You can watch the video here: https://www.youtube.com/watch?v=kDHouMEXHQg
Month: May 2021
Video: Space Science: Mars helicopter Ingenuity experiences anomaly on 6th flight, but lands safely
[Very cool stuff. The helicopter seems to fly itself and make its own corrections itself because it's White controllers are sitting so far away. Jan]
You can watch the video here: https://www.space.com/mars-helicopter-ingenuity-sixth-flight-anomaly
The incident, while stressful, showcased the little chopper’s toughness.
NASA’s Mars helicopter Ingenuity encountered some trouble on its latest Red Planet flight, but the little chopper soldiered through.
Ingenuity lifted off May 22 on its sixth sortie overall and the first flight of its extended mission on Mars, which aims to showcase the scouting potential of Red Planet rotorcraft.
The flight plan called for the 4-lb. (1.8 kilograms) copter to attain an altitude of 33 feet (10 meters), cruise 492 feet (150 m) to the southwest, then move 49 feet (15 m) to the south while snapping photos toward the west, and then zip 164 feet (50 m) to the northeast before touching down.
Video: See the view on Mars from Ingenuity helicopter’s fourth flight
This image was taken from the height of 33 feet (10 meters) by NASA’s Ingenuity Mars helicopter during its sixth flight on May 22, 2021. (Image credit: NASA/JPL-Caltech)
Things went well at first. But 54 seconds into the flight, Ingenuity suffered a glitch that interrupted the flow of images from its navigation camera to its onboard computer, Ingenuity chief pilot Håvard Grip, of NASA’s Jet Propulsion Laboratory in Southern California, wrote in an update on Thursday (May 27).
"This glitch caused a single image to be lost, but more importantly, it resulted in all later navigation images being delivered with inaccurate timestamps," Grip wrote.
"From this point on, each time the navigation algorithm performed a correction based on a navigation image, it was operating on the basis of incorrect information about when the image was taken," he explained. "The resulting inconsistencies significantly degraded the information used to fly the helicopter, leading to estimates being constantly ‘corrected’ to account for phantom errors. Large oscillations ensued."
Ingenuity pitched and rolled more than 20 degrees at some points during the flight, Grip wrote, and experienced spikes in power consumption. But the helicopter managed to power through the anomaly, eventually landing safely within about 16 feet (5 m) of its intended touchdown spot.
"In a very real sense, Ingenuity muscled through the situation, and while the flight uncovered a timing vulnerability that will now have to be addressed, it also confirmed the robustness of the system in multiple ways," Grip wrote.
"While we did not intentionally plan such a stressful flight, NASA now has flight data probing the outer reaches of the helicopter’s performance envelope," he added. "That data will be carefully analyzed in the time ahead, expanding our reservoir of knowledge about flying helicopters on Mars."
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Ingenuity on new Martian airfield – See flight, landing site pics & mission control
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Ingenuity landed on Mars with NASA’s Perseverance rover on Feb. 18. They touched down inside Mars’ Jezero Crater, which harbored a lake and a river delta in the ancient past. On April 3, the helicopter deployed from the rover’s belly, kicking off a month-long, five-flight campaign designed to demonstrate that powered aerial flight is possible on the Red Planet.
That historic campaign went very smoothly, and Ingenuity remained in good health at its conclusion. So NASA approved a mission extension, during which the chopper will perform more directed scouting work.
Perseverance documented Ingenuity’s first five flights but did not do so for the May 22 sortie. The rover is now starting to focus on its own science mission, which involves hunting for signs of long-gone Mars life and collecting samples for future return to Earth.
Source: https://www.space.com/mars-helicopter-ingenuity-sixth-flight-anomaly
Pics: Russia plans to launch a nuclear-powered spacecraft that can travel from the moon to Jupiter
- Russia is building a nuclear-powered spacecraft that can transport heavy cargo in deep space.
- The spacecraft is scheduled to launch on a mission to Jupiter in 2030.
