead author of the new study. “But that’s just because you can’t easily tell which ones are mature and which ones are immature,” he says. “We know that mature males are larger than immature ones, so we had to figure out an unobtrusive way to measure them in the open ocean.” Herman and his team hit on a technique by looking at 20th century whaling records. Biologists with whaling operations in the Southern Ocean had the opportunity to measure many humpbacks killed during the commercial hunts. They determined, based on the weight of males’ testes, that the whales reached sexual maturity at a body length of 11.2 meters. Working independently, whaling biologists in Japan, who also measured killed whales, reached a similar conclusion; they described 11.3 meters as the break point between adolescents and adults. © 2012 American Association for the Advancement of Science
Karen Ravn The authors of a new study write that this plant bug, Coridromius tahitiensis, “lacks precopulatory courtship, and males instead pounce on nearby females, with whom they struggle violently in their attempt to mate.” If you lived on an exotic island where unsafe sex was all too common, you'd find ways to ward off unwanted attention. On Tahiti, the females of two related insect species have had to move their genitals to different sides of their bodies and even impersonate the opposite sex — all to avoid getting pierced in the abdomen by the sexual organs of the wrong males, biologists report. The two insects, which live side by side on the Pacific island of Tahiti and feed on the same plants, are known as Coridromius tahitiensis and Coridromius taravao. Both species follow the aptly named practice of traumatic insemination. With his genital organ reminiscent of a hypodermic needle, the male stabs a female in the side and shoots sperm into her abdomen. The ritual — shared by a number of other invertebrates, including bedbugs (Cimex lectularius) — can cause injury or infection for the female. Not only that, but insects that use this type of reproductive method are not particularly persnickety about partners, so a male of one species may try to mate with another male — or even with a member of another species. Such interspecies mating can be costly to both species in terms of wasted time, energy and sperm, says Nikolai Tatarnic, a biologist who is now curator of insects at the Western Australian Museum in Welshpool. © 2013 Nature Publishing Group,
by Laura Poppick, LiveScience Researchers have widely examined homosexual behavior in mammals and birds, but have addressed it less frequently in insects and spiders. To assess the range of evolutionary explanations for same-sex intercourse in the invertebrate world, a team of biologists from Tel Aviv University in Israel and the Swiss Federal Institute of Technology in Zurich, Switzerland examined roughly 100 existing studies on the topic and compiled the first comprehensive review of homosexuality in invertebrates. The review was published earlier this month in the journal Behavioral Ecology and Sociobiology. The team focused on male-male interactions to simplify the analysis, and found that most of these encounters occurred as accidents. Whereas larger animals have developed more complicated homosexual motivations — like maintaining alliances, which has been found in certain primate and seagull species — insects seem to mistakenly partake in it in a hasty attempt to secure mates. [Gay Animals: Alternate Lifestyles in the Wild] "They have evolved to mate quick and dirty," said study co-author Inon Scharf, an evolutionary ecologist at Tel Aviv University. "They grab every opportunity to mate that they have because, if they become slow, they may give up an opportunity to mate." In some cases, males carry around the scent of females they have just mated with, sending confusing signals to other perusing males. In other cases, males and females look so similar to one another that males cannot tell if a potential mate is a female until he mounts "her" and prepares for the act, Scharf said. © 2013 Discovery Communications, LLC.
by Simon Makin Autism may shape the brains of women differently to those of men. The condition seems to cause female, but not male, brains to look more masculine, suggesting that one controversial view of autism – as an extreme version of the male brain – may need rethinking. Simon Baron-Cohen at the Autism Research Centre in Cambridge, UK, has previously found that men tend to be better at systematising tasks and females better at ones involving empathising. As people with autism tend to be good systematisers and below-average empathisers, he has argued that autism may be an extreme version of the male brain, or EMB. However, the theory is contentious. "The jury is still out," says autism researcher Uta Frith of University College London. That's partly because of the difficulty in pinning down the source of the gender differences. "It's far from clear which male-female differences are biological and which are cultural," says developmental psychologist Caspar Addyman, of the Birkbeck Babylab at the University of London. In their latest study, Baron-Cohen's team used MRI scans to look for differences in the volume of brain regions in 120 adults, split into four equal groups – men and women, with and without autism. The researchers first compared the brains of males with and without autism, then did the same for female brains. They then compared these two differences. "If autism manifests the same in both genders, these two differences should be alike," says Baron-Cohen's colleague at the Autism Research Centre Meng-Chuan Lai, "but if not, they should be different – and this is what we found." © Copyright Reed Business Information Ltd.
