Chapter 8. Hormones and Sex
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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 Bethany Brookshire We all need sleep, but attaining it can be delicate. Insomniacs can’t fall or stay asleep. Travelers suffer from jetlag. Anxiety keeps people up at night. Or maybe it’s just that jackhammer running across the street keeping your eyes open. Some people turn to earplugs, dark curtains or alcohol to soothe them to sleep. But others go to the supplement aisle and pick up melatonin. The hormone melatonin is secreted from our brains at night and helps regulate sleep. But this chemical is not restricted to humans, or even to mammals. The roots of melatonin’s role in our nightly slumbers go back much further in evolutionary history. A new paper focuses in on the role of melatonin in tiny marine creatures called zooplankton. It turns out that these animals use melatonin just as much as we do, suggesting that the origins of sleeplike behavior may lie under the sea. “For every system and feature that makes a human or other animal today, you can ask the question: Where did it start? How did it begin? What was its first role and function, and how did it become more complex?” says study coauthor Detlev Arendt, a zoologist at the University of Heidelberg in Germany. Arendt’s laboratory has been studying the answers to these questions in the marine ragworm Platynereis dumerilii. This unassuming, centipede-like, ocean-dwelling worm produces larvae that float through the open water as zooplankton. These small larvae propel themselves up and down in the water column with movements of their cilia, slender, hair-like appendages that protrude out from the organisms. © 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. .
By Dr Michael Mosley BBC Do you have a "male" or "female" brain? Are there really significant brain differences between the sexes and if so, do these differences matter? BBC Horizon investigates. When it comes to the tricky and explosive question of how much, if at all, male and female behaviour is driven by brain differences, Professor Alice Roberts and I sit on different sides of the fence. I believe that our brains, like our bodies, are shaped by exposure to hormones in the womb and this may help explain why males tend to do better at some tasks (3D rotation), while women tend to do better at others (empathy skills), although there is, of course, an awful lot of overlap and social pressure involved. Alice, on the other hand, thinks these differences are largely spurious, the result of how the tests are carried out. She worries that such claims may discourage girls from going into science. "We live in a country where fewer than three out of ten physics A levels are taken by girls, where just 7% of engineers are women" she points out, before adding "and where men still earn on average nearly 20% more than their female colleagues." So the BBC's Horizon programme asked us to go and explore the science, put forward research that would support our different views, but also look for common ground. BBC © 2014
Keyword: Sexual Behavior
Link ID: 20129 - Posted: 09.29.2014
Posted by James Owen in Weird & Wild Bigger males may get a lot of attention, but sometimes being smaller—and sneakier—is more successful when it comes to mating. In the East African cichlid fish, Lamprologus callipterus, males come in two sizes: giants or dwarves that are 40 times smaller than their beefier rivals. (Watch a video of male cichlid fish fighting.) It’s an example of male polymorphism, a phenomenon in which males of the same species take different forms. Though people vary in height, men don’t come in two different sizes like the cichlids. Several research studies suggest that tall men—those over 5’7″—are more successful in dating and in their careers—but they get divorced at higher rates. But the variation in L. callipterus, which are found only in Lake Tanganyika (map), is “the most extreme there is,” said Michael Taborsky, co-director of the Institute of Ecology and Evolution at the University of Bern, Switzerland. “It’s an enormous size difference.” In a new study, published September 17 in the Proceedings of the Royal Society B, Taborsky and his team linked this gulf in size to the female’s unusual habit of laying eggs in empty snail shells. To attract females, the giant males collect hundreds of these shells, using their mouths to create nesting sites. But while their hefty build is ideal for lugging about the heavy shells and chasing off rivals, the giants can’t access the chambers of their female harem, instead releasing their sperm outside the shell, Taborsky explained. (Also see “Small Squid Have Bigger Sperm—And Their Own Sex Position.”) © 1996-2013 National Geographic Societ
Keyword: Sexual Behavior
Link ID: 20127 - Posted: 09.29.2014
by Laura Sanders Earlier this month, a star running back for the Minnesota Vikings was indicted for whipping his young son bloody with a switch. Leaked photographs allegedly showed Adrian Peterson’s 4-year-old son with cuts and bruises on his legs, back, buttocks and scrotum. As details about the incident emerged, Peterson took to Twitter to say that he’s not a perfect parent but what he did was not abuse. It was discipline. “My goal is always to teach my son right from wrong and that’s what I tried to do that day,” he wrote. Many people, and I’m one of them, that think Peterson’s actions were disgusting. There’s no way that hitting 4-year-old with a switch until his body is cut and bruised is a good way to impart values and morals. Peterson’s extreme actions, done in the name of corporal punishment, ignited a ferocious, emotionally fraught debate over whether it’s OK to hit your kid. The debate reflects deep divides in our society, chasms that track along political, religious, regional and racial lines. Half of all U.S. parents say they’ve spanked their kid. Spanking doesn’t just happen in the privacy of homes, either. Nineteen states allow teachers or principals to hit children. Opponents often point to scientific studies as proof that spanking is bad. And I confess, I originally thought this post was going to describe those results that we’ve all heard: how children who have been spanked are more aggressive and have more behavioral problems. But despite the headlines, the science behind spanking is actually quite limited, says clinical psychologist Christopher Ferguson of Stetson University in DeLand, Fla. “Because it’s a culture war issue, I think a lot of what we hear has misrepresented what is very nuanced science,” he says. © Society for Science & the Public 2000 - 2014.
