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 26, 2013
Seahorses belong to the genus Hippocampus, which gets its name from the Greek words for “horse” and “sea monster.” With their extreme snouts, weirdly coiled bodies and sluggish movements produced by to two puny little fins, these oddly shaped fish seem like an example of evolution gone terribly awry. And yet, new research published today in Nature Communications shows that it is precisely the seahorse’s uncanny looks and slow motions that allow it to act as one of the most stealthy predators under the sea.
Seahorses, like their close relatives the pipefish and sea dragons, sustain themselves by feasting on elusive, spastic little crustaceans called copepods. To do this, they use a method called pivot feeding: they sneak up on a copepod and then rapidly strike before the animal can escape, much like a person wielding a bug swatter tries to do to take out an irritating but otherwise impossible-to-catch fly. But like that lumbering human, the seahorse will only be successful if it is able to get near enough to its prey to strike at very close range. In the water, however, this is an even greater feat than on land because creatures like copepods are extremely sensitive to any slight hydrodynamic change in the currents around them.
So how do those ungainly little guys manage to feed themselves? As it turns out, the seahorse is a more sophisticated predator than appearance might suggest. In fact, it is precisely its looks that make it an ace in the stealth department. To arrive at this surprising conclusion, researchers from the University of Texas at Austin and the University of Minnesota used holographic and particle image velocimetry–fancy ways of visualizing 3D movements and water flow, respectively–to monitor the hunting patterns of dwarf seahorses in the lab.
In dozens of trials, they found that 84 percent of the seahorses’ approaches successfully managed not to sound the copepod’s retreat alarms. The closer the seahorse could get to its unsuspecting prey and the faster it struck, the greater its odds of success, they observed. Once in range of the copepod, seahorses managed to capture those crustaceans 94 percent of the time. Here, you can see that method of attack, in which the seahorse’s giant head looks like a floating bit of marine sludge drifting toward the blissfully ignorant copepod:
The way the seahorse’s movements and morphology–especially its head–interact with the water particles, the researchers found, likely take the credit for its exceptional hunting skill. The animal’s arched neck acts like a spring for generating an explosive strike, they describe, while the shape of its snout–a thin tube with the mouth positioned at the very end–allows it to drift through the water while creating minimal disturbance.
To emphasize this pinnacle of engineering, the team compared water disruptions caused by seahorses with those of sticklebacks, a relative of the seahorse but with a more traditional fishy look. Thanks to the shape and contours of the seahorse’s head, that predator produced significantly less fluid deformation in the surrounding water than the stickleback. The poor stickleback possesses neither the morphology nor posture to generate “a hydrodynamically quiet zone where strikes occur,” the authors describe. In other words, while the seahorse may appear a bit odd so far as fishes go, evolution was obviously looking out for that funny but deadly animal’s best interests.
November 20, 2013
In 1834, Charles Darwin discovered a strange animal during his exploration of Chile’s southern coast. The creature, a small frog, was shaped like a leaf with a pointed nose, but appeared puffed up as if had been blown full of air, like a balloon. As it turned out, those fat male frogs hadn’t been gorging themselves on too many mosquitoes, but instead were enacting duties that earn them distinction as one of nature’s best dads. They were incubating several of their squirming babies in their vocal sac.
These peculiar animals, known as Darwin’s frogs, are today divided into two species, one that occurs in northern Chile, and another that lives in southern Chile and Argentina. When a female Darwin’s frogs lay her eggs, her mate keep a careful watch until the tadpoles hatch. The eager dad then swallows his young, allowing the babies to safely grow within his vocal sac until they turn into frogs and are ready to strike out on their own. Here, you can see a dutiful papa frog seemingly vomit up his living young:
Northerly Darwin’s frogs, however, have not been spotted in the wild since 1980. Researchers are nearly certain the species is extinct. Meanwhile, their southerly cousins are in steep decline and seem to be heading down extinction’s death row as well. For once, it seems that humans are not entirely to blame for these biodiversity disasters (unlike the western black rhino, which bit the dust a couple years ago after enduring decades of poaching for its valuable but medicinally worthless horn, used as an ingredient in traditional Chinese medicine). Instead, the deadly amphibian chytrid fungus, researchers report today in PLoS One, is likely to blame.
The chytrid fungus has popped up in amphibians in North and South America, Europe and Australia. The fungus infects the animals’ skin, preventing them from absorbing water and other nutrients. The fungus can rapidly decimate amphibian populations it comes into contact with, and has been called (pdf) “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction” by the International Union for Conservation of Nature.
