December 11, 2013
It’s long been known that carnivorous plants lure their insect prey in a range of ways: irresistible nectars, vivid colors and alluring scents that range from rose to rotten flesh.
But recently, a group of scientists at the Jawaharlal Nehru Tropical Botanic Garden and Research Institute in India discovered a previously hidden means of beckoning among the most ruthless of greenery. Some carnivorous plants, they discovered, lure insects to their death with a fluorescent glow invisible to the human eye.
Scientists believe that insects are attracted to carnivorous plants by the their odors and colors, but hard evidence as to what exactly lures the bugs to their deaths was previously unknown. In a stroke of serendipity, a team of scientists led by botanist Sabulal Baby put several carnivorous plants they’d been using for unrelated experiments under ultraviolet light, including Nepenthes khasiana, a rare pitcher plant native to India, and photographed what they saw.
“To our great surprise, we found a blue ring on on the pitcher rim,” Baby says. “Then, we looked at other Nepenthes species and the prey traps of other carnivorous plants, including the Venus flytrap, and we consistently found UV-induced blue emissions.” These colors, found in a total of twenty carnivorous plant species and documented in a study published in Plant Biology, were the first time such distinct fluorescent emissions were ever detected in the plant kingdom.
Under normal light, these bright, glowing rims would look green to humans. But an ant—which can’t see red, but is extremely sensitive to blue and violet light—would see rings of blue florescence, the result of metabolic compounds in the plant that absorb UV radiation from the Sun and re-emit it as visible light. Putting the plants under a UV light in an otherwise dark room, as Baby’s team did, amplifies the effect, allowing humans to more clearly see the blue emissions.
To prove that these emissions were involved in the plants’ predation, the scientists constructed an elegant experiment. They monitored live pitcher plants in the field for a ten-day period, cutting them open afterward and seeing how many ants each one caught. Some of the plants, though, were painted with an acetone extract that blocks fluorescent emissions. It’s not clear exactly why the ants would be attracted to the blue light, but the results, produced several times and in several different locations, pretty clearly indicate that it’s the case:
He has yet to test the idea, but Baby says that the plants might use their fluorescence for other purposes as well. Recent field studies in Borneo indicated that some species of pitchers may have a symbiotic relationship with small nocturnal mammals, such as rats, bats and tree shrews—these mammals come and drink nectar from the plants, and deposit nutritious feces nearby, which serve as a fertilizer. “Fluorescence emissions by Nepenthes traps could be acting as major visual cues luring these mammals towards them,” Baby says.
These sorts of normally invisible signals could be way more prevalent in the plant kingdom than we previously realized. A recent study by British scientists, for instance, revealed that bumblebees can detect electric fields produced by flowers, adding another layer of communication to the symbiotic relationship between these two types of organisms. “There could be many other forms of signaling out there, waiting to be found,” Baby says.
December 9, 2013
Shortly after NASA’s Curiosity rover landed on Mars in August 2012, the scientists guiding the device decided to make a temporary detour before heading to the mission’s ultimate destination, Mount Sharp. Last spring, they guided the six-wheeled machine towards Yellowknife Bay, a slight depression with intriguingly lighter-toned sedimentary rocks, and drilled its first two holes in Martian rock in order to collect samples.
Afterward, as Curiosity drove away from Yellowknife Bay, onboard equipment ground the rock samples to a fine dust and chemically analyzed their content in extreme detail to learn as much as possible about the site. Today, the results of that analysis were finally published in a series of articles in Science, and it’s safe to say that the scientists probably don’t regret making that brief detour. Yellowknife Bay, they discovered, was likely once home to a calm freshwater lake that lasted for tens of thousands of years, and theoretically had all the right ingredients to sustain microbial life.
“This is a huge positive step for the exploration of Mars,” said Sanjeev Gupta, an Earth scientist at Imperial College London and a member of the Curiosity team, in a press statement on the discovery. “It is exciting to think that billions of years ago, ancient microbial life may have existed in the lake’s calm waters, converting a rich array of elements into energy.”
