It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, August 24, 2024
A leaky sink: Carbon emissions from forest soil will likely grow with rising temperatures
The soils of northern forests are key reservoirs that help keep the carbon dioxide that trees inhale and use for photosynthesis from making it back into the atmosphere.
But a unique experiment led by Peter Reich of the University of Michigan is showing that, on a warming planet, more carbon is escaping the soil than is being added by plants.
"This is not good news because it suggests that, as the world warms, soils are going to give back some of their carbon to the atmosphere," said Reich, director of the Institute for Global Change Biology at U-M.
"The big picture story is that losing more carbon is always going to be a bad thing for climate," said Guopeng Liang, the lead author of the study published in Nature Geoscience. Liang was a postdoctoral researcher at the University of Minnesota during the study and is now a postdoctoral researcher at Yale University and an exchange fellow at the Institute for Global Change Biology.
By understanding how rising temperatures affect the flow of carbon into and out of soils, scientists can better understand and forecast changes in our planet's climate. Forests, for their part, store roughly 40% of the Earth's soil carbon.
Because of that, there have been many research projects studying how climate change affects the carbon flux from forest soils. But few have lasted for longer than three years and most look at warming either in the soil or in air above it, but not both, Reich said.
In the experiment believed to be the first of its kind led by Reich, researchers controlled both the soil and above-ground temperatures in open air, without the use of any kind of enclosure. They also kept the study running for more than a dozen years.
"Our experiment is unique," said Reich, who is also a professor at the U-M School for Environment and Sustainability. "It's far and away the most realistic experiment like this in the world."
The trade-off is that running such a sophisticated experiment for so long is expensive. The research was supported by the National Science Foundation, the U.S. Department of Energy and the University of Minnesota, where Reich is also a Distinguished McKnight University Professor.
Joining Reich and Liang on the study were colleagues from the University of Minnesota, the University of Illinois and the Smithsonian Environmental Research Center.
The team worked at two sites in northern Minnesota on a total of 72 plots, investigating two different warming scenarios compared with ambient conditions.
In one, plots were kept at 1.7 degrees Celsius above ambient and, in the other, the difference was 3.3 degrees Celsius (or about 3 and 6 degrees Fahrenheit, respectively). Soil respiration—the process that releases carbon dioxide—increased by 7% in the more modest warming case and by 17% in the more extreme case.
The respired carbon comes from the metabolism of plant roots and of soil microbes feeding on carbon-containing snacks available to them: sugars and starches leached out of roots, dead and decaying plant parts, soil organic matter, and other live and dead microorganisms.
"The microbes are a lot like us. Some of what we eat is respired back to the atmosphere," Reich said. "They use the same exact metabolic process we do to breathe CO2 back out into the air."
Although the amount of respired carbon dioxide increased in plots at higher temperatures, it likely didn't jump as much as it could have, the researchers found.
Their experimental setup also accounted for soil moisture, which decreased at warmer temperatures that cause faster water loss from plants and soils. Microbes, however, prefer wetter soils and the drier soils constrained respiration.
"The take-home message here is that forests are going to lose more carbon than we would like," Reich said. "But maybe not as they would if this drying wasn’t happening."
In a world overrun by petroleum-based plastics, scientists are searching for alternatives that are more sustainable, more biodegradable and far less toxic to the environment. Two new studies by biologists at WashU highlight one potential source of game-changing materials: purple bacteria that, with a little encouragement, can act like microscopic factories for bioplastics.
In a world overrun by petroleum-based plastics, scientists are searching for alternatives that are more sustainable, more biodegradable and far less toxic to the environment.
Two new studies by biologists at Washington University in St. Louis highlight one potential source of game-changing materials: purple bacteria that, with a little encouragement, can act like microscopic factories for bioplastics.
A study led by graduate student Eric Conners found that two relatively obscure species of purple bacteria have the ability to produce polyhydroxyalkanoates (PHAs), natural polymers that can be purified to make plastic.
Another study led by research lab supervisor Tahina Ranaivoarisoa showed that genetic engineering could coax a well-studied but notoriously stubborn species of purple bacteria to dramatically ramp up its production of PHAs.
Conners and Ranaivoarisoa work in the lab of Arpita Bose, an associate professor of biology in Arts & Sciences and corresponding author of the new studies. “There’s a huge global demand for bioplastics,” Bose said. “They can be produced without adding CO2 to the atmosphere and are completely biodegradable. These two studies show the importance of taking multiple approaches to finding new ways to produce this valuable material.”
