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.
November 27, 2013
When we think of ants as builders, we normally imagine them digging intricate tunnel networks as part of underground colonies.
But David Hu, Nathan Mlot and a team of other researchers at Georgia Tech are studying a very different type of building behavior specific to one ant species: The ability of Solenopsis invicta to construct bridges, rafts and even temporary shelters using their own bodies as building material.
“Fire ants are capable of building what we call ‘self-aggregations,’” Hu says. “They can build little boats, little houses called bivouacs and even bridges to cross streams by being the building material, linking their bodies together and forming strong networks.”
The ants are now considered an invasive species in 25 states, Asia and Australia, but their unusual behavior is a survival strategy shaped by their native environment: a particular area of wetlands in western Brazil that are flooded frequently. “The ants live underground, but when it begins to flood, they have to gather the colony members, pull them out of the ground and build a floating raft,” Hu says.
When this raft hits land, the ants keep building. To cross small streams during their subsequent migration, they make living bridges that allow the entire colony to scramble to safety. Afterward, using their bodies, they construct a temporary aboveground encampment to provide shelter for the few days it takes to re-dig underground tunnels. All the while, the ants that form the temporary shelter are continuously moving, but still preserving the structure. “It’s really living architecture—it has well-constructed, organized tunnels, brooding rooms,” Hu says. At least for the ants in the inside, this provides protection against hostile weather or predators.
Hu, an engineer, is primarily interested in studying the swarming ants as a novel material with unprecedented characteristics. As part of his group’s recent research, presented yesterday at an annual meeting of the American Physical Society, he and colleagues considered the ants within the context of other “active materials”—substances that can respond to changing conditions, such as self-healing cements that can use the energy in sunlight to expand and fill their own fractures.
“We wanted to characterize what kind of material it is—is it a fluid, or is it a solid, and how does it respond to stress?” he says. “In nature, for instance, these rafts might float down a river and bump into rocks, or raindrops might hit them.”
To test these self-aggregations, Hu’s team used a few techniques, comparing live ant structures to clumped dead ants as a control. Using a rheometer—a device that can precisely measure the stress response and flow of a fluid, and is often applied in industrial situations (such as the development of a new shampoo)—they found that the ants continuously reorganize their structure to maintain stability.
Many materials behave like a solid when stressed by forces moving at certain speeds, and a fluid when stressed by slowed ones. Water, for instance, behaves like a fluid when you stick your hand in it, but a solid when hit by a human body jumping off a diving board—the reason that a belly flop hurts so much.
But the ant structures are a combination of solid and fluid when stressed by forces at all speeds, the researchers found. They actively deform their structure to accommodate a stress (like a fluid) but then bounce back into place afterward (like a solid). Check out what happens when one of their structures is compressed by a petri dish, for instance:
“This makes sense, based on their natural environment,” Hu says. “If they’re floating in a raft down a river, they have no control over where it floats, so if there’s something in the way—say, a twig—you see respond and flow around the twig, kind of like an amoeba.”
The ants’ sheer resiliency and buoyancy is also remarkable. When the researchers tried to push the floating rafts below the water’s surface, they found they could resist a significant amount of force and float back up:
This is enabled, in part, by the ants’ exoskeletons, which are naturally hydrophobic (i.e. they chemically repel water). When many ants clump together to form a structure, water doesn’t penetrate into the gaps between then, so when they’re forced underwater, the air that remains in these cavities helps them float.
Perhaps the biggest mystery of these ants’ remarkable living structures is how the creatures communicate to build them. Most ant communication is based on trails of pheromones left on the ground, but in such an interconnected form, that type of communication seems unlikely. Microscopic examination reveals that the ants grasp each other using both their jaws and little claws on the end of their legs. Noting this, Hu adds, ”We think they’re communicating through touch, but we really don’t understand it yet.”
November 7, 2013
A lot has changed in the last 165 million years. A cluster of islands coalesced to form Europe, the Atlantic Ocean opened up and India collided with the rest of Asia as the world’s tectonic plates gradually drifted to form the continents we know today. Dinosaurs largely went extinct, felled mostly by a mass extinction event some 65 million years ago that was likely caused by an enormous meteorite impact. Eventually, apes came down from the trees, evolved into humans, and migrated out of Africa to cover the planet.
During all this time, though, one thing has stayed exactly the same: The anatomical structure of froghopper genitals.
We know that from a remarkable new fossil excavated from the Jiulongshan Formation in Northeastern China and described in the journal PLOS ONE. The 165-million-year-old fossil, analyzed by researchers at the Capital Normal University in China, captures two of the small insects in the act of copulation—the oldest record of insect sex ever discovered. And though the insects themselves belong to a particular species that went extinct long ago, their genital structures appear to be identical to those of the modern-day froghoppers that are distributed all around the world.
