Chapter 8. Hormones and Sex
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By Andy Coghlan The final brain edit before adulthood has been observed for the first time. MRI scans of 300 adolescents and young adults have shown how the teenage brain upgrades itself to become quicker – but that errors in this process may lead to schizophrenia in later life. The editing process that takes place in teen years seems to select the brain’s best connections and networks, says Kirstie Whitaker at the University of Cambridge. “The result is a brain that’s sleeker and more efficient.” When Whitaker and her team scanned brains from people between the ages of 14 and 24, they found that two major changes take place in the outer layer of the brain – the cortex – at this time. As adolescence progresses, this layer of grey matter gets thinner – probably because unwanted or unused connections between neurons – called synapses – are pruned back. At the same time, important neurons are upgraded. The parts of these cells that carry signals down towards synapses are given a sheath that helps them transmit signals more quickly – a process called myelination. “It may be that pruning and myelination are part of the maturation of the brain,” says Steven McCarroll at Harvard Medical School. “Pruning involves removing the connections that are not used, and myelination takes the ones that are left and makes them faster,” he says. McCarroll describes this as a trade-off – by pruning connections, we lose some flexibility in the brain, but the proficiency of signal transmission improves. © Copyright Reed Business Information Ltd.
Keyword: Development of the Brain
Link ID: 22474 - Posted: 07.26.2016
By Knvul Sheikh Although millions of women use hormone therapy, those who try it in hopes of maintaining sharp memory and preventing the fuzzy thinking sometimes associated with menopause may be disappointed. A new study indicates that taking estrogen does not significantly affect verbal memory and other mental skills. “There is no change in cognitive abilities associated with estrogen therapy for postmenopausal women, regardless of their age,” says Victor Henderson, a neurologist at Stanford University and the study’s lead author. Evidence of positive and negative effects of such hormone therapy has ping-ponged over the years, with some observational studies in postmenopausal women and research in animal models, suggesting it improves cognitive function and memory. But other previous research, including a long-term National Institutes of Health Women’s Health Initiative memory study published in 2004, has suggested that taking estrogen increases the risk of cognitive impairment and dementia in women over 65 years old. Henderson says one explanation for these contradictory findings may be that after menopause begins there is a “critical period” in which hormone therapy could still benefit relatively young women—if they start early enough. So in their study, which appears in the July 20 online Neurology, Henderson and his team recruited 567 healthy women, between ages 41 and 84, to examine how estrogen affected one group whose members were within six years of their last menstrual period and another whose members had started menopause at least 10 years earlier. © 2016 Scientific American
By William Kenower My youngest son, Sawyer, used to spend far more time relating to his imagination than he did to the world around him. He would run back and forth humming, flapping his hands and thumping on his chest. By the time he was in first grade, attempts to draw him out of his pretend world to join his classmates or do some class work led to explosions and timeouts. At 7 he was given a diagnosis of being on the autism spectrum. That was when my wife, Jen, learned about the practice called joining. The idea behind it, which she discovered in Barry Neil Kaufman’s book “Son-Rise,” is brilliant in its simplicity. We wanted Sawyer to be with us. We did not want him to live in this bubble of his own creation. And so, instead of telling him to stop pretending and join us, we started pretending and joined him. The first time Jen joined him, the first time she ran beside him humming and thumping her chest, he stopped running, stopped thumping, stopped humming and, without a single word from us, turned to her and said, “What are you doing?” We took turns joining him every day, and a week later we got an email from his special education teacher telling us to keep doing whatever we were doing. He’d gone from five timeouts a day to one in a week. The classroom was the same, the work was the same – all that was different was that we had found a way to say to him in a language he could understand, “You’re not wrong.” Emboldened by our success, we set about becoming more fluent in this language. For the next couple of years we taught ourselves to join him constantly. This meant that whatever we were doing had to stop whenever we heard him running back and forth and humming. But we could not join him simply to get him to stop running and thumping and humming. We had to join him without any judgment or impatience. That was the trickiest part. The desire to fix him was great. I had come to believe that there were broken people in need of fixing. Sometimes, I looked like one of those people. I was a 40-year-old unpublished writer working as a waiter. My life reeked of failure. Many days I looked in the mirror and asked, “What is wrong with me?” © 2016 The New York Times Company
