The only lemurs so dependent on bamboo that they gnaw on hardened, nutrient-poor stems during the dry season might dwindle away as those seasons grow longer.
Reconstructing the history of the greater bamboo lemur (Prolemur simus) in Madagascar suggests that drier areas over thousands of years already have lost their populations. As the region dries further due to climate change and the bad-bamboo months in the last holdouts lengthen, remaining populations of these critically endangered lemurs might go hungry and fade away too, an international research team warns online October 26 in Current Biology.
Other animals, even another lemur species, will eat lots of bamboo shoots and leaves. But the greater bamboo lemur is the only mammal besides the giant panda that sticks with bamboo during the dry season. That’s when the plants stop sprouting and offer only culm, the tough, old, yellowing stems poor in nutrients. Culm hasn’t reached the hard stage of bamboo that’s used as a building material. “Nobody wants to eat that,” says study coauthor Alistair Evans, an evolutionary morphologist at Monash University in Melbourne, Australia.
This lemur species with its extreme diet had already been feared extinct once, around the middle of the last century, but relic populations turned up. Current survivors remain more toward the eastern part of the island, where dry seasons are apparently survivable, at least for now.
In a big step toward catching up with the rest of the world, the United States cleared the way for using mosquitoes as a commercial pest control for the first time.
The U.S. Environmental Protection Agency has approved using a strain of male Asian tiger mosquitoes (Aedes albopictus) as a biopesticide in the District of Columbia and 20 states, including California and New York. Kentucky-based MosquitoMate was granted the right to sell these mosquitoes, called ZAP Males, for the next five years, the agency announced November 7. These male mosquitoes are not genetically modified. Instead they carry a strain of Wolbachia bacteria that turns them into saboteur dads. When they mate with wild females not carrying the strain, the offspring will die and the population should dwindle. Males don’t bite, so releasing them should not add extra vexation.
Releases of Wolbachia-bearing mosquitoes for pest control already go on in other countries, such as Brazil, although with a different bacterial strain and a different strategy.
This same company has also been testing the effectiveness of a different mosquito species, Aedes aegypti, also carrying bad-dad Wolbachia, near Key West, Fla. (These mosquitoes are not commercially available.) The tests “ended a bit early due to [Hurricane] Irma,” says Stephen Dobson of MosquitoMate, “but we think that we have some good data despite this complication.”
The human brain is teeming with diversity. By plucking out delicate, live tissue during neurosurgery and then studying the resident cells, researchers have revealed a partial cast of neural characters that give rise to our thoughts, dreams and memories.
So far, researchers with the Allen Institute for Brain Science in Seattle have described the intricate shapes and electrical properties of about 100 nerve cells, or neurons, taken from the brains of 36 patients as they underwent surgery for conditions such as brain tumors or epilepsy. To reach the right spot, surgeons had to remove a small hunk of brain tissue, which is usually discarded as medical waste. In this case, the brain tissue was promptly packed up and sent — alive — to the researchers. Once there, the human tissue was kept on life support for several days as researchers analyzed the cells’ shape and function. Some neurons underwent detailed microscopy, which revealed intricate branching structures and a wide array of shapes. The cells also underwent tiny zaps of electricity, which allowed researchers to see how the neurons might have communicated with other nerve cells in the brain. The Allen Institute released the first publicly available database of these neurons on October 25.
A neuron called a pyramidal cell, for instance, has a bushy branch of dendrites (orange in 3-D computer reconstruction, above) reaching up from its cell body (white circle). Those dendrites collect signals from other neural neighbors. Other dendrites (red) branch out below. The cell’s axon (blue) sends signals to other cells that spur them to action. Like the chandelier cell, a Martinotti cell (below) quiets other cells with messages coming from its tangled, tall axon, which spans several layers of the brain’s cortex — the wrinkly, outer layer that’s involved in higher-level thought. And in a basket cell (above), axon branches, which allow the nerve cell to send messages to other neurons, cluster densely around the cell body. Because the neurons play different roles in the brain, the new collection could help researchers figure out the details of those diverse jobs. Similar data exist for cells taken from the brains of other animals, such as mice, but until now, data on live cells from people have been scarce.
“These neurons are amazingly beautiful,” says Ed Lein, a neuroscientist at the Allen Institute who works on the project. “They look like trees. They’re much more complex than similar cells in a mouse.”
When escaping from humans, narwhals don’t just freeze or flee. They do both.
