Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
Nicola Davis The mystery of why sheep get horny in the winter might have been solved, according to new research. Scientists say they have uncovered the key to the mechanism by which changes in the length of the day prompt certain animals to begin breeding, trigger the growth of horns and even change the thickness of their coat. The findings, the team add, could help farmers tinker with the timing of the lambing season. “Now we know what that link is we can start to understand how it can be controlled,” said David Bates, professor of oncology at the University of Nottingham and co-author of the research. It has long been known that changes in animals’ fertility over the seasons is linked to melatonin – a hormone released at night from the pineal gland in the brain. This hormone acts on another gland, the pituitary, affecting the levels of various sex hormones it produces. With the onset of fertility in sheep linked to longer periods of melatonin production, winter is the season for ovine Casanovas. But there is a puzzle. The region of the pituitary gland that detects melatonin is separate to the region that produces sex hormones. As a result, scientists had been baffled as to how melatonin ends up affecting the onset of fertility. “No-one has been able to find what the link is,” said Bates. Now Bates and colleagues from the University of Bristol say they have the answer. Writing in the journal PNAS, the team reveal the missing link is a protein, known as vascular endothelial growth factor, which is made in the region of the pituitary gland that detects melatonin. © 2017 Guardian News and Media Limited
By The Scientist Staff For thousands of years, people have appreciated birdsong as one of nature’s most melodic sounds. And for at least a few centuries, researchers have been talking about—and analyzing— birdsong, some attaching the label “music” to the avian behavior. In the mid-17th century, for example, German scholar Athanasius Kircher transcribed bird song with musical notation. Whether singing avian species hear their calls in a musical sense is, of course, anybody’s guess. But still today, it’s fairly uncontroversial to speak about bird vocalizations using terms such as “song” and “music.” Around the animal kingdom, several nonavians also produce sounds that are sometimes discussed using a musical vocabulary. Whale songs echo through the ocean for hundreds of miles, while frogs and crickets chorus on warm summer nights throughout much of the world. The stringency of the criteria for earning a label such as song varies by taxon, however. Birds, whales, mice, and even bats have a vocal repertoire that includes songs and simpler calls, while any insect or fish that produces sound for the sake of communication is considered, at least by some, to be “singing”—though no scientist seriously compares these species’ chirps and grunts to birdsong. Semantics aside, more and more tonal or cadenced animal communication signals are attracting the attention of researchers. Technological advancements have enabled the study of mouse and bat calls that are broadcast in the ultrasonic range, as well as of the love songs of fruit flies, which vibrate their wings to produce sound within the frequency range of human hearing, but do so a million times more quietly than our ears can detect. And research continues to delve into the musical skills of diverse bird species that have long been recognized for their singing prowess, confirming that there is an overlap between the genes and brain areas involved in bird and human vocal learning. © 1986-2017 The Scientist
by Laura Sanders Amid a flurry of cabinet appointments and immigration policies, the Trump administration has announced one thing it will not do: pursue policies that protect transgender children in public schools. The Feb. 22 announcement rescinds Obama administration guidelines that, among other protections, allow transgender kids to use bathrooms and participate in sports that correspond with their genders, and to be called by their preferred names and pronouns. In a Feb. 23 news briefing, White House press secretary Sean Spicer said that this is a states’ rights issue. “States should enact laws that reflect the values, principles, and will of the people in their particular state,” he said. “That's it, plain and simple.” But this “plain and simple” move could be quite dangerous, even deadly, science suggests. Transgender children, who are born one biological sex but identify as the other, already face enormous challenges as they move through a society that often doesn’t understand or accept them. Consider this: Nearly half (46.5 percent) of young transgender adults have attempted suicide at some point in their lives, a recent survey of over 2,000 people found. Nearly half. For comparison, the attempted suicide rate among the general U.S. population is estimated to be about 4.6 percent. What’s more, a 2015 study in the Journal of Adolescent Health found that transgender youth are two to three times as likely as their peers to suffer from depression and anxiety disorders, or to attempt suicide or harm themselves. These troublesome stats, based on a sample of 180 transgender children and young adults in Boston ages 12 to 29, applied equally to those who underwent male-to-female transitions and those who underwent female-to-male transitions. © Society for Science & the Public 2000 - 2017.
