Forget garlic. In real life, a tomato can defeat a vampire. And researchers have now figured out the first step to vegetable triumph.

The vampires are slim, tangling vines that look like splats of orange or yellow-green spaghetti after a toddler’s dinnertime tantrum. Botanically, the 200 or so Cuscuta species are morning glories gone bad. In the same family as the heavenly blue garden trumpets, the dodders, as they’re sometimes called, lose their roots about a week after sprouting and never grow real leaves. Why bother when you can drain food and water from the neighbors?
A dodder seedling, basically a bare stem, finds that first neighbor by writhing and groping (in slow plant time) toward attractive plant odors. “The Cuscuta can smell its victims,” says Markus Albert of the University of Tübingen in Germany.

Depending on the dodder species, victims include asparagus, melons, sugar beets, petunias, garlic, chrysanthemums and oak trees. Even worse for civilization as we know it, some Cuscuta species vampirize coffee plants and grapevines.
Certain dodders do kill tomato plants. But not the C. reflexa from Asia that Albert studies; instead, it gets its skinny little haustoria whipped. Haustoria are the organs that make plant parasitism possible. When a dodder seedling brushes against tasty prey, a haustorium disk forms and pushes out from the dodder stem with a fast-growing point. “It really looks like a vampire tooth,” Albert says.

If the prey is, say, a soybean plant, it’s doomed. The growing dodder haustorium not only exerts force but also releases enzymes that weaken the bean’s tissue. Haustorium tip cells send out projections that grasp the bean’s inner ducts for water and nutrients, diverting so much that the bean starves.

A tomato plant poked by a haustorium, however, panics. A patch of cells on the stem elongate and burst, forming a scab that stops the intruder. The haustorium stalls and eventually dies.

A gene called CuRe1 lets the tomato recognize the dodder as a dire threat, Albert and colleagues report in the July 29 Science. They transferred the gene to a normally susceptible relative and — Ha! Bite that, vampire! Albert predicts additional biochemistry could be needed to dodder-proof other crops. But for starters, researchers now know the first step in protection: A tomato’s rare power to survive a scary vampire is the ability to get really scared itself.

By sneakily influencing brain activity, scientists changed people’s opinions of faces. This covert neural sculpting relied on a sophisticated brain training technique in which people learn to direct their thoughts in specific ways.

The results, published September 8 in PLOS Biology, support the idea that neurofeedback methods could help reveal how the brain’s behavior gives rise to perceptions and emotions. What’s more, the technique may ultimately prove useful for easing traumatic memories and treating disorders such as depression. The research is still at an early stage, says neurofeedback researcher Michelle Hampson of Yale University, but, she notes, “I think it has great promise.”
Takeo Watanabe of Brown University and colleagues used functional MRI to measure people’s brain activity in an area called the cingulate cortex as participants saw pictures of faces. After participants had rated each face, a computer algorithm sorted their brain responses into patterns that corresponded to faces they liked and faces they disliked. With this knowledge in hand, the researchers then attempted to change people’s face preferences by subtly nudging brain activity in the cingulate cortex.

In step 2 of the experiment, returning to the fMRI scanner, participants saw an image of a face that they had previously rated as neutral. Just after that, they were shown a disk. The goal, the participants were told, was simple: make the disk bigger by using their brains. They had no idea that the only way to make the disk grow was to think in a very particular way.

For 12 people, the researchers made the disk grow when the participants’ brain activity looked like the activity that corresponded to faces they had liked in the first round. For 12 other people, the disk grew when their brain activity mirrored activity elicited by previously unliked faces. Another six people saw the faces, but didn’t do any disk training. This training lasted an hour each day for three days.

At the end of the training, people induced to call up brain activity similar to positive responses rated previously neutral faces as slightly more positive. “By doing this again and again, subjects began to like what was neutral before,” Watanabe says. And people who had called up activity associated with negative responses rated previously neutral faces as slightly more negative. People who hadn’t trained on the disk didn’t change their ratings. These opinion shifts lasted at least three months, later experiments showed.