by Sarah Zielinski Chimps may be cute and have mannerisms similar to humans, but they are wild animals. A new study finds that chimps raised as pets or entertainers have behavioral problems as adults. There are plenty of good reasons why chimpanzees should not be pets or performers, no matter how cute or humanlike they appear: They are wild animals. They can be violent with each other. And they can be violent toward humans — even humans that have a long history with the chimp. Plus, there’s evidence that seeing an adorable chimp dressed up like a miniature human actually makes us care less about the plight of their species. Now comes evidence that the way that chimps are raised to become pets or entertainers — taking them away from other chimps at a young age and putting them in the care of humans, who may or may not feed and care for them properly — has long-term, negative effects on their behavior. “We now add empirical evidence of the potentially negative welfare effects on the chimpanzees themselves as important considerations in the discussion of privately owned chimpanzees,” Hani Freeman and Stephen Ross of the Lincoln Park Zoo in Chicago write September 23 in PeerJ. Freeman and Ross compiled life history and behavioral data on 60 captive chimps living in zoos. Some of the animals had always lived in zoos and grew up in groups of chimpanzees. Six were raised solely by humans and were later placed in zoos after they became too big or too old for their owners to care for them. Others had a more mixed background. © Society for Science & the Public 2000 - 2014
// by Jennifer Viegas Harems -- where a group of females share a single mate -- can be sexual bliss for the male, but the arrangement poses many challenges for him, according to a new study. Male leaders of harems are often overworked and tired finds the study, published in the latest issue of Royal Society Open Science. Gelada baboons exemplify the problems. "Being a gelada leader male is fairly exhausting," co-author David Pappano told Discovery News. "In order to keep the females within his harem happy, gelada leader males spend a lot of time grooming them." "When bachelors are around, leader males often engage in costly displays -- running around, climbing up a tree, and producing a very loud (ee-yow) display call," added Pappano, who is an NSF postdoctoral research fellow at Princeton University's Department of Ecology and Evolutionary Biology. He co-authored the paper with Jacinta Beehner. © 2014 Discovery Communications, LLC.
Keyword: Sexual Behavior
Link ID: 20108 - Posted: 09.24.2014
By Melissa Dahl Recently, I was visiting my family in Seattle, and we were doing that thing families do: retelling old stories. As we talked, a common theme emerged. My brother hardly remembered anything from our childhood, even the stories in which he was the star player. (That time he fell down the basement steps and needed stitches in the ER? Nope. That panicky afternoon when we all thought he’d disappeared, only to discover he’d been hiding in his room, and then fell asleep? Nothing.) “Boys never remember anything,” my mom huffed. She’s right. Researchers are finding some preliminary evidence that women are indeed better at recalling memories, especially autobiographical ones. Girls and women tend to recall these memories faster and with more specific details, and some studies have demonstrated that these memories tend to be more accurate, too, when compared to those of boys and men. And there’s an explanation for this: It could come down to the way parents talk to their daughters, as compared to their sons, when the children are developing memory skills. To understand this apparent gender divide in recalling memories, it helps to start with early childhood—specifically, ages 2 to 6. Whether you knew it or not, during these years, you learned how to form memories, and researchers believe this happens mostly through conversations with others, primarily our parents. These conversations teach us how to tell our own stories, essentially; when a mother asks her child for more details about something that happened that day in school, for example, she is implicitly communicating that these extra details are essential parts to the story. © 2014 The Slate Group LLC
By JAMES GORMAN Are chimpanzees naturally violent to one another, or has the intrusion of humans into their environment made them aggressive? A study published Wednesday in Nature is setting off a new round of debate on the issue. The study’s authors argue that a review of all known cases of when chimpanzees or bonobos in Africa killed members of their own species shows that violence is a natural part of chimpanzee behavior and not a result of actions by humans that push chimpanzee aggression to lethal attacks. The researchers say their analysis supports the idea that warlike violence in chimpanzees is a natural behavior that evolved because it could provide more resources or territory to the killers, at little risk. But critics say the data shows no such thing, largely because the measures of human impact on chimpanzees are inadequate. While the study is about chimpanzees, it is also the latest salvo in a long argument about the nature of violence in people. In studying chimpanzee violence, “we’re trying to make inferences about human evolution,” said Michael L. Wilson, an anthropologist at the University of Minnesota and a study organizer. There is no disagreement about whether chimpanzees kill one another, or about some of the claims that Dr. Wilson and his 29 co-authors make. The argument is about why chimpanzees kill. Dr. Wilson and the other authors, who contributed data on killings from groups at their study sites, say the evidence shows no connection between human impact on the chimpanzee sites and the number of killings. He said the Ngogo group of chimpanzees in Uganda “turned out to be the most violent group of chimpanzees there is,” even though the site was little disturbed by humans. They have a pristine habitat, he said, and “they go around and kill their neighbors.” © 2014 The New York Times Company