By Joshua A. Krisch When Kathleen Gardiner first encountered female mice with Down syndrome, she was surprised to find that the rodents’ brains showed unexpected abnormalities. Gardiner, a neuroscientist at the University of Colorado School of Medicine in Aurora, knew that trisomic male mice typically had perturbed protein levels in their hippocampuses. But these trisomic female mice showed the most serious changes in their cerebellums. “Right away, there’s a brain region sex difference,” Gardiner said. “It’s very interesting to ponder the fact that this could lead to sex differences in the learning, memory, or behavioral abnormalities associated with [Down syndrome].” Although Gardiner recognized that differences between mouse sexes would not necessarily translate into sex differences in humans, she considered the potential implications for clinical studies on Down syndrome therapies. “If we find that males or females are differing not only in their baseline impairment, but in their response to drugs, we need to know that,” she said. “We could be missing a big piece of information that could lead to better or different clinical trials.” Indeed, sex differences in model organisms are becoming increasingly apparent. Studies have shown sex differences in mice can affect cardiovascular health, liver disease, and cancer risk. Many of these studies are now published in Biology of Sex Differences, where Gardiner’s own work on the trisomic female mice appeared. © 1986-2017 The Scientist
By Carolyn Gramling Trilobites—three-sectioned, crablike critters that dominated the early Paleozoic—are so abundant that they have become the gateway fossil for most collectors. But paleontologists have found little evidence of how the extinct arthropods reproduced—until now. Researchers studying a fossil specimen of the trilobite Triarthrus eatoni spotted something odd just next to the animal’s head: a collection of small (about 200 micrometers across), round objects (in light blue, above). Those, they determined, are actually eggs—the first time anyone had observed fossil trilobite eggs right next to the critters themselves. The structures were exceptionally well preserved, the eggs and exoskeletons of the trilobites replaced with an iron sulfide ore called pyrite. They came from the Lorraine Group, a rock formation that spans much of the northeastern United States and dates to the Ordovician period (about 485 million to 444 million years ago); it has long been a mecca for trilobite hunters because of the pyritization. The placement of the eggs is suggestive, the researchers report in the March issue of Geology: They hypothesize that trilobites released their eggs and sperm through a genital pore somewhere in the head—much like modern horseshoe crabs do today. One possible reason for the rarity of the find may be that the brooding behavior of T. eatoni was relatively unusual in the trilobite world: The species tended to prefer a harsh, low-oxygen environment, and may have kept a closer eye on their eggs than other trilobite species. But, the authors note, one idea this finding does lay to rest is that trilobites might reproduce via copulation—a titillating but little-regarded hypothesis based on the fact that trilobites are sometimes found clustered on top of one another. Instead, trilobites were most likely spawners—and, in fact, that clustering behavior may be another parallel to horseshoe crabs, which can climb on top of one another in competition to fertilize released eggs. © 2017 American Association for the Advancement of Science
Patricia Neighmond Many men over 65 with low testosterone levels say their sense of well-being, not to mention sexual function, isn't what it used to be. That's why some doctors prescribe testosterone replacement. But the effectiveness of testosterone has been controversial. Studies of the risks and benefits have been mixed, and the Food and Drug Administration beefed up its warnings about cardiac side effects of testosterone supplementation in 2015. And the findings of five studies released Tuesday aren't likely to clear up the confusion. They appear in JAMA, the journal of the American Medical Association and JAMA Internal Medicine. The studies are collectively called the Testosterone Trials (TTrials) and they compared a testosterone gel, AndroGel, against a placebo. The results are based on 788 men with below normal levels of testosterone studied at 12 sites across the country over a year. Overall, researchers saw improvements in bone density and bone strength in men who used a testosterone gel, which raised their testosterone to levels seen in younger men. In men with unexplained anemia, testosterone also improved iron levels in the blood. (A reviewer of the study raised questions about whether it was done ethically.) But in men using testosterone who had been reporting memory problems at the start of the study, there were no improvements in memory or cognition. And there were worrisome signs of an increase in the risk of cardiovascular problems. © 2017 npr