These deep-diving marine mammals have similar physiological responses to those of an animal frozen in fear: Their heart rate, breathing and metabolism slow, mimicking a “deer in the headlights” reaction. But narwhals (Monodon monoceros) take this freeze response to extremes. The animals decrease their heart rate to as slow as three beats per minute for more than 10 minutes, while pumping their tails as much as 25 strokes per minute during an escape dive, an international team of researchers reports in the Dec. 8 Science. “That was astounding to us because there are other marine mammals that can have heart rates that low but not typically for that long a period of time, and especially not while they’re swimming as hard as they can,” says Terrie Williams, a biologist at the University of California, Santa Cruz. So far, this costly escape has been observed only after a prolonged interaction with humans.
Usually, narwhals will escape natural predators such as killer whales by stealthily slipping under ice sheets or huddling in spots too shallow for their pursuers, Williams says. But interactions with humans — something that will happen increasingly as melting sea ice opens up the Arctic — may be changing that calculus. “When narwhals detect humans, they often dive quickly and disappear from sight,” says Kristin Laidre, an ecologist at the University of Washington in Seattle who studies marine mammals in the Arctic. Williams and her colleagues partnered with indigenous hunters in East Greenland to capture narwhals in nets. Then, the researchers stuck monitoring equipment to the narwhals’ backs with suction cups and released the creatures. The team tracked the tail stroke rate and cardiovascular response of the narwhals after their release, and determined how much energy the animals used during their deep escape dives.
During normal dives, narwhals reduce their heart rate to about 10 to 20 beats per minute to conserve oxygen while spending prolonged time underwater. These regular deep dives to forage for food don’t require rigorous exercise. But during escape dives after being entangled in a net for an hour or longer, “the heart rates were going down to levels of three and four beats per minute, and being maintained at that level for 10 minutes at a time,” Williams says.
The narwhals were observed making multiple dives to depths of 45 to 473 meters in the hours following escape. When fleeing, the tusked animals expended about three to six times as much energy as they normally burn while resting. The authors calculated that the frantic getaway, combined with what they called “cardiac freeze,” severely and rapidly depletes the narwhals’ available oxygen in their lungs, blood and muscles — using 97 percent of the creatures’ oxygen stores compared with 52 percent on normal dives of similar depth and duration.
“There is a concern from our group that this is just pushing the biology of these animals beyond what they can do,” Williams says. As human activity increases in the Arctic, there may be more chance of inciting this potentially harmful escape response in narwhals.
The creatures may also become more vulnerable to other human-caused disturbances, such as seismic exploration, hunting and noise from large vessels and fishing boats. The researchers plan to investigate whether these activities cause the same flee-and-freeze reaction, and whether this extreme response affects narwhals’ long-term health.
This study “provides a new physiological angle on the vulnerability of narwhals to anthropogenic disturbance, which is likely to increase in the Arctic with sea ice loss,” Laidre says. Better understanding the human impacts on narwhals is essential for conservation of this species, she adds.
Discoveries of planets around distant stars have become almost routine. But finding seven exoplanets in one go is something special. In February, a team of planet seekers announced that a small, cool star some 39 light-years away, TRAPPIST-1, hosts the most Earth-sized exoplanets yet found in one place: seven roughly Earth-sized worlds, at least three of which might host liquid water (SN: 3/18/17, p. 6).
These worlds instantly became top priorities in the search for life outside the solar system. “TRAPPIST-1 is on everybody’s wish list,” says exoplanet astronomer Lisa Kaltenegger of Cornell University. But the planets and their dim star have also stoked a raging debate about what makes a planet habitable in the first place. Astrophysicist Michaël Gillon of the University of Liège in Belgium and colleagues found the family of worlds orbiting the ultracool dwarf star, dubbed TRAPPIST-1 for the small telescope in Chile used to discover its planets.
“I don’t think the cachet of that system is going away anytime soon,” says exoplanet expert Sara Seager of MIT.
The TRAPPIST telescope team first announced in May 2016 that the star had three temperate, rocky planets. Staring at the system with the Spitzer Space Telescope for almost three weeks straight revealed that the third planet was actually four more — all Earth-sized, and three of them are in the star’s habitable zone, the region where temperatures are right for liquid water on a planet’s surface. A seventh planet was caught crossing the star as well, though follow-up observations showed it is too cold for life as we know it (SN: 6/24/17, p. 18). Similar but different Planets orbiting the star TRAPPIST-1 are a lot alike in some ways and distinct in others. The slideshow below shows each planet’s specs, including how long it takes to orbit the dwarf star, distance from the star (in astronomical units), and radius and mass relative to Earth. The number of worlds alone makes the TRAPPIST-1 system a good spot to look for life. An alien observing our solar system would think Venus, Earth and Mars all fall in the habitable zone. But only one is inhabited. The fact that TRAPPIST-1 has so many options increases the odds that the system hosts life, Seager says.
