Surprising new study redraws family tree of domesticated and ‘wild’ horses

Thought to be the world’s last-remaining ‘wild’ horse, Przewalski’s horses actually descend from horses domesticated by the Botai people about 5,500 years ago. Credit: Lee Boyd

There are no such things as “wild” horses anymore.

Research published in Science today overturns a long-held assumption that Przewalski’s horses, native to the Eurasian steppes, are the last wild horse species on Earth. Instead, phylogenetic analysis shows Przewalski’s horses are feral, descended from the earliest-known instance of horse domestication by the Botai people of northern Kazakhstan some 5,500 years ago.

Further, the new paper finds that modern domesticated horses didn’t descend from the Botai horses, an assumption previously held by many scientists.

“This was a big surprise,” said co-author Sandra Olsen, curator-in-charge of the archaeology division of the Biodiversity Institute and Natural History Museum at the University of Kansas, who led archaeological work at known Botai villages. “I was confident soon after we started excavating Botai sites in 1993 that we had found the earliest domesticated horses. We went about trying to prove it, but based on DNA results Botai horses didn’t give rise to today’s modern domesticated horses—they gave rise to the Przewalski’s horse.”

The findings signify there are no longer true “wild” horses left, only feral horses that descend from horses once domesticated by humans, including Przewalski’s horses and mustangs that descend from horses brought to North America by the Spanish.

“This means there are no living wild horses on Earth—that’s the sad part,” said Olsen. “There are a lot of equine biologists who have been studying Przewalskis, and this will be a big shock to them. They thought they were studying the last wild horses. It’s not a real loss of biodiversity—but in our minds, it is. We thought there was one last wild species, and we’re only just now aware that all wild horses went extinct.”

Some of the Botai horses were found to carry genetic variants causing white and leopard coat spotting patterns. Credit: Ludovic Orlando, reworked by Sean Goddard and Alan Outram.

Many of the horse bones and teeth Olsen excavated at two Botai sites in Kazakhstan, called Botai and Krasnyi Yar, were used in the phylogenetic analysis. The international team of researchers behind the paper sequenced the genomes of 20 horses from the Botai and 22 horses from across Eurasia that spanned the last 5,500 years. They compared these ancient horse genomes with already published genomes of 18 ancient and 28 modern horses.

“Phylogenetic reconstruction confirmed that domestic horses do not form a single monophyletic group as expected if descending from Botai,” the authors wrote. “Earliest herded horses were the ancestors of feral Przewalski’s horses but not of modern domesticates.”

Olsen said the findings give rise to a new scientific quest: locating the real origins of today’s domesticated horses.

“What’s interesting is that we have two different domestication events from slightly different species, or separate sub-species,” she said. (The Przewalski’s horse’s taxonomic position is still debated.) “It’s thought that modern-day domesticated horses came from Equus ferus, the extinct European wild horse. The problem is they were thought to have existed until the early 1900s. But, the remains of two individuals in St. Petersburg, Russia, are probably feral, too, or at least probably had some domesticated genes.”

Olsen led excavation of Botai sites associated with the earliest-known domestication of horses. Credit: Sandra Olsen

Olsen began excavating Botai village sites in Kazakhstan in 1993 after the fall of the Soviet Union made the region accessible to western scientists. Some of the horse remains collected by Olsen were tested as part of the new study showing their ancestry of modern-day Przewalskis.

The Botai’s ancestors were nomadic hunters until they became the first-known culture to domesticate horses around 5,500 years ago, using horses for meat, milk, work and likely transportation.

“Once they domesticated horses they became sedentary, with large villages of up to 150 or more houses,” said Olsen, who specializes in zooarchaeology, or the study of animal remains from ancient human occupation sites. “They lived primarily on horse meat, and they had no agriculture. We had several lines of evidence that supported domestication. The fact the Botai were sedentary must have meant they had domesticated animals, or plants, which they didn’t have. More than 95 percent of the bones from the Botai sites were from horses—they were in a sense mono-cropping one species with an incredible focus. If they were hunting horses on foot, they would have quickly depleted bands of horses in the vicinity of the villages and would have had to go farther afield to hunt—it wouldn’t have been feasible or supported that large human population.”

The KU researcher also cited bone artifacts from Botai sites used to make rawhide thongs that might have been fashioned into bridles, lassos, whips, riding crops and hobbles, as further evidence of horse domestication. Moreover, the Botai village sites include horse corrals.

“We found a corral that contained high levels of nitrogen and sodium from manure and urine,” said Olsen. “It was very concentrated within that corral. The final smoking gun was finding residues of mares’ milk in the pottery. It’s commonplace today in Mongolia and Kazakhstan to milk horses—when it’s fermented it has considerable nutritional value and is very high in vitamins.”