- Russia eventually hopes to build a nuclear-powered space station using similar technology.
Russia is planning to send a nuclear-powered spacecraft to the moon, then Venus, then Jupiter.
Roscosmos, Russia’s federal space agency, announced Saturday that its "space tug" – the term for a spacecraft that transports astronauts or equipment from one orbit to another – is scheduled to launch on an interplanetary mission in 2030.
The spacecraft’s energy module, named "Zeus," is designed to generate enough power to propel heavy cargo through deep space. It’s essentially a mobile nuclear-power plant.
Several countries have their eyes on similar technology as a way to shorten trips in space. Right now, spacecraft rely on solar power or gravity to accelerate. But that means it could take more than three years for astronauts to conduct a round-trip visit to Mars. NASA estimates that a nuclear-powered spacecraft could shave a year off that timeline.
The US hopes to put a nuclear-power plant – a 10-kilowatt reactor integrated with a lunar lander – on the moon as early as 2027. So far, however, NASA has only sent one nuclear reactor to space, on a satellite in 1965. Other spacecraft, like the Mars Curiosity and Perseverance rovers, are also nuclear-powered, but they don’t use a reactor.
Russia, meanwhile, has put more than 30 reactors in space. It’s "Zeus" module would advance those efforts by using a 500-kilowatt nuclear reactor to propel itself from one planet to the next, according to Russian state news agency Sputnik.
The mission plan calls for the spacecraft to approach the moon first, then head toward Venus, where it can use the planet’s gravity to shift directions toward its final destination, Jupiter. That would help conserve propellant.
The entire mission would last 50 months (a little over four years), according to Alexander Bloshenko, Roscosmos’ executive director for long-term programs and science. During a presentation in Moscow on Saturday, Bloshenko said Roscosmos and the Russian Academy of Sciences are still working to calculate the flight’s ballistics, or trajectory, as well as the amount of weight it can carry.
The mission may ultimately be a precursor to a new frontier of Russian spaceflight: Sputnik reported that Russia is designing a space station that uses the same nuclear-powered technology.
Nuclear energy has advantages over solar power in space
A concept of a NASA spacecraft that would use nuclear thermal propulsion.NASA
Most spacecraft get their energy from a few sources: the sun, batteries, or unstable atoms called radioisotopes.
NASA’s Juno spacecraft at Jupiter, for instance, uses solar panels to generate electricity. Solar power can also be used to charge batteries in a spacecraft, but the energy source becomes less potent as a spacecraft gets farther from the sun. In other cases, lithium batteries can help power shorter missions on their own. The Huygens probe, for instance, used batteries to briefly land on Saturn’s moon, Titan, in 2005.
NASA’s twin Voyager spacecraft use radioisotopes (sometimes called "nuclear batteries") to survive the harsh environments of the outer solar system and interstellar space, but that’s not the same as bringing a nuclear reactor on board.
Nuclear reactors offer several advantages: They can survive cold, dark regions of the solar system without requiring sunlight. They’re also reliable for long periods of time – the "Zeus" nuclear reactor is designed to last 10 to 12 years. Plus, they can propel spacecraft to other planets in less time.
But nuclear power has its challenges, too. Only certain types of fuel, like highly enriched uranium, can withstand a reactor’s extremely high temperatures – and they may not be the safe to use. In December, the US prohibited the use of highly enriched uranium to propel objects into space if a mission is possible with other nuclear fuel or non-nuclear power sources.
Russia is gearing up for a nuclear-powered space station
ISS crew member Sergey Kud-Sverchkov lands in a remote area in Kazakhstan on April 17, 2021.NASA/Bill Ingalls/Reuters
Russian engineers began developing the "Zeus" module in 2010 with the goal of sending it to orbit within two decades. They’re on track to meet that mark.
Engineers started manufacturing and testing a prototype in 2018, Sputnik reported. Roscosmos also signed a contract last year worth 4.2 billion rubles (R800 million) that put Arsenal, a design company based in St. Petersburg, in charge of a preliminary design.