By Greta Keenan The ocean might seem like a quiet place, but listen carefully and you might just hear the sounds of the fish choir. Most of this underwater music comes from soloist fish, repeating the same calls over and over. But when the calls of different fish overlap, they form a chorus. Robert McCauley and colleagues at Curtin University in Perth, Australia, recorded vocal fish in the coastal waters off Port Headland in Western Australia over an 18-month period, and identified seven distinct fish choruses, happening at dawn and at dusk. You can listen to three of them here: The low “foghorn” call is made by the Black Jewfish (Protonibea diacanthus) while the grunting call that researcher Miles Parsons compares to the “buzzer in the Operation board game” comes from a species of Terapontid. The third chorus is a quieter batfish that makes a “ba-ba-ba” call. “I’ve been listening to fish squawks, burble and pops for nearly 30 years now, and they still amaze me with their variety,” says McCauley, who led the research. Sound plays an important role in various fish behaviours such as reproduction, feeding and territorial disputes. Nocturnal predatory fish use calls to stay together to hunt, while fish that are active during the day use sound to defend their territory. “You get the dusk and dawn choruses like you would with the birds in the forest,” says Steve Simpson, a marine biologist at the University of Exeter, UK. © Copyright Reed Business Information Ltd.
Elizabeth Eaton A prehistoric marine reptile may have given birth to its young alive. A fossil from South China may be the first evidence of live birth in the animal group Archosauromorpha, scientists report February 14 in Nature Communications. Today Archosauromorpha is represented by birds and crocodiles — which both lay eggs. Whether this fossil really is the first evidence of live birth in Archosauromorpha depends on how another group of semiaquatic animals is classified, says Michael Caldwell, a vertebrate paleontologist with the University of Alberta in Canada. Placement of Choristodera, a now-extinct group that included a freshwater reptile that gave live birth, remains murky, with some researchers putting them with Archosauromorpha and others with a group that includes snakes and lizards. “Our discovery is the first of live birth in reptiles with undoubted archosauromorph affinity,” says Jun Liu, a paleontologist at Hefei University of Technology in China. Researchers have speculated that the biology of archosauromorphs prevented their reproductive traits from evolving, says study coauthor Chris Organ, an evolutionary biologist with Montana State University in Bozeman. This find may disprove that view. “Ancestrally, the science suggests that live birth is not absolutely prohibited,” Organ says. Even though birds and crocodiles haven’t yet evolved to give life birth, this discovery suggests that it’s possible. |© Society for Science & the Public 2000 - 2016
Moises Velasquez-Manoff This Valentine’s Day, as you bask in the beauty of your beloved, don’t just thank his or her genes and your good fortune; thank microbes. Research on the microbes that inhabit our bodies has progressed rapidly in recent years. Scientists think that these communities, most of which live in the gut, shape our health in myriad ways, affecting our vulnerability to allergic diseases like hay fever, how much weight we put on, our susceptibility to infection and maybe even our moods. They can also, it seems, make us sexy. Susan Erdman, a microbiologist at M.I.T., calls it the “glow of health.” The microbes you harbor, she argues, can make your skin smooth and your hair shiny; they may even put a spring in your step. She stumbled on the possibility some years ago when, after feeding mice a probiotic microbe originally isolated from human breast milk, a technician in her lab noticed that the animals grew unusually lustrous fur. Further observation of males revealed thick skin bristling with active follicles, elevated testosterone levels and oversize testicles, which the animals liked showing off. Microbes had transformed these animals into rodent heartthrobs. When given to females, the probiotic also prompted deeper changes. Levels of a protein called interleukin 10, which helps to prevent inflammatory disease and ensure successful pregnancy, went up, as did an important hormone called oxytocin. Oxytocin, often called the love hormone, helps mammals bond with one another. Our bodies may release it when we kiss (and mean it), when women breast-feed, even when people hang out with good friends. And the elevated oxytocin Dr. Erdman saw had important effects during motherhood. Some of the mice in her studies were eating a high-fat, high-sugar diet — junk-foody fare that’s known to shift the microbiome into an unhealthy state. Not surprisingly perhaps, mothers that didn’t imbibe the probiotics were less caring and tended to neglect their pups. But mothers that had high oxytocin thanks to the probiotic were nurturing and reared their pups more successfully. © 2017 The New York Times Company