The Botai buried horses with their snouts pointing southeast toward the rising sun. Credit: Sandra Olsen

Interestingly, Olsen found that after slaughtering horses, the Botai buried some horse skulls and necks in pits with their snouts facing the southeast, toward where the sun rose in the morning in autumn. Mongols and Kazakhs slaughter most of their horses at that time of year because that is when they retain the most amount of nutritious fat in their bodies.

“It’s interesting because throughout the Indo-European diaspora there’s a strong connection between the sun god and the horse,” she said. “It may be that Botai people spoke an early proto-Indo-European language, and they also connected the horse to the sun god. Later in time, and this idea is in the historical record for the Indo-European diaspora, it was believed the sun god was born in the east and rode across the sky in a chariot, pulled by white horses. According to the belief, he would then die in the west and be reborn every day.”

The team behind the paper believe Przewalski’s horses likely escaped from domestic Botai herds in eastern Kazakhstan or western Mongolia.

Excavation at the Botai site, Northern Kazakhstan, 2017. Credit: Alan Outram / University of Exeter

“They started developing a semi-wild lifestyle like our mustangs, but they still have a wild appearance,” Olsen said. “This is partly why biologists assumed they were genuinely wild animals. They have an upright mane, something associated with wild equids. They also have a dun coat, like the ones you see in the Ice Age cave paintings in France and Spain made when horses were wild. Their size, however, is very similar to what you see at Botai and other sites.”

By 1969, Przewalski’s horses were declared extinct in the wild, and all living today originated from just 15 individuals captured around 1900. Today, there are approximately 2,000 Przewalski’s horses, all descended from those captured horses, and they have been reintroduced on the Eurasian steppes. In a sense, the horses have fared better than the peoples who once domesticated them.

“The Botai people seem to have vanished from their homeland in northern Kazakhstan,” said Olsen. “Perhaps they migrated eastward to Mongolia since the later Bronze Age people there shared the practice of ritually burying the horse’s head and neck pointing toward the rising sun in the autumn, the time of year they were slaughtered. That’s a very specific shared trait.”

Explore further:
After 100 years in captivity, a look at the world’s last truly wild horses

More information:
C. Gaunitz el al., “Ancient genomes revisit the ancestry of domestic and Przewalski’s horses,” Science (2018). … 1126/science.aao3297

Journal reference:

Provided by:
University of Kansas

Invasion of the body-snatching fungus

The fungus infects the cicada and essentially hijacks their behavior. Credit: Yessenia Carrero/UConn

UConn researchers recently documented in Nature Scientific Reports a gory and fascinating relationship between periodical cicadas and a fungus that infects them, hijacks their behavior, and causes a scene straight out of a zombie movie.

“It’s a fun story for us, not for the cicadas,” says UConn ecology and evolutionary biology researcher and adjunct faculty member John Cooley.

Though researchers have known about the fungus for around 100 years, Cooley and his colleagues David Marshall, a postdoc, and lab technician Kathy Hill have published new findings about the infection.

The story starts with the cicadas’ emergence, when around 2 to 5 percent are infected with spores of a fungus called Massospora cicadina. Though the fungus infects both male and female cicadas, the researchers discovered that early in the emergence, the infection – at this point called a Stage I infection – causes curious behavioral changes in males where, in addition to their normal mating behaviors, they will exhibit wing flicking that is typically seen only in female cicadas.

The infected male cicadas put on a ruse, much like the Sirens of Greek myths; they flick their wings like a female, and lure in healthy unsuspecting males, who get close enough to be exposed to the spores, leading to their doom. The diseased males will also attempt to copulate with the uninfected females, exposing them to even more spores.

The infection results in the insect’s abdomen becoming distended as it fills with powdery, white fungal spores eventually to the point of bursting open or falling off altogether. When the abdomen falls off, the genitalia are lost with it – but that doesn’t stop the cicadas from their eager quest to copulate.

Cicadas infected by the spores passed around by the initially infected cicadas exhibit what is called a Stage II infection, following the same infection cycle as that seen in Stage I infections, in some cases acting normally despite the lack of genitalia and large portions of their abdomens, and spewing spores wherever they go.

The fungus’s job is complete, the spores are spread and ready to infect future generations.

Growing body of research

Cooley says the research into similar infections by parasites or fungi has been observed in other species, for instance in beetles, fruit flies, and even mammals, and has led to a growing body of literature over the past 10 years or so.

Of the cicada infections, Cooley says, “This phenomenon is the ultimate evolutionary arms race, where the host loses because they are rendered sterile or evolutionarily irrelevant by the fungus in order to spread the spores.”

He anticipates that this area of research will continue to heat up in coming years, as more details of these arms races are uncovered.