To identify chytrid as the likely culprit behind the Darwin’s frogs disappearance and decline, researchers from Chile, the UK and Germany conducted a bit of historical sleuthing. They dug up hundreds of archived specimens of Darwin’s frogs and closely related species dating from 1835 until 1989, and then tested them all for fungal spores (the problematic form of chytrid fungus was first recorded in the 1930s and reached epidemic-status around 1993, but researchers aren’t certain of when it first emerged). They also took around 800 skin swabs between 2008 and 2012 from 26 populations of still-living southern Darwin’s frogs and other similar frog species that live nearby.
Six of the old museum specimens, all collected between 1970 and 1978–just before the northern Darwin’s frog’s disappearance–tested positive for the disease. More than 12 percent of the living frogs tested positive for the fungal spores. In places where the Darwin’s frog has gone extinct or is experiencing drastic declines, however, rates of infection jumped to 30 percent in other amphibian species. Although these events don’t prove that the fungus killed the northern Darwin’s frogs and are now wiping out the southern species, the researchers strongly suspect that is the case.
Despite evidence that the disease has spread throughout the Darwin’s frog’s range, the researchers are not giving up on hope to save one of the world’s greatest dads from extinction. “We may have already lost one species, the Northern Darwin’s frog, but we cannot risk losing the other one,” Claudio Soto-Azat, the study’s lead author, said in a statement. ”There is still time to protect this incredible species.”
November 12, 2013
When it comes to sex, males and females are not always equal in their desires. No, you haven’t stepped into a couples therapy class.
Welcome to the animal kingdom, where what’s good for one gender could in fact be detrimental for the other. Similar to the struggle between a parasite and its host, some species are locked in an evolutionary arms race between the sexes, with each gender battling to put its best interests forth. Although male and female sexual preferences and tactics are as variable as the thousands of species they represent, a particular species of snake provides an interesting example of conflict that can occur during mating itself, researchers describe in the journal Proceedings of the Royal Society B.
The authors focused their paper on an intimate discussion of red-sided garter snake behaviors. When red-sided garter snakes are ready to mate, several dozen males find their way to a female. Just as she is emerging from hibernation into the warm spring air, the males–which slithered forth days earlier–swarm over her, forming a “mating ball.” Here’s one, from thamnophis14 on YouTube–it’s mesmerizing to watch:
Rather than pick the nicest looking or most impressive male, mating is more of a crapshoot for the female, with the closest male latching on as soon as the female presents herself by opening her cloaca, an orifice that leads into the vagina. But sometimes, things get a bit ugly: males may go so far as to cut the female’s oxygen supply off, which triggers a panic reaction in the female, who releases feces and musk. In doing so, however, she opens up her cloaca, effectively allowing the males to sneak in and get what they want.
Female red-sided garter snakes, not surprisingly, prefer to get copulation over and done with. They attempt to bid their mate goodbye as soon as he has handed over his sperm, and sometimes, even sooner than that. This way, females can get on with their business–which oftentimes entails finding another mate of their choosing. To shake the males off, the female may perform a “body roll,” essentially flipping around until the male detaches.
The males, however, prefer to stick around. The longer they hold on, the more sperm they can transfer and the less chance that another male will snag their female. Sometimes, males take their mate guarding to extremes. Red-sided garter snake males, like some other snake species, may physically plug up the female’s genitals with a ”gelatinous copulatory plug,” preventing her from mating with other males even if he is not around, and stopping her from potentially ejecting his sperm after mating. Over the next few days, however, the plug will dissolve, giving the female a second chance at selecting a mate of her choice under less frantic circumstances.
Researchers aren’t sure what triggers the males to plug up the females. They suspect the female’s “body roll” behavior–essentially a “Get off me!” signal–may have something to do with it. Powerful muscular movements within the female’s vagina may also help to push the male out, but at the same time increase the chances that he attempts to issue a plug.
Finally, to further aid in mating, males of red-sided garter snakes and some other species evolved a special organ whose name and appearance resembles something from a medieval torture chamber: the basal spine. A blunt apparatus covered in small spikes, the basal spine acts as a “grappling hook” for allowing the male to hold the female in place during mating (a process that often makes the females bleed, by the way), some researchers suspect. Overall, however, the basal spine’s adaptive role is a bit of a mystery.
To find out how the snakes’ genital traits influence sexual conflict and behaviors, the researchers caught 42 wild red-sided garter males in Manitoba, Canada, during the spring mating season. They also scooped up newly emerged females, and put two of those females into a small outdoor enclosure with the males. They allowed the snakes to mate naturally while they monitored the duration of copulation, the behaviors involved and whether or not the males left a mating plug behind. Males that copulated for five minutes or more were more likely to leave a plug behind, they found, and the longer the copulation period, the larger the plug.