Patti Neighmond It's tough to be a teenager. Hormones kick in, peer pressures escalate and academic expectations loom large. Kids become more aware of their environment in the teen years — down the block and online. The whole mix of changes can increase stress, anxiety and the risk of depression among all teens, research has long shown. But a recent study published in the journal Pediatrics suggests many more teenage girls in the U.S. may be experiencing major depressive episodes at this age than boys. And the numbers of teens affected took a particularly big jump after 2011, the scientists note, suggesting that the increasing dependence on social media by this age group may be exacerbating the problem. Psychiatrist Ramin Mojtabai and colleagues at Johns Hopkins University Bloomberg School of Public Health wanted to know whether rates of depression among teens had increased over the past decade. They analyzed federal data from interviews with more than 172,000 adolescents. Between 2005 and 2014, the scientists found, rates of depression went up significantly — if extrapolated to all U.S. teens it would work out to about a half million more depressed teens. What's more, three-fourths of those depressed teens in the study were girls. The findings are just the latest in a steady stream of research showing that women of all ages experience higher rates of depression compared to men, says psychologist and author Catherine Steiner-Adair. And no wonder, she says — despite gains in employment, education and salary, women and girls are still "continually bombarded by media messages, dominant culture, humor and even political figures about how they look — no matter how smart, gifted, or passionate they are." © 2017 npr
By STEPH YIN If you’re reading this at home, pause and put on a song you can’t resist dancing to. Go on, bop your head to the beat. Let yourself wiggle a bit. Throw in some arms and legs. If you’re reading this at work, maybe imagine these things at your desk. As you’re dancing, pay attention to where and how you’re moving. How much are you swaying your hips? Are your legs moving together or independently of each other? How vigorously are you moving your torso? You should note those movements, because very specific patterns may make some people appear to be better dancers than others. That’s the conclusion of a study published on Thursday in Scientific Reports, in which researchers asked 200 people to rate 39 female dancers. A few features stood out as contributing to higher-quality dance: big hip swings, and the right and left limbs moving independently of one another (which the researchers describe as asymmetric arm and thigh movements). The researchers speculate that those moves serve two purposes for heterosexual women. “One is, they’re showing off their reproductive quality, perhaps their hormonal status, to males,” said Nick Neave, an associate professor of psychology at Northumbria University in England and an author of the paper. “Another is, they’re showing off how good they are to female rivals.” In 2011, the same researchers reported that women preferred certain dance moves by men, especially exaggerated movements in the upper body. In other studies, Dr. Neave and his colleagues have found links between male dance attractiveness and risk-taking, as well as handgrip strength, a marker for overall body strength. “We know that dance moves are signaling strength and vigor in males,” Dr. Neave said. “Now we’re beginning to do the same research with females.” In the study, his team asked 39 female university students in Britain to dance alone to a drum beat. The researchers used a motion-capture system to track the women’s moves. They animated each dancer as an avatar to try to make sure that only the dance movements — and no other physical features — would affect ratings. Then they recruited 57 men and 143 women to watch 15-second clips of the avatars and rate them each on a numeric scale. © 2017 The New York Times Company
Having a thicker outer layer of the brain is linked to an increased likelihood of having autism. The cerebral cortex is the wrinkled outer layer of the brain that is responsible for many of our most human traits, including thought, language and consciousness. This layer is typically thicker in men than in women, and its structure has been linked to differences in personality. Now brain scans have shown that women who have a more male-like brain structure are three times more likely to have been diagnosed with autism. The study compared the brains of 98 men and women with high functioning autism with those of 98 people who don’t have autism. These findings provide new insights into the brain’s role in sex differences in autism, according to the team that did the study. Autism is thought to be two to five times more common in men than in women, and some think the condition is caused by having an “extreme male brain”. Journal reference: JAMA Psychiatry, DOI: 10.1001/jamapsychiatry.2016.3990 © Copyright Reed Business Information Ltd.