This type of research has to be performed in the field, and it’s hard to predict where the fungus will be present. The best sites for studying these unfortunate cicadas have been almost stumbled upon. As Cooley explains, “I’d be driving along and say ‘Holy smoke, there are a lot of dead cicadas in this spot. What’s going on?'”

He says the findings on this hijacking fungus are an excellent example of the importance of basic scientific research and observation, and may ultimately lead to a scientific breakthrough.

“Basic research is sometimes not very exciting, it can be a lot of sitting around watching bugs,” he observes. “You never really know in advance what the payoffs and applications will be. But basic research may lead to someone having an ‘Aha’ moment. Maybe this could lead to new biocontrol, maybe the fungus could secrete something to alter metabolism or nervous behavior. We’ll have to see where it goes.”

Explore further:
How fungus manipulate fruit flies into hosting spores and releasing them

More information:
John R. Cooley et al, A specialized fungal parasite (Massospora cicadina) hijacks the sexual signals of periodical cicadas (Hemiptera: Cicadidae: Magicicada), Scientific Reports (2018). DOI: 10.1038/s41598-018-19813-0

Journal reference:
Scientific Reports

Provided by:
University of Connecticut

Damage encourages maple species to become female, study finds

Male flowers, left, and female flowers on striped maple branches. Credit: Jennifer Blake-Mahmud, Rutgers University

A few years ago, Rutgers researcher Jennifer Blake-Mahmud was working on a botany project in Virginia when colleagues pointed out a striped maple, a common tree in the understory of mountain forests from Nova Scotia to Georgia.

“They told me, ‘We think it switches sex from year to year, but we don’t know why,’ and I said, ‘No way! How can that be?’ Blake-Mahmud said. “And that was when I decided I needed to find out what was going on.”

In research published in the journal Trees: Structure and Function, Blake-Mahmud reports that striped maples not only change their sex periodically, but that they can wait until the last minute – three weeks before flowering – to do it. The switch appears to be triggered by physical damage, which can prompt a branch to flower female if it’s cut off a male tree.

Blake-Mahmud, a doctoral student in the School of Graduate Studies at Rutgers University-New Brunswick, cut branches from healthy, mature striped maples from state forests in northern New Jersey. She took the samples to her lab, where she let them flower.

She expected that striped maples, like most trees, would prepare themselves for reproduction by fashioning the tiny flower sex parts many months before they flowered. Apple trees, for instance, have already made their buds for the next year just six-weeks after flowering finishes for this year. Surprisingly, the cuttings from her striped maples waited…and waited…and waited to finish developing. Even three weeks before natural blooming time, the buds were still flexible and could bloom female if cut off the tree or male if left untouched. This means that the tree can wait until very late to make up its mind about which kind of flowers – male or female – to have. “These trees were the arboreal equivalent of last-minute Christmas shoppers,” Blake-Mahmud said

The trigger turned out to be the act of cutting a branch off the tree – physical damage. And most of the branches taken from male trees expressed themselves as female when they bloomed in the greenhouse. Blake-Mahmud said this suggests that physical damage plays a role in sex expression, although she isn’t certain yet what sort of damage. She noted that even without people cutting off branches, striped maples lead a perilous life. “There are deer rubbing their antlers against them, bears scratching against them, taller trees that die and fall on them,” she said.

Blake-Mahmud’s co-author and adviser is Lena Struwe, a professor of plant biology, ecology, evolution and natural resources in the School of Environmental and Biological Sciences.

Blake-Mahmud noted that arboreal sex isn’t a field that many people are familiar with. When she explains that she’s a botanist who studies how plants express sex, she often gets two reactions. “People say, ‘Whoa, plants have sex?'” Assured that plants do, people then often ask why she doesn’t study sex in animals. “I tell them that sex in plants is much more complex, much more interesting, than sex in animals,” she said. “If you’re interested in reproduction, plants are definitely the way to go.”

Explore further:
Downed trees not necessarily a lost cause

Provided by:
Rutgers University

Explaining coprophagy – why do dogs eat their own poo?

Don’t give him the chance. Credit: Shutterstock

Dogs are scavengers. As many dog owners know to their cost, dogs often have a penchant for things that we find less than palatable. If it’s not counter or table surfing, it might be raiding the kitchen rubbish bin or snacking on rich pickings from the park, street or elsewhere.

Occasionally, those rich pickings include poo, much to the disgust of many owners. That poo can be from a range of species (birds, horses, rabbits, cattle, sheep, deer, and in my own dogs’ case, cat poo is a particular favourite). But sometimes, dogs have a desire to consume either their own or other dogs’ faeces. This behaviour is called coprophagy, literally translated as “faeces eating” and, unsurprisingly, many dog owners don’t like it.