Link ID: 22451 - Posted: 07.16.2016
By Rebecca Brewer, Jennifer Murphy, There is a persistent stereotype that people with autism are individuals who lack empathy and cannot understand emotion. It’s true that many people with autism don’t show emotion in ways that people without the condition would recognize. But the notion that people with autism generally lack empathy and cannot recognize feelings is wrong. Holding such a view can distort our perception of these individuals and possibly delay effective treatments. We became skeptical of this notion several years ago. In the course of our studies of social and emotional skills, some of our research volunteers with autism and their families mentioned to us that people with autism do display empathy. Many of these individuals said they experience typical, or even excessive, empathy at times. One of our volunteers, for example, described in detail his intense empathic reaction to his sister’s distress at a family funeral. Yet some of our volunteers with autism agreed that emotions and empathy are difficult for them. We were not willing to brush off this discrepancy with the ever-ready explanation that people with autism differ from one another. We wanted to explain the difference, rather than just recognize it. So we looked into the overlap between autism and alexithymia, a condition defined by a difficulty understanding and identifying one’s own emotions. People with high levels of alexithymia (which we assess with questionnaires) might suspect they are experiencing an emotion, but are unsure which emotion it is. They could be sad, angry, anxious or maybe just overheated. About 10 percent of the population at large — and about 50 percent of people with autism — has alexithymia. © 2016 Scientific American
By Tara Parker-Pope Hoping to alert parents to “red flags” that might signal autism, two advocacy groups yesterday launched a Web site, the ASD Video Glossary, that provides online glimpses of kids with autism to worried parents. But some experts fear the site, though well intentioned, also may cause anxiety among parents whose children are perfectly fine. The site contains videos that show subtle differences in how kids with autism speak, react, play and express themselves. The organizations behind it, Autism Speaks and First Signs, hope that parents who see resemblances in their own kids will be emboldened to seek early diagnosis and treatment, which many experts believe can improve outcomes for kids with autism. Visitors to the new site must register in order to watch the videos, and in the first two hours of its release, more than 10,000 people did so. Yet some researchers fear the video glossary is certain to be troubling for the parents of children without autism, too, because the behavior of kids without the condition can resemble that depicted in the videos. “Just as there’s a spectrum in autism…there’s a spectrum in normal development,” Dr. Michael Wasserman, a pediatrician at Ochsner Medical Center in New Orleans told the Associated Press. “Children don’t necessarily develop in a straight line.” But Amy Wetherby, a professor of communications disorders at Florida State University who helped create the site, said the videos would embolden parents to persist when doctors don’t listen to legitimate concerns about a child’s behavior. As she told the Associated Press, sometimes “parents are the first to be concerned, and the doctors aren’t necessarily worried,” she said. “This will help give them terms to take to the doctor and say, ‘I’m worried about it.”’ © 2016 The New York Times Company
Link ID: 22432 - Posted: 07.13.2016
By David Dobbs It’s difficult to tell what Gina Pace wants unless you already know what she wants. But sometimes that’s easy, and this is one of those times: Gina wants pizza. “I-buh!” she says repeatedly—her version of “I want.” We all do. We are sitting at Abate’s in New Haven, Connecticut, a town famous for—among other things—pizza and science. Gina and her father, Bernardo, who live on Staten Island in New York City, have made the two-hour drive here for both. The pizza is in the oven. The science is already at the table, represented by Abha Gupta, a developmental pediatrician at Yale’s renowned Child Study Center. Gupta is one of the few scientific experts on a condition that Bernardo and Gina know through hard experience. Gina, now 24, was diagnosed 20 years ago with childhood disintegrative disorder, or CDD. CDD is the strangest and most unsettling developmental condition you have probably never heard of. Also known as Heller’s syndrome, for the Austrian special educator who first described it in 1908, it is a late-blooming, viciously regressive form of autism. It’s rare, striking about 1 or 2 in every 100,000 children. After developing typically for two to 10 years (the average is three or four), a child with CDD will suffer deep, sharp reversals along multiple lines of development, which may include language, social skills, play skills, motor skills, cognition, and bladder or bowel control. The speed and character of this reversal varies, but it often occurs in a horrifyingly short period—as short as a couple of months, says Gupta. In about 75 percent of cases, this loss of skills is preceded by days or weeks in which the child experiences intense anxiety and even terror: nightmares and waking nightmares and bouts of confused, jumpy disturbance that resemble psychosis.
