December 4, 2013
In 1917, British artist Norman Wilkinson experienced a eureka moment while serving in the Royal Naval Volunteer Reserve. Throughout the month of April, German U-boats had been mercilessly torpedoing British ships, sending around eight of those vessels per day into the watery abyss. Hiding a ship traveling on the open ocean from plain sight was impossible, Wilkinson knew, but a bit of artistic trickery may be able to muddle the Germans’ ability to accurately judge the exact location of that ship, he realized.
From that idea, Wilkinson devised a type of camouflage called “razzle dazzle” (its slightly more serious name is dazzle camouflage). The technique consists of squashing together contrasting geometric patterns, shapes and colors to create a pattern of optics that would confuse enemies by distorting the object’s dimensions and boundaries. All in all, more than 2,000 ships received such a makeover, although the scheme’s effectiveness seemed to produce mixed results.
By World War II, razzle dazzle had largely fallen out of favor, but as it turns out, this technique lives on in the natural world. High contrast patterns–nature’s equivalent to dazzle camouflage–are used by animals ranging from snakes to zebra to fish. Like those hidden World War I ships, many creatures seem to use dazzle patterns to conceal themselves from predators. Until now, however, researchers hadn’t considered the flipside of this relationship: could predators use razzle dazzle to sneak up on prey as they mounted an attack?
To investigate this possibility, biologist Roger Santer of Aberystwyth University in the U.K. turned to locusts. These insects are particularly well suited for vision studies due to something called a single lobula giant movement detector neuron, a unique cell that specializes in detecting looming objects (think of a car speeding towards you, or a hand reaching for your face). Researchers think this neuron works by measuring the shape and movement of patterns of light and dark across the eye. Whatever the mechanism, as looming objects approach a locust, its detector neuron fires away, alerting the insect to imminent potential danger and triggering it to flee.
To see how the locusts responded to dazzle camouflage, Santer created an array of visual patterns using a graphics software. He situated the locusts just in front of the computer monitor, and then projected a simulated approach of those objects from about 10 meters away to about 0.07 meters from the cowering insects. The objects varied in contrast: black, grey or white on a grey background. Around 20 locusts took part in the experiment, and Santer measured their cellular reactions to the various shapes through copper wires inserted into the locusts’ neck.
The locusts’ neurological responses to the looming objects depended on which patterns they saw, Santer reports in Biology Letters. Squares with both a darker-than-background top and bottom half elicited the strongest panic response, followed by squares with a dark upper half, but a bottom half that was the same color as the background. Squares that had an upper half that was dark but a bottom half that was bright (in other words, the razzle dazzle ones) produced a significantly weaker panic response, as did squares that were brighter than the background. Finally, squares that were the same color as the background produced no response at all.
These results are interesting in that they correlate with similar dazzle tests performed on humans, who also had trouble quickly registering dazzle patterns. However, at this point, whether or not locust predators actually use dazzle to catch their unsuspecting insect prey remains a matter of speculation. Though lab tests confirm this strategy might work, Santer did not investigate whether or not a dazzle dance of death is carried out in the real world.
Hypothetically speaking, dazzle camouflage, Santer concludes, would help a predator but would not be the most effective way of snagging a locust lunch. Instead, classic camouflage–blending in with the background rather than creating an optical illusion–seems to be the most effective means of tricking would-be prey. However, in the case that other selection pressures favor high-contrast patterns (such as if females of a predator species prefer bold stripes in males), Santer thinks that predators could indeed evolve to give ‘em the old razzle dazzle.
October 14, 2013
In the 20 years since the movie Jurassic Park fantasized about how dinosaurs could be cloned from blood found in ancient amber-trapped mosquitoes, fossil collectors have been on the hunt for a similar specimen. Over the years, a few different groups of scientists have claimed to find a fossilized mosquito with ancient blood trapped in its abdomen, but each of these teams’ discoveries, in turn, turned out to be the result of error or contamination.
Today, it was announced that we finally have such a specimen, a blood-engorged mosquito that’s been preserved in shale rock for around 46 million years in northwestern Montana. The most astounding thing about the discovery? It was made three decades ago by an amateur fossil hunter—a geology graduate student named Kurt Constenius—then left to sit in a basement, and only recognized recently by a retired biochemist named Dale Greenwalt who’s been working to collect fossils in the Western U.S. for the Smithsonian Museum of Natural History.
The specimen, described in a paper Greenwalt published with museum researchers and entomologist Ralph Harbach today in the Proceedings of the National Academy of Sciences, is trapped in stone, not amber, and (unfortunately for Jurassic Park enthusiasts) it’s not old enough to be filled with dinosaur blood. But it is the first time we’ve found a fossilized mosquito with blood in its belly.