Ironically, dogs are often fastidious at keeping their sleeping areas clean by removing their faeces. Dogs will also actively avoid areas contaminated with poo from other dogs. This is probably an innate behaviour that has evolved to prevent the spread of disease. So given that eating poo does carry disease risk, why do dogs do it? A recent study has shed further light on the subject and could help us manage the behaviour.

First, it seems that not all dogs eat each other’s poo. The study found that only 16% of more than 1,000 dog owners surveyed saw their dogs consume canine faeces at least six times or more (the study’s definition of coprophagy). And 77% recorded never seeing their pets eat other dogs’ poo.

The research showed that several key factors appear to have no effect on whether your dog is a poo-eater. These included age, gender, whether the dog has been spayed or neutered, whether it was housetrained, whether it had been weaned or removed from its mother early, and what the rest of its diet was like. Evidence also suggests that the plethora of products designed to prevent or treat coprophagy, or punishing your dog for eating poo, have no effect on reducing the behaviour.

Instead, the recent study suggests the best way to predict whether a dog eats faeces is how much access to poo they have. This is particularly the case if the faeces are fresh, with over 80% of coprophagic dogs only consuming poo less than two days old. It seems that keeping your dog away from fresh poo is the most effective strategy for stopping them eating it. This is yet another reason to promote regular poo picking and responsible dog ownership, both at home and out walking.

In the survey, dogs described as “greedy” and those in households with two or more dogs were more likely to be coprophagic. Terriers and hounds were also more likely to be coprophagic, as were Shetland sheepdogs, with 41% of those in the study recorded as eating poo. Poodles, on the other hand, appeared to defy their name and shun the practice.

Yet none of this explains why certain dogs will eat poo if they can. It might simply be that some dogs like it and have learned, either by accident or with intent, to consume faeces. Perhaps dogs do it if their owners or other dogs they come into contact with show a particular interest in faeces. After all, we know that dogs often synchronise their behaviour with their owners (though it’s unlikely that most affected owners are coprophagic).

Evolutionary leftover

But the study authors suggest that coprophagy is something much more basic. It’s possible that poo eating is an evolutionary remnant from dogs’ ancestors, where faeces could be a source of disease, especially from parasites. Removing faeces early by eating it might represent a way of cleaning it up to prevent infectious parasites developing in the days after it’s deposited. And dogs today may indulge in exactly the same behaviour.

So what should you do if the prospect of your pet eating poo fills you with horror? Aside from owning a single, non-greedy poodle, the best thing to do is simply to prevent your dog having access to poo, especially the fresh stuff. Clean up after your dog, encourage others to do the same, and try training your dog to resist the temptation to eat poo by rewarding them with an alternative tasty snack.

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Researchers warn of deadly parvovirus strain spreading in Australian dogs

Provided by:
The Conversation

How urban heat affects bee populations

Credit: Elsa Youngsteadt

North Carolina is home to 500 species of wild bees, yet only a subset of these are common in cities and suburbs. People encourage wild bees by planting flowers and creating pollinator gardens to provide the pollen and nectar bees need. However, even gardens rich with flowers do not have the same bee abundance or diversity as natural areas. So, there must be things besides flowers that limit urban bee communities. But what are they?

In a recent paper, we show that one of these factors is the urban heat island effect. The urban heat island effect is caused by impervious surfaces – like cement and pavement – that absorb heat from the sun, making cities hotter than surrounding rural areas. We sampled bees for two years in 18 yards and parks around Raleigh, NC. These yards differed in flower abundance and diversity, but also differed in temperature. The hottest yards had about a third as many bees as yards just 2°C (about 3.6°F) cooler.

In addition, hot yards had fewer bees from species that we previously found to be sensitive to heat and more bees from species we found to be heat tolerant. We know from previous research that high temperatures can reduce bee survival by making them more susceptible to pathogens or less able to forage.

Yards with lots of flowers still had more bees and more kinds of bees than yards with few flowers but this was mitigated by yard temperature.

In other words, simply adding flowers to otherwise hot sites with lots of impervious surface cover is unlikely to restore pollinator communities. To amplify the benefits provided by flowers, you could plant trees to shade driveways and sidewalks, reducing the temperature of a yard. We wouldn’t expect other animals to thrive in poor habitats just by providing them with food. Bee conservation requires habitat restoration.

(This is a guest post by Steve Frank, an associate professor of entomology at NC State University.)