Purple bacteria are a special group of aquatic microbes renowned for their adaptability and ability to create useful compounds from simple ingredients. Like green plants and some other bacteria, they can turn carbon dioxide into food using energy from the sun. But instead of green chlorophyll, they use other pigments to capture sunlight.
The bacteria naturally produce PHAs and other building blocks of bioplastics to store extra carbon. Under the right conditions, they can keep producing those polymers indefinitely.
As the WashU biologists report this week in Microbial Biotechnology, two little-known species of purple bacteria in the genus Rhodomicrobium showed a remarkable willingness to produce polymers, especially when energized with small amounts of electricity and nourished with nitrogen. “It’s worth taking a look at bacteria that we haven’t looked at before,” Conners said. “We haven’t come close to realizing their potential.”
Rhodomicrobium bacteria have unusual properties that make them intriguing contenders as natural bioplastic factories. “It’s a unique bacteria that looks very different from other purple bacteria,” Conners said. While some species float around cultures as individual cells, this particular genus forms interconnected networks that seem especially well-equipped to produce PHA.
Other types of bacteria can also produce bioplastic polymers with some help. As reported inApplied and Environmental Microbiology, the WashU researchers used genetic engineering to coax impressive levels of PHAs out of Rhodopseudomonas palustris TIE-1, a well-studied species typically reluctant to produce the polymers. “TIE-1 is a great organism to study, but it’s historically not been the best for producing PHA,” Ranaivoarisoa said.
Several genetic tweaks helped boost the output of PHA, but one approach was especially successful. Researchers saw impressive results when they inserted a gene that increased the natural enzyme RuBisCO, the catalyst that helps plants and bacteria capture carbon from air and water. With the help of the super-charged enzyme, the usually sluggish bacteria turned into relative PHA powerhouses. The researchers are optimistic a similar approach could be possible with other bacteria that might be able to produce even higher levels of bioplastics.
In the near future, Bose plans to take a closer look at the quality and possible uses of the polymers produced in her lab. “We hope these bioplastics will produce real solutions down the road.”
MSU study finds placebos reduce stress, anxiety, depression — even when people know they are placebos
Michigan State University
EAST LANSING, Mich. – A study out of Michigan State University found that nondeceptive placebos, or placebos given with people fully knowing they are placebos, effectively manage stress — even when the placebos are administered remotely.
Researchers recruited participants experiencing prolonged stress from the COVID-19 pandemic for a two-week randomized controlled trial. Half of the participants were randomly assigned to a nondeceptive placebo group and the other half to the control group that took no pills. The participants interacted with a researcher online through four virtual sessions on Zoom. Those in the nondeceptive placebo group received information on the placebo effect and were sent placebo pills in the mail along with and instructions on taking the pills.
The study, published in Applied Psychology: Health and Well-Being, found that the nondeceptive group showed a significant decrease in stress, anxiety and depression in just two weeks compared to the no-treatment control group. Participants also reported that the nondeceptive placebos were easy to use, not burdensome and appropriate for the situation.
“Exposure to long-term stress can impair a person’s ability to manage emotions and cause significant mental health problems long-term, so we’re excited to see that an intervention that takes minimal effort can still lead to significant benefits,” said Jason Moser, co-author of the study and professor in MSU’s Department of Psychology. “This minimal burden makes nondeceptive placebos an attractive intervention for those with significant stress, anxiety and depression.”
The researchers are particularly hopeful in the ability to remotely administer the nondeceptive placebos by health care providers.
“This ability to administer nondeceptive placebos remotely increases scalability potential dramatically,” said Darwin Guevarra, co-author of the study and postdoctoral scholar at the University of California, San Francisco, “Remotely administered nondeceptive placebos have the potential to help individuals struggling with mental health concerns who otherwise would not have access to traditional mental health services.”
Michigan State University has been advancing the common good with uncommon will for more than 165 years. One of the world’s leading public research universities, MSU pushes the boundaries of discovery to make a better, safer, healthier world for all while providing life-changing opportunities to a diverse and inclusive academic community through more than 400 programs of study in 17 degree-granting colleges.
Credit: Marc Mapalo (amber); Franz Anthony (artistic reconstruction)
Tardigrades, often called “water bears”, are fascinating microscopic organisms known for their incredible resilience—they can survive anything from deadly radiation to arctic temperatures to the vacuum of space. And though today they can be found anywhere on Earth where there’s water, the evolutionary history of these eight-legged micro-animals remains relatively mysterious because of their sparse fossil record.