The Associated Press The biggest study of its kind suggests autism might be linked with inducing and speeding up labour, preliminary findings that need investigating since labour is induced in increasing numbers of U.S. women, the authors and other autism experts say. It's possible that labour-inducing drugs might increase the risk — or that the problems that lead doctors to start labour explain the results. These include mothers' diabetes and fetal complications, which have previously been linked with autism. There is a growing consensus that risks for autism occur before birth or soon after.There is a growing consensus that risks for autism occur before birth or soon after. (Veejay Villafranca/Getty ) Like most research into autism causes, the study doesn't provide conclusive answers, and the authors say the results shouldn't lead doctors to avoid inducing labour or speeding it up since it can be life-saving for mothers and babies. Simon Gregory, lead author and an associate professor of medicine and medical genetics at Duke University, emphasized, "We haven't found a connection for cause and effect. One of the things we need to look at is why they were being induced in the first place." Government data suggest 1 in 5 U.S. women have labour induced — twice as many as in 1990. Smaller studies suggested a possible tie between induced labour and autism, but the new research is the largest to date, involving more than 600,000 births. The government-funded study was published online Monday in JAMA Pediatrics. © CBC 2013
Roger Dobson Older male nightingales have perfected an art that would be the envy of men having a mid-life crisis: a trick that makes them more attractive to females than their younger male competitors. Their mastery of successful courtship is achieved with a dazzling array of up to 100 trills a second, far more than their younger competitors can manage, and more than any other investigated bird, according to new research. That ability, backed up by a sophisticated playlist of about 200 songs, means that they are probably seen as better mates by young trill-seeking females. Singing so many trills at peak frequency requires a lot of physical effort and, as a result, it has evolved as a sign on fitness, say the researchers. "Females could assess the age of the male singer by the trill rate, and mate preferably with older ones," says the zoologist Dr Valentin Amrhein, who led the study at the University of Basel, Switzerland. "This makes sense for the females because older males have more experience with defending their territory or with raising young, and therefore have a better reproductive performance." The research, being published in the Journal of Avian Biology, shows that older birds can come up with 100 trills a second, making them the fastest singers. They also performed about 200 different song types, but the researchers think it is the immediate impact of the trills that is attracting the females. It would take more than an hour for the male to go through his whole song list. "Since the performance of these sounds is very demanding, the rate at which they can be repeated is limited. Trying to sing rapidly increasing sounds in fast repetition is very hard for us humans as well," says Dr Amrhein. "Singing rapid broadband trills comes at a certain price for the male nightingale, so trilling is a good indicator for mate quality." © independent.co.uk
Autism affects male and female brains differently, a study has suggested. UK experts studied brain scans of 120 men and women, with half of those studied having autism. The differences found in the research, published in journal Brain, show more work is needed to understand how autism affects girls, the scientists say. Experts said girls with the condition could be more stigmatised than boys - and it could be harder for them to be diagnosed at all. Autism affects 1% of the population and is more prevalent in boys, so most research has focused on them. In this study, scientists from the Autism Research Centre at the University of Cambridge used magnetic resonance imaging (MRI) to examine how autism affects the brain of males and females. The study looked at the difference between the brains of typical males and those with autism - and then females with and without autism. They found the brains of females with autism "look" more like - but still not the same as - healthy males, when compared with healthy females. But the same kind of difference was not seen in males with autism - so their brains did not show "extreme" male characteristics. Dr Meng-Chuan Lai, who worked on the study said: "What we have known about autism to date is mainly male-biased. BBC © 2013
// by Jennifer Viegas Single parenting takes on new extremes for certain starfish that are hermaphrodites -- male and female at the same time and, in some cases, self-fertilizing. The species faces high risk of extinction, according to new research. The dire situation faced by the non-mating starfish, Parvulastra parvivipara and Parvulastra vivipara, helps to explain why so many organisms, including humans, have sex. Genetic diversity and the dispersal of youngsters support population growth. The plight of the starfish, documented in the latest issue of the journal Biology Letters, reveals how a life without sex but with self-fertilization could result in eventual oblivion. “There are quite a few reasons why these species are vulnerable,” senior author Michael Hart of Simon Fraser University’s Department of Biological Sciences told Discovery News. “The whole species could be wiped out.” Hart and his team studied the starfish, which are restricted to high intertidal pools of South Australia and Tasmania. These starfish also go by the nickname "sea cushions," since they look a bit more like a cushion than a star when viewed from the side. Most adult starfish of other species do reproduce via a separate male and female. Females usually produce eggs that males fertilize in the seawater. At that point, the fertilized eggs develop and grow before becoming little starfish that will attach themselves to the substrate and start the whole process over again. © 2013 Discovery Communications, LLC.