Explore further:
Sick bees eat healthier

More information:
April L. Hamblin et al. Wild bee abundance declines with urban warming, regardless of floral density, Urban Ecosystems (2018). DOI: 10.1007/s11252-018-0731-4

Elsa Youngsteadt et al. Urbanization Increases Pathogen Pressure on Feral and Managed Honey Bees, PLOS ONE (2015). DOI: 10.1371/journal.pone.0142031

Journal reference:

Provided by:
North Carolina State University

The mystery behind the proboscis monkey’s big nose

Male proboscis monkeys weigh about 20 kilograms while females are roughly half that. The long nose is only found in males. Credit: Kyoto University / Masuda Lab

Exaggerated male traits, such as a large nose, can be great for attracting females, finds a study of proboscis monkeys in Malaysia.

Scientists from Cardiff University, the Danau Girang Field Centre, Kyoto University and Sabah Wildlife Department, found a clear link between the nose size of the male monkeys and the number of females in their harems, clearly showing that size does matter!

Dr. Sen Nathan, Assistant Director of Sabah Wildlife Department and Ph.D. student at Cardiff University and Danau Girang Field Centre, said: “Although the unique nature of the ‘odd-nosed’ proboscis monkey has long been admired as an extremely attractive visual feature by biologists, explanations for its evolution have so far been gleaned more from folklore than from science.

“We show evidence supporting both male-male competition and female choice as causal factors in the evolution of enlarged male noses. We also observed that nasal enlargement modified the resonance properties of male vocalisations, which probably encode male quality. Our results therefore indicate that the audiovisual contributions of enlarged male noses serve as advertisements to females in their mate selection.”

During the study, morphological measurements and behavioural observations in free-ranging proboscis monkeys were carried out in the Lower Kinabatangan Wildlife Sanctuary. The researchers also recorded the vocalisations of male and female proboscis monkeys at three different zoos: Yokohama Zoo in Japan, Singapore Zoo and Low Kawi Zoo (Sabah).

Dr. Ikki Matsuda, from Chubu University and Kyoto University in Japan, said: “Based on the collected data, we tested the correlations between body mass, facial characteristics, testicular volume, vocalisations, and number of harem females in captive and free-ranging proboscis monkeys.

“In addition to finding that enlarged male noses serve as advertisements to females in mate selection, we also found that males with larger noses also tended to have larger body mass and testis. This suggests that nose enlargement is a reliable predictor of social dominance and high sperm count.”

Dr. Benoit Goossens, Director of Danau Girang Field Centre and Reader at Cardiff University, added: “We expect our study will shed light on the hypothesis of audiovisual coevolution of exaggerated male traits in primate lineages and provide further evidence for the evolutionary pathway of enlarged noses in proboscis monkeys.

“The proboscis monkey is endemic to Borneo and is a totally protected species in Sabah. Every piece of information that allows us to better understand the behavior of these charismatic animals is important.

“Now our tour guides will be able to tell their guests that size matters, and that males with larger noses attract more females in their harem.”

This study ‘Nasalization by Nasalis larvatus: larger noses audiovisually advertise conspecifics in proboscis monkeys’ is published in Science Advances.

Explore further:
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More information:
H. Koda el al., “Nasalization by Nasalis larvatus: Larger noses audiovisually advertise conspecifics in proboscis monkeys,” Science Advances (2018).

Journal reference:
Science Advances

Provided by:
Cardiff University

Distinguishing males from females among king penguins

Male female couple. Credit: Hannah Kriesell

It is difficult to distinguish males from females among King Penguins, but a new Ibis study reveals that King Penguins can be sexed with an accuracy of 100% based on the sex-specific syllable pattern of their vocalisations. Using the beak length, King Penguin individuals can be sexed with an accuracy of 79%.

The new findings may help investigators understand how King Penguins choose mates, and they offer a cost- effective, non-invasive technique for researchers to sex King Penguins in the field.

“The sex-specific syllable pattern in King Penguin calls is a very interesting finding, both from an evolutionary perspective as it is rare in non-passerine species, but also because it allows researchers with very little training to reliably identify the gender of King Penguins without handling the individuals,” said lead author Hannah Kriesell, of the Centre Scientifique de Monaco and the University of Strasbourg.

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Love on the rocks: Penguins celebrating Valentine’s Day

More information:
Hannah J. Kriesell et al, Sex identification in King Penguins Aptenodytes patagonicus through morphological and acoustic cues, Ibis (2018). DOI: 10.1111/ibi.12577

Theory suggests root efficiency, independence drove global spread of flora

Researchers from Princeton University and the Chinese Academy of Sciences have posed a theory of plant evolution based on root adaptations that allowed plants to become more efficient and independent. The cross sections above show that the roots of plants such as the subtropical oak species Lithocarpus chintungensis (largest cross section, center left) and the tropical species Parashorea chinensis (lower-right of largest cross section) retained their ancestral thickness and reliance on the symbiotic fungi (purple ring) that surround the root to help it obtain nutrients. As plant species spread from their nutrient-rich tropical origins, however, the root tips of plants such as the desert shrub species Tamarix ramosissima (left of largest cross section) evolved to be thinner so they could more efficiently explore soil for nutrients, and they have less dependence on symbiotic fungi. Credit: Zeqing Ma, Chinese Academy of Sciences

A new theory of plant evolution suggests that the 400 million-year drive of flora across the globe may not have been propelled by the above-ground traits we can see easily, but by underground adaptations that allowed plants to become more efficient and independent.