The rock-encased specimen was originally excavated sometime during the early 80s, when Constenius, then pursuing a master’s degree in geology from the University of Arizona, found hundreds of fossilized insects during weekend fossil-hunting trips with his parents at the Kishenehn Formation in northwestern Montana, near Glacier National Park. In the years since, they’d simply left the fossils sitting in boxes in their basement in Whitefish, Montana and largely forgotten about them.
Enter Greenwalt, who began volunteering at the museum in 2006, cataloging specimens for the paleobiology department. In 2008, he embarked on his own project of collecting fossils from the Kishenehn every summer, in part because he’d read in an insect evolution textbook an offhand mention of Constenius’ discoveries, which had never been rigorously described in the scientific literature.
In the years since, Greenwalt has collected thousands of specimens from 14 different orders of insects. The collection site is remote—he has to raft the Flathead River that runs along the border of the park to a place where the river has cut down through layers of rock of the Kishenehn Formation, which includes shale that formed the bottom of a lake during the Eocene epoch, some 46 million years ago.
“It is a fantastic fossil insect site, arguably one of the best in the world,” he says, noting that a rare combination of circumstances—thin layers of fine-grained sediment and a lack of oxygen—led to a “mind-boggling degree of preservation.” Working there, he’s made a number of significant finds, collecting specimens that led to the description of two new insect species (pdf).
After Greenwalt met the Constenius family in Whitefish and described his work, they decided to donate their fossil collection to the museum. When he began cataloging the boxes the fossils and came across this particular specimen, “I immediately noticed it—it was obvious that it was different,” he says. He suspected that the mosquito’s darkly opaque abdomen, trapped in a thin piece of shale, might contain 46-million-year old blood.
Staff from the museum’s mineral sciences lab used a number of techniques to scan the specimen up close, including energy dispersive X-ray spectroscopy. “The first thing we found is that the abdomen is just chock full of iron, which is what you’d expect from blood,” Greenwalt says. Additionally, analysis using a secondary ion mass spectrometer revealed the presence of heme, the compound that give red blood cells their distinctive color and allows them to carry oxygen throughout the body. Other tests that showed an absence of these compounds elsewhere in the fossil.
The findings serve as definitive evidence that blood was preserved inside the insect. But at this point, scientists have no way of knowing what creature’s fossilized blood fills the mosquito’s abdomen. That’s because DNA degrades way too quickly to possibly survive 46 million years of being trapped in stone (or in amber, for that matter). Recent research had found it has a half-life of roughly 521 years, even under ideal conditions.
This means that even if we miraculously had some DNA of the ancient creature, there are currently a ton of technical problems that prevent the cloning similar to that in Jurassic Park from becoming a reality. Assembling a full genome from DNA fragments requires us to have an understanding of what the whole genome looks like (which we don’t have in this case), and turning that into a living, breathing animal would necessitate putting that DNA into an ovum of a living species very closely related to the mystery creature that we don’t know in the first place.
So, alas, no resurrected ancient creatures will roam free thanks to this new find. Still, the find is scientifically significant, helping scientists better understand the evolution of blood-feeding insects. Previously, the closest thing to a blood-engorged mosquito that scientists had found was a mosquito with remnants of the malaria parasite inside its abdomen (pdf). Though that provides indirect evidence that mosquitoes fed on blood 15-20 million years ago, this new discovery represents the oldest direct evidence of blood-sucking behavior. It also shows for the first time that biological molecules such as heme can survive as part of the fossil record.
October 3, 2013
For some humans, storms–with their raging winds and rains, passionate bursts of lightening and bone-rattling thunder–are prompts for romantic snuggling up. Likewise, few can argue that kissing in the pouring rain, Hollywood-style, isn’t a pretty thrilling experience. Insects, however, beg to differ. For them, overcast skies are the ultimate sexual buzz kill.
To assess how big of a turn-off rain is for insects, a team of Brazilian and Canadian researchers gathered together collections of three versatile arthropods: curcurbit beetles, true armyworm moths and potato aphids. Insects, they knew, possess hairs and waxy coatings to help repel water, and some, like mosquitoes, are known to have no problem flying through raindrops. On the other hand, too much heavy rain and wind can kill the little guys. So when it came to the question of how their tiny research subjects would handle sex in a storm, the team wasn’t sure what to expect.
Storms form when different air pressures collide, and the researchers decided to use decreasing air pressure as a proxy for impending rain. The team wanted to examine changes in any insect mating behaviors, including courtship and the deed itself, so they performed a number of experiments, which they describe in a paper published in PLoS One.
First, they exposed around 70 male curcurbit beetles to virgin female sex pheromones–chemical odors that normally would drive the males into a frenzy of desire–while subjecting the bugs to different barometric pressures, including stable, increasing (usually associated with clear weather but strong winds) and decreasing atmospheric pressures. Under stable or increasing pressure, they found, the male beetles eagerly scuttled into the section of their container where the pheromone was concentrated. But when the pressure was decreasing, the males were significantly less enthusiastic about initiating a meeting with a potential blushing beetle bride. In fact, they usually ignored the cues.