Participants were simply told to make the disk bigger; they had no idea what the disk actually represented. “These results are fascinating in showing how nonconscious brain activity can be utilized to modify brain function and behavior in a targeted way,” says neuroscientist Rafi Malach of the Weizmann Institute of Science in Israel.

By showing that neurofeedback can influence complex mental processes, this study and others raise the possibility that similar methods could change the brain in desirable ways. Perhaps this sort of neural training could get rid of problematic patterns of thinking, such as those that come with abnormal fear and depression, Watanabe says.

A freaky fish with a head like a dolphin and a body like a tank may be to thank for human jaws.

The discovery of a 423-million-year-old armored fish from China suggests that the jaws of all modern land vertebrates and bony fish originated in a bizarre group of animals called placoderms, researchers report in the Oct. 21 Science.

Along with a different placoderm fossil from 2013, the new find, named Qilinyu rostrata, is helping rewrite the story of early vertebrate evolution, says paleontologist John Maisey of the American Museum of Natural History in New York City, who was not involved with the work.
“We’ve suddenly realized we had it all wrong,” he says.

The jaws of humans — and dogs, salmon, lizards and all other bony vertebrates — contain three key bones: the maxilla and premaxilla of the upper jaw, and the dentary of the lower jaw.

“Anything from a human being to a cod has recognizably the same set of bones in the head,” says study coauthor Per Ahlberg, a paleontologist at Uppsala University in Sweden. The big question, he says, is “Where did these bony jaws come from?”

More than a hundred million years before dinosaurs walked the Earth, fishes called placoderms thrived under water. Scientists knew that these armored fishes were early jawed animals, but their jaws were unusual: “They look like sheet metal cutters,” Ahlberg says. “They’re these horrible bony blades that slice together.”
The blades, called gnathal plates, looked so peculiar that most scientists thought that the three-part jaw of humans originated in an early bony fish and that placoderms were just a funny little side branch in the vertebrate family tree. “The established view is that placoderms had evolved independently and that our jaw bones must have a separate origin,” Ahlberg says.
Placoderms are a highly debated group of animals, says paleontologist Martin Brazeau of Imperial College London. No one quite knew where to place them.
In 2013, Ahlberg and colleagues found a new clue in a 419-million-year old fossil that had the body of a placoderm, but the three-part jaw of a bony fish. Such an animal, called Entelognathus primordialis, “could never have been predicted from the fossil record,” says paleontologist Gavin Young of Australian National University in Canberra.

That work bolstered the idea that placoderms weren’t, in fact, their own odd group that dead-ended hundreds of millions of years ago — some were actually the ancestors of bony fish (and thus humans). But it was just one fossil, Ahlberg notes. “You don’t want to draw too big of conclusions from one animal.”

Two animals, though, is a different story. Qilinyu, the new fossil Ahlberg and colleagues describe, had an armored skull and trunk and was probably about the length of a box of tissues. Like Entelognathus, Qilinyu has a three-part, bony fish–like jaw, though the creature looks a bit more like a typical placoderm, Ahlberg says. The two fossils “form almost perfect intermediates” between placoderms and bony fishes, he says. Ahlberg and his colleagues suspect the key jaw elements of bony fish (and all land vertebrates) evolved from those bony blades of placoderms.

“This is part of our own early evolutionary history,” Ahlberg says. “It shows where our own jaws came from.”

Maisey puts it another way: “We are all fundamentally placoderms.”

Chipmunks and other rodents’ light stripes are painted with a recycled brush, a new study suggests.

A protein previously known to guide facial development was repurposed at least twice during evolution to create light-colored stripes on rodents, researchers report November 2 in Nature. The protein, called ALX3, could be an important regulator of stripes in other mammals, including cats and raccoons, says Michael Levine, a developmental biologist at Princeton University who was not involved in the new study.
Some research has shown how butterflies and other insects create their often elaborate wing patterns (SN: 7/17/10, p. 28). But scientists still don’t understand the biological machinery used by mammals to generate the dots, spots, splotches and stripes that decorate their coats. Uncovering the molecular equipment may shed light on the evolutionary processes that help animals camouflage themselves and adapt to their environments.