Now, in an important study published in the journal Communications Biology, Associate Professor Javier Ortega-Hernández and PhD candidate Marc Mapalo (both in the Department of Organismic and Evolutionary Biology at Harvard) were able to shed some light on that history—as well as confirm another entry in the fossil record, which now stands at a mere four specimens.
In their study,the team took another look at a piece of amber found in Canada in the 1960s that contains the known fossil tardigrade Beorn leggi and another presumed tardigrade that couldn’t be substantively described at the time. Using confocal laser microscopy, a method usually employed for studying cell biology, the researchers were able to examine the tiny structures of the fossil tardigrades in stunning detail.
Ortega-Hernández and Mapalo’s study provides not only a definitive classification of B. leggi in the tardigrade family tree, but the identification of a new species of tardigrade as well.
“Both of them are found in the same piece of amber that dates to the Cretaceous Period, which means that these water bears lived alongside dinosaurs,” Ortega-Hernández said. “The images of B. leggi show seven well-preserved claws, with the claws that curve toward the body being smaller than those curving away from it, a pattern found in modern-day tardigrades.”
The second, previously unidentified specimen, had claws of similar length on each of its first three pairs of legs, but longer outer claws on its fourth set of legs. The team named it Aerobius dactylus, from “aero” meaning relating to air—because the fossil appears to be floating on air in the amber—and “dactylo”, or finger, after its one long claw.
The impetus for applying this new technology t0 known fossils came when Mapalo, a self-described “paleo-tardigradologist,” came across the 2019 book, Water Bears: The Biology of Tardigrades.
“In one of the chapters, they had a photo of the oldest fossil tardigrade that was visualized using both normal microscopy and confocal laser microscopy,” Mapalo said. “And that gave me the idea to use that with the fossil that I'm working with right now.”
That fossil, encased in a piece of amber from the Dominican Republic, turned out to be a new species of tardigrade. Mapalo, along with Ortega-Hernández and researchers from the New Jersey Institute of Technology, published their findings in a 2021 paper in the Proceedings of the Royal Society B.
Ortega-Hernández said that, in their latest study, both fossils serve as critical calibration points for what’s called molecular clock analysis, which help scientists estimate the timing of key evolutionary events.
For example, the latest findings suggest that modern tardigrades likely diverged during the Cambrian Period over 500 million years ago. The research also sheds light on the origin of cryptobiosis, the technical name for the remarkable ability of tardigrades to survive extreme conditions by entering a state of stasis.
”The study estimates that this survival mechanism likely evolved during the mid to late Paleozoic, which may have played a crucial role in helping tardigrades endure the end-Permian mass extinction, one of the most severe extinction events in Earth’s history,” Ortega-Hernández said.
Ortega-Hernández and Mapalo’s research represents a significant advancement in the field of paleontology because it offers new avenues for exploring the evolutionary history of one of the most resilient life forms on the planet.
“Before I started my PhD, there were only three known fossil tardigrades, and now there’s four,” Mapalo said. “Most, if not all, of the fossil tardigrades were really discovered by chance. With the Dominican amber, researchers were looking for fossil ants, and they happened to see a fossil tardigrade there.
“That's why, whenever I have a chance, I always tell researchers who are working with amber fossils to check if maybe there's another tardigrade in there, waiting to be found.”
Beorn leggi in amber
Credit
Marc Mapalo
Cretaceous tardigrades
Left: Ventral view of Beorn leggi photographed with transmitted light under compound microscope (A), with autofluorescence under confocal microscop (B), and schematic drawing; Right: Habitus of Aerobius dactylus ventral (A,D) and dorsal view (E,F) photographed using confocal microscope and compound microscope. Schematic drawing (C), specimen and claws viewed in inverted greyscale to highlight autofluorescence intensity (D,F)
Cretaceous amber inclusions illuminate the evolutionary origin of tardigrades
Fisheries research overestimates fish stocks
GEOMAR expert calls for more realistic stock assessments
Helmholtz Centre for Ocean Research Kiel (GEOMAR)
Many fish stocks around the world are either threatened by overfishing or have already collapsed. One of the main reasons for this devastating trend is that policymakers have often ignored the catch limits calculated by scientists, which were intended to be strict thresholds to protect stocks. But it has now become clear that even these scientific recommendations were often too high.
