Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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ByDavid Malakoff This bird might look like a holiday ornament, but it is actually a rare half-female, half-male northern cardinal (Cardinalis cardinalis, pictured with female plumage on the left and male plumage on the right) spotted a few years ago in Rock Island, Illinois. Researchers have long known such split-sex “gynandromorphs” exist in insects, crustaceans, and birds. But scientists rarely get to extensively study a gynandromorph in the wild; most published observations cover just a day or so. Observers got to follow this bird, however, for more than 40 days between December 2008 and March 2010. They documented how it interacted with other birds and even how it responded to recorded calls. The results suggest being half-and-half carries consequences: The cardinal didn’t appear to have a mate, and observers never heard it sing, the researchers report this month in The Wilson Journal of Ornithology. On the other hand, it wasn’t “subjected to any unusual agonistic behaviors from other cardinals,” according to the paper. Intriguingly, another gynandromorph cardinal sighted briefly in 1969 had the opposite plumage, they note: the male’s bright red plumes on the right, the drabber female feathers on the left. © 2014 American Association for the Advancement of Science
Keyword: Sexual Behavior
Link ID: 20442 - Posted: 12.27.2014
By Sandhya Sekar A well-fed female mantis is irresistible to a male. She’s chock-full of eggs and draws him in by producing high levels of pheromones. Now, a new study reveals that starving females can deceive males by enticing them to their doom. Researchers have found that female false garden mantises (Pseudomantis albofimbriata, pictured) that were fed just a quarter of what others got actually produced more pheromones than well-fed females—and attracted almost twice the number of males. This is despite the fact that the number of eggs in the starved females was less than 10, compared with more than 60 eggs in well-fed females. The finding, reported online today in the Proceedings of the Royal Society B, is the first experimental demonstration of sexual deception using false chemical signals in any animal. The starving females seem to be treating the males as easy prey to gain nutritional benefits and potentially produce more eggs. © 2014 American Association for the Advancement of Science
Katie Langin In the first couple of years after birth, sea lion sons seem to be more reliant on their mothers—consuming more milk and sticking closer to home—than sea lion daughters are, according to a study on Galápagos sea lions published in the December issue of the journal Animal Behaviour. The young males venture out to sea on occasion, but their female counterparts dive for their own food much more often. The curious thing is, it's not like the young males aren't capable of diving. As one-year-olds, males can dive to the same depth as females (33 feet, or 10 meters, on a typical dive). It's also not like their mother's milk is always on hand. Sea lion moms frequently leave their growing offspring for days at a time to find food at sea. (Watch a video of a Galápagos sea lion giving birth.) And yet, despite all this, for some reason sons are far less likely than daughters to take to the sea and seek out their own food. "We always saw the [young] males around the colony surfing in tide pools, pulling the tails of marine iguanas, resting, sleeping," said Paolo Piedrahita, a Ph.D. student at Bielefeld University in Germany and the lead author of the study. "It's amazing. You can see an animal—40 kilograms [88 pounds]—just resting, waiting for mom." © 1996-2014 National Geographic Society.