Previously, Curiosity found ancient evidence of flowing water and an unusual type of rock that likely formed near water, but this is the strongest evidence so far that Mars may have once sustained life. The chemical analysis of the two rocks (named “John Klein” and “Cumberland”) showed that they were mudstones, a type of fine-grained sedimentary rock that generally forms at the bottom of a calm body of water, as small sediment particles gradually settle on one another and are eventually cemented together.
Isotope analysis indicated that these rocks formed sometime between 4.5 and 3.6 billion years ago, either during Mars’ Noachian period (in which the planet was likely much warmer, had a thicker atmosphere and may have had abundant surface water) or early on in its Hesperian period (in which it shifted to the dry, colder planet we see currently).
Additionally, a number of key elements for the establishment of life on Earth—including carbon, hydrogen, oxygen, sulfur, nitrogen and phosphorous—were found in detectable quantities in the rocks, and chemical analysis indicated that the water was likely of a relatively neutral pH and low in salt content. All of these discoveries increase the chance that the ancient lake could have served as a habitat for living organisms.
The scientists hypothesize that the microorganisms most likely to live in this environment would have been chemolithoautotrophs, a type of microbe that derives energy by breaking down rocks and incorporates carbon dioxide from the air. On Earth, these types of organisms are most often found near hydrothermal vents on the ocean floor, where they thrive off chemicals emitted into the water.
Obviously, this isn’t direct proof of life, but rather circumstantial evidence that it may have once existed. Still, it’s yet another vindication of Curiosity’s mission, which is to determine the planet’s habitability. Over the coming months and years, the scientists guiding the rover plan to keep sampling sedimentary rocks on the planet’s surface, hoping to find further evidence of potentially-habitable ancient environments and perhaps even direct evidence of now-extinct living organisms.
For more, head over to NASA’s webcast of the press conference announcing the findings, which occurred today at noon EST.
December 4, 2013
Since its discovery in 1990, La Sima de los Huesos, an underground cave in Northern Spain’s Atapuerca Mountains, has yielded more than 6,000 fossils from 28 individual ancient human ancestors, making it Europe’s most significant site for the study of ancient humans. But despite years of analysis, the exact age and even the species to which these individuals belonged has been in doubt.
Now, though, an international group of scientists has extracted and sequenced DNA from the fossilized femur of one of these individuals for the first time. The resulting data—which represent the oldest genetic material ever sequenced from a hominin, or ancient human ancestor—finally give us an idea of the age and lineage of these mysterious individuals, and it’s not what many scientists expected.
The fossilized bone tested, a femur, is roughly 400,000 years old. But the big surprise is that, although scientists had previously believed the fossils belonged to Neanderthals because of their anatomical appearance, the DNA analysis actually shows they’re more closely related to Denisovans, a recently-discovered third lineage of human ancestors known only from DNA isolated from a few fossils found in Siberia in 2010. The findings, published today in Nature, will force anthropologists to further reconsider how the Denisovans, Neanderthals and the direct ancestors of modern-day humans fit together in a complicated family tree.
The analysis was enabled by recent advances in methods for recovering ancient DNA fragments developed at the Max Planck Institute for Evolutionary Anthropology in Germany, previously used to analyze the DNA of a cave bear fossil found in the same cave. “This wouldn’t have been possible just two years ago,” says Juan Luis Arsuaga, a paleontologist at the University of Madrid who led the initial excavations of the cave and collaborated on the new study. “And even given these new methods, we still didn’t expect these bones to preserve DNA, because they’re so old—ten times older than some of the oldest Neanderthals from whom we’ve taken DNA.”
After extracting a two grams of crushed bone from the femur, a group of scientists led by Matthias Meyer isolated the mitochondrial DNA (mtDNA), a pool of genetic material that’s distinct from the DNA in the chromosomes located in our cells’ nuclei. Instead, this mtDNA lives in our cells’ mitochondria—microscopic organelles responsible for cellular respiration—and is much shorter in length than nuclear DNA.
