Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases

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By Christie Aschwanden The Olympic stadium was quiet on Wednesday morning, and spectators in the sparsely filled stands seemed to pay little notice to South African runner Caster Semenya as she cruised to an easy win in her first-round heat of the 800 meters. But on Saturday evening, when Semenya will contest the 800-meter final, she’ll have the world’s eyes on her. “There is no more certain gold medal in the Rio Olympics than Semenya,” wrote Ross Tucker, an exercise scientist in South Africa, on his blog, The Science of Sport. “She could trip and fall, anywhere in the first lap, lose 20m, and still win the race.” If she does indeed dominate, some sports fans will be cheering Semenya, while others will be less inclined to celebrate, believing that she has an unfair advantage over her rivals. Semenya made headlines in 2009 amid rumors that track’s governing body, the International Association of Athletics Federations, had required her to undergo tests to confirm that she was female. Media accounts have reported that she has hyperandrogenism, a condition that causes higher-than-average testosterone levels — an allegation that neither Semenya nor the IAAF has publicly confirmed. Semenya’s case is the latest saga in sport’s checkered history of sex testing, a task that is purportedly aimed at creating an even playing field but — as I’ve discussed previously — raises serious questions about how athletics organizations treat women. Her muscular build, deep voice and remarkable results had raised suspicions among some of Semenya’s rivals about whether she was really a woman. “Just look at her,” said Mariya Savinova, a Russian runner now tangled in her country’s doping scandal.

Keyword: Sexual Behavior; Hormones & Behavior
Link ID: 22601 - Posted: 08.25.2016

By Melinda Wenner Moyer The science of sleep is woefully incomplete, not least because research on the topic has long ignored half of the population. For decades, sleep studies mostly enrolled men. Now, as sleep researchers are making a more concerted effort to study women, they are uncovering important differences between the sexes. Hormones are a major factor. Estrogen, progesterone and testosterone can influence the chemical systems in the brain that regulate sleep and arousal. Moreover, recent studies indicate that during times of hormonal change—such as puberty, pregnancy and menopause—women are at an increased risk for sleep disorders such as obstructive sleep apnea, restless legs syndrome and insomnia. Women also tend to report that they have more trouble sleeping before and during their menstrual periods. And when women do sleep poorly, they may have a harder time focusing than sleep-deprived men do. In one recent study, researchers shifted the sleep-wake cycles of 16 men and 18 women for 10 days. Volunteers were put on a 28-hour daily cycle involving nearly 19 hours of awake time followed by a little more than nine hours of sleep. During the sleep-shifted period, the women in the group performed much less accurately than the men on cognitive tests. The findings, published in April of this year in the Proceedings of the National Academy of Sciences USA, may help explain why women are more likely than men to get injured working graveyard shifts. In addition, a study conducted in 2015 in teenagers reported that weekday sleep deprivation affects cognitive ability more in girls than in boys. © 2016 Scientific American

Keyword: Sleep; Sexual Behavior
Link ID: 22568 - Posted: 08.18.2016

by Helen Thompson Some guys really know how to kill a moment. Among Mediterranean fish called ocellated wrasse (Symphodus ocellatus), single males sneak up on mating pairs in their nest and release a flood of sperm in an effort to fertilize some of the female’s eggs. But female fish may safeguard against such skullduggery through their ovarian fluid, gooey film that covers fish eggs. Suzanne Alonzo, a biologist at Yale University, and her colleagues exposed sperm from both types of males to ovarian fluid from female ocellated wrasse in the lab. Nesting males release speedier sperm in lower numbers (about a million per spawn), while sneaking males release a lot of slower sperm (about four million per spawn). Experiments showed that ovarian fluid enhanced sperm velocity and motility and favored speed over volume. Thus, the fluid gives a female’s chosen mate an edge in the race to the egg, the researchers report August 16 in Nature Communications. While methods to thwart unwanted sperm are common in species that fertilize within the body, evidence from Chinook salmon previously hinted that external fertilizers don’t have that luxury. However, these new results suggest otherwise: Some female fish retain a level of control over who fathers their offspring even after laying their eggs. Male ocellated wrasse come in three varieties: sneaky males (shown) that surprise mating pairs with sperm but don’t help raise offspring; nesting males that build algae nests and court females; and satellite males, which protect nests from sneakers but staying out of parenting. |© Society for Science & the Public 2000 - 2016

Keyword: Sexual Behavior; Evolution
Link ID: 22563 - Posted: 08.17.2016

Carl Zimmer An eye is for seeing, a nose is for smelling. Many aspects of the human body have obvious purposes. But some defy easy explanation. For biologists, few phenomena are as mysterious as the female orgasm. While orgasms have an important role in a woman’s intimate relationships, the evolutionary roots of the experience — a combination of muscle contractions, hormone release, and intense pleasure — have been difficult to uncover. For decades, researchers have put forward theories, but none are widely accepted. Now two evolutionary biologists have joined the fray, offering a new way of thinking about the female orgasm based on a reconstruction of its ancient history. On Monday, in The Journal of Experimental Zoology, the authors conclude that the response originated in mammals more than 150 million years ago as a way to release eggs to be fertilized after sex. Until now, few scientists have investigated the biology of distantly related animals for clues to the mystery. “For orgasms, we kept it reserved for humans and primates,” said Mihaela Pavlicev, an evolutionary biologist at University of Cincinnati College of Medicine and an author of the new paper. “We didn’t look to other species to dig deeper and look for the origin.” The male orgasm has never caused much of a stir among evolutionary biologists. The pleasure is precisely linked to ejaculation, the most important step in passing on a male’s genes to the next generation. That pleasure encourages men to deliver more sperm, which is evolutionarily advantageous. For women, the evolutionary path is harder to figure out. The muscle contractions that occur during an orgasm are not essential for a woman to become pregnant. And while most men can experience an orgasm during sex, it’s less reliable for women. © 2016 The New York Times Company