The technology could aid Russia’s efforts to develop a new space station by 2025. The BBC reported last month that Russia plans to cut ties with the International Space Station – which it shares with the US, Japan, Europe, and Canada – that year.
Russia launched the ISS in partnership with the US in 1998. But Russian Deputy Prime Minister Yury Borisov told the state TV channel Russia 1 last month that the ISS’s condition "leaves much to be desired." Indeed, the station has recently experienced air leaks and a breakdown of its oxygen-supply system.
NASA has cleared the ISS to fly until at least 2028, but the agency will likely de-orbit the station in the next 10 to 15 years.
Source: https://www.businessinsider.co.za/russia-nuclear-powered-spacecraft-moon-venus-jupiter-2021-5
Science: Exercise: How the way you move can change the way you think and feel
[I'm not subscribed to this site so I can't get the full article. Our sedentary lifestyle is very bad for us. And even I'm guilty of this. We need to move more. Jan]
New research suggests the connection between exercise and the brain goes deeper than you might think. These six kinds of movement can help make you more creative, boost your self-esteem and reach altered states of consciousness
FILTER-FEEDERS aside, humans are the only creatures that can get away with sitting around all day. As a species, we have been remarkably successful at devising ways to feed, entertain ourselves and even find mates, all while barely lifting a finger.
True, this is a sign of just how clever and adaptable we are. But there is a huge cost to our sedentary ways, not only to our bodies, but also our minds. Falling IQs and the rise in mental health conditions have both been linked to our lack of physical movement.
But the connection between movement and the brain goes deeper than you might think. A revolutionary new understanding of the mind-body connection is revealing how our thoughts and emotions don’t just happen inside our heads, and that the way we move has a profound influence on how our minds operate. This opens up the possibility of using our bodies as tools to change the way we think and feel.
Evidence is starting to stack up that this is indeed the case, and it isn’t all about doing more exercise. In my new book, Move! The new science of body over mind, I explore emerging research in evolutionary biology, physiology, neuroscience and cell biology to find out which body movements affect the mind and why.
Whatever it is that you want from your mind – more creativity, improved resilience or higher self-esteem – the evidence shows that there is a way of moving the body that can help. Here is my pick of the best ways to use your body to achieve a healthier, better-functioning mind.
Faraway NASA probe detects the eerie hum of interstellar space
The classic 1979 sci-fi horror film "Alien" was advertised with the memorable tagline, "In space no can hear you scream." It did not say anything about humming.
Instruments aboard NASA’s Voyager 1 spacecraft, which nine years ago exited our solar system’s outer reaches, have detected a faint monotonous hum caused by the constant vibrations of the small amounts of gas found in the near-emptiness of interstellar space, scientists said.
It essentially represents the background noise present in the vast expanse between star systems. These vibrations, called persistent plasma waves, were identified at radio frequencies in a narrow bandwidth during a three-year period as Voyager 1 traverses interstellar space.
"The persistent plasma waves that we’ve just discovered are far too weak to actually hear with the human ear. If we could hear it, it would sound like a single steady note, playing constantly but changing very slightly over time," said Stella Koch Ocker, a Cornell University doctoral student in astronomy and lead author of the study published this week in the journal Nature Astronomy.
The Voyager 1 spacecraft, launched in September 1977, is currently located about 14.1 billion miles (22.7 billion km) from Earth – roughly 152 times the distance between our planet and the sun – and is still obtaining and transmitting data.
Having decades ago visited the huge planets Jupiter and Saturn, Voyager 1 is now providing insight into interstellar space.
The immense regions between star systems in a galaxy are not a complete vacuum. The stew of matter and radiation present in low densities – mostly gas – is called the interstellar medium. About 15% of the visible matter in our Milky Way galaxy is composed of this interstellar gas, dust and energetic particles like cosmic rays.
