Month: August 2021

[This is fascinating. Some of this stuff is taking us well into the incredible unknown…. science fiction stuff. Jan]

Physicists have created the first ever two-dimensional supersolid — a bizarre phase of matter that behaves like both a solid and a frictionless liquid at the same time.

Supersolids are materials whose atoms are arranged into a regular, repeating, crystal structure, yet are also able to flow forever without ever losing any kinetic energy. Despite their freakish properties, which appear to violate many of the known laws of physics, physicists have long predicted them theoretically — they first appeared as a suggestion in the work of the physicist Eugene Gross as early as 1957.

Now, using lasers and super-chilled gases, physicists have finally coaxed a supersolid into a 2D structure, an advancement that could enable scientists to crack the deeper physics behind the mysterious properties of the weird matter phase.

Related: 12 stunning quantum physics experiments

Of particular interest to the researchers is how their 2D supersolids will behave when they’re spun in a circle, alongside as the tiny little whirlpools, or vortices, that will pop up inside them.

"We expect that there will be much to learn from studying rotational oscillations, for example, as well as vortices that can exist within a 2D system much more readily than in 1D," lead author Matthew Norcia, a physicist at Innsbruck University’s Institute for Quantum Optics and Quantum Information (IQOQI) in Austria, told Live Science in an email.

To create their supersolid, the team suspended a cloud of dysprosium-164 atoms inside optical tweezers before cooling the atoms down to just above zero Kelvin (minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius) using a technique called laser-cooling.

Firing a laser at a gas typically heats it up, but if the photons (light particles) in the laser beam are traveling in the opposite direction of the moving gas particles, they can actually cause slow and cool the gas particles. After cooling the dysprosium atoms as far as they could with the laser, the researchers loosened the "grip" of their optical tweezers, creating just enough space for the most energetic atoms to escape.

Since "warmer" particles jiggle faster than cooler ones, this technique, called evaporative cooling, left the researchers with just their super-cooled atoms; and these atoms had been transformed into a new phase of matter — a Bose-Einstein condensate: a collection of atoms that have been super-cooled to within a hair’s breadth of absolute zero.

When a gas is cooled to near zero temperature, all its atoms lose their energy, entering into the same energy states. As we can only distinguish between the otherwise identical atoms in a gas cloud by looking at their energy levels, this equalizing has a profound effect: The once disparate cloud of vibrating, jiggling, colliding atoms that make up a warmer gas then become, from a quantum mechanical point of view, perfectly identical.

This opens the door to some truly weird quantum effects. One key rule of quantum behavior, Heisenberg’s uncertainty principle, says you cannot know both a particle’s position and its momentum with absolute accuracy. Yet, now that the Bose-Einstein condensate atoms are no longer moving, all of their momentum is known. This leads to the atoms’ positions becoming so uncertain that the places they could possibly occupy grow to be larger in area than the spaces between the atoms themselves.

Instead of discrete atoms, then, the overlapping atoms in the fuzzy Bose-Einstein condensate ball act as if they are just one giant particle. This gives some Bose-Einstein condensates the property of superfluidity — allowing their particles to flow without any friction. In fact, if you were to stir a mug of a superfluid Bose-Einstein condensate, it would never stop swirling.

The researchers used dysprosium-164 (an isotope of dysprosium) because it (alongside its neighbor on the periodic table Holmium) is the most magnetic of any discovered element. This means that when the dysprosium-164 atoms were supercooled, in addition to becoming a superfluid, they also clumped together into droplets, sticking to each other like little bar magnets.

By "carefully tuning the balance between long-range magnetic interactions and short-range contact interactions between atoms," Norcia said, the team was able to make a long, one dimensional tube of droplets that also contained free-flowing atoms — a 1D supersolid. That was their previous work.

To make the leap from a 1D to a 2D supersolid, the team used a larger trap and dropped the intensity of their optical tweezer beams across two directions. This, alongside keeping enough atoms in the trap to maintain a high enough density, finally allowed them to create a zig-zag structure of droplets, similar to two offset 1D tubes sitting next to each other, a 2D supersolid.