A gene that affects the brain's dopamine system appears to have influenced mothers' behavior during a recent economic downturn, researchers say. At the beginning of the recession that began in 2007, mothers with the "sensitive" version of a gene called DRD2 became more likely to strike or scream at their children, the researchers say. Mothers with the other "insensitive" version of the gene didn't change their behavior. But once it appeared that the recession would not become a full-fledged depression, the "sensitive" mothers became less likely than "insensitive" mothers to engage in harsh parenting. "You have the same genes, and with a different environment it's a completely different story," says , a professor of contemporary urban problems at Columbia University. "I think that's the most amazing part of what we found." Garfinkel and four other researchers in the Proceedings of the National Academy of Sciences. The surprising finding came about because Garfinkel and the other researchers happened to be studying "fragile" families in 20 large cities when the 2007 recession began. One of the things they were tracking was reports of harsh parenting, including spanking, hitting or screaming at a child, he says. Previous research had found that harsh parenting is more common during economic hard times, so Garfinkel says that's what researchers expected to see during the 2007-2009 period, often called the Great Recession. ©2013 NPR
By Luciana Gravotta Small gains now or big rewards later? The conundrum plagues every decision we make, whether we are investing or dieting. Now researchers find that men and women use different strategies to make such choices. Researchers use gambling games to understand what we do when immediate rewards are pitted against long-term gains. Most of these games find no major differences in how men and women play. An experimental setup called the Iowa Gambling Task (IGT), however, finds consistent—and large—differences between the behavior of men and women: men are better at figuring out the strategy that reaps the bigger payoff. Players are given four decks of cards, and they choose one card at a time from any deck they want. Each card has a win or loss amount on it, and each deck has its own unique payout pattern. Two of the decks contain cards that dole out large or frequent rewards, but consistently choosing cards from these decks leads to losses in the long run. The other two decks provide a modest amount of cash per win but less loss over time, so they offer long-term gains for players who pick from them most frequently. These patterns are carefully obscured so that the winning strategy is not obvious. A review published in February in Behavioural Brain Research finds that men focus on the big picture, watching their total earnings and quickly homing in on which of the decks will lead to gains in the long run. Women focus on details such as the frequencies of wins and losses for each deck, missing the overall impact each deck has on their total balance. Sensitive to losses, women tend to switch to a different deck as soon as they are pinged with a setback, making it more difficult for them to identify the prize deck. © 2013 Scientific American
By CARL ZIMMER “Monogamy is a problem,” said Dieter Lukas of the University of Cambridge in a telephone news conference this week. As Dr. Lukas explained to reporters, he and other biologists consider monogamy an evolutionary puzzle. In 9 percent of all mammal species, males and females will share a common territory for more than one breeding season, and in some cases bond for life. This is a problem — a scientific one — because male mammals could theoretically have more offspring by giving up on monogamy and mating with lots of females. In a new study, Dr. Lukas and his colleague Tim Clutton-Brock suggest that monogamy evolves when females spread out, making it hard for a male to travel around and fend off competing males. On the same day, Kit Opie of University College London and his colleagues published a similar study on primates, which are especially monogamous — males and females bond in over a quarter of primate species. The London scientists came to a different conclusion: that the threat of infanticide leads males to stick with only one female, protecting her from other males. Even with the scientific problem far from resolved, research like this inevitably turns us into narcissists. It’s all well and good to understand why the gray-handed night monkey became monogamous. But we want to know: What does this say about men and women? As with all things concerning the human heart, it’s complicated. © 2013 The New York Times Company
Elizabeth Pollitzer Transplanting muscle-derived stem cells into diseased muscle regenerates it — a phenomenon that holds major potential for human therapies. But for years, researchers were puzzled by the unpredictability of these cells — sometimes they would promote fast regeneration, at other times none at all. Then, in 2007, a group led by Johnny Huard, a stem-cell researcher at the University of Pittsburgh in Pennsylvania, hit on the rather surprising explanation — sex1. Muscle stem cells taken from female mice regenerate new muscle much faster than those from male mice when transplanted into diseased muscle of mice of either sex. Researchers have also found that cells taken from male and female mice respond differently to stress2, and that human cells exhibit wildly different concentrations of many metabolites across