Keyword: Sexual Behavior; Hormones & Behavior
Link ID: 22501 - Posted: 08.02.2016

Nicola Davis Female orgasm has perplexed scientists, fuelled an equality movement and propelled Meg Ryan to fame. Now researchers say they might have found its evolutionary roots. The purpose of the euphoric sensation has long puzzled scientists as it is not necessary for conception, and is often not experienced by women during sex itself. But scientists in the US have come up with an answer. Human female orgasm, they say, might be a spin-off from our evolutionary past, when the hormonal surges that accompany it were crucial for reproduction. “It is important to stress that it didn’t look like the human female orgasm looks like now,” said Mihaela Pavličev, co-author of the study from Cincinnati children’s hospital. “We think that [the hormonal surge] is the core that was maybe modified further in humans.” Writing in the journal JEZ-Molecular and Developmental Evolution, Pavličev and co-author Günter Wagner from Yale University describe how they delved into the anatomy and behaviour of a host of placental mammals to uncover the evolutionary origin of female orgasm, based on the hormonal surges associated with it. In mammals such as cats and rabbits, these surges occur during sex and play a crucial role in signalling for eggs to be released from the female’s ovaries. By contrast in a variety of other mammals, including humans and other primates, females ovulate spontaneously. © 2016 Guardian News and Media Limited

Keyword: Sexual Behavior; Hormones & Behavior
Link ID: 22498 - Posted: 08.01.2016

By PAM BELLUCK The World Health Organization is moving toward declassifying transgender identity as a mental disorder in its global list of medical conditions, with a new study lending additional support to a proposal that would delete the decades-old designation. The change, which has so far been approved by each committee that has considered it, is under review for the next edition of the W.H.O. codebook, which classifies diseases and influences the treatment of patients worldwide. “The intention is to reduce barriers to care,” said Geoffrey Reed, a psychologist who is coordinating the mental health and behavior disorders section in the upcoming edition of the codebook, called the International Classification of Diseases, or I.C.D. Dr. Reed, a professor at the National Autonomous University of Mexico and an author of the new study, said the proposal to remove transgender from the mental disorder category was “not getting opposition from W.H.O.,” suggesting that it appears likely to be included in the new edition. The revised volume would be the first in more than 25 years, and is scheduled to be approved in May 2018. Removing the mental health label from transgender identity would be a powerful signifier of acceptance, advocates and mental health professionals say. “It’s sending a very strong message that the rest of the world is no longer considering it a mental disorder,” said Dr. Michael First, a professor of clinical psychiatry at Columbia University and the chief technical consultant to the new edition of the codebook, which is known by its initials and the edition number I.C.D.-11. “One of the benefits of moving it out of the mental disorder section is trying to reduce stigma.” © 2016 The New York Times Company

Keyword: Sexual Behavior
Link ID: 22484 - Posted: 07.27.2016

By Jesse Singal As anyone who has read much about the subject can attest, the discussion about kids with gender dysphoria — that is, discomfort with their body and the feeling that they should have been born the other sex, or that they are the other sex — can get extremely heated and tricky. Much of the controversy stems from questions of age: How young is too young to help a child socially transition — that is, to change their name and pronoun, and possibly the way they present themselves? To prescribe them cross-sex hormones to begin the process of physically transitioning? For children with persistent gender dysphoria who are approaching adolescence, current best practice is to prescribe them so-called puberty blockers. Delaying the onset of puberty both forestalls the sometimes very uncomfortable experience of a child going through puberty in a body they aren’t comfortable in, and buys them and their families time to figure out what to do. Sometimes, this eventually leads to the prescription of cross-sex hormones, and sometimes it leads to surgery after that. Some people, though, are arguing that kids — particularly those who have socially transitioned at a young age — shouldn’t have to wait that long. Recently in the Guardian, for example, Kate Lyons reported on the current state of this debate in Britain: specifically, whether children who identify as transgender should be given access to cross-sex hormones, or possibly even surgery, at younger ages than what is current practice. © 2016, New York Media LLC.

Keyword: Sexual Behavior
Link ID: 22483 - Posted: 07.27.2016

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

Keyword: Hormones & Behavior; Attention
Link ID: 22470 - Posted: 07.23.2016

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.

Keyword: Sexual Behavior; Biological Rhythms
Link ID: 22417 - Posted: 07.09.2016

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.

Keyword: Hormones & Behavior; Development of the Brain
Link ID: 22407 - Posted: 07.08.2016

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

Keyword: Epigenetics; Genes & Behavior
Link ID: 22391 - Posted: 07.02.2016

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

Keyword: Sexual Behavior; Evolution
Link ID: 22388 - Posted: 07.02.2016

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.

Keyword: Sexual Behavior; Aggression
Link ID: 22383 - Posted: 07.01.2016

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.

Keyword: Chemical Senses (Smell & Taste); Sexual Behavior
Link ID: 22377 - Posted: 06.30.2016

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

Keyword: Sexual Behavior; Evolution
Link ID: 22374 - Posted: 06.29.2016

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 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.

Keyword: Sexual Behavior; Evolution
Link ID: 22358 - Posted: 06.25.2016

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