With the task of its creation behind them, the physicists now want to use their 2D supersolid to study all of the properties that emerge from having this extra dimension. For instance, they plan to study vortices that emerge and are trapped between the droplets of the array, especially as these eddies of swirling atoms, at least in theory, can spiral forever.

This also brings researchers one step closer to the bulk, 3D, supersolids envisioned by early proposals like Gross’, and the even more alien properties they may have.

The researchers published their findings Aug. 18 in the journal Nature.

Source: https://www.livescience.com/first-2d-supersolid.html?utm_source=SmartBrief&utm_medium=email&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_content=C9CD1E7B-5808-4D61-9CFD-A048B7CD63FB&utm_term=23709803-d360-4259-9c73-be4ff46b5c71

[This is astounding. Jan]

Scientists used an unconventional method of creating nuclear fusion to yield a record-breaking burst of energy of more than 10 quadrillion watts, by firing intense beams of light from the world’s largest lasers at a tiny pellet of hydrogen.

Researchers at the Lawrence Livermore National Laboratory in Northern California said they had focused 192 giant lasers at the National Ignition Facility (NIF) onto a pea-size pellet, resulting in the release of 1.3 megajoules of energy in 100 trillionths of a second — roughly 10% of the energy of the sunlight that hits Earth every moment, and about 70% of the energy that the pellet had absorbed from the lasers. The scientists hope one day to reach the break-even or "ignition" point of the pellet, where it gives off 100% or more energy than it absorbs.

The energy yield is significantly larger than the scientists expected and much greater than the previous record of 170 kilojoules they set in February.

The researchers hope the result will expand their ability to research nuclear fusion weapons, the NIF’s core mission, and that it could lead to new ways to harness energy from nuclear fusion — the process that powers the sun and other stars. Some scientists hope that nuclear fusion could one day be a relatively safe and sustainable method for generating energy on Earth.

"This result is a historic step forward for inertial confinement fusion research, opening a fundamentally new regime for exploration and the advancement of our critical national security missions," Kim Budil, the director of Lawrence Livermore National Laboratory, said in a statement.

CLOSE
Giant lasers
Modern nuclear power plants use nuclear fission, which generates energy by splitting the heavy nuclei of elements like uranium and plutonium into lighter nuclei. But stars can generate even more energy from nuclear fusion, a process of smashing together lighter nuclei to make heavier elements.

Stars can fuse many different elements, including carbon and oxygen, but their main energy source comes from the fusion of hydrogen into helium. Because stars are so large and have such strong gravity, the fusion process takes place at very high pressures within the star.

Most Earthbound efforts to generate energy from fusion, such as the giant ITER project being built in France, instead use a doughnut-shaped chamber called a tokamak to confine a thin plasma of hot, neutron-heavy hydrogen inside strong magnetic fields.

Scientists and engineers have worked for more than 60 years to achieve sustainable nuclear fusion within tokamaks, with only limited success. But some researchers think they will be able to sustain fusion in tokamaks within a few years, Live Science previously reported. (ITER is not projected to do this until after 2035.)

The method developed at Lawrence Livermore National Laboratory is one of a few ways of achieving nuclear fusion without using a tokamak.

Instead, the NFI uses an array of laser-light amplifiers the size of three football fields to focus laser beams on hydrogen fuel pellets in a 33-foot-wide (10 meters) spherical metal "target chamber." These lasers are the world’s most powerful, capable of generating up to 4 megajoules of energy.

The method was originally designed so that scientists could study the behavior of hydrogen in thermonuclear weapons — so-called hydrogen bombs — but scientists think it could also have applications for generating energy from nuclear fusion.

Though stars can fuse many different elements, their main energy source comes from the fusion of hydrogen into helium.

Fusion power
Although the NIF setup couldn’t be used in a fusion power plant — its lasers can only fire about once a day, while a power plant would need to vaporize several fuel pellets every second — there are efforts to modify the process so that it can be used commercially.

Plasma physicist Siegfried Glenzer of the SLAC National Accelerator Laboratory at Stanford University, who previously worked at the Livermore facility but was not involved in the new research, told The New York Times that scientists at SLAC are working on a lower-powered laser system that could fire much more rapidly.