Next, around 70 virgin armyworm moth females were plopped into a similar experimental setting. The moths were on the cusp of peak mating season, during which females “call” to males by releasing potent cocktails of sex pheromones. When the pressure dropped, the females apparently did not feel frisky, releasing significantly less of the come-hither concoctions than under the environment of stable or increasing pressure. In nature, the researchers point out, females usually chose a nice spot high on an extended leaf to do this–in other words, the spot most likely to be splattered with rain and result in their getting washed away.
The researchers then took the obvious next step, putting both beetle and moth males and virgin females together. The male moths seemed totally turned off by both the decreasing and increasing pressure, mating fewer times under those conditions than in the stable control group.
The male beetles behaved a bit more curiously, however. When pressure was normal or increasing, the male beetles took their time setting the mood and impressing their lucky ladies by intertwining their antenna and performing other sexy pre-copulation behaviors.
When the pressure was decreasing, however, the males were all business. They skipped courtship entirely, jumped on the females and quickly got things over and done with. The researchers found this to be a bit puzzling since the males did not respond to the female hormones under decreasing pressures, but did go ahead and initiate a quickie when females were standing right next to them. This rushed copulation could be because of a “perceived reduction in life expectancy”–in other words, an it’s-the-end-of-the-world-so-let’s-do-it mentality–although that would require further investigation, they say.
Finally, the potato aphids were subjected to similar experiments. The researchers observed that females raised their backsides and hind legs into the air (the aphid’s version of a “come and get it” calling) less often in both increasing and decreasing pressure conditions. Like the moths, the team points out, the females chose the edge of a leaf to perform this booty call, so any hint of wind could potentially spell disaster for them. As for the males, not surprisingly, they, too, had no success in mating under neither the increasing or decreasing pressure conditions, perhaps because they agree that literally getting blown away during copulation is not the way to go.
The evidence, the team writes, was pretty conclusive: insects are not turned on by storms. This applies to all facets of mating, including an aversion to seeking, encouraging or initiating sex when there’s even a chance that precipitation and wind might be involved.
Although each species had their kinks–the beetles would still do it, albeit quickly, and the moths and aphids hated both increasing and decreasing pressure–the team thinks the results are general enough and cover a diverse enough spread of species to likely apply to many insects. Probably, they write, this aversion evolved as a way to avoid injury, death by drowning or being swept away by strong winds.
While the team is eager to probe even more arthropod species to confirm and better understand these behavioral patterns, they conclude that insects, at least, seem unwilling to die for love.
The importance of bees in our food system often goes unappreciated. Just by going about their daily business, these insects are responsible for pollinating three-quarters of the 100 crop species that provide roughly 90 percent of the global food supply. The most recent estimate for the economic value of this bee activity is that it’s worth over $200 billion.
But in recent years, an alarming number of bee colonies across North America and Europe have begun to collapse. As part of the phenomenon, formally known as Colony Collapse Disorder, worker bees fail to return to the hive after their pollen-collecting trips nearby. We still don’t fully understand what’s driving this trend, but the list of culprits likely includes pesticides, viral infections, intensive agriculture and perhaps even the practice of feeding bees high fructose corn syrup in place of the honey we take from them.
New research, though, suggests there may be an overlooked problem: the exhaust fumes produced by diesel-powered engines. As described in a study published today in Scientific Reports, a group of researchers from the UK’s University of Southampton found that the pollution produced by diesel combustion reduces bees’ ability to recognize the scent of various flowers—a key sense they use in navigating and finding food sources.
“Honeybees have a sensitive sense of smell and an exceptional ability to learn and memorize new odors,” Tracey Newman, a neuroscientist who worked on the study, said in a press statement. “Our results suggest that that diesel exhaust pollution alters the components of a synthetic floral odor blend, which affects the honeybee’s recognition of the odor. This could have serious detrimental effects on the number of honeybee colonies and pollination activity.”
To come to the finding, the group used extract from rapeseed flowers to create a scent that mimics the natural smell of several different flowers that the bees normally pollinate. In a sealed glass vessel, they mixed the scented air with diesel exhaust at a variety of concentrations, ranging from those that meet the EPA’s standards for ambient air quality to worst-case scenarios—concentrations of diesel pollutants (specifically the highly reactive NOx gases, nitric oxide and nitrogen dioxide) that greatly exceed these standards but are commonly detected in urban areas.