By Karl Gruber For most birds the night brings a well-deserved rest. But for some, it is time for more risqué activities. Nocturnal birds sing at night – no surprises there – mainly to attract mates or repel rivals, the same reasons other birds sing at daytime. But a small number of species active by day also occasionally sing at night. Why they invest time and energy in such behaviour has been something of a mystery. Now Antonio Celis-Murillo at the Illinois Natural History Survey in Champaign and his colleagues think they have an answer – and it wasn’t what they expected. The team spent two years studying field sparrows, Spizella pusilla, a common bird across eastern North America. Active during the day, these birds are territorial and largely monogamous, though they engage in occasional infidelity. The researchers observed 28 pairs in the wild, recording the songs of territorial males, as well as those of intruder and neighbouring males. They then conducted playback experiments at night, studying the responses of the pairs. “I was surprised to see what these birds were up to,” says Celis-Murillo. The males sing to attract other male’s partners, and these females are all too willing to wake up for a night-time rendezvous. The team also found that males sang more during periods when females were reproductively receptive, and that the females responded to such song more often when they were fertile. The female’s mate didn’t appear to kick up a fuss and counter-sing – which would be expected if nocturnal songs served to repel rivals. © Copyright Reed Business Information Ltd.
By Jessica Hamzelou TEENAGE pregnancies have hit record lows in the Western world, largely thanks to increased use of contraceptives of all kinds. But strangely, we don’t really know what hormonal contraceptives – pills, patches and injections that contain synthetic sex hormones – are doing to the developing bodies and brains of teenage girls. You’d be forgiven for assuming that we do. After all, the pill has been around for more than 50 years. It has been through many large trials assessing its effectiveness and safety, as have the more recent patches and rings, and the longer-lasting implants and injections. But those studies were done in adult women – very few have been in teenage girls. And biologically, there is a big difference. At puberty, our bodies undergo an upheaval as our hormones go haywire. It isn’t until our 20s that things settle down and our brains and bones reach maturity. “If a drug is going to be given to 11 and 12-year-olds, it needs to be tested in 11 and 12-year-olds,” says Joe Brierley of the clinical ethics committee at Great Ormond Street Hospital in London. Legislation introduced in the US in 2003 and in Europe in 2007 was intended to make this happen but a New Scientist investigation can reveal that there is still scant data on what contraceptives actually do to developing girls. The few studies that have been done suggest that tipping the balance of oestrogen and progesterone during this time may have far-reaching effects, although there is not yet enough data to say whether we should be alarmed. © Copyright Reed Business Information Ltd.
By David Shultz Making eye contact for an appropriate length of time is a delicate social balancing act: too short, and we look shifty and untrustworthy; too long, and we seem awkward and overly intimate. To make this Goldilocks-like dilemma even trickier, it turns out that different people prefer to lock eyes for different amounts of time. So what’s too long or too short for one person might be just right for another. In a new study, published today in Royal Society Open Science, researchers asked a group of 498 volunteers to watch a video of an actor staring out from a screen and press a button if their gazes met for an uncomfortably long or short amount of time (above). During the test, the movement of their eyes and the size of their pupils were recorded with eye-tracking technology. On average, participants had a “preferred gaze duration” of 3.3 seconds, give or take 0.7 seconds. That’s a pretty narrow band for someone on their first date! Making things even harder, individual preferences can also be measured: Researchers found that how quickly people’s pupils dilated—an automatic reflex whenever someone looks into the eyes of another—was a good indicator of how long they wanted to gaze. The longer their preferred gaze, the faster their pupils expanded. The differences are so subtle, though, that they can only be seen with the eye-tracking software—making any attempts to game the system is likely to end up awkward rather than informative. © 2016 American Association for the Advancement of Science.