Glenzer hopes energy from nuclear fusion will become prominent in the efforts to replace fossil fuels, which have been dominated by solar energy and other technologies in recent years. "This is very promising for us, to achieve an energy source on the planet that won’t emit CO2," he said in the Times article, referring to the greenhouse gas carbon dioxide.

Physicist Stephen Bodner, who formerly headed laser plasma research at the Naval Research Laboratory in Washington, D.C., but is now retired, is critical of some details of the NIF’s design. But he admits he is surprised by the results, which approached the "ignition" of the pellet — the point where it emits as much or more energy than it absorbed. "They have come close enough to their goal of ignition and break-even to call it a success," Bodner told the Times.

Although Bodner favors a different design, "it demonstrates to the skeptic that there is nothing fundamentally wrong with the laser fusion concept," he said. "It is time for the U.S. to move ahead with a major laser fusion energy program."

Source: https://www.livescience.com/fusion-experiment-record-breaking-energy.html?utm_source=SmartBrief&utm_medium=email&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_content=C9CD1E7B-5808-4D61-9CFD-A048B7CD63FB&utm_term=23709803-d360-4259-9c73-be4ff46b5c71

Dan Caselden was up late on November 3, 2018, playing the video game Counter-Strike, when he made astronomy history. Every time he died, he would jump on his laptop to check in on an automated search he was running of NASA space telescope images.

Suddenly, in the early hours of the morning, something bizarre popped into view. “It was very confusing,” said Caselden. “It was moving faster than anything I’ve discovered. It was faint and fast, which made it very weird.”

Caselden emailed the astronomers he was working with as part of the Backyard Worlds: Planet 9 project. Once they ruled out the possibility that it was an image artifact, they realized they were looking at something wholly unusual, an exceedingly faint object 50 light-years away blazing through the galaxy at 200 kilometers per second. It was given the name WISE 1534-1043, but by virtue of its singular characteristics and chance discovery, it soon earned the nickname “The Accident.”

Astronomers now think Caselden found a brown dwarf — a failed star that lacks the necessary bulk to begin nuclear fusion in its core. “It forms like a star,” said Sarah Casewell, an astronomer at the University of Leicester in the U.K. “However, it never gains enough mass to fuse hydrogen into helium and start burning anything.”

The discovery of the Accident highlighted how we still have much to learn about brown dwarfs. These objects range in mass from an estimated 13 times the mass of Jupiter to 75 times or more, but exactly where those two boundaries lie is an ongoing dilemma. “People argue about that in conferences all the time,” said Beth Biller, an astronomer at the University of Edinburgh in the U.K., particularly the lower limit. While 13 Jupiter masses is roughly the mass at which deuterium fusion can take place — the characteristic that differentiates brown dwarfs from gas giant planets — the boundary can vary. “There’s nothing special about 13 Jupiter masses,” said Biller. “It’s completely ad hoc.”

Brown dwarfs also vary greatly in temperature. The hottest ones have surface temperatures of around 2,000 degrees Celsius — “about that of a candle flame,” said Biller. The coldest are below 200 degrees. As they do not have their own source of heat, brown dwarfs will gradually cool over billions of years to these lower temperatures. (Subdwarfs, which blur the boundary further between planets and brown dwarfs, can be cooler still. An object called WISE 0855-0714 is below freezing. “It’s the coldest object we know of outside of our solar system,” said Biller.)

What a brown dwarf might look like up close is also unclear. Despite their name — proposed by astronomer Jill Tarter in 1975 — they are likely not brown. They’re more orange or red. “For better or worse it’s stuck as a name,” said Davy Kirkpatrick, an astronomer at the California Institute of Technology.

They also have atmospheres, and those atmospheres may show some kind of banding and spotlike storms, like on Jupiter. Last year, Biller and her colleagues used these storms to measure the wind speed on a brown dwarf about 34 light-years away. They first watched features in its atmosphere come into and out of view as they rotated, and then compared this speed to a measurement of the object’s interior rotation speed gleaned from its magnetic field. Comparing the two values, the researchers calculated a wind speed of over 2,300 kilometers per hour — more than five times that of Jupiter’s winds.