There’s another quirk of mtDNA that makes it especially valuable as a means of studying the evolution of ancient humans: Unlike your nuclear DNA, which is a mix of DNA from both your parents, your mtDNA comes solely from your mother, because most of a sperm’s mitochondria are found in its tail, which it sheds after fertilization. As a result, mtDNA is nearly identical from generation to generation, and a limited number of distinct sequences of mtDNA (called haplogroups) have been observed in both modern humans and ancient human ancestors. Unlike anatomical characteristics and nuclear DNA, which can vary within a group and make it difficult to confidently distinguish one from another, mtDNA is generally consistent, making it easier to link a particular specimen with a lineage.
Which is why, when the researchers compared the femur’s mtDNA to previously sequenced samples from Neanderthals, from a Denisovan finger bone and tooth found in Siberia and from many different modern humans, they found it so surprising that it more closely resembled the Denisovans. “This was really unexpected,” Arsuaga says. “We had to think really hard to come up with a few scenarios that could potentially explain this.”
Anthropologists had already known that all three lineages (humans, Neanderthals and Denisovans) shared a common ancestor, but it’s far from clear how all three groups fit together, and the picture is further clouded by the fact that interbreeding may have occurred between them after they diverged. Helpfully, comparing the femur’s mtDNA to the Neanderthal, Denisovan and modern human samples allowed the researchers to estimate its age—based upon known rates of mtDNA mutation, the previously established ages of the other samples, and the degree of difference between them—leading to the 400,000 year figure.
To explain how a Neanderthal-looking individual could come to have Denisovan mtDNA during this time period, the scientists present several different hypothetical scenarios. It’s possible, for instance, that the fossil in question belongs to a lineage that served as ancestors of both Neanderthals and Denisovans, or more likely, one that came after the split between the two groups (estimated to be around 1 million years ago) and was closely related to the latter but not the former. It’s also a possibility that the femur belongs to a third, different group, and that its similarities to Denisovan mtDNA are explained by either interbreeding with the Denisovans or the existence of yet another hominin lineage that bred with both Denisovans and the La Sima de los Huesos population and introduced the same mtDNA to both groups.
If this sounds like a complicated family tree to you, you’re not alone. This analysis, along with earlier work, adds further mystery to an already puzzling situation. Initial testing on the Denisovan finger bone found in Siberia, for instance, found that it shared mtDNA with modern humans living in New Guinea, but nowhere else. Meanwhile, it was previously thought that Neanderthals had settled in Europe and Denisovans further east, on the other side of the Ural Mountains. The new analysis complicates that idea.
For now, the researchers believe the most plausible scenario (illustrated below) is the femur belongs to a lineage that split off from Denisovans sometime after they diverged from the common ancestor of both Neanderthals and modern humans. But perhaps the most exciting conclusion to come out of this work is that it proves that genetic material can survive for at least 400,000 years, and can be analyzed even after that amount of degradation. Armed with this knowledge and the new techniques, anthropologists can now attempt to genetically survey many other ancient specimens in hopes of better understanding our family tree.
December 3, 2013
Scientific equipment that’s left unattended in the field can provide all sorts of interesting information. It can, for instance, snap photographs of exotic and shy wild animals, or analyze the noises coming from an ecosystem to identify the species living there.
But often, leaving valuable instruments scattered outside risks interference or destruction from an unavoidable force of nature: humans. Data isn’t regularly collected or published on the topic, but it’s well known among field scientists that leaving equipment in highly-trafficked areas leaves it vulnerable to petty vandalism and theft.
This unfortunate trend was recently on the mind of Holger Goerlitz, a scientist at Germany’s Max Planck Institute for Ornithology who studies animal behavior (specifically, how bats use echolocation within their environment) and leaves his field equipment unattended to do so. “As part of a project, I wanted to deploy automated equipment that would sit in the field for several nights,” he says. “So my colleagues and I were concerned about how to protect this equipment. We considered using chains and video cameras. And then suddenly we had this random idea: Let’s see what would be a good label to attach to the equipment to reduce vandalism.”