As an ultracool dwarf, TRAPPIST-1 rides the edge of what counts as a star. Such stars burn through their nuclear fuel so slowly that they can live for many billions of years, which gives any life on their planets a long time to grow and evolve. This star’s habitable zone is also incredibly close in, offering astronomers many chances to observe the planets orbiting their star.
The three planets in the habitable zone cross in front of the star every 6.10, 9.21 and 12.35 days. If two or more turn out to be habitable, then they could share life among them, either by tossing meteorites back and forth or — in the case of spacefaring civilizations — by deliberate space travel. Future space-based observatories will be able to see starlight filtering through the planets’ atmospheres, if the planets have atmospheres. Gillon and colleagues are looking for signs of escaping hydrogen, a signal that an atmosphere might be there. “We’re already preparing,” he says.
But ultracool dwarfs are also ill-tempered. They tend to emit frequent, powerful stellar flares, which could rip away a planet’s atmosphere, threatening any potential for life. The planet-hunting Kepler space telescope recently watched TRAPPIST-1 for 80 days and saw it flare 42 times. One of those flares was as strong as Earth’s 1859 Carrington Event, among the strongest geomagnetic storms ever observed.
But there are other promising systems. Recently, a similar star, Ross 128, only 11 light-years from Earth and much calmer than TRAPPIST-1, was found to have an Earth-mass planet, making it a better place to look for life, researchers reported in November in Astronomy & Astrophysics.
Whether such stars are good or bad for life is an old and open question (SN: 6/24/17, p. 18). TRAPPIST-1’s advantage is in its numbers. “We can check it, not just with one planet but with many planets,” Kaltenegger says. “You have hotter than Earth, like Earth and colder than Earth. If you wanted Goldilocks, this is the ideal scenario.”
TRAPPIST-1 is just an opening act. A bigger, more sensitive observatory called SPECULOOS is expected to be fully operational in the Chilean desert in early 2019, Gillon says. SPECULOOS will seek planets around 1,000 ultracool dwarf stars over 10 years. “We are at the edge of maybe detecting life around another star,” he says. “It’s really a possibility.”
The holiday onslaught is upon us. For some families with children, the crush of holiday gifts — while wonderful and thoughtful in many ways — can become nearly unmanageable, cluttering both rooms and minds.
This year, I’m striving for simplicity as I pick a few key presents for my girls. I will probably fail. But it’s a good goal, and one that has some new science to back it. Toddlers play longer and more creatively with toys when there are fewer toys around, researchers report November 27 in Infant Behavior and Development. Researchers led by occupational therapist Alexia Metz at the University of Toledo in Ohio were curious about whether the number of toys would affect how the children played, including how many toys they played with and how long they spent with each toy. The researchers also wondered about children’s creativity, such as the ability to imagine a bucket as a drum or a hat.
In the experiment, 36 children ages 18 to 30 months visited a laboratory playroom twice while cameras caught how they played. On one visit, the room held four toys. On the other visit, the room held 16 toys.
When in the playroom with 16 toys, children played with more toys and spent less time with each one over a 15-minute session, the researchers found. When the same kids were in a room with four toys, they stuck with each toy longer, exploring other toys less over the 15 minutes.
What’s more, the quality of the children’s play seemed to be better when fewer toys were available. The researchers noted more creative uses of the toys when only four were present versus 16. Metz and colleagues noticed that initial attempts to play with a toy were often superficial and simple. But if a kid’s interest stuck, those early pokes and bangs turned into more sophisticated manners of playing. This type of sustained engagement might help children learn to focus their attention, a skill Metz likened to a “muscle that they have to exercise.” This attentional workout might not happen if kids are perpetually exposed to lots of distracting toys.
The toys used in the study didn’t include electronic devices such as tablets. Only one of the four toys and only four of the 16 toys used batteries. Noisy toys may have their own troubles. They can cut down on parent-child conversations, scientists have found. It’s possible that electronics such as televisions or tablets would have even greater allure than other toys.
Nor do the researchers know what would happen if the study had been done in kids’ houses and with their own toys. It’s possible that the novelty of the new place and the new toys influenced the toddlers’ behavior. (As everyone knows, the toys at a friend’s house are way better than the toys a kid has at home, even when they are literally the exact same toy.)