Much of the interstellar medium is in what is called an ionized, or electrically charged, state called plasma.
"Interstellar plasma is extremely diffuse compared to what we’re used to on Earth. In this plasma, there are about 0.1 atoms for every cubic centimeter, whereas the air we breathe on Earth has billions of atoms for every cubic centimeter," Ocker said.
Voyager 1 previously detected disturbances in the gas in interstellar space triggered by occasional flares from our sun. The new study instead reveals the steady vibrations unrelated to solar activity that could be a constant feature in interstellar space. This hum has a frequency of about 3 kilohertz (kHz).
"When the plasma oscillations are converted to an audio signal, it sounds like a tone that varies. It’s a bit eerie," said Cornell University astronomy professor and study co-author James Cordes.
After 44 years of travel, Voyager 1 is the most distant human-made object in space.
"Voyager 1 will keep going but its power supply will run out most likely this decade after up to 50 years of service," Cordes said. "There are conceptual designs being made for future probes whose intended purpose is to reach further than the Voyager spacecraft. That is the message I find appealing: our reach is expanding into interstellar space."
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Video: Science: Volcanoes in space – Volcanoes might create life on other planets
[This is a science video, and it mentions the role of volcanoes in creating life on Earth, and very possibly on other planets in space. Jan]
Video: Science: Weird Fact: The Universe is expanding ever faster – stars are disappearing from the sky
[This is an interesting point. This discussion by this scientist shows how very fast the universe is expanding. This takes a bit of thinking to wrap your mind around it but it seems to be quite firmly proven that the universe is expanding ever faster. Even though it is only 14 billion years old, it's width is 92 billion light years. Something like 20 stars a second are disappearing from the night sky … and these stars will NEVER be seen again … because of the expanding universe! Jan]
Photos: Scientists discover ‘living fossil’ thought to have been extinct for 273mn years on ocean floor near Japan
[A living fossil fish was discovered off the coast of South Africa in the 1930s. This is an interesting find. Jan]
Two symbiotic marine lifeforms who somehow evaded the prying eyes of human scientists and ‘disappeared’ from the fossil record over a quarter of a billion years ago have been found thriving offshore of Japan.
The creatures in question are non-skeletal corals and crinoids, or sea lilies, who were found proliferating on the floor of the Pacific Ocean, 100 meters (330 feet) below the surface, off the coasts of Honshu and Shikoku in Japan.
They managed to survive undetected, having gone AWOL from the fossil record for longer than modern humans are thought to have existed (200,000-300,000 years ago).
“These specimens represent the first detailed records and examinations of a recent syn vivo association of a crinoid (host) and a hexacoral (epibiont),” the researchers wrote.
Crinoids and corals shared a long, symbiotic relationship together millions of years ago, in which the corals would use the crinoids to climb higher off the seafloor to gain access to more food found in passing ocean currents.
The joint Polish-Japanese research team, led by paleontologist Mikolaj Zapalski of the University of Warsaw in Poland, used stereoscopic microscopy to conduct a ‘hands-off’ examination of the Paleozoic-era pals before scanning them using microtomography to gain a look at their interior structures.
They completed their non-invasive investigation using DNA barcoding to identify the exact species.
The researchers found that these newly rediscovered specimens did not modify the structure of the crinoids’ skeletons, providing a possible clue as to why they disappeared from the fossil record for so long; fossils of soft-bodied organisms are vanishingly rare.
Science & Evolution: Hybrid Animals Are Not Nature’s Misfits
In the 20th century, animals such as mules and ligers that had parents of different species were considered biological flukes, but genetic sequencing is beginning to unravel the critical role of hybridization in evolution.
Ashley Yeager
May 1, 2021
This liger cub and other hybrid animals were thought to be biological rarities, but recent studies have revealed cross-species animals are more common than once thought.