In the European Union (EU), for example, fisheries are primarily managed through allowable catch limits, known as quotas, which are set by the European Council of Agriculture Ministers on the basis of scientific advice and recommendations from the European Commission. A new study by Australian scientists (Edgar et al.) shows that already the scientific advice has been recommending catch limits that were too high.
The journal Science, where the study is published today, asked two of the world’s most cited fisheries experts, Dr Rainer Froese from the GEOMAR Helmholtz Centre for Ocean Research Kiel and Dr Daniel Pauly from the University of British Columbia, to interpret the findings. In their Perspective Paper, they advocate for simpler, yet more realistic models based on ecological principles, and call for more conservative stock assessments and management when uncertainties arise.
For the study, Edgar et al. analysed data from 230 fish stocks worldwide and found that stock assessments have often been overly optimistic. They overestimated the abundance of fish and how quickly stocks could recover. Particularly affected are stocks that have already shrunk due to overfishing. The overestimates led to so-called phantom recoveries, where stocks were classified as recovered while, in reality, they continued to decline. “This resulted in insufficient reductions in catch limits when they were most urgently needed,” explains Dr Rainer Froese. “Unfortunately, this is not just a problem of the past. Known overestimates of stock sizes in recent years are still not used to corrected this error in current stock assessments”.
The research by Edgar et al. also shows that almost a third of stocks classified by the Food and Agriculture Organization (FAO) as “maximally sustainably fished” have instead crossed the threshold into the “overfished” category. Moreover, the number of collapsed stocks (those with less than ten per cent of their original biomass) within the overfished category is likely to be 85 per cent higher than previously estimated.
But what causes these distortions in stock assessments? Standard stock assessments use models that can include more than 40 different parameters, such as fish life history, catch details, and fishing effort. This large number of parameters makes the assessments unnecessarily complex, write Froese and Pauly. The results can only be reproduced by a few experts with access to the original models, data and settings. Moreover, many of the required input parameters are unknown or difficult to estimate, leading modelers to use less reliable values that have worked in the past. Froese notes: “Such practices can skew the results towards the modelers' expectations”.
The authors therefore call for a revision of current stock assessment models. They advocate simpler, more realistic models based on ecological principles. They also call for greater use of the precautionary principle: when in doubt, conservative estimates should be used to protect stocks. “In essence, sustainable fishing is simple,” says Dr Rainer Froese. “Less fish biomass should be taken than is regrown.” Fish must be allowed to reproduce before they are caught, environmentally friendly fishing gear must be used and protected zones must be established. The functioning of important food chains must be preserved by reducing catches of forage fish such as anchovies, sardines, krill or herring – these are the principles of ecosystem-based sustainable fishing. Froese adds: “Four of these five principles can be implemented even without knowledge of stock sizes.”
(Santa Barbara, Calif.) — While a mosquito bite is often no more than a temporary bother, in many parts of the world it can be scary. One mosquito species, Aedes aegypti, spreads the viruses that cause over 100,000,000 cases of dengue, yellow fever, Zika and other diseases every year. Another, Anopheles gambiae, spreads the parasite that causes malaria. The World Health Organization estimates that malaria alone causes more than 400,000 deaths every year. Indeed, their capacity to transmit disease has earned mosquitoes the title of deadliest animal.
Male mosquitoes are harmless, but females need blood for egg development. It’s no surprise that there’s over 100 years of rigorous research on how they find their hosts. Over that time, scientists have discovered there is no one single cue that these insects rely on. Instead, they integrate information from many different senses across various distances.
A team led by researchers at UC Santa Barbara has added another sense to the mosquito’s documented repertoire: infrared detection. Infrared radiation from a source roughly the temperature of human skin doubled the insects’ overall host-seeking behavior when combined with CO2 and human odor. The mosquitoes overwhelmingly navigated toward this infrared source while host seeking. The researchers also discovered where this infrared detector is located and how it works on a morphological and biochemical level. The results are detailed in the journalNature.
“The mosquito we study, Aedes aegypti, is exceptionally skilled at finding human hosts,” said co-lead author Nicolas DeBeaubien, a former graduate student and postdoctoral researcher at UCSB in Professor Craig Montell’s laboratory. “This work sheds new light on how they achieve this.”
Guided by thermal infrared
It is well established that mosquitoes like Aedesaegypti use multiple cues to home in on hosts from a distance. “These include CO2 from our exhaled breath, odors, vision, [convection] heat from our skin, and humidity from our bodies,” explained co-lead author Avinash Chandel, a current postdoc at UCSB in Montell’s group. “However, each of these cues have limitations.” The insects have poor vision, and a strong wind or rapid movement of the human host can throw off their tracking of the chemical senses. So the authors wondered if mosquitoes could detect a more reliable directional cue, like infrared radiation.