Because brown dwarfs bridge the gap between stars and planets, they can help us understand both. At the upper end of the mass scale, the boundary between the largest brown dwarfs and the smallest stars can give us insights into how nuclear fusion begins. An object needs to reach temperatures of around 3 million degrees Celsius in its core to kick-start nuclear fusion, said Nolan Grieves of the University of Geneva in Switzerland; this ignites a chain reaction that turns hydrogen into helium. But no one is exactly sure how much mass is needed for that to happen, and at what point a brown dwarf becomes a star. “There’s a lot of aspects of stellar evolution that our knowledge is still pretty uncertain on,” said Biller. “Where that fusion limit is exactly is one of those questions.”

Recent work led by Grieves identified five high-mass brown dwarfs with masses between 77 and 98 times that of Jupiter. “They’re right on the border where hydrogen fusion starts to take place,” said Grieves. It’s unclear at the moment, however, which side of the boundary these five objects actually sit on. “We don’t know the true nature of these objects,” said Grieves, “because they’re so close to this limit.”

Some brown dwarfs may even be so starlike that they could host their own planets. “We know of some brown dwarf systems that look like they have protoplanetary disks around them,” said Kirkpatrick. “And there’s every indication that there are probably brown dwarfs that have their own exoplanets in orbit around them as well. A holy grail is to find a brown dwarf with a transiting exoplanet.”

On the opposite end of the brown dwarf mass scale lies the Accident. It’s an extremely small, cold and faint object — “just barely at the level where we could detect it,” said Kirkpatrick. Astronomers are eager to work out what the difference is between a low-mass brown dwarf and a high-mass gas giant planet. This makes small and faint brown dwarfs like the Accident useful targets.

The Accident also appears to be made of some strange stuff. As the universe ages, supernovas spit out lots of heavier elements such as carbon and oxygen — what astronomers call “metals.” Because of this, old objects that formed early in the universe’s history tend to have few metals, while new objects have more. Yet despite being found in our local solar neighborhood — home mostly to young, metal-rich stars — the Accident appears to be metal-poor. “We think this is probably an older brown dwarf, probably one that was created before the Milky Way had all the metal enrichment it does now,” said Kirkpatrick. Casewell added it was likely “one of the first brown dwarfs formed” in our galaxy, originating in the outer galactic halo surrounding the Milky Way and then migrating inward.

As with so many other phenomena in our universe, the finding highlights that these puzzling yet mysterious objects come in all manner of flavors, and fitting them into rigidly defined categories is no simple task. Caselden, meanwhile, hopes he can contribute more to the field in future, perhaps homing in on similar objects now he knows what to look for. “I want to find another Accident,” he said. “And I want to have it not be an accident.”

Correction: August 5, 2021
An earlier version of this article stated that stellar cores need to reach temperatures of 100 million degrees Celsius to sustain nuclear fusion. While this is true for Sun-like stars, extremely low-mass stars can burn hydrogen at temperatures as low as 3 million degrees Celsius.

Source: https://www.quantamagazine.org/neither-star-nor-planet-a-strange-brown-dwarf-puzzles-astronomers-20210804/

[I didn't even know the females in animal species were contesting for mates. Hmmmm. Well, as they say, "All is fair, in love and war".  Jan]

s the midday sun hangs over the Scandinavian spruce forest, a swarm of hopeful suitors takes to the air. They are dance flies, and it is time to attract a mate. Zigzagging and twirling, the flies show off their wide, darkened wings and feathery leg scales. They inflate their abdomens like balloons, making themselves look bigger and more appealing to a potential partner.

Suddenly, the swarm electrifies with excitement at the arrival of a new fly, the one they have all been waiting for: a male. It’s time for the preening flock of females to shine.

The flies are flipping the classic drama reenacted across the animal kingdom, in which eager males with dazzling plumage, snarls of antlers or other extraordinary traits compete for a chance to woo a reluctant female. Such competitions between males for the favor of choosy females are enshrined in evolutionary theory as “sexual selection,” with the females’ choices molding the evolution of the males’ instruments of seduction over generations.