The results don’t pinpoint the optimal number of toys for optimal child development, Metz says. “It’s a little preliminary to say this is good and that is bad,” she says. But she points out that many kids are not in danger of having too few toys. In fact, the average number of toys the kids in the study had was 87. Five families didn’t even provide toy counts, instead answering “a lot.”
“Because of the sheer abundance of toys, there’s no harm in bringing out a few at a time,” Metz says.
That’s an idea that I’ve seen floating around, and I like it. I’ve already started packing some of my kids’ toys out of sight, with the idea to switch the selection every so often (or more likely, never). Another recommendation I’ve seen is to immediately hide away some of the new presents, which aren’t likely to be missed in the holiday pandemonium, and break them out months later when the kids need a thrill.
If more nerve cells mean more smarts, then dogs beat cats, paws down, a new study on carnivores shows. That harsh reality may shock some friends of felines, but scientists say the real surprises are inside the brains of less popular carnivores. Raccoon brains are packed with nerve cells, for instance, while brown bear brains are sorely lacking.
By comparing the numbers of nerve cells, or neurons, among eight species of carnivores (ferret, banded mongoose, raccoon, cat, dog, hyena, lion and brown bear), researchers now have a better understanding of how different-sized brains are built. This neural accounting, described in an upcoming Frontiers in Neuroanatomy paper, may ultimately help reveal how brain features relate to intelligence. For now, the multispecies tally raises more questions than it answers, says zoologist Sarah Benson-Amram of the University of Wyoming in Laramie. “It shows us that there’s a lot more out there that we need to study to really be able to understand the evolution of brain size and how it relates to cognition,” she says.
Neuroscientist Suzana Herculano-Houzel of Vanderbilt University in Nashville and colleagues gathered brains from the different species of carnivores. For each animal, the researchers whipped up batches of “brain soup,” tissue dissolved in a detergent. Using a molecule that attaches selectively to neurons in this slurry, researchers could count the number of neurons in each bit of brain real estate.
For most animals, the team found the expected numbers of neurons, given a certain brain size. Those expectations came in part from work on other mammals’ brains. That research showed that with the exception of primates (which pack in lots of neurons without growing bigger brains), there’s a predictable relationship between the size of the cerebral cortex — the wrinkly outer layer of the brain that’s involved in thinking, learning and remembering — and the number of neurons contained inside it.
Story continues below interactive graphic Feeling brainy Comparing brain size and number of nerve cells in the cerebral cortex among several animal species revealed some surprises. Golden retrievers, for example, have many more nerve cells than cats, and brown bears have an unexpectedly low number of nerve cells given the relatively large size of their brain. Raccoons have a surprising number of nerve cells considering their small noggin. It’s too early, however, to say how neuron number relates to animal intelligence.
Tap or click the graph below for more information.
But some of the larger carnivores with correspondingly larger cortices had surprisingly few neurons. In fact, a golden retriever — with 623 million neurons packed into its doggy cortex —topped both lions and bears, the team found. (For scale, humans have roughly 16.3 billion neurons in the cortex.)
The brown bear is especially lacking. Despite being about 10 times bigger than a cat’s cortex, the bear’s cortex contained roughly the same number of neurons, about 250 million. “It’s just flat out missing 80 percent of the neurons that you would expect,” Herculano-Houzel says. She suspects that there’s a limit to how much food a big predator can catch and eat, especially one that hibernates. That caloric limit might also cap the number of energetically expensive neurons.
Another exception — but in the opposite direction — was the raccoon, which has a cat-sized brain but a doglike neuron number, a finding that fits the nocturnal mammal’s reputation as a clever problem-solver. Benson-Amram cautions that it’s not clear how these neuron numbers relate to potential intelligence. Raccoons are very dexterous, she says, and it’s possible that a beefed-up brain region that handles touch, part of the cortex, could account for the neuron number.
Herculano-Houzel expected large predators such as lions to have lots of neurons. “We went into this study with the expectation that being a predator would require smarts,” she says. But in many cases, a predator didn’t seem to have more neurons than its prey. A lion, for instance, has about 545 million neurons in its cerebral cortex, while a blesbok antelope, which has a slightly smaller cortex, has about 571 million, the researchers previously found.
It’s too early to say how neuron number relates to animal intelligence. By counting neurons, “we’ve figured out one side of that equation,” Herculano-Houzel says. Those counts still need to be linked to animals’ thinking abilities.