In the new study, evolutionary developmental biologist Ricardo Mallarino of Harvard University and colleagues examined the multicolored stripes of African striped mice (Rhabdomys pumilio). Two light-colored stripes, each flanked by black stripes, run down the mice’s backs. A strip of fur the same brownish color as most of the rest of the body separates the dark-light-dark striping. The patterns are created by three types of hair: Hairs with banded yellow shafts growing from a black base populate the strip in the middle, while completely black hairs from base to tip are found in the black stripes. Hairs with a black base but no pigment in the shaft make up the light stripes.
Those unpigmented hairs were mysterious, says Hopi Hoekstra, the Harvard evolutionary biologist who led the new study. Usually, white hair arises because animals have a mutation that prevents cells from making pigments, she says. But since the African striped mice carry no such mutations, it was clear that the mice must create the stripes in a different way.
In vertebrates, pigment-producing cells called melanocytes migrate around the body as the embryo develops. One way stripes could form is by melanocytes moving to create the pattern. Previous research in zebrafish indicated that stripes on the fish’s sides form that way (SN: 2/22/14, p. 9). Light stripes might result if the melanocytes don’t migrate into a strip of the mice’s skin, the researchers reasoned. Hair would grow there, but wouldn’t have any pigment. That’s the first thing Mallarino checked. He examined white stripes in the skin of striped mouse embryos a couple of days before birth. Melanocytes had no trouble infiltrating the light striped area, he found. But once in the stripe, the cells did not mature properly and so made no pigment.

To find out what might be stopping melanocytes from producing pigment, the researchers examined gene activity in the different types of stripes in the mouse embryos. In the light stripes, the gene that produces ALX3 is much more active than it is in the brown or black stripes, the researchers discovered. That result was a surprise because no one knew that ALX3 is involved in pigmentation, Hoekstra says. It was known for helping to regulate the formation of bones and cartilage in the face.

It wasn’t clear whether the high levels of ALX3 caused the light stripes or not. So Hoekstra’s team did experiments in lab mouse cells to find out how the protein might affect pigmentation. Raising levels of ALX3 in cells interfered with activity of a gene called Mitf, a master regulator of pigment production and melanocyte maturation.

It turns out that even in lab mice more of the protein is made on the belly, which tends to be light colored. Previous pigmentation research failed to turn up ALX3 because researchers were working with white mice, Hoekstra says.
Eastern chipmunks (Tamias striatus), which last shared a common ancestor with African striped mice about 70 million years ago, also made more ALX3 in the light stripes on their flanks, the researchers found. The results suggest that different rodents independently recycled ALX3’s ability to make light-colored belly fur and used it to also paint light stripes on the back. Stripes may help rodents that are active during the day blend into the background and avoid the sharp eyes of predators, Hoekstra says.

Evolution tends to be thrifty, often reusing old genes for new purposes, says Nipam Patel, an evolutionary developmental biologist at the University of California, Berkeley. The new study is “a really nice illustration that evolution isn’t biased,” he says. “It takes what it gets and works with that.”

The researchers still don’t know why ALX3 gets turned up in the light stripes. Another protein may turn on its production, or rodents have found other ways to dial up ALX3 production in certain places. Researchers need to discover what turns on ALX3 to pinpoint the exact evolutionary change responsible for the striped pattern, Patel says.

There are few simple answers in science. Even seemingly straightforward questions, when probed by people in search of proof, lead to more questions. Those questions lead to nuances, layers of complexity and, more often than we might expect, conclusions that contradict initial intuition.