By Pippa Stephens Health reporter, BBC News Women are more likely than men to display symptoms of depression when in a position of authority at work, according to US scientists. In men, authority, such as the ability to hire and fire people, decreases depressive symptoms, the study said. The study, published in the Journal of Health and Social Behaviour, looked at 2,800 middle-aged men and women. One expert said the study showed the need for more women in authority and more varied female role models. Scientists at the University of Texas at Austin interviewed 1,300 male and 1,500 female graduates from Wisconsin high schools over the phone in 1993 and 2004, when they were aged about 54 and 64. Researchers asked participants about job authority and about the number of days in the past week they felt depressive symptoms, such as feeling sad and thinking one's life is a failure. When the job included hiring, firing and influencing pay, women were predicted to have a 9% increased rate of depressive symptoms than women without authority. Meanwhile, men had a 10% decreased rate of depressive symptoms. The study said it controlled for other factors that could cause depression, such as hours worked per week, whether people had flexible hours and how often workers were checked by a supervisor. Scientists also said men were more likely to decide when to start and finish work than women and were less frequently monitored by their advisers. Lead researcher Tetyana Pudrovska said: "These women have more education, higher incomes, more prestigious occupations, and higher levels of job satisfaction and autonomy than women without job authority. Yet they have worse mental health than lower status women." BBC © 2014
By Elahe Izadi Putting very little babies through numerous medical procedures is especially challenging for physicians, in part because reducing the pain they experience is so difficult. Typically for patients, "the preferred method of reducing pain is opiates. Obviously you don't want to give opiates to babies," says neurologist Regina Sullivan of NYU Langone Medical Center. "Also, it's difficult to know when a baby is in pain and not in pain." In recent years, research has shown environmental factors, like a mother or caregiver having contact with a baby during a painful procedure, appears to reduce the amount of pain felt by the baby, at least as indicated by the child's behavior, Sullivan said. But she and Gordon Barr of the University of Pennsylvania, an expert in pain, were interested in whether a mother's presence actually changed the brain functioning of a baby in pain. So Sullivan and Barr turned to rats. Specifically mama and baby rats who were in pain. And they found that hundreds of genes in baby rats' brains were more or less active, depending on whether the mothers were present. Sullivan and Barr presented their committee peer-reviewed research before the Society for Neuroscience annual meeting Tuesday. They gave mild electric shocks to infant rats, some of which had their mothers around and others who didn't. The researchers analyzed a specific portion of the infants' brains, the amygdala region of neurons, which is where emotions like fear are processed.
By Kelly Servick Dean Hamer finally feels vindicated. More than 20 years ago, in a study that triggered both scientific and cultural controversy, the molecular biologist offered the first direct evidence of a “gay gene,” by identifying a stretch on the X chromosome likely associated with homosexuality. But several subsequent studies called his finding into question. Now the largest independent replication effort so far, looking at 409 pairs of gay brothers, fingers the same region on the X. “When you first find something out of the entire genome, you’re always wondering if it was just by chance,” says Hamer, who asserts that new research “clarifies the matter absolutely.” But not everyone finds the results convincing. And the kind of DNA analysis used, known as a genetic linkage study, has largely been superseded by other techniques. Due to the limitations of this approach, the new work also fails to provide what behavioral geneticists really crave: specific genes that might underlie homosexuality. Few scientists have ventured into this line of research. When the genetics of being gay comes up at scientific meetings, “sometimes even behavioral geneticists kind of wrinkle up their noses,” says Kenneth Kendler, a psychiatric geneticist at Virginia Commonwealth University in Richmond. That’s partially because the science itself is so complex. Studies comparing identical and fraternal twins suggest there is some heritable component to homosexuality, but no one believes that a single gene or genes can make a person gay. Any genetic predispositions probably interact with environmental factors that influence development of a sexual orientation. © 2014 American Association for the Advancement of Science.
Carl Zimmer In the early 1970s, Sarah Blaffer Hrdy, then a graduate student at Harvard, traveled to India to study Hanuman langurs, monkeys that live in troops, each made up of several females and a male. From time to time, Dr. Hrdy observed a male invade a troop, driving off the patriarch. And sometimes the new male performed a particularly disturbing act of violence. He attacked the troop’s infants. There had been earlier reports of infanticide by adult male mammals, but scientists mostly dismissed the behavior as an unimportant pathology. But in 1974, Dr. Hrdy made a provocative counter proposal: infanticide, she said, is the product of mammalian evolution. By killing off babies of other fathers, a male improves his chances of having more of his own offspring. Dr. Hrdy went on to become a professor at the University of California, Davis, and over the years she broadened her analysis, arguing that infanticide might well be