Yet it’s becoming clear that this traditional picture of sexual selection is woefully incomplete. Dramatic and obvious reversals of the selection scenario, like that of the dance flies, aren’t often observed in nature, but recent research suggests that throughout the tree of animal life, females jockey for the attention of males far more than was believed. A new study hosted on the preprint server biorxiv.org has found that in animals as diverse as sea urchins and salamanders, females are subject to sexual selection — not as harshly as males are, but enough to make biologists rethink the balance of evolutionary forces shaping species in their accounts of the history of life.

The new work turns a spotlight on a lopsidedness in sexual selection research that may have robbed evolutionary studies on about half of all animal species of important context. Scientists have reported scattered evidence of female sexual selection in the past, but more often they haven’t had reason to look for it. That could now be changing.

“We really don’t know very much compared to how much we’ve worked on the male side of things,” said Tommaso Pizzari, an evolutionary biologist at the University of Oxford who was not involved with the new paper. “Sexual selection in females is still relatively unknown. It’s still barely charted territory.”

Michele Aldeghi
The concept of sexual selection dates back to Charles Darwin’s first writings on natural selection — briefly mentioned in The Origin of Species, and then covered more extensively in The Descent of Man — where he detailed reproductive preferences between the sexes as potentially driving evolutionary change. Within the framework of conventional natural selection, it makes sense that individuals prefer fit mates. But a key point of sexual selection is that attractiveness to potential mates can be a criterion for selection in itself, independently of how it affects fitness otherwise. Members of one sex can develop traits and behaviors appealing to the other that directly conflict with survival-driven natural selection. Taken to extremes, this can result in the unwieldy, exceptionally elongated display feathers of some male birds, for example, which are only useful in the mating contests that the males stage.

The Victorian View of Females
Yet from its very beginning, the science focused on males as the objects of sexual selection. Darwin saw females as reluctantly picking mates from gaggles of desperate male suitors. He was open to the idea of sexual selection in either direction, but the intensity of the obvious competitions for mates among males fed the idea that sexual selection happened primarily to males; the females were prizes to be won. Females might be setting the terms of the mating competitions, but it was the males who were truly being reshaped through evolution by those choices.

Darwin’s perspective was typical of his time. Theories about sexual selection were born “in the Victorian era, when you had these certain sexual stereotypes about how women should behave,” said Rebecca Boulton, an evolutionary biologist at the University of Exeter in the U.K. “And so, because the field essentially sprung up at that time, it was like, ‘Of course females aren’t mating with multiple males. Of course they’re coy or choosy.”

This viewpoint has contributed to a ubiquitous bias in how sexual selection has been investigated in the last century and a half, the researchers behind the new study argue. They estimate that studies of male-male competition and the phenomenon of female choice are 10 times more common than studies targeting the reverse.

Photo of two female wattled jacanas fighting.
Two female wattled jacanas (Jacana jacana) fight for control over territory and the potential male mates it holds.

NJDemong
“A lot of people are influenced by the culture that they live in and the things that [they] see,” said Salomé Fromonteil, a graduate student in evolutionary biology now at Uppsala University in Sweden and Ludwig Maximilian University in Munich, and lead author on the study. “It’s influenced by what we read, and what they read is that sexual selection works on males primarily.”

There are undeniable exceptions. Some that have caught researchers’ attention are in species with “sex roles” that are flipped from the conventional arrangement, as in the dance flies. Females of the American tropical wading birds called wattled jacanas (Jacana jacana) keep and defend territories rich in male mates. Among the seahorses and other pipefish, males even take on the job of “pregnancy” by internally incubating their young in a specialized pouch.

Still, scientists studying sexual selection have mostly continued to defer to Darwin’s initial observations in the 19th century. It was generally accepted that males — with their propensity for ornaments and courtship displays — experienced greater sexual selection pressures.

“Of course, that’s not how research should be,” said Tim Janicke, an evolutionary biologist at the Center for Functional and Evolutionary Ecology at the University of Montpellier in France, and senior author of the new study. “If the aim is to describe general patterns in nature, we need data-driven syntheses behind this.”