His team’s results, based on 60 pieces of fake scientific equipment scattered in four different Munich parks and published last week in Methods in Ecology and Evolution, may surprise you. They found that friendly labels that gave information about the project and the researcher led to about 40 percent fewer instances of equipment interference—either theft, vandalism or park visitors simply moving or trying to open up the equipment—as compared to neutral labels or ones that threatened surveillance and punishment.
They found this out by distributing boxes that looked vaguely like scientific instruments (above)—basically, plastic boxes with car antennas and fake cameras attached—for one week in each park, right next to a footpath, and checking for interference with the objects daily. All of the boxes had a similar warning label identifying it as properly of the Planck Institute and giving Goerlitz’ contact information, but the tone of the messages differed slightly.
A third of the boxes had neutral messages (translated to English, they read “Part of an experiment—Please do not touch”), while another third had threatening warnings (“‘Part of an experiment—Every theft will be reported to the police! GPS monitored!”) and the remaining third had a friendly, personalized note (“Part of my thesis–Please do not touch–Please call me if you have any questions and would like to know more.”) The friendly label also had a picture of a juvenile squirrel, to give passersby an idea of the researcher’s work:
The researchers checked the boxes daily, and had even placed pebbles inside so they could determine if the boxes had been picked up and moved. They also counted how many were pried open, vandalized or stolen.
Apparently, at least in these German city parks, the impulse to steal or vandalize is one that can be dislodged by just a bit of information about the potential victim, presented in a friendly way. Simply knowing that the device was important to one particular researcher—likely a student, given the word “thesis”—led visitors to interfere with the equipment about half as frequently. Over the course of a month, 39 instances of interference occurred with a box with a friendly label, compared to 59 with a neutral label and 67 with a threatening label.
Although the researchers were heartened by the finding, they were surprised, especially due to the fact that the threatening labels were the least successful. They imagine that the friendly label worked primarily by establishing the personal connection, perhaps aided by the squirrel photo, but the threatening label’s ineffectiveness is a mystery. “We don’t know why this was the case,” Goerlitz says. “It could be that people didn’t believe the threatening label, or that they thought, ‘oh, there’s a GPS device inside, this could be valuable.’” The fact that it was the only label that included the word “theft” might indicate that simply implanting the idea in people’s minds influenced them to engage in it.
But, although there’s obviously a lot more work to be done—this was conducted with a small sample of people over a short time period in one particular German city—this finding about friendly labels is a positive and potentially helpful one. If presented with the chance, people can be influenced to help science succeed if they’re treated in a respectful way and informed about what’s going on. Despite the enormous amount of money spent annually on scientific equipment, very little research has actually been done in this area to date, and more work to see how this might apply to people in different cultures, for instance, may aid scientists around the world in their efforts to protect their surveying instruments.
Goerlitz, for one, is ready to start using this finding to better safeguard his own equipment that monitors bat echolocation. “In my labels, I’ll try to be informative and friendly to people,” he says. “I think if you expose people to what you’re doing, they’ll be much more supportive of it.”
December 2, 2013
It’s a platitude that we’ve all heard dozens of times, whether to justify our treatment of other species or simply to celebrate a carnivorous lifestyle: humans are the top of the food chain.
Ecologists, though, have a statistical way of calculating a species’ trophic level—its level, or rank, in a food chain. And interestingly enough, no one ever tried to rigorously apply this method to see exactly where humans fall.
Until, that is, a group of French researchers recently decided to use food supply data from the U.N Food and Agricultural Organization (FAO) to calculate human tropic level (HTL) for the first time. Their findings, published today in the Proceedings of the Natural Academy of Sciences, might be a bit deflating for anyone who’s taken pride in occupying the top position.
On a scale of 1 to 5, with 1 being the score of a primary producer (a plant) and 5 being a pure apex predator (a animal that only eats meat and has few or no predators of its own, like a tiger, crocodile or boa constrictor), they found that based on diet, humans score a 2.21—roughly equal to an anchovy or pig. Their findings confirm common sense: We’re omnivores, eating a mix of plants and animals, rather than top-level predators that only consume meat.