At all concentrations, just one minute after they added the pollutants, gas chromatography testing revealed that two of the main flower-scented chemicals in the original blend were rendered undetectable, degraded by the nitrogen dioxide. Previously, they’d trained 30 honeybees to remember the flowers’ scent—by rewarding them with a sip of sucrose when they extended their proboscis in response to smelling it—but when the scent had been altered by the exposure to diesel fumes, just 30 percent of the bees were still able to recognize it and extend their proboscis. They confirmed that the NOx gases in particular were to blame by repeating the experiments with isolated versions of them, instead of the whole range of diesel pollutants, and arriving at the same results.
It’s a small study on one bee population using one flowers’ scent, but it’s a concern. That’s because, although the study specifically looked at NOx gases that resulted from the burning of diesel, the gases are also produced by your car’s gasoline-burning engine. When NOx measurements are averaged out, few areas exceed the EPA’s standards, but in many urban locales during periods of high traffic, NOx levels can be much higher—high enough, this testing suggests, to disrupt bees’ ability to smell flowers.
It follows that diesel fumes could play a role in Colony Collapse Disorder: If bees are less effective at navigating and finding nectar, they might be more likely to get lost in large numbers. Colony collapse is typically characterized by the continual disappearance of worker bees during their travels—so it’s possible that the effects of engine exhaust plays a role.
“Diesel exhaust is not the root of the problem,” said Newman said in a press briefing. “But if you think of a situation where a bee is dealing with viral infections, mites, all the other stresses it has to deal with—another thing that makes it harder for the bee to work in its environment is likely to have detrimental consequences.”
September 20, 2013
In a species of tiger moth native to the Arizona desert, scientists have discovered a new weapon in the endless evolutionary arms race between predator and prey. New research shows that the moths, Bertholdia trigona, have the ability to detect and jam bats’ biological sonar—the technique that allows bats to “see” through echolocation. The moths’ remarkable ability, which as far as scientists know is unique in the animal kingdom, allows the insect to evade hungry bats and fly away.
Evidence of this ability was first uncovered in 2009, by a group led by Aaron Corcoran, a wildlife biologist who was then a PhD student at Wake Forest University. “It started with a question has been out there for a while, since the 1960s—why do some moths produce clicking sounds when bats attack them?” Corcoran explains.
Scientists knew that most species of tiger moths that emitted ultrasonic clicking sounds did so to signal their toxicity to bats—similar to how, for example, poison dart frogs are brightly colored so that predators can easily associate their striking hues with toxic substances and learn to look elsewhere for food. This particular species, though, emitted about ten times as much sound as most moths, indicating that it might be serving a different purpose entirely.
To learn more, he and colleagues collected trigona moths, put them in a mesh cage, attached them to ultra-thin filaments to keep track of their survival, and introduced brown bats. “If the sounds are for warning purposes, it’s well-documented that the bats have to learn to associate the clicks with toxic prey over time,” he says. “So if that were the case, at first, they’d ignore the clicks and capture the moth, but eventually they’d learn that it’s toxic, and avoid it.”
But that wasn’t what happened. The bats didn’t have to learn to avoid the moths—rather, Corcoran says, “they couldn’t catch them right from the beginning.” The reason for this, they determined, was that the moths were using the clicks to jam the bats’ sonar.
A bat’s sonar works like this: Normally—because they hunt at night and their eyesight is so poorly developed—bats send out ultrasonic noises and analyze the path they take as they bounce back to “see” their environment. But when approached by the bats, the moths produced their own ultrasonic clicking sounds at a rate of 4,500 times per second, blanketing the surrounding environment and cloaking themselves from sonar detection.
“This effectively blurs the acoustic image the bat has of the moth,” Corcoran says. “It knows there’s a moth out there, but can’t quite figure out where it is.”
But the experiment left a remaining question: How did the moths know when to activate their anti-bat signal? The team’s latest work, published this summer in PLOS ONE, shows that the trigona moths are equipped with a built-in sonar detection system.
As the bats approach, they increase the frequency of their calls to paint a more detailed picture of their prey. Corcoran’s team hypothesized that the moths listen to this frequency, along with the raw volume of the bats’ calls, to determine when they’re in danger of attack.
To test this idea, he attached tiny microphones to moths to record the exact sounds they heard when attacked by bats. He also stationed microphones a few feet away. The mics near the moths heard a slightly different sound profile of approaching bats. Then, he played each of these sounds to an entirely different group of moths to see their responses.
The moths that heard the recordings only began emitting their own ultrasonic noises when the researchers played the sounds heard by the moths actually in peril—and not the sounds that would be heard by moths a few feet away from the one in danger. By analyzing the two acoustic variables (volume and frequency), the moths could effectively differentiate between the two.
The moths click “only when they can confidently determine that they’re getting attacked,” Corcoran says. This makes sense, because the ability to figure out exactly when they’re in danger is particularly crucial for this species of tiger moths—unlike other, toxic species, these ones taste good to bats.