Within about 10 cm, these insects can detect the heat rising from our skin. And they can directly sense the temperature of our skin once they land. These two senses correspond to two of the three kinds of heat transfer: convection, heat carried away by a medium like air, and conduction, heat via direct touch. But energy from heat can also travel longer distances when converted into electromagnetic waves, generally in the infrared (IR) range of the spectrum. The IR can then heat whatever it hits. Animals like pit vipers can sense thermal IR from warm prey, and the team wondered whether mosquitoes, like Aedes aegypti, could as well.
The researchers put female mosquitoes in a cage and measured their host-seeking activity in two zones. Each zone was exposed to human odors and CO2 at the same concentration that we exhale. However, only one zone was also exposed to IR from a source at skin temperature. A barrier separated the source from the chamber prevented heat exchange through conduction and convection. They then counted how many mosquitoes began probing as if they were searching for a vein.
Adding thermal IR from a 34º Celcius source (about skin temperature) doubled the insects’ host-seeking activity. This makes infrared radiation a newly documented sense that mosquitoes use to locate us. And the team discovered it remains effective up to about 70 cm (2.5 feet).
“What struck me most about this work was just how strong of a cue IR ended up being,” DeBeaubien said. “Once we got all the parameters just right, the results were undeniably clear.”
Previous studies didn’t observe any effect of thermal infrared on mosquito behavior, but senior author Craig Montell suspects this comes down to methodology. An assiduous scientist might try to isolate the effect of thermal IR on insects by only presenting an infrared signal without any other cues. “But any single cue alone doesn’t stimulate host-seeking activity. It’s only in the context of other cues, such as elevated CO2 and human odor that IR makes a difference,” said Montell, the Duggan and Distinguished Professor of Molecular, Cellular, and Developmental Biology. In fact, his team found the same thing in tests with only IR: infrared alone has no impact.
A trick for sensing infrared
It isn’t possible for mosquitoes to detect thermal infrared radiation the same way they would detect visible light. The energy of IR is far too low to activate the rhodopsin proteins that detect visible light in animal eyes. Electromagnetic radiation with a wavelength longer than about 700 nanometers won’t activate rhodopsin, and IR generated from body heat is around 9,300 nm. In fact, no known protein is activated by radiation with such long wavelengths, Montell said. But there is another way to detect IR.
Consider heat emitted by the sun. The heat is converted into IR, which streams through empty space. When the IR reaches Earth, it hits atoms in the atmosphere, transferring energy and warming the planet. “You have heat converted into electromagnetic waves, which is being converted back into heat,” Montell said. He noted that the IR coming from the sun has a different wavelength from the IR generated by our body heat, since the wavelength depends on the temperature of the source.
The authors thought that perhaps our body heat, which generates IR, might then hit certain neurons in the mosquito, activating them by heating them up. That would enable the mosquitoes to detect the radiation indirectly.
Scientists have known that the tips of a mosquito’s antennae have heat-sensing neurons. And the team discovered that removing these tips eliminated the mosquitoes’ ability to detect IR.
Indeed, another lab found the temperature-sensitive protein, TRPA1, in the end of the antenna. And the UCSB team observed that animals without a functional trpA1 gene, which codes for the protein, couldn’t detect IR.
The tip of each antenna has peg-in-pit structures that are well adapted to sensing radiation. The pit shields the peg from conductive and convective heat, enabling the highly directional IR radiation to enter and warm up the structure. The mosquito then uses TRPA1 — essentially a temperature sensor — to detect infrared radiation.
Diving into the biochemistry
The activity of the heat-activated TRPA1 channel alone might not fully explain the range over which mosquitoes were able to detect IR. A sensor that exclusively relied on this protein may not be useful at the 70 cm range the team had observed. At this distance there likely isn’t sufficient IR collected by the peg-in-pit structure to heat it enough to activate TRPA1.
Fortunately, Montell’s group thought there might be more sensitive temperature receptors based on their previous work on fruit flies in 2011. They had found a few proteins in the rhodopsin family that were quite sensitive to small increases in temperature. Although rhodopsins were originally thought of exclusively as light detectors, Montell’s group found that certain rhodopsins can be triggered by a variety of stimuli. They discovered that proteins in this group are quite versatile, involved not just in vision, but also in taste and temperature sensing. Upon further investigation, the researchers discovered that two of the 10 rhodopsins found in mosquitoes are expressed in the same antennal neurons as TRPA1.