Some studies, including one by Benson-Amram, have found correlations between brain size, neuron number and problem-solving skills across species. But finding ways to measure intelligence across different species is challenging, she says. “I find it to be a really fun puzzle, but it’s a big challenge to think, ‘Are we asking the right questions?’”
The hardy souls who manage to push shorts season into December might feel some kinship with the thirteen-lined ground squirrel.
The critter hibernates all winter, but even when awake, it’s less sensitive to cold than its nonhibernating relatives, a new study finds. That cold tolerance is linked to changes in a specific cold-sensing protein in the sensory nerve cells of the ground squirrels and another hibernator, the Syrian hamster, researchers report in the Dec. 19 Cell Reports. The altered protein may be an adaptation that helps the animals drift into hibernation. In experiments, mice, which don’t hibernate, strongly preferred to hang out on a hot plate that was 30° Celsius versus one that was cooler. Syrian hamsters (Mesocricetus auratus) and the ground squirrels (Ictidomys tridecemlineatus), however, didn’t seem to notice the chill until plate temperatures dipped below 10° Celsius, notes study coauthor Elena Gracheva, a neurophysiologist at Yale University.
Further work revealed that a cold-sensing protein called TRPM8 wasn’t as easily activated by cold in the squirrels and hamsters as in rats. Found in the sensory nerve cells of vertebrates, TRPM8 typically sends a sensation of cold to the brain when activated by low temperatures. It’s what makes your fingertips feel chilly when you’re holding a glass of ice water. It’s also responsible for the cooling sensation in your mouth after you chew gum made with menthol.
The researchers looked at the gene that contains the instructions to make the TRPM8 protein in ground squirrels and switched up parts of it to find regions responsible for tolerance to cold. The adaptation could be pinned on six amino acid changes in one section of the squirrel gene, the team found. Cutting-and-pasting the rat version of this gene fragment into the squirrel gene led to a protein that was once again cold-sensitive. Hamster TRPM8 proteins also lost their cold tolerance with slightly different genetic tweaks in the same region of the gene.
The fact that it’s possible to make a previously cold-resistant protein sensitive to cold by transferring in a snippet of genetic instructions from a different species is “really quite striking,” says David McKemy, a neurobiologist at the University of Southern California in Los Angeles. As anyone who’s lain awake shivering in a subpar sleeping bag knows, falling asleep while cold is really hard. Hibernation is different than sleep, Gracheva emphasizes, but the squirrels and hamsters’ tolerance to cold may help them transition from an active, awake state to hibernation. If an animal feels chilly, its body will expend a lot of energy trying to warm up — and that’ll work against the physiological changes needed to enter hibernation. For example, while hibernating, small mammals like the ground squirrel slow their pulse and breathing and can lower their core body temperature to just a few degrees above freezing.
Modifications to TRPM8 probably aren’t the only factors that help ground squirrels ignore the cold, Gracheva says, especially as the thermometer drops even closer to freezing. “We think this is only part of the mechanism.”
Scientists also aren’t sure exactly how TRPM8 gets activated by cold in the first place. A detailed view of TRPM8’s structure, obtained using cryo-electron microscopy, was published by a different research group online December 7 in Science. “This is a big breakthrough. We were waiting for this structure for a long period of time,” Gracheva says. Going forward, she and colleagues hope that knowing the protein’s structure will help them link genetic adaptations for cold tolerance in TRPM8 with specific structural changes in the protein.
Cold weather often brings with it hot takes on so-called man flu. That’s the phenomenon in which the flu hits men harder than women — or, depending on who you ask, when men exaggerate regular cold symptoms into flu symptoms. In time for the 2017–2018 flu season, one researcher has examined the scientific evidence for and against man flu.
“The concept of man flu, as commonly defined, is potentially unjust,” Kyle Sue, a clinician at Memorial University of Newfoundland in St. John’s, Canada, writes December 11 in BMJ. Motivated by his own memorable bout of flu, he says, Sue began looking into man flu research and summarizes the work in a review article that’s part of BMJ’s Christmas issue, which traditionally features humorous takes on legitimate research. There might be a reason men come across as wimps. In the United States, more men than women died from flu-related causes from 2007 to 2010 across several age groups, researchers reported in the American Journal of Epidemiology in 2013. An analysis of data on the 2004 to 2010 flu seasons in Hong Kong found that in children and adults, males were more likely to be hospitalized for the flu than females.
Sue isn’t the first to make a case for man flu. A prevailing explanation for men’s susceptibility says that women have higher levels of the hormone estradiol, which can boost the immune system, while men have higher levels of testosterone, which can sometimes suppress the immune system. However, these hormones interact with the immune system in other ways as well.