In the 1990s, researchers asking “How do we fight oxygen-hungry cancer cells?” offered an obvious solution: Starve them of oxygen by cutting off their blood supply. But as Laura Beil describes in “Deflating cancer”, oxygen deprivation actually drives cancer to grow and spread. Scientists have responded by seeking new strategies: Block the formation of collagen highways, for instance, or even, as Beil writes, give the cells “more blood, not less.”
In “DNA tests inflate species counts,” Tina Hesman Saey reports on the complications of classifying species. Genetic analyses alone, she writes, can detect too many differences, overestimating species numbers. Some tools appear to be, as Darwin would have put it, “hair-splitters” rather than “lumpers.” Identifying species is hard in part because “What is a species?” has no single answer. The notion of reproductive isolation, which splits species according to whether they can produce fertile offspring, has little meaning for asexual organisms, for instance. And isolation itself is a matter of degree. Accounting for speciation in progress is yet another challenge. At what point is a split declared official?

There are countless more examples. The question of what led to the dinosaurs’ demise was solved years ago, we thought. But remaining mysteries inspired a special report earlier this year (SN: 2/4/17, p. 16). And don’t even get me started on “How long does a neutron last?” in Emily Conover’s story “Neutron longevity remains elusive.”

In The Pursuit of Simplicity, physicist Edward Teller described science as a search for simplicity. If that’s the case, the quest is never-ending. With each new insight comes yearning for further insights. I cannot, at this moment, think of a single question that doesn’t demand more exploration. There are answers to be sure, and scientific truths, but for what line of questioning are all the details resolved? Where isn’t there a lingering “why” or “how”? (Think that I’m wrong? Send your ideas to editors@sciencenews.org.)

Wanting to know is innate. Children ask “Why is the sky blue?” or “Where do babies come from?” And parents struggle to answer at the right level of detail. Where does the question begin, and where does it end? What is the best angle of approach? As kids grow up, their questions become more specific, and the answers they receive more complex. Perhaps it’s the students who most appreciate complexity who decide to become scientists. They learn to use the tools of science, which uncovered the complexity in the first place, to try to tame it — diving in ever deeper. And so people end up studying dim and distant galaxies to understand “How did the universe evolve?”, and vats of microbes and methylmercury to ask “How will climate change affect food webs?”

Simplicity may be a gift, but I think complexity is much more interesting. It is one of the great joys of doing science — and of writing about it.

A hard look at experimental setups may start to explain dueling predictions on whether ocean acidification will boost, or choke, vital marine nitrogen fixers. So far, the new look trends toward choking.

As people release more and more carbon dioxide into the air, the ocean takes up the gas and edges closer toward acidity. In these shifting waters, marine microbes called Trichodesmium could falter in adding nitrogen, a critical input for marine food webs, says Dalin Shi of Xiamen University in China. And the problem could be exacerbated in acidifying seas where iron is scarce — for instance, in wide swaths of tropical and subtropical waters such as the southern Atlantic and Pacific oceans, Shi and colleagues report April 27 in Science.
The question of how Trichodesmium cyanobacteria are reacting to the changing ocean makes a big difference in predicting how other marine life, from whales to mere specks of floating plankton, will react, too. Nitrogen, essential to life for such basic processes as building DNA and proteins, makes up much of Earth’s atmosphere. Yet most living things can’t do any chemistry with the atmospheric form, two nitrogen atoms fiercely triple-bonded to each other. Trichodesmium microbes, however, can crack those bonds and transform nitrogen into more usable forms. These cyanobacteria may account for up to half of the nitrogen fixed in the ocean.

Lab research in the past 10 years generally suggested that increasing CO2 encouraged the photosynthetic Trichodesmium to grow more abundantly and supply more usable nitrogen. The rates varied, however. But when Shi and colleagues tried their version of the experiment, they found a decrease in nitrogen fixation, not an increase. “I was very excited, and I was really puzzled,” says Shi, who published the results in 2012.

After a string of detailed lab work, from culturing lab microbes to sampling wild cyanobacteria, he and colleagues propose an explanation for the contradictions. For one thing, much of the previous lab work used a recipe for artificial seawater that permitted contamination by toxic metals and forms of nitrogen, the researchers concluded. These unwanted additions introduced unexplained variety to the results.