by Bethany Brookshire Gender bias works in subtle ways, even in the scientific process. The latest illustration of that: Scientists recommend women less often than men as reviewers for scientific papers, a new analysis shows. That seemingly minor oversight is yet another missed opportunity for women that might end up having an impact on hiring, promotions and more. Peer review is one of the bricks in the foundation supporting science. A researcher’s results don’t get published in a journal until they successfully pass through a gauntlet of scientific peers, who scrutinize the paper for faulty findings, gaps in logic or less-than-meticulous methods. The scientist submitting the paper gets to suggest names for those potential reviewers. Scientific journal editors may contact some of the recommended scientists, and then reach out to a few more. But peer review isn’t just about the paper (and scientist) being examined. Being the one doing the reviewing “has a number of really positive benefits,” says Brooks Hanson, an earth scientist and director of publications at the American Geophysical Union in Washington, D.C. “You read papers differently as a reviewer than you do as a reader or author. You look at issues differently. It’s a learning experience in how to write papers and how to present research.” Serving as a peer reviewer can also be a networking tool for scientific collaborations, as reviewers seek out authors whose work they admired. And of course, scientists put the journals they review for on their resumes when they apply for faculty positions, research grants and awards. |© Society for Science & the Public 2000 - 2017.
By Chelsea Whyte It was a gruesome scene. The body had severe wounds and was still bleeding despite having been lying for a few hours in the hot Senegalese savanna. The murder victim, a West African chimpanzee called Foudouko, had been beaten with rocks and sticks, stomped on and then cannibalised by his own community. This is one of just nine known cases where a group of chimpanzees has killed one of their own adult males, as opposed to killing a member of a neighbouring tribe. These intragroup killings are rare, but Michael Wilson at the University of Minnesota says they are a valuable insight into chimp behaviour such as male coalition building. “Why do these coalitions sometimes succeed, but not very often? It’s at the heart of this tension between conflict and cooperation, which is central to the lives of chimpanzees and even to our own,” he says. Chimps usually live in groups with more adult females than males, but in the group with the murder it was the other way round. “When you reverse that and have almost two males per every female — that really intensifies the competition for reproduction. That seems to be a key factor here,” says Wilson. Jill Pruetz at Iowa State University, who has been studying this group of chimpanzees in south-eastern Senegal since 2001, agrees. She suggests that human influence may have caused this skewed gender ratio that is likely to have been behind this attack. In Senegal, female chimpanzees are poached to provide infants for the pet trade. Fall from power Thirteen years ago, Foudouko reigned over one of the chimp clans at the Fongoli study site, part of the Fongoli Savanna Chimpanzee Project. As alpha male, he was “somewhat of a tyrant”, Pruetz says. © Copyright Reed Business Information Ltd.