“There is some evidence that men make weaker immune responses to some viruses than women, but how this happens and whether it is seen across all viruses is still unclear to me,” notes John Upham, professor of respiratory medicine at Queensland University in Australia.
Sue’s review also cites evidence that women respond better to some flu shots than men do. Sex differences in immune response could have real consequences when it comes to vaccine choice, Upham says. It’s also unclear what the evolutionary drivers for immune differences between the sexes might be. And studies of how the male and female immune systems respond differently all come with caveats, Sue notes: Such studies are often in mice rather than humans, have limited data or don’t account for health differences such as smoking habits and tendency to go to the doctor. Upham adds that studying differences in flu cases among men in Western versus non-Western societies could reveal the degree to which learned behavior plays a role in “man flu.”
As much as he’d like to help out his half of the species, Sue says, “we cannot yet conclude that this phenomenon is real, but the current evidence is suggestive that it may be.” Not surprising, his review has met just as much skepticism as previous man flu treatises.
Regardless of the possibility that men may be immunologically weaker than women, Sue says, both flu-stricken men and women alike “could benefit from resting in a safe, comfortable place with a recliner and TV.”
Rising carbon dioxide levels could leave some tiny lake dwellers defenseless. Like the oceans, some lakes are experiencing increasing levels of the greenhouse gas, a new study shows. And too much CO2 in the water may leave water fleas, an important part of many lake food webs, too sleepy to fend off predators.
Detailed observations of lake chemistry over long periods of time are rare. But researchers found data from 1981 to 2015 on four reservoirs in Germany, allowing the scientists to calculate how much CO2 levels had risen and how much pH levels, measuring acidity in the water, had dropped, the scientists report online January 11 in Current Biology.
Rising CO2 in Earth’s atmosphere has also increased levels of the gas dissolved in the oceans, making them more acidic (SN: 5/27/17, p. 11). Studies show that ocean acidification alters the behaviors of marine species (SN Online: 2/2/17). It’s less clear how rising atmospheric CO2 levels are affecting freshwater bodies, or how their denizens are coping with change, says aquatic ecologist Linda Weiss of Ruhr University Bochum in Germany. Comparing the data from the four reservoirs showed that, in those 35 years, the average CO2 level across all lakes rose by about 560 microatmospheres, a unit of pressure. Two of the water bodies experienced a roughly fourfold increase in CO2 levels. For pH, the overall average value dropped from 8.13 to 7.82.
In the lab, the team examined the effect that high CO2 had on the behavior of two species of water fleas, or pinhead-sized lake dwellers also known as Daphnia. The miniature crustaceans are at the bottom of many freshwater food webs. When predators such as the larvae of phantom midges feed on Daphnia, the predators release a chemical signal that cues various species of water fleas to arm themselves with an array of defenses. Some raise forbidding neck spikes; others grow giant “helmets” that make the critters tougher to swallow. But the water fleas’ sense of danger seemed to be dulled in waters with high CO2 levels. The team tested the critters in waters containing both chemical predator cues and CO2 at partial pressures of 2,000, 11,000 and 16,000 microatmospheres. Although 2,000 microatmospheres is considered high, it is now common enough in lakes that the team used it as the control case. Both species were less defensive at 11,000 and 16,000 microatmospheres (considered worst-case scenario values for many lakes) — displaying fewer neck spikes or developing smaller crests.
Further tests revealed that the elevated CO2 was responsible, rather than the reduced pH. Although it’s unclear exactly how the elevated carbon dioxide leads Daphnia to lower its defenses, the researchers suggest the CO2 acts as a narcotic and blunts the senses.
The variability between lakes in terms of setting and chemistry makes it difficult to draw firm conclusions from the findings, Weiss says. Many lakes are warming (SN: 5/13/17, p. 18). And many are already saturated in carbon dioxide and expelling it into the atmosphere. Others are absorbing it and becoming more acidic.
It is also unclear how other freshwater species, including predators, might be affected at different CO2 levels and in different environments, says Caleb Hasler, an organismal biologist at the University of Winnipeg in Canada, who was not involved in the study. “There’s been a bit of work done on phytoplankton, some on zooplankton, freshwater fishes and mussels. If anything, the effect seems to be highly variable.”
But studies such as this that show long-term trends in CO2 levels are an important part of solving the puzzle, Hasler says. And “showing that there is an impact on an important species is pretty significant.”