By Jennifer Balmer Each summer, leatherback sea turtles (Dermochelys coriacea) migrate thousands of kilometers from their tropical breeding grounds to feed in cooler waters. Yet how the animals know when to begin their long journey back south at the end of the season has mostly remained a mystery. New findings, to be published in an upcoming issue of the Journal of Experimental Marine Biology and Ecology, suggest that leatherback sea turtles may be able to sense seasonal changes in sunlight by means of an unpigmented spot on the crown of their head—known as the pink spot (pictured). Researchers conducted an examination of the anatomical structures beneath the pink spot and found that the layers of bone and cartilage were remarkably thinner than in other areas of the skull. This thin region of the skull allows the passage of light through to an area of the brain, called the pineal gland, that acts as biological clock, regulating night-day cycles and seasonal patterns of behavior. The authors suggest that the lack of pigment in the crowning pink spot and thin skull region underlying it act as a “skylight,” allowing the turtles to sense the subtle changes in sunlight that accompany changing seasons, signaling them to return south when autumn approaches. © 2014 American Association for the Advancement of Science
|By Gary Stix A biochemical produced in the brain called oxytocin has entered popular culture in recent years as the “love,” “cuddle” or “bonding” hormone. That’s a lot to choose from. Oxytocin plays a role in producing contractions at childbirth and in helping in lactation, but we’ve known that for more than a century. Experiments in the 1990s showed that it was instrumental in leading prairie voles, known for their monogamous behavior, to pick a lifelong mate. Later studies then demonstrated that the chemical contributes to trust and social interactions in various animals, including humans. After the vole study, interest in the nine–amino acid peptide started to rise. In a TED talk economist Paul Zak called it “the moral molecule” because of its link to trust, empathy and prosperity. The Internet DIY brain-makeover market then took up the meme. Vero Labs of Daytona Beach, Fla., sells “Connekt” oxytocin spray for $79 that purports to “strengthen workplace bonds” and “increase positive self-awareness.” The company has also come out with a his-and-her“Attrakt” spray that mixes oxytocin with pheromones—chemical sex attractants that help mice get it on, but whose role in triggering mating behavior in humans is hotly disputed. (Researchers who study oxytocin warn prospective buyers away from these purchases, saying that long-term use in humans has not been studied.) © 2014 Scientific American
// by Richard Farrell Conventional thinking has long held that pelvic bones in whales and dolphins, evolutionary throwbacks to ancestors that once walked on land, are vestigial and will disappear millions of years from now. But researchers from University of Southern California and the Natural History Museum of Los Angeles County (NHM) have upended that assumption. The scientists argue in a paper just published in the journal Evolution that cetacean (whale and dolphin) pelvic bones certainly do have a purpose and that they're specifically targeted, by selection, for mating. The muscles that control a cetacean's penis are attached to the creature's pelvic bones. Matthew Dean, assistant professor at the USC Dornsife College of Letters, Arts and Sciences, and Jim Dines, collections manager of mammalogy at NHM, wanted to find out if pelvic bones could be evolutionarily advantageous by impacting the overall amount of control an individual creature has with its penis. The pair spent four years examining whale and dolphin pelvic bones, using a 3D laser scanner to study the shape and size of the samples in extreme detail. Then they gathered as much data as they could find -- reaching back to whaler days -- on whale testis size relative to body mass. The testis data was important because in nature, species in "promiscuous," competitive mating environments (where females mate with multiple males) develop larger testes, relative to their body mass, in order to outdo the competition. © 2014 Discovery Communications, LLC.
By LISA SANDERS, M.D. On Thursday, we challenged Well readers to take on the case of a 19-year-old man who suddenly collapsed at work after months of weakness and fatigue dotted with episodes of nausea and vomiting. More than 500 of you wrote in with suggested diagnoses. And more than 60 of you nailed it. The cause of this man’s collapse, weakness, nausea and vomiting was… Addisonian crisis because of Addison’s disease Addison’s disease, named after Dr. Thomas Addison, the 19th-century physician who first described the disorder, occurs when the adrenal glands stop producing the fight-or-flight hormones, particularly cortisol and adrenaline and a less well known but equally important hormone called aldosterone that helps the body manage salt. In Addison’s, the immune system mistakenly attacks the adrenal glands as if they were foreign invaders. Why this happens is not well understood, but without these glands and the essential hormones they make, the body cannot respond to biological stress. The symptoms of Addison’s are vague. That’s one reason it’s so hard to diagnosis. Patients complain of weakness and fatigue. They often crave salt. And when confronted with any stress — an infection or an injury — patients with Addison’s may go into adrenal crisis, characterized by nausea and vomiting, low blood pressure and, sometimes, physical collapse. Their blood pressure may drop so low that oxygen-carrying blood cannot reach the extremities, causing skin to turn blue; if blood fails to reach even more essential organs, it can lead to death. © 2014 The New York Times Company
Keyword: Hormones & Behavior
Link ID: 20037 - Posted: 09.06.2014