Also, Shi and collaborators demonstrated that rising CO2 alone can stimulate the microbes’ growth but that the watery slide toward ocean acidity can depress the microbes’ ability to fix nitrogen. And if the cyanobacteria are growing in water short on iron, an essential nutrient for them, the slowdown in nitrogen fixation can overwhelm any positive growth effects from extra CO2.

The paper could be a big help in resolving the contradictions among experiments, says oceanographer Douglas Capone of the University of Southern California in Los Angeles.

Orly Levitan, an author of what may have been the first study of acidification boosting nitrogen fixation, says she would consider changing her seawater recipe based on the new paper if she were to revisit this work. Yet Levitan, who studies plankton at Rutgers University in New Brunswick, N.J., cautions against extrapolating too far. A look at wild Trichodesmium suggests that the cyanobacteria may have unexpected ways of compensating in iron-starved waters, enhancing the capture of minerals from dust settling out of the air, for instance. It’s too early, she says, to close discussion on what will happen in the complexities of the real ocean.

For black adults, moving out of a racially segregated neighborhood is linked to a drop in blood pressure, according to a new study. The finding adds to growing evidence of an association between a lack of resources in many predominately black neighborhoods and adverse health conditions among their residents, such as diabetes and obesity.

Systolic blood pressure — the pressure in blood vessels when the heart beats — of black adults who left their highly segregated communities decreased just over 1 millimeter of mercury on average, researchers report online May 15 in JAMA Internal Medicine. This decline, though small, could reduce the overall incidence of heart failure and coronary heart disease.
“It’s the social conditions, not the segregation itself, that’s driving the relationship between segregation and blood pressure,” says Thomas LaVeist, a medical sociologist at George Washington University in Washington, D.C., who was not involved with the study. “Maybe hypertension is not so much a matter of being genetically predisposed.” That’s important, LaVeist adds, because it means that racial health disparity “can be fixed. It’s not necessarily contained in our DNA; it’s contained in the social DNA.”

Racial segregation can impact a neighborhood’s school quality, employment opportunities or even whether there is a full-service grocery store nearby. Social policies that improve residents’ access to education, employment and fresh foods can “have spillover effects in health,” says Kiarri Kershaw, an epidemiologist at Northwestern University Feinberg School of Medicine in Chicago.

Kershaw and colleagues examined data from a study of how cardiovascular disease progresses in healthy adults, aged 18 to 30, who were recruited from four locations: Chicago, Minneapolis, Oakland, Calif., and Birmingham, Ala. The researchers specifically looked at blood pressure readings for 2,280 black participants, recorded at six points over 25 years, and noted their addresses at the time of each reading. A neighborhood’s designation of high, medium or low racial segregation was based on the percentage of black residents in the neighborhood compared with the larger metropolitan area or county, Kershaw says.

At the start of the study in the mid-1980s, 1,861 participants were living in highly segregated neighborhoods. A temporary move to a less segregated neighborhood, the researchers found, was associated with a 1 millimeter of mercury drop in blood pressure on average.

If the change of address was permanent — as it was for 243 participants — the impact was greater. On average, blood pressure dropped close to 6 millimeters of mercury for those who moved to low-segregation neighborhoods, and nearly 4 millimeters for a move to a medium-segregation neighborhood.
A 2015 study in the Journal of the American Heart Association estimates that a decrease in systolic blood pressure of 1 millimeter of mercury could result in several thousand fewer cases of heart failure, stroke and coronary heart disease annually in the U.S. population of black adults aged 45 to 64, Kershaw says.

Along with other research on racial segregation and health, the findings suggest that policies that improve housing conditions, educational resources and employment opportunities “will have implications for the health of individuals,” LaVeist says. “Social policy is health policy.”

If you could put Uranus’ moon Cressida in a gigantic tub of water, it would float.

Cressida is one of at least 27 moons that circle Uranus. Robert Chancia of the University of Idaho in Moscow and colleagues calculated Cressida’s density and mass using visible variations in an inner ring of Uranus as the planet passed in front of a distant star. The moon’s density is 0.86 grams per cubic centimeter and its mass is 2.5 x 1017 kilograms. These results, reported online August 28 at arXiv.org, are the first to reveal any details about the moon. Knowing its density and mass helps researchers determine if and when Cressida might collide with another of Uranus’ moons.