a common feature of mammalian life. She spurred generations of scientists to document the behavior in hundreds of species. “She’s the goddess of all this stuff,” said Kit Opie, a primatologist at University College London. Forty years after Dr. Hrdy’s initial proposal, two evolutionary biologists at the University of Cambridge have surveyed the evolution of infanticide across all mammals. In a paper published Thursday in Science, the scientists concluded that only certain conditions favor the evolution of infanticide — the conditions that Dr. Hrdy had originally proposed. “My main comment is, ‘Well done,'” said Dr. Hrdy. She said the study was particularly noteworthy for its scope, ranging from opossum to lions. The authors of the new study, Dieter Lukas and Elise Huchard, started by plowing through the scientific literature, looking for evidence of infanticide in a variety of mammalian species. The researchers ended up with data on 260 species, and in 119 of them — over 45 percent — males had been observed killing unrelated young animals. © 2014 The New York Times Company
Carl Zimmer Milk is not just food. The more closely scientists examine it, the more complexity they find. Along with nutrients like protein and calcium, milk contains immune factors that protect infants from disease. It hosts a menagerie of microbes, too, some of which may colonize the guts of babies and help them digest food. Milk even contains a special sugar that can fertilize that microbial garden. Now, it turns out, milk also contains messages. A new study of monkeys, published in the journal Behavioral Ecology, demonstrates that a hormone present in milk, cortisol, can have profound effects on how babies develop. Infant monkeys rely on cortisol to detect the condition of their mothers, the authors suggest, then adjust their growth and even shift their temperaments. Jeffrey French, a neuroendocrinologist at the University of Nebraska at Omaha who was not involved in the study, praised its “remarkable sophistication” and said that it helped to change how we think about breast milk. “Milk serves almost like a pheromone, a chemical signal sent from one individual to another,” he said. Katie Hinde, a behavioral biologist at Harvard and lead author on the new study, and her colleagues studied 108 rhesus macaque mothers nursing infants at the California National Primate Research Center. The researchers collected samples of milk, measuring how much energy each provided and the cortisol it contained. Dr. Hinde and her colleagues also measured how much weight each nursing monkey gained and tracked its behavior. Cortisol serves many functions in mammals, but it is best known as a stress hormone. When cortisol courses through our bodies, it prepares us to handle alarming or fearful situations, increasing the brain’s consumption of glucose and suppressing the digestive system. © 2014 The New York Times Company
by Catherine Brahic Once described as the finest sound in nature, the song of the North American hermit thrush has long captivated the human ear. For centuries, birdwatchers have compared it to human music – and it turns out they were on to something. The bird's song is beautifully described by the same maths that underlies human harmonies. To our ears, two notes usually sound harmonious together if they follow a set mathematical relationship. An octave is a doubling of frequencies. Tripling the frequency of sound produces a perfect fifth, quadrupling is yet another octave, and quintupling produces a perfect third. These relationships define the most common major chords – the ones that, across human cultures, we tend to find most pleasant to listen to. Early studies sought to determine whether these mathematical relationships also governed the notes in bird song. Studies in the white-throated sparrow and the northern nightingale-wren failed to find the same musical intervals as those used in human music, and deemed birdsong to be something different entirely. Making tweet music The song of the hermit thrush challenges that conclusion. Tecumseh Fitch of the University of Vienna in Austria and colleagues analysed recordings taken in the wild of 70 full songs from this species. They isolated the frequencies corresponding to each note, and calculated the relationships between pitches appearing in each song. Lo and behold, the vast majority of songs used notes that fitted the same simple mathematical ratios as human harmony. What's more, Fitch says the thrush can produce other notes - meaning it must choose to use these harmonic chords. © Copyright Reed Business Information Ltd.
Joan Raymond TODAY contributor It’s well established that baby talk plays a huge role in helping the wee widdle babies learn to tawk. And — no surprise — moms talk more to babies than dads do. But it seems that the baby's sex plays a role, too: Moms may be talking more to their infant daughters than their sons during the early weeks and months of a child’s life. In a new study published Monday in the online edition of Pediatrics, researchers looked at the language interactions between 33 late preterm and term infants and their parents by capturing 3,000 hours of recordings. Somewhat surprisingly, the researchers found that moms interacted vocally more with infant daughters rather than sons both at birth and 44 weeks post-menstrual age (equivalent to 1 month old.) Male adults responded more frequently to infant boys than infant girls, but the difference did not reach statistical significance, say the researchers. “We wanted to look more at gender and factors that affect these essentially mini-conversations that parents have with infants,” says lead author and neonatologist Dr. Betty Vohr, director of the Neonatal Follow-Up Program at Women & Infants Hospital of Rhode Island. “Infants are primed to vocalize and have reciprocal interactions.”