Nicola Davis Girls as young as six years old believe that brilliance is a male trait, according research into gender stereotypes. The US-based study also found that, unlike boys, girls do not believe that achieving good grades in school is related to innate abilities. Andrei Cimpian, a co-author of the research from New York University, said that the work highlights how even young children can absorb and be influenced by gender stereotypes – such as the idea that brilliance or giftedness is more common in men. Are gendered toys harming childhood development? Read more “Because these ideas are present at such an early age, they have so much time to affect the educational trajectories of boys and girls,” he said. Writing in the journal Science, researchers from three US universities describe how they carried out a range of tests with 400 children, half of whom were girls, to probe the influence of gender stereotypes on children’s notions of intelligence and ability. In the first test, a group of 96 boys and girls of ages five, six and seven, were read a story about a highly intelligent person, and were asked to guess the person’s gender. They were then presented with a series of pictures showing pairs of adults, some same-sex, some opposite sex, and were asked to pick which they thought was highly intelligent. Finally, the children were asked to match certain objects and traits, such as “being smart”, to pictures of men and women. © 2017 Guardian News and Media Limited
By NATALIE ANGIER Whether personally or professionally, Daniel Kronauer of Rockefeller University is the sort of biologist who leaves no stone unturned. Passionate about ants and other insects since kindergarten, Dr. Kronauer says he still loves flipping over rocks “just to see what’s crawling around underneath.” In an amply windowed fourth-floor laboratory on the east side of Manhattan, he and his colleagues are assaying the biology, brain, genetics and behavior of a single species of ant in ambitious, uncompromising detail. The researchers have painstakingly hand-decorated thousands of clonal raider ants, Cerapachys biroi, with bright dots of pink, blue, red and lime-green paint, a color-coded system that allows computers to track the ants’ movements 24 hours a day — and makes them look like walking jelly beans. The scientists have manipulated the DNA of these ants, creating what Dr. Kronauer says are the world’s first transgenic ants. Among the surprising results is a line of Greta Garbo types that defy the standard ant preference for hypersociality and instead just want to be left alone. The researchers also have identified the molecular and neural cues that spur ants to act like nurses and feed the young, or to act like queens and breed more young, or to serve as brutal police officers, capturing upstart nestmates, spread-eagling them on the ground and reducing them to so many chitinous splinters. Dr. Kronauer, who was born and raised in Germany and just turned 40, is tall, sandy-haired, blue-eyed and married to a dentist. He is amiable and direct, and his lab’s ambitions are both lofty and pragmatic. “Our ultimate goal is to have a fundamental understanding of how a complex biological system works,” Dr. Kronauer said. “I use ants as a model to do this.” As he sees it, ants in a colony are like cells in a multicellular organism, or like neurons in the brain: their fates joined, their labor synchronized, the whole an emergent force to be reckoned with. © 2017 The New York Times Company
written by Claire Lehmann I learned about Debra through reading her LA Times op-ed on the futility of gender neutral parenting. I got in touch with Debra because I wanted to learn more about her field of sex neuroscience, her own research and her thoughts on studying sex differences in the brain. Because the study of sex and sex differences is often fraught with political roadblocks, I also wanted to get a picture of how a neuroscientist-sex researcher approaches some of these contentious issues. Hi Debra, thanks for chatting to Quillette. Can you briefly tell us who you are — where you studied, who was your supervisor and what made you interested in neuroscience, in particular sex neuroscience? I am a sex researcher at York University in Toronto and I write about the science of sex for several media outlets, including Playboy. For my PhD, which I just defended, I worked with Dr. Keith Schneider, who has pioneered new methods in high-resolution fMRI and is the Director of the University of Delaware’s Center for Biomedical and Brain Imaging, and Dr. James Cantor at the University of Toronto, who is a world expert in the brain imaging of pedophilia. I remember opening up a textbook during my first neuroscience course as an undergraduate student, seeing images from an fMRI study, and thinking it was incredible. I decided to pursue neuroscience in grad school and had the opportunity to do a placement in sexology as part of my Master’s degree. That’s how I got hooked! And I haven’t looked back. © 2017 Quillette
In the mood? Feeling sexy and romantic has been linked to a hormone named kisspeptin. Researchers hope the chemical may help treat people with some sexual problems. Kisspeptin occurs naturally in the body, where it stimulates the release of other signalling chemicals that have been linked to reproduction. Now a study of 29 heterosexual young men has found that injections of the hormone enhance the brain’s response to sexual and romantic pictures of couples. After injection, MRI scans showed increased activity in the regions of the brain that are usually stimulated by sexual arousal and romance. But this activity was only prompted by arousing pictures – non-sexy images did not have the same effect. “Our findings indicate that kisspeptin could play a role in stimulating some of the emotions and responses that lead to sex and reproduction,” says Waljit Dhillo, at Imperial College London. “Ultimately, we are keen to look into whether kisspeptin could be an effective treatment for psychosexual disorders.” The team now plans to study the effects of the hormone in a larger group of people, including women as well as men. Journal reference: Journal of Clinical Investigation © Copyright Reed Business Information Ltd.