As plant species spread north and south from their nutrient-rich tropical beginnings, the fine tips of their roots became narrower and more widespread to help them explore increasingly poor soil for vital nutrients, according to a Feb. 21 study in the journal Nature led by researchers from Princeton University and the Chinese Academy of Sciences (CAS) in Beijing. In addition, as plants spread into unpredictable environments such as arid deserts they grew less dependent on the symbiotic fungi—or mycorrhiza—that colonize roots and help host plants obtain the essential plant nutrients nitrogen and phosphorous.

The findings reconsider how plants adapted to new environments as they evolved, said corresponding author Lars Hedin, the George M. Moffett Professor of Biology and chair and professor of ecology and evolutionary biology and the Princeton Environmental Institute. Scientists have in the past focused on above-ground characteristics, primarily leaf traits and the efficiency with which plants absorb sunlight for photosynthesis, he said.

Instead, Hedin said, he and his colleagues have found for the first time that root diameter and reliance on fungi—or the lack thereof—are the traits that most consistently characterize the plant community across entire biomes, which are large distinct communities of animals and plants such as a desert, temperate forest or savanna.

“These are the secret strategies that plants have used over time to take over the world,” Hedin said. “Our goal was to unlock the understanding of those strategies, and our findings offer a new global theory for plant evolution. Hidden underground there has been a tremendous game of survival-of-the-fittest and we are fortunate to have the first-ever view of the science of that game.

“This work has major implications for conservation and our stewardship of the plant world,” Hedin continued. “It provides some of the hidden, below-ground rules by which plants survive and spread. It’s a global view of plant evolution at a time when global rules are essential for building climate models and understanding the biosphere.”

Mingzhen Lu, first Princeton author and a graduate student in Hedin’s research group, said that if root traits do in fact determine a plant’s ability to withstand a particular environment, these findings could be valuable in conserving endangered species or projecting how plants might adapt to climate change.

“Our findings simplify how we can practically characterize a plant’s strategy for obtaining nutrients,” Lu said. “Knowing their underlying nutrient strategy will help us know how to preserve them, or know the conditions under which they could or could not survive.”

Kurt Pregitzer, the Thomas Reveley Professor and dean of the College of Natural Resources at the University of Idaho, said this work could be especially useful in combating invasive species, which, in a highly mobile world, increasingly threaten biodiversity. Pregitzer is familiar with the research but had no role in it.

“Invasive species cause widespread displacement of native plants and tremendous economic impacts across the globe,” Pregitzer said. “This study may open entirely new lines of scientific investigation that help us better understand how invasive-plant root systems help these exotic species outcompete native plants.”

The Nature paper is unique for its scale and careful application of scientific methods, Pregitzer said. “This study is the first conducted across a wide range of terrestrial environments and it demonstrates that plant species have evolved root strategies that are conserved within corresponding families, genera and species,” he said. “These root traits likely facilitate plant success in highly competitive natural ecosystems.”

The researchers spent two years examining a database of root traits consisting of 369 species from seven biomes (above): desert, grassland, Mediterranean, boreal, temperate, subtropical and tropical. Woody biomes are identified as shades of tan-to-yellow and non-woody biomes are in shades of green. The researchers found that plants in tropical (light orange) and subtropical biomes (beige) exhibited the largest range of root-tip diameters, from less than 0.25 millimeters up to 1 millimeter. These plants rely on soil fungi to provide nutrients, a similar strategy to that of Earth’s earliest land plants. Plants in biomes characterized by poor soil, cold winters and/or infrequent precipitation have a narrow root-diameter range ideal for that environment. The desert (light green) and grassland (green) species studied all had root diameters of less than 0.25 millimeters. Credit: Lars Hedin and Mingzhen Lu, Department of Ecology and Evolutionary Biology

The researchers spent two years examining a uniquely large database of root traits consisting of 369 species from seven biomes: desert, grassland, Mediterranean, boreal, temperate, subtropical and tropical.