by Bethany Brookshire In many scientific fields, the study of the body is the study of boys. In neuroscience, for example, studies in male rats, mice, monkeys and other mammals outnumber studies in females 5.5 to 1. When scientists are hunting for clues, treatments or cures for a human population that is around 50 percent female, this boys-only club may miss important questions about how the other half lives. So in an effort to reduce this sex bias in biomedical studies, National Institutes of Health director Francis Collins and Office of Research on Women’s Health director Janine Clayton announced in May a new policy that will roll out practices promoting sex parity in research, beginning with a requirement that scientists state whether males, females or both were used in experiments, and moving on to mandate that both males and females are included in all future funded research. The end goal will be to make sure that NIH-funded scientists “balance male and female cells and animals in preclinical studies in all future [grant] applications” to the NIH. In 1993, the NIH Revitalization Act mandated the inclusion of women and minorities in clinical trials. This latest move extends that inclusion to cells and animals in preclinical research. Because NIH funds the work of morethan 300,000 researchers in the United States and other countries, many of whom work on preclinical and basic biomedical science, the new policy has broad implications for the biomedical research community. And while some scientists are pleased with the effort, others are worried that the mandate is ill-conceived and underfunded. In the end, whether it succeeds or fails comes down to interpretation and future implementation. © Society for Science & the Public 2000 - 2014
By David Bornstein Shortly after the birth of her daughter, Andrea became severely depressed. She was 17 at the time and she didn’t fully understand what she was going through; she just felt like a failure. “I felt like I didn’t want to be alive,” she recalls. “I felt like I didn’t deserve to be alive. I felt like a bad person and a bad mother, and I was never going to get any better.” When her baby persisted in crying, she felt her frustration mount quickly. “I was hitting a boiling point,” she says. “I was at a point where I didn’t want to deal with anything. Sometimes I would just let her cry — but then I would feel very bad afterwards.” Depression is the most common health problem women face. In the United States, outside of obstetrics, it is the leading cause of hospitalizations among women ages 15 to 44. It’s estimated that 20 percent to 25 percent of women will experience depression during their lifetimes, and about one in seven will experience postpartum depression. For low-income women, the rates are about twice as high. As my colleague Tina Rosenberg has reported, the World Health Organization ranks depression as the most burdensome of all health conditions affecting women (as measured by lost years of productive life). Postpartum depressions are often assumed to be associated with hormonal changes in women. In fact, only a small fraction of them are hormonally based, said Cindy-Lee Dennis, a professor at the University of Toronto and a senior scientist at Women’s College Research Institute, who holds a Canada Research Chair in Perinatal Community Health. The misconception is itself a major obstacle, she adds. Postpartum depression is often not an isolated form of depression; nor is it typical. “We now consider depression to be a chronic condition,” Dennis says. “It reoccurs in approximately 30 to 50 percent of individuals. And a significant proportion of postpartum depression starts during the pregnancy but is not detected or treated to remission. We need to identify symptoms as early as possible, ideally long before birth.” © 2014 The New York Times Company
Daniel Cressey The history of sex may have to be rewritten thanks to a group of unsightly, long-extinct fish called placoderms. A careful study1 of fossils of these armour-plated creatures, which gave rise to all current vertebrates with jaws, suggests that their descendants — our ancient ancestors — switched their sexual practices from internal to external fertilization, an event previously thought to be evolutionarily improbable. “This was totally unexpected,” says John Long, a palaeontologist at Flinders University in Adelaide, Australia, and lead author of the study, published in Nature1. “Biologists thought that there could not be a reversion back from internal fertilization to external fertilization, but we have shown it must have happened this way.” Go back far enough in your family tree — before placoderms — and your ancestors were rather ugly jawless fish who reproduced through external fertilization, in which sperm and eggs are expelled into the water to unite. Some of these distant relatives later gave rise to the jawless fish called lampreys that lurk in seas today and still use this method of reproduction. Bony organ Long's team studied placoderms, one of the earliest groups of jawed animals, and found structures in fossils that they interpret as bony ‘claspers’ — male organs that penetrate the female and deliver sperm. © 2014 Nature Publishing Group,