Voyager 2 discovered Cressida and several other moons when the spacecraft flew by Uranus in 1986. Those moons, plus two others found later, are the most tightly packed in the solar system and orbit within 20,000 kilometers of Uranus. Such close quarters puts the moons on collision courses. Based on the newly calculated mass and density of Cressida, simulations suggest that it will slam into the moon Desdemona in under a million years. Cressida’s density indicates it is made of mostly water ice. If the other moons have similar compositions, they may have lower than expected masses, which means this and other collisions may happen in the more distant future. Determining what the moons are made of may also reveal their post-collision fate: Will they merge, bounce off of each other or shatter?

The Cassini spacecraft has snapped its penultimate pics of Saturn’s moon Titan.

This image, shot September 11 as Cassini swung past the moon at a distance of about 119,049 kilometers, shows Titan’s lake region near its north pole. “The haze has cleared remarkably as the summer solstice has approached,” Cassini Project Scientist Linda Spilker said in a news conference September 13.

Cassini performed 127 close flybys of Titan over the course of its 13-year mission, and used the moon’s gravity to adjust its trajectory each time. Those gravity assists let the team create a full global map of Titan.

Future engineers will borrow that trick to explore Jupiter’s moon Europa with the Clipper mission, which is planned to launch in the 2020s. “Cassini pioneered that whole concept,” Jim Green, head of NASA’s planetary science division director, said at the news conference.

On this final pass, Titan’s gravity had one last job. It nudged Cassini on its final trajectory: making a beeline for Saturn. Tomorrow, the probe will spend its last full day in space snapping images of its greatest hits: Saturn and the rings, Titan, a small moon forming within the rings informally dubbed “Peggy,” the moon Enceladus, ring ripples called propellers and finally, the location of its own demise. The spacecraft will disintegrate above the gas giant’s cloud tops early in the morning of September 15.

The funniest thing I’ve ever said to any botanist was, “What is a species?” Well, it certainly got the most spontaneous laugh. I don’t think Barbara Ertter, who doesn’t remember the long-ago moment, was being mean. Her laugh was more of a “where do I even start” response to an almost impossible question.

At first glance, “species” is a basic vocabulary word schoolchildren can ace on a test by reciting something close to: a group of living things that create fertile offspring when mating with each other but not when mating with outsiders. Ask scientists who devote careers to designating those species, however, and there’s no typical answer. Scientists do not agree.

“You may be stirring up a hornet’s nest,” warns evolutionary zoologist Frank E. Zachos of Austria’s Natural History Museum Vienna when I ask my “what is a species” question. “People sometimes react very emotionally when it comes to species concepts.” He should know, having cataloged 32 of them in his 2016 overview, Species Concepts in Biology.

The widespread schoolroom definition above, known as the biological species concept, is No. 2 in his catalog, which he tactfully arranges in alphabetical order. This single concept has been so pervasive that whenever Science News publishes something about species interbreeding, readers want to know if we have lost our grip on logic. Separate species, by definition, can do no such thing.
As concerned readers question our reports of hybrid species, a vast debate among specialists over how to define and identify species rolls on. The biological species concept has drawbacks, to put it gently, for coping with much of the variety and oddness of life. Alternative concepts have pros and cons, too. As specialists argue over the fine details of species concepts, I’m struck by how often the word “fuzzy” comes up.

Also striking is how at least some of the people who actually appraise species for a living have made peace with the perpetual tumult over defining just what it is they get up in the morning to study. The ambiguities seemed less jarring to me after a September conversation with the Smithsonian’s Kevin de Queiroz, deep in the maze of doors and corridors behind the scenes at the National Museum of Natural History in Washington, D.C. As a systematic biologist, he studies the evolutionary histories of reptiles, and designates species, which explains a door we passed marked “Alcohol Room.” Fire regulations require special handling for jars of animal specimens preserved in alcohol. In the cacophony of species concepts, de Queiroz sees some commonality.