These data were compiled over the course of a decade in the lab of late co-corresponding author Dali Guo, a professor at CAS’ Institute of Geographic Sciences and Natural Resources Research. First author Zeqing Ma is a research associate in Guo’s lab and co-author Xiangliang Xu is a colleague of Guo’s. The paper’s co-authors also included root experts Richard Bardgett, professor of ecology at the University of Manchester in the UK; David Eissenstat, professor of woody plant physiology at Pennsylvania State University; and M. Luke McCormack, a research associate at the University of Minnesota.

The researchers found that plants in tropical and subtropical biomes exhibited the largest diameter range for the finest root tips that forage for nutrients, from less than 0.25 millimeters up to 1 millimeter. These thicker-rooted plants employ what the authors call a “conservative” strategy — similar to that of Earth’s earliest land plants—that relies on the soil fungi prevalent in wet, warm tropical and subtropical soils to provide nutrients. The researchers refer to nutrient-rich soil in consistently sultry environs as “predictable.”

Meanwhile, fine-root diameters in “unpredictable” biomes characterized by poor soil, cold winters and/or infrequent precipitation fall within a narrower range ideal for that environment. For instance, the desert and grassland species studied all had root diameters of less than 0.25 millimeters. Root tips in these biomes evolved to be thinner so they could more efficiently explore soil for every unit of carbon the plant expends, and they have less dependence on symbiotic fungi.

The extensive data the researchers used allowed them to explore the evolution of plant roots to an extent never before possible, Lu said. “Below-ground plant ecology has been understudied, limited by a paucity of data,” he said. “Because of that, the governing rule of what’s going on below ground has been very poorly known.”

“Thus far,” Hedin added, “everybody has quite naturally tried to understand how plants are organized by looking at above-ground traits. But our findings do not follow the above-ground theories—that was a surprise.”

The study reveals that root and leaf evolution have followed different paths, Pregitzer said. Plant ecologists have known that the form and function of leaves are essential to a plant species’ success, but “we did not understand if this was true across the tremendous diversity of plant root systems,” he said.

“Interestingly, little was known about how plant roots have evolved to facilitate success in their native habitats,” Pregitzer said. “Now we know that leaves and roots have responded to different evolutionary selective pressures, and we can start building a better understanding of how root form and function drive plant success within the tremendous biological diversity we see on Earth.”

The findings align with ideas explored at Princeton that suggest that plants—rather than being passive features of their environment—have actively adapted to and shaped their environments, Hedin said. He was senior author of a 2015 paper in Nature Plants that suggested that ecosystems take their various forms because plants behave in ways that not only benefit themselves but also determine the productivity and composition of their habitats.

“Over evolutionary time, it’s as if plants have actively explored the best strategies to safeguard their own survival,” Hedin said. He and Lu brought this perspective to the database put together by their colleagues at CAS.

“We understood from a plant perspective how to bring evolutionary questions to their unique global dataset,” Hedin said. “It was this great collaboration where we combined new ideas with years of painstaking fieldwork to produce this great result. It couldn’t have happened without both sides.”

The paper, “Evolutionary history resolves global organization of root functional traits,” was published online by the journal Nature Feb. 21.

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More information:
Evolutionary history resolves global organization of root functional traits, Nature (2018).

Team finds the movement behavior of an anole species to be more dynamic than previously thought

Anolis sagrei, also known as the Bahaman anole or De la Sagra’s Anole, is highly invasive. Credit: Bonnie Kircher

Anolis lizards have a thing or two to teach humans about love—or in scientific speak, sexual selection—at least when it comes to territoriality.

Decades of behavioral research on the lizard’s mating systems have resulted in near-unanimous agreement among scientists that the males maintain restricted, static territories to defend exclusive mating access to females within these territories and are consequently polygamous.

However, recent genetic data shows that female Anolis sagrei—a brown lizard native to Cuba and the Bahamas but well established in Florida—also have multiple partners.

UC Santa Barbara behavioral ecologist Ambika Kamath and colleague Jonathan Losos of Washington University in Saint Louis eschew the framework of territoriality. Rather, they quantify movement patterns of the lizards and estimate encounters between potential mates. Their finding: The species’ movement behavior can be more dynamic than previously thought, leading females to frequently encounter multiple males and suggesting the possibility that female mate choice may be an important selective force.

Kamath’s and Losos’ research is published in the Proceedings of the Royal Society B.

“Understanding animals’ movement patterns and the encounters they bring about is a key step in characterizing a population’s mating system and essential for determining how behavior both facilitates and is subject to sexual selection,” explained Kamath, a postdoctoral scholar in UCSB’s Department of Ecology, Evolution, and Marine Biology. “The movement patterns of these lizards revealed not only that a majority of males (60 percent) encountered multiple females but also that most females (78 percent) encountered multiple males over the first three months of the breeding season. This suggests potentially complex mating patterns with ample scope for female choice.”