Clare Pain Eating a high fat and high carb diet resulted in inflammation in the brain - at least in male mice. We'll have to wait to see if the same process applies to male humans. The detrimental impact of junk food seems to be connected to inflammation in the brains of male mice, with the brains of females protected by oestrogen, according to research published today in Cell Reports. Dr Deborah Clegg, who led the study while at University of Texas Southwestern Medical Centre, Dallas, USA, was building on existing research that links brain inflammation with obesity and heart disease in male mice. "We embarked on this research because [the link with inflammation] had been shown in male mice, so we asked ourselves, do the same processes occur in females?" explains Clegg. Previous research has shown that one cause of inflammation in the hypothalamus - the part of the brain that controls energy balance - is palmitic acid, a saturated fatty acid found in palm oil, dairy products and meat, and common in high fat food. The team looked at male and female mice, fed either their normal diet or a 'high fat' diet. Besides containing 42 per cent fat, the high fat diet was also high in carbohydrates making it a good correlate of human junk food, says Clegg. © 2014 ABC
by Penny Sarchet He's sexy and he knows it. The little devil frog is noisy in pursuit of a partner, and doesn't care who hears him. The little devil frog's fearlessness in the face of hungry predators could be down to his toxicity. The little devil, Oophaga sylvatica, is a member of the dendrobatid group of poisonous frogs. His bright colours warn predators that he is unsafe to eat, which Juan Santos of the University of British Columbia in Vancouver, Canada, believes has allowed the evolution of more flamboyant mating calls. Santos and his colleagues examined the calls, colourings and toxicity of 170 species of frog, including the little devil. They found a strong relationship between the volume of a frog's call and its aposematism – markings that warn of its toxicity. In general, the more toxic a frog, the brighter and more noticeable it is – and the louder and more rapidly it sings (Proceedings of the Royal Society B ). Non-toxic frogs are camouflaged and call from less exposed perches, says Santos. "Females can have a significant effect on the selection of the most noisy males, given that predators will avoid these aposematic individuals," says Santos. The male's calls can travel over long distances, in an attempt to attract a mate. But it's not just about attracting a female frog's attention – it's about letting her know how desirable he is. © Copyright Reed Business Information Ltd.
BY Bethany Brookshire Stress is our coping response. Whether emotional or physical, stress is how organisms react to upheaval in their lives. And in many cases, that response requires tradeoffs. An animal will make it through now, but may come out with fewer fat stores or a shorter life span. But a new study shows that under certain conditions, developmental stress in male zebra finches might have a positive effect, in the form of more offspring to carry on his genes. Ondi Crino, a biologist now at Macquarie University in Sydney, examined how stress during development might affect reproductive success in male zebra finches. She purchased 10 male and 10 female zebra finches from pet shops near the University of Montana. The birds were allowed to pair off and nest. When the first batch of chicks was 12 days old, Crino fed half of the male offspring peanut oil, and half peanut oil with the hormone corticosterone mixed in. Both humans and finches produce stress-related hormones. Humans produce cortisol, while finches produce corticosterone. These two hormones increase during times of stress and cause many of the negative effects we associate with worry and pressure. So administering corticosterone is one method of “stressing” an animal without changing anything else in its environment. The dose was in the range of what a young bird might experience in the midst of a natural upheaval such as a cold snap or famine. After 16 days of the peanut oil supplement, the young male birds receiving corticosterone were smaller than their relaxed counterparts. They also had a larger spike in their own corticosterone levels when they were stressed. But over time, the chicks that received corticosterone appeared to grow out of their stressful upbringing. By adulthood they were the same size as controls, and they did not show frazzled feathers or pale colors that might indicate a rough chickhood. © Society for Science & the Public 2000 - 2014
By Melissa Hogenboom Science reporter, BBC News A small group of neurons that respond to the hormone oxytocin are key to controlling sexual behaviour in mice, a team has discovered. The researchers switched off these cells which meant they were no longer receptive to oxytocin. This "love hormone" is already known to be important for many intimate social situations. Without it, female mice were no more attracted to a mate than to a block of Lego, the team report in journal Cell. These neurons are situated in the prefrontal cortex, an area of the brain important for personality, learning and social behaviour. Both when the hormone was withheld and when the cells were silenced, the females lost interest in mating during oestrous, which is when female mice are sexually active. At other times in their cycle they responded to the males with normal social behaviour. The results were "pretty fascinating because it was a small population of cells that had such a specific effect", said co-author of the work Nathaniel Heintz of the Rockefeller University in New York. "This internal hormone gets regulated in many different contexts; in this particular context, it works through the prefrontal cortex to help modulate social and sexual behaviour in female mice. "It doesn't mean it's uniquely responsible because the hormone acts in several important places in the brain but it does show that this particular cell type is required for this aspect of female social behaviour," Dr Heintz told BBC News. To silence the neurons, the team used toxins that block the ability of the cells to transmit signals to other neurons - technology that has recently revolutionised the ability to study small populations of neurons. BBC © 2014