ABOVE: FROM © ISTOCK.COM, W1ZZARD
The whale’s teeth were what had caught molecular ecologist Eline Lorenzen’s attention. Of the 18 chompers lining the front of the skull’s mouth, some were twisted, not unlike a narwhal’s tusk. But the 30-year-old specimen, hidden away in the basement of the Natural History Museum of Denmark at the University of Copenhagen, didn’t have a tusk at all. When Lorenzen became director of the museum in 2015, she decided to examine the skull more closely. Working with a team of collaborators, she extracted genetic material and compared it with DNA from the teeth of narwhal and beluga specimens in the museum. The skull, it turned out, was the first-ever confirmed narluga, the son of a beluga dad and a narwhal mom.
A deeper dive into the history of the skull (it had been found fixed atop a hunter’s home) revealed that this animal may not have been the only one of its kind. The hunter said he’d seen it with two other similar-looking whale creatures, and he, apparently, isn’t the only one to have seen a narluga. In fact, they are common enough that natives of western Greenland have a word for the narwhal-beluga hybrid, itorsaq.
Because several narlugas have been spotted before, researchers suspect that the creatures may be fertile, and that some narlugas may be the product of two narluga parents rather than one beluga and one narwhal. That notion challenges naturalists’ traditional view of hybrids as the result of maladaptive crossings, such as when a female horse mates with a male donkey and gives birth to a sterile mule. If the hybrids can’t reproduce, they would seem to be irrelevant evolutionarily, but studies of the narluga and other naturally occurring hybrids have begun to hint that such offspring may not be the biological misfits they were once thought to be. They are not evolutionary dead-ends, and in some cases, may serve as evolutionary accelerators.
“We’re beginning to realize that hybridization exists in the evolutionary history of many organisms we didn’t expect it to, including Homo sapiens,” Scott Taylor, an evolutionary ecologist at the University of Colorado Boulder, tells The Scientist.
Snowshoe Hares Borrow from Black-Tailed Jackrabbits
At some point in the past, black-tailed jackrabbits (Lepus californicus) and snowshoe hares (L. americanus) crossbred, with the hybrids mating again with snowshoe hares. A combination of whole-genome and whole-exome sequencing revealed that the resultant hares retained a variation of the Agouti gene that led to brown, rather than white, coat color in hare populations experiencing mild, less snowy winters, allowing them to better blend into the drab surroundings of dirt and dead leaves. See full infographic: WEB |
Hybridization’s benefits are not a new idea
As far back as the 1930s, botanists realized that hybridization plays a role in the evolution of plant species. In 1938, Edgar Anderson and Leslie Hubricht laid out the idea of introgression to describe the hybridization of species of herbaceous perennial wildflowers of the Tradescantia genus. The crosses led to offspring with an even split of parental genetic material, and typically those offspring then repeatedly bred with one of the original parent species, while still retaining genetic material from the other parent species. Alternatively, hybrids bred with other hybrids, and, eventually, entirely new plant species would emerge.
Zoologists knew about these and other examples of hybridization in the plant world, but there was a perception, Taylor says, that cross-species breeding was much less common in animals. That idea stemmed from biologist Ernst Mayr’s description in the 1940s of the biological characteristics that defined species—essentially, any animal population that could not or did not breed with other, similar populations. For more than two decades, including in his 1963 book Animal Species and Evolution, Mayr argued that “the evolutionary importance of hybridization seems small in the better-known groups of animals.” But the idea is not universally accepted, Taylor says. “I don’t know a lot of evolutionary biologists who study hybridization who adhere strictly to that concept.”
Despite the dogma that hybrid animals in nature were rare and therefore not catalysts of evolutionary innovation, some biologists continued to study them, curious to uncover the barriers that prevented them from becoming new species, identify the new gene combinations created by hybridization, and understand how natural selection acted upon them. Focusing on animals in what scientists call hybrid zones—geographical regions in which two species interbreed to produce offspring of mixed ancestry—researchers in the late 1980s and early 1990s began to show that, contrary to the prevailing viewpoint, hybridization was a valid mechanism of evolutionary change—one that could radically influence an animal’s ability to adapt to its environment.