Knocking out TRPA1 eliminated the mosquito’s sensitivity to IR. But insects with faults in either of the rhodopsins, Op1 or Op2, were unaffected. Even knocking out both the rhodopsins together didn’t entirely eliminate the animal’s sensitivity to IR, although it significantly weakened the sense.
Their results indicated that more intense thermal IR — like what a mosquito would experience at closer range (for example, around 1 foot) — directly activates TRPA1. Meanwhile, Op1 and Op2 can get activated at lower levels of thermal IR, and then indirectly trigger TRPA1. Since our skin temperature is constant, extending the sensitivity of TRPA1 effectively extends the range of the mosquito’s IR sensor to around 2.5 ft.
A tactical advantage
Half the world’s population is at risk for mosquito-borne diseases, and about a billion people get infected every year, Chandel said. What’s more, climate change and worldwide travel have extended the ranges of Aedes aegypti beyond tropical and subtropical countries. These mosquitoes are now present in places in the US where they were never found just a few years ago, including California.
The team’s discovery could provide a way to improve methods for suppressing mosquito populations. For instance, incorporating thermal IR from sources around skin temperature could make mosquito traps more effective. The findings also help explain why loose-fitting clothing is particularly good at preventing bites. Not only does it block the mosquito from reaching our skin, it also allows the IR to dissipate between our skin and the clothing so the mosquitoes cannot detect it.
“Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal,” DeBeaubien said. “Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.”
In addition, to the Montell team, Vincent Salgado, formerly at BASF, and his student, Andreas Krumhotz, contributed to this study.
Pits at the end of the mosquito’s antennae shield the peg-like structures that detect thermal IR.
Credit
DeBeaubien and Chandel et al.
Journal
Nature
Article Title
Thermal infrared directs host-seeking behaviour in Aedes aegypti mosquitoes
A new study led by scientists from the University of Bristol has revealed what animals do after they have feigned death in order to avoid being killed by a predator and what the context of this behaviour is.
Many animals, as a last-ditch defence, become motionless after being contacted by a predator.
This behaviour is so common that it's recognised in such phrases as “playing possum”. It is even said to occur in humans in extreme circumstances.
In previous studies, carried out by the same team using antlion larvae, scientists noticed that they become motionless after being individually handled.
At one point the larvae needed to be weighed, which with such small insects can be very difficult, if they move on the pan of the weighing balance, determining their mass can be a challenge.
However, when the antlion larvae were dropped, very gently, onto the pan of a weighing balance, they remained completely stationary for more than enough time for their weight to be recorded accurately.
Emeritus Professor Nigel Franks from the University of Bristol’s School of Biological Sciences, who led the study, said: “We chose to investigate this so-called ‘death-feigning’ behaviour and we found that the amount of time individual antlions remain stationary is completely unpredictable for any one individual.
“This is confirmed by looking at the durations of post-contact immobility in a large number of antlions. Such data shows an exponential distribution. So just as with radioactive atoms, when an individual changes state is unpredictable, but the population pattern is perfectly predictable.”
The study shows that the behaviour of antlions hiding in plain sight, in this way, is likely to be adaptive because a predator having picked up and then dropped an antlion larva could not know how long to wait for its potential victim to move again and once more become a recognisable prey item. Indeed, one of the antlions recorded remained completely stationary for more than an hour.
Even though it cannot be predicted when a motionless antlion will spring back to life this does not mean that the predator will necessarily have left the scene to look for alternative prey.
The team’s next question was what animals do after playing possum. In the new study, they show that what antlions do depends on the situation in which they find themselves.
Antlion larvae are burrowing animals and might seek safety in submerging into the friable substrate where they normally build their pits. But it is quite possible that a predator might drop an antlion on to a hard substrate that wouldn't permit escape through borrowing.
By using sophisticated automated video tracking of the intermittent locomotion of individual antlions on different substrates researchers found that what an antlion does after terminating its period of motionlessness depends on what escape strategies are available.
Professor Franks added: “Our study might well be the first to determine what animals do after they have played dead, and we show that what they do is context dependent. It is a trade-off. So, our work opens up the field of studying life after death in the huge range of animals that exhibit death feigning, thanatosis or what we prefer to call post-contact immobility.”
Journal
PLoS ONE
Subject of Research
Animals
Article Title
'Seeking safety: Movement dynamics after post-contact immobility’