Carl Zimmer Our genes are not just naked stretches of DNA. They’re coiled into intricate three-dimensional tangles, their lengths decorated with tiny molecular “caps.” These so-called epigenetic marks are crucial to the workings of the genome: They can silence some genes and activate others. Epigenetic marks are crucial for our development. Among other functions, they direct a single egg to produce the many cell types, including blood and brain cells, in our bodies. But some high-profile studies have recently suggested something more: that the environment can change your epigenetic marks later in life, and that those changes can have long-lasting effects on health. In May, Duke University researchers claimed that epigenetics could explain why people who grow up poor are at greater risk of depression as adults. Even more provocative studies suggest that when epigenetic marks change, people can pass them to their children, reprogramming their genes. But criticism of these studies has been growing. Some researchers argue that the experiments have been weakly designed: Very often, they say, it’s impossible for scientists to confirm that epigenetics is responsible for the effects they see. Three prominent researchers recently outlined their skepticism in detail in the journal PLoS Genetics. The field, they say, needs an overhaul. “We need to get drunk, go home, have a bit of a cry, and then do something about it tomorrow,” said John M. Greally, one of the authors and an epigenetics expert at the Albert Einstein College of Medicine in New York. © 2016 The New York Times Company
By JAN HOFFMAN About 1.4 million adults in the United States identify as transgender, double a widely used previous estimate, according to an analysis based on new federal and state data. As the national debate escalates over accommodations for transgender people, the new figure, though still just 0.6 percent of the adult population, is likely to raise questions about the sufficiency of services to support a population that may be larger than many policy makers assumed. “There’s a saying: ‘You don’t count in policy circles until someone counts you,’” said Gary J. Gates, a demographer and former research director of the group that did the analysis, the Williams Institute at the U.C.L.A. School of Law, which focuses on law and policy issues related to sexual orientation and gender identity. The Williams Institute is the research group that produced a widely accepted estimate five years ago. Its new number was drawn from a much larger federal database than it used to reach the earlier projection of 0.3 percent, or 700,000 people. Noting that younger adults ages 18 to 24 were more likely than older ones to say they were transgender, researchers said that the new estimates reflected in part a growing awareness of transgender identity. The analysis may also reflect the limits of self-reporting in obtaining definitive data. In some states seen as more accepting, more adults identified themselves as transgender. In some states perceived as more resistant, fewer adults did so, even though the surveys were anonymous. The percentage of adults identifying as transgender by state ranged from lows of 0.30 percent in North Dakota, 0.31 percent in Iowa and 0.32 percent in Wyoming to highs of 0.78 percent in Hawaii, 0.76 percent in California and 0.75 percent in Georgia. In some states the results at first glance seemed surprising. In New York, for example, the percentage was 0.51; in Texas it was 0.66. © 2016 The New York Times Company
Keyword: Sexual Behavior
Link ID: 22389 - Posted: 07.02.2016
by Sarah Zielinski Among people, a man stepping aside to let a woman pass through a door first is seen as a gentlemanly — if a bit old-fashioned — act. Among banana fiddler crabs, though, this behavior is a trap — one that lets a male crab coerce a female into a mating she may not have preferred. To catch the attention of a female and lure her into his burrow, a male banana fiddler crab stands outside the entrance to his cave and waves the larger of his two claws. A female will look him over and consider his size, the color of his claw and how he’s waving it. If she likes what she sees, she’ll approach him. She might decide to enter his burrow and check it out, and once inside, she might stick around for mating if she thinks that the burrow has the right conditions for rearing her embryos. When a female approaches a male and his burrow, most males enter first, letting their potential mate follow him down. But many male crabs take another approach, stepping aside and following her into the lair — letting a male trap the female inside and mate with her, researchers report June 15 in PLOS ONE. Christina Painting of the Australian National University in Canberra and colleagues observed banana fiddler crabs in Darwin, Australia, during two mating seasons, watching what happened as males waved their claws and females made their choice. When a female was interested in a male, the guys entered the burrow first 32 percent of the time. While females were more likely to enter a burrow if a male entered first (71 percent versus only 41 percent when the guy stepped aside), the trapping strategy was more successful in getting a mating out of the meeting. When the male followed the female in, 79 percent of females stuck around the mate. But waiting for her to follow resulted in a pairing only 54 percent of the time. © Society for Science & the Public 2000 - 2016
By Maya Smith Bonobos (pictured) are known as the peaceful ape. They’re less aggressive than their chimpanzee cousins, and when they have disagreements they’re more likely to make love, not war. Now, a new study reveals one way females keep the peace. In most primate societies, female genitals swell to advertise that they’re ready to mate, leading to fighting among males as they jostle for a partner. But in bonobos, the swellings only indicate fertility half the time, according to a study in the wild published this week in BMC Evolutionary Biology. The findings confirm what scientists have observed in captivity. The researchers behind the new study hypothesize females may have evolved the behavior to gain the upper hand in mating. Because males cannot look to sexual swellings as a reliable indicator of fertility, the females are free to choose their mates. And that helps everyone get along. © 2016 American Association for the Advancement of Science.