the sexes3. Evidence is mounting that cells differ according to sex, irrespective of their history of exposure to sex hormones. These differences could have major implications for the susceptibility to and course of many diseases, their diagnosis and treatment. However, most cell biologists do not note whether the cells they are using come from males or females4. Between 1997 and 2001, ten prescription drugs were withdrawn from the market by the US Food and Drug Administration (FDA), eight of which were more dangerous to women than to men (see go.nature.com/ksindo). The ingredients used in non-prescription drugs can also pose greater health risks to women. In 2000, for instance, the FDA took steps to remove phenylpropanolamine, a component of many over-the-counter medications, from all drug products because of a reported increased risk of bleeding into the brain or into tissue around the brain in women but not in men. Such drug therapies are developed through basic research — but what if sex-related differences in studied cells contribute in a significant way to the observed effects? © 2013 Nature Publishing Group
By Melissa Hogenboom Science reporter, BBC News Male zebra finches that fail to socialise with females during adolescence are less successful at courtship later in life, a study says. This effect mimics the "loser effect" where, after a defeat, an animal is more likely to lose a subsequent fight. Social friendships at a young age were also found to be more important than physical and social attractiveness. The findings are reported in Proceedings of the Royal Society B: Biological Sciences. The loser effect has been well demonstrated in many species, from spiders and fish to birds. After a fight hormonal levels change which negatively affects performance in further fights. Now scientists have found a similar effect for mating. Adolescent males who failed to pair with a juvenile female were later unsuccessful with females they encountered in adulthood. Scientists also paired young males as a control in the experiment. They found that if males failed to pair with another male, it had no effect on their later success. Mylene Mariette, from the University de Saint-Etienne, France, and lead author of the study said: "We know that social interaction is important for some aspects of development, like the role of males to teach youngsters to sing, but so far no study has looked at the effect of how interaction between juveniles affects their behaviour as adults." BBC © 2013
By CARL ZIMMER The golden lion tamarin, a one-pound primate that lives in Brazil, is a stunningly monogamous creature. A male will typically pair with a female and they will stay close for the rest of their lives, mating only with each other and then working together to care for their young. To biologists, this deeply monogamous way of life — found in 9 percent of mammal species — is puzzling. A seemingly better evolutionary strategy for male mammals would be to spend their time looking for other females with which to mate. “Monogamy is a problem,” said Dieter Lukas of the University of Cambridge in a telephone news conference on Monday. “Why should the male keep to one female?” The evolution of monogamy has inspired many different ideas. “These hypotheses have been suggested for the past 40 years, and there’s been no resolution of the debate,” said Kit Opie of the University College London in an interview. On Monday, Dr. Opie and Dr. Lukas each published a large-scale study of monogamy that they hoped would resolve the debate. But they ended up coming to opposing conclusions, which means the debate over monogamy continues. Dr. Lukas, co-author of a paper in the journal Science with Tim Clutton-Brock of Cambridge, looked at 2,545 species of mammals, tracing their mating evolution from their common ancestor some 170 million years ago. The scientists found that mammals shifted from solitary living to monogamy 61 times over their evolution. They then searched for any factors that these mammals had in common. They concluded that monogamy evolves when females become hostile with one another and live in ranges that do not overlap. When females live this way, they set up so much distance between one another that a single male cannot prevent other males from mating with them. Staying close to one female became a better strategy. Once males began doing so, they sometimes evolved to provide care to their offspring as well. © 2013 The New York Times Company
By Susan Milius When a peacock fans out the iridescent splendor of his train, more than half the time the peahen he’s displaying for isn’t even looking at him. That’s the finding of the first eye-tracking study of birds. In more than 200 short clips recorded by eye-tracking cameras, four peahens spent less than one-third of the time actually looking directly at a displaying peacock, says evolutionary biologist Jessica Yorzinski of Purdue University in West Lafayette, Ind. When peahens did bother to watch the shimmering male, they mostly looked at the lower zone of his train feathers. The feathers’ upper zone of ornaments may intrigue human observers, but big eyespots there garnered less than 5 percent of the female’s time, Yorzinski and her colleagues report July 24 in the Journal of Experimental Biology. These data come from a system that coauthor Jason Babcock of Positive Science, an eye-tracking company in New York City, engineered to fit peahens. Small plastic helmets hold two cameras that send information to a backpack of equipment, which wirelessly transmits information to a computer. One infrared head camera focuses on an eye, tracking pupil movements. A second camera points ahead, giving the broad bird’s-eye view. The rig weighs about 25 grams and takes some getting used to. If a peahen with no experience of helmets gets the full rig, Yorzinski says, “she just droops her head to the ground.” Adding bits of technology gradually, however, let Yorzinski accustom peahens to walking around, and even mating, while cameraed up. © Society for Science & the Public 2000 - 2013