By NANCY L. SEGAL and SATOSHI KANAZAWA In 1973, the biologist Robert Trivers and the computer scientist Dan Willard made a striking prediction about parents and their offspring. According to the principles of evolutionary theory, they argued, the male-to-female ratio of offspring should not be 50-50 (as chance would dictate), but rather should vary as a function of how good (or bad) the conditions are in which the parents find themselves. Are the parents’ resources plentiful — or scarce? The Trivers-Willard hypothesis holds that when their conditions are good, parents will have more male offspring: Males with more resources are likely to gain access to more females, thereby increasing the frequency with which their genes (and thus their parents’ genes) are preserved in future generations. Conversely, male offspring that lack resources are likely to lose out to males that have more resources, so in bad conditions it pays for parents to “invest” more in daughters, which will have more opportunities to mate. It follows, as a kind of corollary, that when parents have plentiful resources they will devote those resources more to their sons, whereas when resources are scarce, parents will devote them more to their daughters. In short: If things are good, you have more boys, and give them more stuff. If things are bad, you have more girls, and give more of your stuff to them. Is this hypothesis correct? In new research of ours, to be published in the April issue of The Journal of Experimental Child Psychology, we suggest that in the case of breast-feeding, at least, it appears to be. In recent years, evidence has emerged suggesting that in various mammalian species, breast milk — which is, of course, a resource that can be given to children — is tailored for the sex of each offspring. For example, macaque monkey mothers produce richer milk (with higher gross energy and fat content) for sons than for daughters, but also provide greater quantities of milk and higher concentrations of calcium for daughters than for sons. © 2017 The New York Times Company
By Alice Klein Who needs men? A female shark separated from her long-term mate has developed the ability to have babies on her own. Leonie the zebra shark (Stegostoma fasciatum) met her male partner at an aquarium in Townsville, Australia, in 1999. They had more than two dozen offspring together before he was moved to another tank in 2012. From then on, Leonie did not have any male contact. But in early 2016, she had three baby sharks. Intrigued, Christine Dudgeon at the University of Queensland in Brisbane, Australia, and her colleagues began fishing for answers. Zoologger: The amphibious fish that mates with itself One possibility was that Leonie had been storing sperm from her ex and using it to fertilise her eggs. But genetic testing showed that the babies only carried DNA from their mum, indicating they had been conceived via asexual reproduction. Some vertebrate species have the ability to reproduce asexually even though they normally reproduce sexually. These include certain sharks, turkeys, Komodo dragons, snakes and rays. However, most reports have been in females who have never had male partners. There are very few reports of asexual reproduction occurring in females with previous sexual histories, says Dudgeon. An eagle ray and a boa constrictor, both in captivity, are the only other female animals that have been documented switching from sexual to asexual reproduction. © Copyright Reed Business Information Ltd.
Keyword: Sexual Behavior
Link ID: 23110 - Posted: 01.17.2017