A Narwhal Tries Beluga’s Teeth
A genetic analysis of a rare skull found at the Natural History Museum of Denmark showed that in the past few decades a male beluga (Delphinapterus leucas) and a female narwhal (Monodon monoceros) mated, creating a hybrid called a narluga that looked a bit like both. The animal’s 18 teeth were small, like a beluga’s, and twisted, like a narwhal’s tusk. Those teeth may have changed the way the narluga fed, not hunting on cod, squid, and shrimp in the water column as both of its parents did, but instead feeding off the bottom. Its teeth may have allowed it and others like it to occupy a different ecological niche than its parents. See full infographic: WEB |
The thousands of cichlids in Africa’s lakes
Evidence for hybrid-driven adaptation is perhaps nowhere more profound than in the warm, tropical waters of Lake Victoria in Africa. There, more than 500 species of bony fishes called cichlids that sport brilliant orange, yellow, and blue hues, roam the lake’s 2,400 cubic kilometers. Some species eat only plants, others eat invertebrates, the bigger species eat other fish, and still more feed on Lake Victoria’s detritus. “There’s incredible diversity of species that live together in the same ecosystem,” evolutionary ecologist Ole Seehausen of the University of Bern tells The Scientist. “This struck me as a beautiful system, the interaction between ecology and evolution . . . to study speciation.”
When Seehausen began to study the lake’s cichlids roughly 30 years ago, it wasn’t clear how the hundreds of species there had evolved. They weren’t geographically isolated, a common driver of speciation. Rather, the fish were all living in the same lake and could interact, yet there was still incredible cichlid diversity. Something else appeared to be driving their speciation.
With continued observation, Seehausen and others found that the barriers preventing the species in the lakes from mating were rather “shallow,” with some of the major ones being behavioral in nature. Males, for example, were defending their territories from males of both the same and other species, or females were choosing flashing mates of only their own species. That last barrier, based on color signaling, began to break down, Seehausen says, when the clarity of the water diminished in the 1990s, a result of wastewater from farms and other human activities polluting the lake. “It turns out that when you change the visual signaling, and the perception of those signals, then not much more is needed to break down reproductive isolation, so many species then hybridize,” Seehausen says.
Something similar appears to have happened thousands of years ago in Lake Victoria. Genetic analyses of the cichlids have revealed that their vast diversity can be traced back to a hybridization of two divergent lineages around 150,000 years ago. And Lake Victoria wasn’t the only body of water in the region where hybridization appeared to play an important role in speciation. Further investigation revealed that cross-species mating had happened and continued to occur in nearby lakes, where it was driving cichlid diversity. “This was replicated in several different lakes across Africa,” Seehausen says.
As scientists began to look for other examples of hybridization in the wild, both past and present, they were not disappointed. Genetic analyses have revealed crosses between coyotes and gray wolves, polar bears and brown bears, chimpanzees and bonobos, finches in the Galapagos Islands, fish called sculpin, and even modern humans and Neanderthals.
See “Neanderthal DNA in Modern Human Genomes Is Not Silent”
Researchers suspect that hybridization events are perhaps becoming more common, as human disturbances shift species ranges in ways that promote breeding across similar species. In Colorado, for example, two varieties of small, nonmigratory birds—black-capped chickadees and mountain chickadees—have recently hybridized in areas being heavily developed by humans. “If you look at the map and squint, the places they’re hybridizing seems to correlate nicely with places that humans have modified, whether that’s the front range of the Rocky Mountains or Albuquerque, New Mexico,” he says. His team hypothesizes that the species, which split some 1.5 million years ago, breed with each other in modified habitats because a resource needed by both, either breeding grounds or certain food sources, is bringing the birds together.
On occasion, a mountain chickadee (above) may mate with a black-capped chickadee.