The researchers characterized sexual selection by examining the predictors of male reproductive success at two levels. First, they asked whether the number of potential mates encountered by males was associated with their phenotype (the spatial extent of their movement and body size). Second, Kamath and Losos tested three hypotheses to understand the phenotypic differences between potential and actual mates: if females bear offspring sired by males they encounter more frequently; if males encountered later in the breeding season are more likely to sire offspring than those met earlier; and if females disproportionately bear offspring sired by larger males.

“Consistent with previous genetic descriptions of anole mating systems, most females—64 to 81 percent—bore offspring sired by more than one male,” Kamath said. “In addition, we found that sexual selection favored males that were bigger and moved over larger areas, though the effect of body size cannot be disentangled from last-male precedence.”

According to Kamath, these findings raise questions about research assumptions. “If these lizards are not territorial like previously thought, how do we understand the decisions they make?” she asked. “Are there frameworks we can use to think about individuals’ decisions that would enable us to predict patterns of selection, both natural and sexual? Our research leaves the field wide open in terms of finding better ways that don’t rely on constraining frameworks such as territoriality for describing animals’ social lives.”

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More information:
Estimating encounter rates as the first step of sexual selection in the lizard Anolis sagrei, Proceedings of the Royal Society B (2018). rspb.royalsocietypublishing.or … .1098/rspb.2017.2244

Journal reference:
Proceedings of the Royal Society B

Provided by:
University of California – Santa Barbara

Triplefin fish found to have controlled iris radiance

Triplefin Tripterygion delaisi with red ocular spark in the field. Credit: © Nico K. Michiels, Uni Tübingen

A team of researchers with the University of Tübingen in Germany has found an example of a fish that is able to control light reflected from organs next to its pupils—a form of photolocation. In their paper published in the journal Royal Society Open Science, the group describes their study of the fish and their findings and also offers some theories on the purpose of the skill.

As the authors note, several species have been found to use bounced sound to navigate or locate prey—forms of echolocation. And other sea creatures use light reflected off their own organs to help them see better in deep water. In this new effort, the researchers have found an example of a fish that is able to control such organs—a first.

The fish is the triplefin, and it is rather small at just two to three inches in length. They are native to the eastern part of the Atlantic Ocean and the western part of the Mediterranean Sea. They typically live in shallow areas, but some live in much deeper water at depths up to 50 meters, where sunlight is obscured. Prior research has shown that the fish hunt by lying still near the sea floor until prey comes near—at that point, they swim closer and strike quickly. But what sets the triplefin apart from other fish is the glowing red or blue that surrounds its pupils.

The researchers discovered that the eye color often changes back and forth as the fish stalks its prey, suggesting it could change the color on demand. The light is not emitted from the eyes, the researchers note, but is instead reflected from available light coming down from above. Thus, to change the color on demand, the fish would have to be able to physically move eye components to reflect different parts of the light spectrum.

Tripterygiidae Tripterygion delaisi. Credit: © Nico K. Michiels, Uni Tübingen

To test for this, the researchers looked at the reflective eye regions in the iris, which they called “ocular sparks” and found that simple eye movements could indeed allow them to adjust color on-demand. They also tested the fish by adding different colored backgrounds to a tank filled with water and found that the fish tended to reflect blue light when there was a red background and vice versa—and also when small prey was near. Both observations, the team notes, show the fish is truly able to control its photolocation abilities.

Michiels et al. Figure 1. Credit: © Nico K. Michiels, Uni Tübingen

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More information:
Nico K. Michiels et al. Controlled iris radiance in a diurnal fish looking at prey, Royal Society Open Science (2018). DOI: 10.1098/rsos.170838

Active sensing using light, or active photolocation, is only known from deep sea and nocturnal fish with chemiluminescent ‘search’ lights. Bright irides in diurnal fish species have recently been proposed as a potential analogue. Here, we contribute to this discussion by testing whether iris radiance is actively modulated. The focus is on behaviourally controlled iris reflections, called ‘ocular sparks’. The triplefin Tripterygion delaisi can alternate between red and blue ocular sparks, allowing us to test the prediction that spark frequency and hue depend on background hue and prey presence. In a first experiment, we found that blue ocular sparks were significantly more often ‘on’ against red backgrounds, and red ocular sparks against blue backgrounds, particularly when copepods were present. A second experiment tested whether hungry fish showed more ocular sparks, which was not the case. However, background hue once more resulted in a significant differential use of ocular sparks. We conclude that iris radiance through ocular sparks in T. delaisi is not a side effect of eye movement, but adaptively modulated in response to the context under which prey are detected. We discuss the possible alternative functions of ocular sparks, including an as yet speculative role in active photolocation.

Journal reference:
Royal Society Open Science