In 2016, Janicke and his team dove into the published literature measuring the strength of sexual selection acting on a variety of animal species and compared those values between the sexes. That study, published in Science Advances, confirmed that males experience a higher degree of sexual selection than females did.

Photo of a pair of seahorses.
A pair of mated seahorses. The reproductive roles in seahorses are flipped from the usual pattern in nature, with the male carrying fertilized eggs in its pouch until the young hatch.

Bae Jiwon
But as further examples of species likely to be undergoing female sexual selection accumulated, Janicke and his team were struck by a question that their study had not addressed: Just how common is sexual selection among females? They began to wonder whether it was “something rare, or whether it’s actually a general pattern,” Janicke said.

In early 2020, Janicke and Fromonteil were planning to start an empirical study on sexual selection in beetles to probe that question. Then the COVID-19 pandemic and the institutional shutdowns it triggered made laboratory experiments suddenly infeasible. But a meta-analysis of the data from the 2016 study could be done even in “confinement,” as Janicke puts it.

To compare the relative strength of sexual selection in a wide range of species, the scientists needed some way of quantifying that selection intensity. They settled on a method using the Bateman gradient, a measurement named after the 20th-century British geneticist Angus John Bateman.

More Mates, More Sexual Selection
Bateman recognized that while males can produce many sperm at low metabolic cost, females have to make relatively high investments in far fewer eggs. In the 1940s, his research on fruit flies led Bateman to propose that this fundamental divergence in gamete investment drives apart the mating strategies of males and females: To maximize their reproductive capacity, males might routinely seek out and compete for many mating partners, while females might instead evolve to be choosy.

Other researchers built on this idea, developing the Bateman gradient to describe the fitness benefits of having multiple mating partners. The measurement is the slope of the line comparing reproductive output to the number of mating events — in effect, it shows how sharply an organism’s number of offspring increases with more mating. The steeper the positive slope, the greater the fitness benefit of more mating events, which in most species means having more mates. (By mating with multiple males rather than just one, a female can sometimes hedge her bets about which mate will produce the fittest offspring.)

“If there’s positive selection on having more mating partners, this should translate into competition for mating partners,” said Janicke. “And this competition is basically the essence of Darwinian sexual selection.” For this reason, Bateman gradients are a common way of indirectly quantifying sexual selection.

From a sweep of the scientific literature, the team compiled 111 Bateman gradients calculated for females in 72 animal species, ranging from beetles to mollusks to mammals. The gradients varied widely, but they clustered in the positive range. The team also found, as expected, that species with “polyandrous” females who had access to many partners simultaneously had Bateman gradient values considerably greater than those of species with “monandrous” females who mostly mated with one male at a time.

Udo Schmidt
The findings suggest that — as has long been presumed for males — females get a fitness boost from multiple matings, and that opens the door to widespread sexual selection. The positive female Bateman gradients don’t appear to be as large as those for males, Janicke said, but their pervasiveness hints at the importance of sexual selection in the evolution of females, even in species seen as having “typical” sex roles.

While acknowledging that the Bateman gradient is a “powerful measurement to quantify sexual selection,” Janicke noted that it only reflects selection directly related to the act of mating. In species that spawn profusions of eggs, such as many fish as well as corals and other marine invertebrates, there are opportunities for selection after mating, too, with eggs competing for access to sperm, or sperm having choice capabilities that affect fertilization. Janicke’s study did not extend to this kind of post-mating sexual selection. It’s therefore possible that even more female sexual selection occurs than the new study suggests, but future work will need to test that possibility.

For Pizzari, the study “confirms something that I think we have been, as a community, beginning to realize for quite some time now: that sexual selection is potentially quite important in females across a number of species, as well as for males.”

Sexual selection in females is still relatively unknown. It’s still barely charted territory.

Tommaso Pizzari, University of Oxford

Alternative explanations, however, do still need to be tested. Some of the gradients that Janicke’s team identified may be rooted in certain females’ inherent attractiveness to males due to their reproductive output. “It may well be that the females that have more eggs to produce … happen to attract a lot more males simply because they have a higher reproductive value,” Pizzari said. If so, it wouldn’t be that more matings were more beneficial to females, “it’s that males are more interested in mating with fecund females.”