Ertter, affiliated with the University of California, Berkeley and the College of Idaho in Caldwell, embraces the ambiguity. “Why do we expect that nature is nice and neat and clean? Because it’s more convenient for us,” she says. “It’s up to us to figure it out, not to demand that it’s one way or another.”
Problems with the old standard
The biological species concept has an intuitive appeal. Elephants don’t mate with oak trees to produce really big acorns. Horses can mate with donkeys, but the resulting mules are infertile. The most famous form of this species definition may be from evolutionary biologist Ernst Mayr, who wrote in 1942: “Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.” Famous, yes, but limited.
Modern genetics has revealed that much of the diversity of life on Earth is found in single-celled organisms that reproduce asexually by splitting in two — thus flummoxing the definition. Of course the single-celled hordes still form … somethings. There isn’t just one vast smear of microbial life where all shapes, sizes, body features and chemistry can be found in any old mix. There are clusters with shared traits, some of which cause human and agricultural diseases and some of which photosynthesize in the ocean, producing as much as 70 percent of the oxygen that we and other living things breathe. Humans need to understand the history of microbes and have names to talk about these influential organisms.

Rather than deciding that these microbes are just not species, which is one popular view, microbiome researcher Seth Bordenstein suggests “just twisting the biological species concept ever so slightly.” Genes don’t shuffle around via sex, but there’s still kidnapping of genes from other asexuals. This process might count as something like interbreeding, says Bordenstein, of Vanderbilt University in Nashville. With that interpretation, the biological species concept “could apply to microbes.” Sort of.

But one-celled microbes aren’t the only asexuals. Even vertebrates have their no-sex scandals. New Mexico whiptail lizards are a species: Aspidoscelis neomexicanus. Yet females lay eggs with no male fertilization; males don’t exist.

And plant reproduction, oy. The blends of sex and no-sex don’t fit into a tidy biological species concept. Consider a new variety of a western North American species that Ertter and botanist Alexa DiNicola of the University of Wisconsin–Madison named this year. Potentilla versicolor var. darrachii belongs to a genus that’s closely related to strawberries. Plants in the genus open little five-petaled flowers and readily form classic seeds that mix genes from pollen and ovule. On occasion, though, the genes in the seed’s embryo are only mom’s. “They basically use seeds as a form of cloning,” Ertter says. The male pollen in these cases merely jump-starts formation of the seed’s food supply.

That’s just one reason Potentilla is “one of the messiest genera you can imagine,” Ertter says. She and DiNicola hauled collectors’ gear on a backpacking trip in Oregon to sample some of the plants. The team found signs that one species was hybridizing readily with another; the species were so different that even a nonbotanist could tell them apart (leaves shaped like a feather versus an open fan). Sharing genes across species is evidently common in this genus and not at all rare among plants.

Such shenanigans have led Ertter to what she calls the “fuzzy species concept.” After looking at all the kinds of evidence she might muster for a plant, from its genes and distribution to the details of petals, leaf hairs and other parts, she sides with the preponderance of data to designate a species.

Concept zoo
There can be a lot of messiness in picking out the limits of species, but that’s OK with philosopher Matt Haber of the University of Utah in Salt Lake City. He organized three conferences this year on the complications of determining what’s a species when fire hoses of genetic information spew signs of unexpected gene mixing and tell different stories depending on the genes tracked.

“Just because boundaries are fuzzy,” Haber says, “doesn’t mean they aren’t actually boundaries.” We may not be used to thinking about species distinctions this way, but other familiar distinctions have similar “gradient boundaries,” as he calls them. “Cold and hot weather,” he says. We recognize winter weather as different from summer even though fall and spring have neither a sharp switch point nor a smooth slide. Species, too, could have zones of erratic mixing but still overall be defined as species.

There are a whole lot of species concepts, says Richard Richards, a philosopher of biology at the University of Alabama in Tuscaloosa. “We use different rules for different kinds of organisms,” he says. “For vertebrates, the interbreeding rule is useful. Not so for the many kinds of nonsexually reproducing organisms out there.”