ROBERT TAYLOR
Climate change may also be driving hybridization between species. Evolutionary biologists have seen pulses of cross-breeding as species shift where they live to higher or lower latitudes or altitudes to find cooler temperatures. When they move into those regions, the barriers to hybridization, such as differences in mate choice or other factors, might disappear. “There are definitely compelling examples” of climate change or environmental shifts influencing hybridization, says Molly Schumer, an evolutionary biologist at Stanford University, “and my suspicion is it’s pretty widespread.”
Obviously not all cases of hybridization involved the equal swapping of genes to form a completely new creature, as appeared to often happen with the cichlids, but in just the last few years, “the consensus has been that hybridization in animals in particular is hugely widespread and much more common than was appreciated,” Schumer says. The question in the field now, she says, is if this gene swapping is common, “what is it doing?”
Fish in Troubled Waters
When the waters in Lake Victoria in Africa became increasingly murky in the 1990s after mineral and farm runoff levels increased, two species of cichlids (Haplochromis nyererei and Neochromis sp. Bihiru scraper) no longer selectively mated with conspecifics, whom they had previously identified based on color. They hybridized readily, and others in the lake did too, creating new species, some of which have pervaded the altered ecological niches and adapted to them better than their parent species have. See full infographic: WEB |
Cross-breeding’s advantages and disadvantages
In the case of cichlid hybrids, Seehausen found that not only did the hybrids have similar developmental and reproductive rates to non-hybrids, in some ways individuals with a genetic mishmash of two distinct species created were actually more suited to a particular environment or food source than their parents were.
A few years ago, Joana Meier, an evolutionary genomicist at the University of Cambridge who did her graduate work and a postdoctoral stint with Seehausen, delved into the genetics of the cichlids and spotted one type of hybrid that caught her attention: dwarf species that combine the body shape of a plant-eating species with the predatory habits of a bigger species that dines on other fish. “Genetically, they’re like a mix of both,” she says. “In some cases, they have higher fitness [than either parent species] in different ecological niches.” Seehausen has also shown this in the lab, creating hybrids that don’t thrive on the food the parent species ate, but gobble down a new type of food and begin to flourish.
Schumer is seeing something similar in the hybridization of two related species of swordtail fish, Xiphophorus malinche and X. birchmanni. The fish live in the rivers of the Mexican state of Hidalgo and have begun hybridizing within the last 50 to 100 generations, probably as a result of some human disturbance to the river, she explains. The fish rely on their sense of smell and the signals in those scents to choose mates, but the contaminants in the rivers appear to be blocking the fish from picking out their own species, Schumer says, so they’ve ended up mating across species boundaries. It turns out, that the mix-up could be helping both species survive by boosting genetic diversity.
Different species of swordtail fish, including Xiphophorus birchmanni (left) and X. malinche (top), can interbreed to form hybrid offspring (bottom).
DAN POWELL
Swordtail cross-breeding is “really, really recent and gives us a good snapshot to [see] what’s happening right after hybridization,” Schumer says. Her genetic studies, along with those from other researchers investigating recent hybridization events, seem to show that right after these crosses occur, the genome of the hybrid undergoes incredible reorganization. “There’s a lot of purging of deleterious alleles and rapid evolution happening right after you collide these two divergent genomes.” The original swordtail parent species are closely related, differing by only 0.5 percent in their genetic makeup, Schumer’s studies show. Still, that small bit of genetic variation leads to substantial shifts in the species’ tolerances to cold, adaptation to elevation, and even an extra-long fin extension, called the sword, seen on X. birchmanni but not on X. malinche.
On the flip side, mushing together the two swordtail species’ genomes can cause issues in the offspring, with many not being able to reproduce. The combination of genes can even cause the hybrids to develop tumorous melanoma, which the parents don’t. “One of the biggest questions in the field,” Schumer says, “is: In this really rapid genome evolution happening after hybridization, how are all of these mechanisms—positive effects of hybridization, negative effects of hybridization, interactions with the environment, social interactions—playing out?”