by Brian Mustanski, Ph.D. There is a lot of interest in the question of if too much sex, sexual desire, masturbation, or viewing of pornography is an addiction like to alcohol or cocaine. In fact, an early version of the new DSM-V manual of mental disorders included a “hypersexuality” diagnosis, but this diagnosis was not included in the finalized version. One tool to study addiction is to look at how the brain responds to those substances or cues of those substances. Until recently, this neuroscience approach had not been used to study hypersexuality. A new study published in the journal Socioaffective Neuroscience & Psychology has tested the brain’s response to sexual stimuli among a group of individuals who identified as having problems controlling their use of online pornography. This new study was published by my colleague (and fellow Indiana University Psychology alumni) Dr. Nicole Prause, who is an Assistant Research Scientist in the Department of Psychiatry at the University of California- Los Angeles and a Research Scientist at the Mind Research Network. Below are her answers to my questions about this new study. What was the purpose of the study? Some clinicians describe patients who report problems decreasing their sexual behaviors, such as viewing many hours of sexual films online every day, as sexually “addicted” or “hypersexual”. Our study tested whether people who report such problems look like other addicts from their brain responses to sexual images. Studies of drug addictions, such as cocaine, have shown a consistent pattern of brain response to images of the drug of abuse, so we predicted that we should see the same pattern in people who report problems with sex if it was, in fact, an addiction. © Copyright 1991-2013 Sussex Publishers, LLC
by Sarah C. P. Williams Researchers think they've hit on why a common obesity gene causes weight gain: Those who carry a version of it don't feel full after eating and take in extra calories. That's because the variant of the FTO gene in question, which one in six individuals carry, leads to higher levels of ghrelin, a hormone involved in mediating appetite and the body's response to food, researchers have discovered. While most studies on FTO have relied on mice, the new work analyzed blood samples and brain scans from humans. "This is a very exciting piece of research," says geneticist Andrew Hattersley of the Peninsula Medical School in Exeter, U.K., who was not involved in the new study. "There is a lot of work that's been done on the mechanism of FTO in animals, but you have to be careful about applying those lessons to people. So it's nice to finally see work done in humans." Hattersley was part of a team that in 2007 reported that people who had one version of the FTO gene, called AA, weighed an average of 3 kilograms more than those with the TT version of the gene. Since then, studies in mice have shown that in everyone, there are high levels of the FTO protein in brain areas that control energy balance. Researchers have also found that animals with the AA version tend to eat more and prefer high-fat food compared with those with the TT version. But why FTO had this effect wasn't known. © 2010 American Association for the Advancement of Science.
An Ontario researcher has discovered that common male crickets talk trash, dance and brag after winning a fight. The discovery has caught the attention of fellow researchers and National Geographic magazine. Lauren Fitzsimmons, a Natural Sciences and Engineering Research Council postdoctoral research fellow at the University of Windsor, discovered the brash behaviour. Fitzsimmons placed pairs of male crickets in a small, clear arena, which always led to fights. The arena included a viewing area for other crickets. She set up three audience situations: a male watching and listening to a fight, a female watching and listening to a fight, or no audience. The combatants bit, pushed and flipped each other around the ring. "After a series of these bouts, one male will kind of sulk away and not interact anymore, while the other will perform a song and dance," Fitzsimmons said. She said the winning cricket would "shake his body back and forth" and chirp in victory. "When we had a male audience watching, the male would produce more of these victory displays," Fitzsimmons said. "The speculation is they can tell there is another individual there, and they’re showing off. "We know females prefer dominant males and males who win fights." © CBC 2013
The lifetime rate of diagnosis of anxiety disorders is higher in women, with 33 percent experiencing an anxiety disorder in their lifetime, as compared with 22 percent of men. Experts believe this difference arises from a combination of hormonal fluctuations, brain chemistry and upbringing: women more often feel responsible for the happiness of others, such as their children or their spouse. © 2013 Scientific American