There are only 33 known fossils that show insects mating worldwide, and the previous oldest—which contains fossilized midges in the act of copulation—dates to 135 million years ago. These sorts of fossils are so rare because of the nature of fossilization: an organism is buried in dirt or sediment sometime after its death and its skeletal remains are slowly replaced by minerals or converted into new compounds over time.
So, for the act of copulation to be fossilized, it means that two insects would have to die while mating, then fall to the ground locked in the mating position. The excavation site, in Ningcheng County, may help explain how this happened: Most of the fossils there were created as the result of a volcanic eruption, which appears to have knocked all sorts of creatures into a lake, so it’s quite possible that the insects died, their mating bodies stuck to the plant stem they were perched on, then the entire plant settled to the lake bottom with them on it.
The researchers are sure that the fossil depicts the act of mating, rather than two insects lying next to each other, because of their inspection of the insects’ reproductive parts. The fossil shows the male’s aedeagus—roughly, the insect equivalent of a penis—inserted into the female’s bursa copulatrix, the organ that receives sperm for fertilization.
Although the creatures differ slightly from known froghoppers, the anatomical structure of their genitals—even down to the number of segments in the male’s aedeagus—is the same as those of modern-day froghoppers. For that reason, the researchers named the new species Anthoscytina perpetua: “From the Latin perpet, eternal love, in reference to this everlasting copulation,” they write in the paper.
One thing that may have changed, though, is the position these insects assume while they’re mating. From the fossil, it seems that ancient froghoppers faced each other, belly-to-belly, in order to mate. Currently, froghoppers usually do it rather differently, laying side-by-side on their stomachs, with the male’s aedeagus twisting underneath to enter the female:
October 29, 2013
One of the freakiest parts of getting bitten by a tick is the
insect arachnid’s incredible tenacity: If one successfully pierces your skin and you don’t pull it off, it can hang on for days at a time, all the while sucking your blood and swelling in size.
Despite plenty of research into ticks and the diseases they carry, though, scientists have never fully understood the mechanics by which
the insects they use their mouths to penetrate skin and attach themselves so thoroughly. To address that, a group of German researchers recently used specialized microscopes and high-speed video cameras to capture a castor bean tick burrowing into a mouse’s bare skin in real time.
Their work, published today in Proceedings of the Royal Society B, produced all sorts of new revelations about the structure and function of the tick’s mouthparts. Perhaps the most harrowing part of the research, though, is the microscopic video they captured, shown at an accelerated speed above.
The team of scientists, led by Dania Richter of Charité Medical School in Berlin, conducted the work by placing five ticks on the ears of lab mice and letting them have their fill of blood. Unbeknownst to the ticks, though, they’d been caught on camera—and by analyzing the footage, along with detailed scanning electron microscope images of the ticks’ mouth appendages, the researchers found that the insects’ bites are really a highly specialized two-step process.
To begin, after the tick has climbed aboard a host animal, a pair of sharp structures called chelicerae, which are located at the end of its feeding appendage, alternate in poking downward. As they gradually dig, their barbed ends prevent them from slipping out, and the tick slowly and shallowly lodges itself in the skin, as seen in the first few seconds of the video.
After about 30 or so of these small digging movements, the tick switches to phase two (shown just after the video above zooms in). At this point, the insect simultaneously flexes both of the telescoping chelicerae, causing them to lengthen, and pushes them apart in what the researchers call “a breaststroke-like motion,” forming a V-shape.
With the tips of the chelicerae anchored in the skin, flexing them outward causes them to penetrate even deeper. When this occurs, the tick’s hypostome—a razor-sharp, even-more-heavily-barbed spear—plunges into the host’s skin and attaches firmly.
The tick’s not done, however: It repeats this same breaststroke five or six times in a row, pushing the hypostome deeper and deeper until it’s fully implanted. With the hypostome firmly in place, the tick begins drawing blood—sucking the fluid up to its mouth through a grooved channel that lies in between the chelicerae and hypostome—and if left interrupted, will continue until it’s sated days later.
This new understanding of how ticks accomplish this feat, the researchers say, could help us someday figure out how to prevent transmission of the most feared risk of a tick bite: Lyme disease. Scientists know that the disease is caused by several different species of bacteria that adhere to the inner lining of the tick’s gut and typically make the jump into a human’s bloodstream only after a full day of feeding. Knowing how ticks are able to attach themselves so stubbornly could eventually allow us to determine a means of thwarting their advances, before the Lyme-bearing bacteria have a chance to cross the species barrier.
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.