By Patrick Monahan Birds are perhaps best known for their bright colors, aerial prowess, and melodic songs. But research presented in Austin last week at the Evolution Conference shows that bacteria have granted some birds another important attribute: stink. Having long taken a back seat to sight and sound, scent is becoming more and more recognized as an important sense for songbirds, and dark-eyed juncos (Junco hyemalis, pictured) are no stranger to it. When these common birds clean their feathers—or preen—they spread pungent oil from their “preen glands” all over their bodies. The act is important for enticing mates: Three of the gland’s smelly chemicals are found in very different quantities in the two sexes, and males with a more masculine musk end up with more offspring. Females with a more feminine scent profile are more successful, too. But juncos likely aren’t making their perfume alone: Lots of those preen gland chemicals are naturally made by bacteria. And new work is making the bird-bacteria link even more firm. When researchers inject antibiotics into the juncos’ preen glands, the concentrations of three smelly molecules tend to decrease—the same three molecules that juncos find sexy in the right proportions, Danielle Whittaker of Michigan State University in East Lansing told attendees. So it seems like juncos may actually be picking mates based on their bacterial—rather than self-produced—body odor, a first for birds. © 2016 American Association for the Advancement of Science.
Nicola Davis Death by cannibalism might seem like a high price to pay for a fleeting moment of passion, but male praying mantises are doing it for the kids, new research suggests. Scientists have discovered that female praying mantises who eat their mates after sex produce a greater number of eggs than those who do not, with the bodies of the ill-fated males used to aid their production. Of the species of praying mantises known to exhibit sexual cannibalism it is estimated up to 28% of males are eaten by their partner. After mating, the female stores the male’s sperm and later uses it to fertilise the eggs that she produces. The authors say the new study backs up a long-mooted theory that males could have evolved a behavioural trait of self-sacrifice to boost their reproductive success. “There is an obvious cost – you are dead, you have lost all future mating possibilities,” said William Brown, of the State University of New York at Fredonia, who co-authored the research. “We measure costs and benefit in terms of offspring production,” he added. If, by dying, the male can boost the number of offspring produced by one female, the theory goes, it could outweigh the downsides of missing out on future conquests. Published in the journal Proceedings of the Royal Society B by researchers in the US and Australia, the new study reveals how scientists unpicked the influence of cannibalism on the production of offspring in the praying mantis Tenodera sinensis, by tracking what happened to male ejaculate and bodily tissues after mating. © 2016 Guardian News and Media Limited
By Christie Aschwanden What is gender? It might sound like the kind of question that college students debate in a liberal arts class.1 But for the International Olympic Committee, it’s a practical question that demands a hard and fast answer. As at previous Olympic Games, athletes competing in Rio de Janeiro will be segregated into women’s events and men’s events, and that means the IOC needs a way to sort women from men. New IOC guidelines issued in November allow athletes who have transitioned to another gender to compete without sex reassignment surgery. The rules allow athletes who’d previously identified as female to compete in the male category without restriction, because they would not gain an advantage from their previous gender. Those who transition from male to female, on the other hand, must meet several requirements. The athlete must declare a female identity, and this identity cannot change for at least four years. The athlete must also document that her total serum testosterone levels have remained below a certain limit for a minimum of 12 months before competing, and these levels must remain under the threshold as long as she’s competing. The Olympic committee’s decision is a “huge step forward for everybody in the [transgender] community,” Caitlyn Jenner told me last week. “You can still have your old parts, which I think is very forward thinking.” Jenner is a trans woman who won the gold medal in the decathlon at the 1976 Olympics when she was Bruce Jenner, and she’s keeping the anatomical details of her own transition private. The public “is obsessed with — do you have it, or don’t have it?” she said, but “a trans person’s body parts is nobody’s business.”
Keyword: Sexual Behavior
Link ID: 22373 - Posted: 06.29.2016
By Elizabeth Pennisi Cave fish have long fascinated biologists because of their missing eyes and pale skin. Now, one researcher is studying them for another reason: Their behavior may provide clues to the genetic basis of some human psychiatric disorders. Last week at the 23rd International Conference on Subterranean Biology in Fayetteville, Arkansas, he demonstrated how drugs that help people with schizophrenia and autism similarly affect the fish. “I think there is a lot of potential” for these fish to teach us about mental disorders, says David Culver, an evolutionary biologist at American University in Washington, D.C., who was not involved in the study. Culver adds that—like other work on the cause of cave fish blindness—the new research may also have implications for human disease. A decade ago, the lead author on the new study, Masato Yoshizawa, wanted to understand brain evolution by investigating the effects of natural selection on behavior. The Mexican tetra (Astyanax mexicanus), a cave fish with very close surface relatives, seemed an excellent prospect for that work. Because the two populations can interbreed, it’s easier to pin down genes that might be related to the neural defects underlying behavioral differences. Such breeding studies are not possible in humans. The blind cave fish differ from their surface relatives in several notable ways. They don’t have a social structure and they don’t school. Instead, they lead solitary lives—a behavior that makes sense given their lack of natural predators. They also almost never sleep. They are hyperactive, and—unlike other fish—they are attracted to certain vibrations in the water. Finally, they tend to do the same behavior over and over again and seem to have higher anxiety than their surface relatives. © 2016 American Association for the Advancement of Science.