What’s called the agamospecies concept applies to asexual organisms and cobbles together genetic or other observable similarities. The ecological species concept emphasizes adaptations to particular environmental zones. The nothospecies concept applies to plants arising when parent species hybridize. And so on. That’s not even counting “the cynical species concept,” which Zachos has heard defining a species as “whatever a taxonomist says it is.”

Land and money
Species definitions can have ramifications, financial and otherwise, for the wider world. Choosing one species concept over another can change how a creature gets classified, which could determine whether conservation laws protect it. The coastal California gnatcatcher’s status as a distinct subspecies makes it eligible for federal protection to keep the bird’s shrub-land as habitat rather than a real estate development. Critics have argued, however, that the bird isn’t distinct enough from its relatives to merit special protection.

Mammal specialists are switching over to what’s called a phylogenetic concept, Zachos says. The phylogenetic concept allows populations to upgrade to full species status if they share an ancestor and have some unique trait, such as a particular gene. Among the complex consequences of following this concept is possible “taxonomic inflation,” he warns. A 2011 rethink of the ungulate group of sheep, goats, antelope and more ballooned the species count from 143 to 279, for instance. In biology as in economics, “inflation causes devaluation,” Zachos says. “People get bored. If one of the tiger species goes extinct, they say, ‘So what? There are five more.’ ”

As individual taxonomists choose their pet concepts, “ ‘species’ are often created or dismissed arbitrarily,” argued two researchers from Australia in the June 1 Nature. The duo warned of potential “anarchy” and went as far as calling for an international organization to reduce the chaos.

“A long list of silly examples of complications caused by poor taxonomic governance” pushed conservation biologist Stephen Garnett of Charles Darwin University in Darwin to cowrite the piece. Standardizing species concepts across broad groups, mammals and reptiles, for instance, would reduce the chaos, says coauthor Leslie Christidis, a taxonomist at Southern Cross University in Coffs Harbour. The notion of standard-setting in determining species has stirred a bit of agreement and a lot of dissent. “We united the taxonomic community — unfortunately against us,” he says.

The furor illustrates the diversity of ways that people are sorting out what a species is among life’s various organisms. Historian and philosopher of biology John S. Wilkins of the University of Melbourne in Australia was almost kidding when he wrote that there are “n+1 definitions of ‘species’ in a room of n biologists.”
The commons
Thinking about the seemingly intractable ambiguities of the species concepts got a lot easier for me after my visit with de Queiroz. His office was the opposite of the Hollywood biologist’s jumble of dessicated specimens, dangling skeletons and tottering towers of books. The long room was mostly filled with rows of librarian-tidy metal bookcases hiding a desk cave at the far end. When I asked him what a species is, he didn’t laugh. He explained that there’s more agreement than the swarm of species concepts might suggest.

The concepts have in common their references to organisms in a population lineage, or line of descent. As evolutionary time passes, a lineage moves away and its various connected populations grow separate from others of the same ancestry. The concepts share the basic idea that a species is a “separately evolving metapopulation lineage,” he says.

To identify those lineages in practice, however, requires finding evidence of interbreeding or patterns of shared traits. Adding such criteria to the concepts is what creates the crazy diversity. Defining the term species is “not the problem,” he says. “The problem is in identifying a species.”

He calls up a map on his computer from a recent paper a former lab member published on fringe-toed lizards. Colored blobs float over dark lines of a map of the western United States. Three blobs are clearly designated species based on multiple lines of evidence. Three lizard patches, however, are perplexing. Various ways of testing these lizard populations lead to contradictory results.

No matter how badly we want the process of applying a species definition to be clear-cut for all creatures in all cases, “it just isn’t,” de Queiroz says. And that’s exactly what evolutionary biology predicts. Evolution is an ongoing process, with lineages splitting or rejoining at their own pace. Exploring a living, ever-evolving world of life means finding and accepting fuzziness.