If that is the case, however, then Jonathan Henshaw, an evolutionary biologist at the University of Freiburg in Germany who was also not involved with the study, thinks that empirical tests could help isolate this effect. “If you really wanted to know what the causal effect of mating on reproductive success is, the best thing would be to do as others have done and actually manipulate the number of mates that are available to individual females,” he said.

Experiments could also help reveal whether sexual selection is playing out in these females in the wild, and how selection might be influencing the traits that females use to compete with one another. “The potential for … different mechanisms of sexual selection is there,” Boulton said. “Whether that’s what’s actually happening is something that is a little bit harder to tease apart.”

Confrontations and Decorations
Now that scientists are becoming more aware that they should look for evidence of female sexual selection, the traits and behaviors it cultivates in females may become more obvious. Black grouse (Tetrao tetrix) were considered a classic example of male sexual selection: The males have distinct, vivid coloration, and they compete for females in elaborate courtship display arenas called leks. But recent evidence suggests that while the males are putting on their show, the females are also aggressively jockeying for their choices. Female Mediterranean fruit flies (Ceratitis capitata) take a very similar approach. Certain dung beetle females have even evolved horns that may be used for battling with other females in contests over access to males.

But such intrasexual combat isn’t likely to develop in most females, Boulton argues. Fighting has an inherent risk of bodily harm — something that males can more easily afford since they just need to survive until copulation. Female reproductive success takes time: They have to live long enough to lay all their eggs, and sometimes to care for the newborns. “Whereas the males, they’ve kind of got less to lose,” she said.

The ornaments and competitions that females use to gain mates may sometimes have been overlooked because they are more subtle and look like pared-down versions of what males sport. For instance, female Malurus fairy wrens are undergoing sexual selection on their bill and plumage coloration independently of similar pressures on the males. Both male and female chickens (Gallus gallus) have fleshy ornamental combs. Hens prefer roosters with bigger combs as mates, but the roosters give more sperm to hens with bigger combs, too.

Photo of a female fairy wren.
A female emperor fairy wren (Malurus cyanocephalus). Studies suggest that the females in this genus experience sexual selection that acts on their bill and plumage.

Nigel Voaden
Such ornamentation traits in females are sometimes viewed as byproducts of sexual selection on a female’s male ancestors — “leaky sexual dimorphism,” Pizzari said. But he argues that males may pay attention to these ornaments, which could give them evolutionary significance in the females. “They might have been the target of adaptive selection in their own right.”

Another trait that males commonly seem to key in on is female body size, Boulton said. Males tend to prefer bigger and heavier females. This preference might be rooted in the value of size as a signal of the females’ overall health and reproductive potential, but it could also be a platform for female competitiveness.

No matter how female animals respond to sexual selection in nature, the new findings help reiterate how much of it went largely undetected by science for many decades. Part of the rigid stereotyping around research into sexual selection was likely informed by culture and patriarchal attitudes.

The stereotype of male-centered sexual selection may also have persisted so stubbornly “because there’s a kernel of truth in it — that in the vast majority of species, males do gain more from additional matings than females do,” Henshaw said. The pitfall is that “it’s sort of easy to go from that truth to an opposite stereotype which says that ‘generally speaking, females don’t gain anything from extra matings.’ But then you’ve kind of gone too far.”

Extreme physical differences between the sexes in some species may also have blunted the search for the more hidden but widespread sexual selection among females. “If you have a species that shows this striking sexual dimorphism, you might not start to study intrasexual selection among females,” Janicke said, because male selection would seem like the default explanation.

And yet, despite the weight of human assumptions and sensory biases, a pattern is beginning to rise to the surface: Female sexual selection is the norm. “Generally speaking, sexual selection operates on females,” Fromonteil said.

Janicke plans to continuously update the database with Bateman gradients as they are published. “This database will grow and grow, and we’ll see what other kinds of questions we can still address with this. But I am very confident that this pattern on sexual selection for females will not change,” he said.

Source: https://www.quantamagazine.org/mating-contests-among-females-may-shape-their-evolution-20210802/