By Patrick Monahan The soft, blinking lights of fireflies aren’t just beautiful—they may also play a role in creating new species. A new study shows that using light-up powers for courtship makes species split off from each other at a faster pace, providing some of the clearest evidence yet that the struggle to find mates shapes the diversity of life. The firefly’s glow, like the enormous claws of fiddler crabs and the elaborate dances of manakins, was sculpted by the struggle for sex. Scientists have long thought that this kind of mating-driven natural selection—called “sexual selection”—could make species split into two. Say females in two populations prefer different color patterns in males: Even if the populations have the same needs in every other way, that simple preference could make them split into species with males of separate colors. “A lot of closely related species differ in sexual traits,” says Emily Ellis, an evolutionary biologist at the University of California (UC), Santa Barbara. But actually linking this kind of evolution to species proliferation is a hard idea to test. “So many people have looked at this and found differing results,” she says—possibly because they looked at smaller groups, like birds, rather than across the whole tree of life. That’s where bioluminescence comes in. Many groups of living organisms, from insects to fish to octopuses, emit light, whether to ward off predators, dazzle prey, or attract mates. It’s a trait that has evolved more than 40 times across the animal kingdom, Ellis says. © 2016 American Association for the Advancement of Science.
By Ruth Williams The offspring of certain mice fed a high-fat diet have altered gut microbiomes and may be prone to autism-like behaviors including social deficits, according to a study published today (June 16) in Cell. But treating these offspring with a specific microbial species they lack can rectify the animals’ social behavior. “There’s growing evidence that the microbiome, particularly early in life, can have long-term effects on brain development and behavior,” said anatomist and neuroscientist John Cryan of University College Cork in Ireland who was not involved in the study. “What this paper does is take advantage of the fact that we get our microbiome from our mums, and looks at what happens if the mum disturbs her microbiome during pregnancy.” According to the US Centers for Disease Control and Prevention, one in 68 U.S. children have autism spectrum disorder (ASD). Recent evidence suggests that the risk of ASD is increased for the offspring of mothers with obesity. In both humans and non-human primates, the offspring of obese mothers have also been shown to have abnormal microbiomes. And some people with ASD have imbalanced gut microbes, or dysbiosis. Baylor College of Medicine’s Mauro Costa-Mattioli and colleagues sought to better understand how maternal obesity, the microbiome, and ASD are interconnected. The team turned to mice for answers. The researchers gave female animals high-fat diets before setting up matings, later finding that a “large proportion” of the offspring exhibited ASD-like behaviors, including reduced social interaction, repetitive behaviors, and anxiety. The team analyzed the microbiomes of these offspring, finding that they differed from those of control animals. © 1986-2016 The Scientist
Link ID: 22336 - Posted: 06.18.2016
Susan Milius The Nyctibatrachus humayuni frogs live only in India’s Western Ghats, a region of still-unexplored biodiversity. Video now shows that the mating male of the species positions himself loosely on a female’s back, with his hands on the ground or leaves. From this position, called a dorsal straddle, the male then releases sperm directly onto the female’s back. Then, in an unusual move, he retreats before she lays the eggs. Sperm trickling down the female’s back and legs fertilize the eggs, an international research team reports June 14 in PeerJ. It’s the first time biologists have documented this loose straddling position. More typically, male frogs, which don’t deliver sperm into a female reproductive tract, hold tight and contact freshly deposited eggs to fertilize them. Bombay night frogs do on occasion crawl over their eggs, but researchers found the eggs are already fertilized. Biologists studying the challenges of external fertilization have previously cataloged six basic forms of male frog mating grasp, or amplexus. Four take some kind of back-hug approach or a head straddle. Other species position themselves rump-to-rump or, in what’s called glued amplexus, with the male dangling from a behemoth female. Position is hardly the only unexpected feature of courting Bombay night frogs. Females give courtship croaks, one of only a few dozen female-vocal species among the 6,500-plus known kinds of frogs. © Society for Science & the Public 2000 - 2016
Keyword: Sexual Behavior
Link ID: 22326 - Posted: 06.16.2016