To be clear, this doesn’t imply that we’re middle-level in that we routinely get eaten by higher-level predators—in modern society, at least, that isn’t a common concern—but that to be truly at the “top of the food chain,” in scientific terms, you have to strictly consume the meat of animals that are predators themselves. Obviously, as frequent consumers of rice, salad, bread, broccoli and cranberry sauce, among other plant products, we don’t fit that description.
The researchers, led by Sylvain Bonhommeau of the French Research Institute for Exploitation of the Sea, used FAO data to construct models of peoples’ diets in different countries over time, and used this to calculate HTL in 176 countries from 1961 to 2009. Calculating HTL is fairly straightforward: If a person diet is made up of half plant products and half meat, his or her trophic level will be 2.5. More meat, and the score increases; more plants, and it decreases.
With the FAO data, they found that while the worldwide HTL is 2.21, this varies widely: The country with the lowest score (Burundi) was 2.04, representing a diet that was 96.7 percent plant-based, while the country with the highest (Iceland) was 2.54, reflecting a diet that contained slightly more meats than plants.
On the whole, since 1961, our species’ overall HTL has increased just slightly—from 2.15 to 2.21—but this averaged number obscures several important regional trends.
A group of 30 developing nations in Southeast Asia and Sub-Saharan Africa (shown in red)—including Indonesia, Bangladesh and Nigeria, for example—have had HTLs below 2.1 during the entire period. But a second group of developing countries that includes India and China (shown in blue) has slightly higher HTL measures that have consistently risen over time, going from around 2.18 to over 2.2. The HTLs of a third group, shown in green (including Brazil, Chile, South Africa and several countries in Southern Europe), have risen further, from around 2.28 to 2.33.
By contrast, HTL in the world’s wealthiest countries (shown in purple)—including those in North America, Northern Europe and Australia—was extremely high for most of the study period but decreased slightly starting during the 1990s, going from around 2.42 to 2.4. A fifth group of small, mostly island countries with limited access to agricultural products (shown in yellow, including Iceland and Mauritania) has seen more dramatic declines, from over 2.6 to less than 2.5.
These trends closely correlate, it turns out, with a number of World Bank development indicators, such as gross domestic product, urbanization and education level. The basic trend, in other words, is that as people become wealthier, they eat more meat and fewer vegetable products.
That has translated to massive increases in meat consumption in many developing countries, including China, India, Brazil and South Africa. It also explains why meat consumption has leveled off in the world’s richest countries, as gains in wealth leveled off as well. Interestingly, these trends in meat consumption also correlate with observed and projected trends in trash production—data indicate that more wealth means more meat consumption and more garbage.
But the environmental impacts of eating meat go far beyond the trash thrown away afterward. Because of the quantities of water used, the greenhouse gases emitted and the pollution generated during the meat production process, it’s not a big leap to speculate that the transition of huge proportions of the world’s population from a plant-based diet to a meat-centric one could have dire consequences for the environment.
Unfortunately, like the garbage problem, the meat problem doesn’t hint at an obvious solution. Billions of people getting wealthier and having more choice over the diet they eat, on a basic level, is a good thing. In an ideal world, we’d figure out ways to make that transition less damaging while still feeding huge populations. For example, some researchers have advocated for offbeat food sources like meal worms as a sustainable meat, while others are trying to develop lab-grown cultured meat as an environmentally-friendly alternative. Meanwhile, some in Sweden are proposing a tax on meat to curb its environmental cost while government officials in the UK are urging consumers to cut back on their demand for meat to increase global food security and to improve health. Time will tell which approaches stick.
In the meantime, simply keeping track of the amount of meat we’re eating as a society via HTL could provide a host of useful baseline information. As the authors write, “HTL can be used by educators to illustrate the ecological position of humans in the food web, by policy makers to monitor the nutrition transition at global and national scales and to analyze the effects of development on dietary trends, and by resource managers to assess the impacts of human diets on resource use.”
In other words, monitoring the intricacies of our middling position on the food chain may yield scientific fodder to tackle problems like food security, obesity, malnutrition and environmental costs of the agricultural industry. A heavy caseload for a number that ranks us on the same trophic level as anchovies.