BY Sarah Zielinski Bird’s nests come in a wide variety of shapes and sizes, and they’re built out of all sorts of things. Hummingbirds, for instance, create tiny cups just a couple centimeters wide; sociable weavers in Africa, in contrast, work together to build huge nests more than two meters across that are so heavy they can collapse trees. There are nests built on rocky ledges, in mounds on the ground, high in trees and on the edges of buildings. Bowerbirds even construct their nests as tiny houses decorated with an artistic eye to attract the ladies. So perhaps it’s not all that surprising the no one had ever investigated whether birds camouflage their nests to protect their eggs against potential predators. It would make sense that they do, but if you were to test it, where would you start? For Ida Bailey of the University of St. Andrews in Fife, Scotland, and colleagues, the answer was zebra finches. Male finches usually build nests in dense shrubs and layer the outside of the nests with dry grass stems and fine twigs. Predators, usually birds, take a heavy toll on the zebra finches, though. Since birds tend to hunt based on sight rather than smell, camouflaging a nest might work to protect the eggs sequestered inside. And even better, because zebra finches have good color vision, building a camouflaged nest might be possible. So Bailey’s team gathered 21 pairs of zebra finches, some of which were already housed at the University of Glasgow in Scotland, while others were bought from a local pet store. The researchers set each pair up in its own cage. Two walls of the cage were lined with colored paper, and a nest cup was placed in that half of the cage. Then the birds were given two cups containing colored paper — one color that matched the walls and a second contrasting color. The results of the study appear October 1 in The Auk. © Society for Science & the Public 2000 - 2014.
By Sarah C. P. Williams When a group of male katydids croon a tune in nearly perfect synchrony, it means the insects are after the ladies. But they’re not aligning their singing with each other to come across as larger or louder, a new study finds; each male is trying to beat out the others to be the first—by mere milliseconds—to hit a note. Katydids, also known as bush crickets (Mecopoda elongata), are among a handful of insects that make noise by rubbing a hind leg on one wing. Scientists knew that the sound attracted females, but they didn’t know why the males sang in synchrony. In the new study, researchers recorded and analyzed the choral performances of 18 different groups of four male katydids. Then, they let females choose between the males in each group. Females preferred males that were the first to broadcast each tone, even if it were only 70 milliseconds ahead of others in the group, the team reports online today in Royal Society Open Science. Moreover, the females preferred these lead singers to katydids that were singing alone—but the increased volume of the chorus didn’t seem to draw more females to the group as a whole. Singing in a group, the authors of the new study hypothesize, might help keep males on a steady rhythm—another trait that female katydids in the study preferred. But more work is needed to figure out why females chose the steadiest, leading singer, and whether the observation holds true in all species of katydids, like the round-headed katydid (pictured) that's more common in North America. © 2014 American Association for the Advancement of Science
By Fredrick Kunkle Years ago, many scientists assumed that a woman’s heart worked pretty much the same as a man’s. But as more women entered the male-dominated field of cardiology, many such assumptions vanished, opening the way for new approaches to research and treatment. A similar shift is underway in the study of Alzheimer’s disease. It has long been known that more women than men get the deadly neurodegenerative disease, and an emerging body of research is challenging the common wisdom as to why. Although the question is by no means settled, recent findings suggest that biological, genetic and even cultural influences may play heavy roles. Of the more than 5 million people in the United States who have been diagnosed with Alzheimer’s, the leading cause of dementia, two-thirds are women. Because advancing age is considered the biggest risk factor for the disease, researchers largely have attributed that disparity to women’s longer life spans. The average life expectancy for women is 81 years, compared with 76 for men. Yet “even after taking age into account, women are more at risk,” said Richard Lipton, a physician who heads the Einstein Aging Study at Albert Einstein College of Medicine in New York. With the number of Alzheimer’s cases in the United States expected to more than triple by 2050, some researchers are urging a greater focus on understanding the underlying reasons women are more prone to the disease and on developing gender-specific treatments. .