Afterwards, they divided the males into two groups. Unlucky males in the experimental group suffered a bit of genital mutilation: the researchers clipping off the animals’ basal spines (they did use anesthesia). Males in the other group were left intact. After a four day recovery period, the males were again introduced to two new, unmated females.
This time, the researchers found, the males without a basal spine mated for a significantly shorter duration than the control group. Eight out of 14 of the males lacking basal spines copulated for less than one minute (they were usually shaken off by female body rolls) and did not leave a plug in the female. Moreover, five of them did not manage to eject any sperm.
Next, it was the females’ turn. The researchers collected 24 unmated females. They anesthetized the lady parts of half the females, and used a placebo injection for the others. Females that lost feeling down south, they found, mated for significantly longer than females that were not anesthetized. However, the anesthetized females, compared to the natural ones, received smaller mating plugs even though the copulation period was longer. This may be because those numb females did not struggle, the researchers write, or it could be that the plugs adhere better to engaged vaginal muscles.
Although more experimentation is needed to work out some of the specifics, genital features clearly play significant roles in sexual conflict in this species, the researchers write. In other words, males and females are out for themselves. The males’ strategy increases the chance that they will inseminate a female and thus pass on their own genes, while the females’ strategy increases the chance of insemination from a male they actually want. “The evolution of the basal spine allows males to gain more control over copulation duration, forcing females to evolve some counter trait to regain some control, leading to sexually antagonistic coevolution,” the authors write.
While these tactics may sound brutal to a human reader, the fact that the snakes have evolved these traits prove that they work for the species. And as a small comfort for the snakes, this battle of the sexes is nowhere near the level of brutality seen in the mating behavior of bed bugs–perhaps one of the most graphic example of sexual conflict in the animal kingdom. For that species, males impale the female’s abdomens in a process called traumatic insemination. Compared to being stabbed in the gut, mating plugs may not seem so extreme after all.
November 6, 2013
New species of insects, worms and other creepy-crawlers are announced on a monthly basis. Similarly, just last week, two new humpback dolphin species splashed into the headlines. And in October, news broke that early humans may have included fewer species than previously thought. This forces the question: what does it take to be a distinct species?
More than 70 official species definitions exist, of which 48 are widely accepted and used by scientists. And there’s no hard rule that scientists must stick to just one definition; some apply a handful of species definitions when approaching the topic. “I personally go to my lab every day and use five species definitions to conduct research,” says Sergios-Orestis Kolokotronis, a molecular ecologist at Fordham University, and co-author of the new dolphin study, published in Molecular Ecology. “And I sleep just fine amidst this uncertainty.”
Species definitions oftentimes do not translate from one organism to another. Dolphins may become isolated by distance and behavior that prevents them from reproducing, but in other cases–such as bacteria, which reproduce asexually–these distinguishing markers do not apply. Thus, the definition of what constitutes a species varies depending on whether scientists are studying dolphins, monkeys, insects, jellyfish, plants, fungi, bacteria, viruses or other organisms, Kolokotronis explains. And likewise, methods for investigating those species also vary. “Whoever figures out THE unifying species definition across the Domains of Life gets the Crafoord Prize!” Kolokotronis jokes.
In the case of the four dolphin species, each occupy different sections of ocean around the world, including in the Atlantic off West Africa (Sousa teuszii), in the central to western Indo-Pacific (Sousa plumbea), in the eastern Indian and western Pacific (Sousa chinensis) and in northern Australia (researchers are in the process of working on a name for that one–Sousa bazinga, anyone?).
While the humpback dolphins look quite similar, their genetics tells a different story. Researchers collected 235 tissue samples and 180 skulls throughout the animals’ distribution, representing the biggest dataset assembled to date for the animals. The team analyzed mitochondrial and nuclear DNA from the tissue, which revealed significant variations between those four populations. They also compared the skulls for morphological differences.
Although the line between species, sub-species and populations is a blurry one, in this case, the researchers are confident that the four dolphins are divergent enough to warrant the “species” title. The mitochondrial DNA turned up genetic signatures distinct enough to signal a separate species, and likewise, differences in the dolphins skulls supported this divergence. Although the nuclear DNA provided a slightly more confounding picture, it still clearly showed differences between the four species.
“We can confidently say that such strong divergence means these populations are demographically and evolutionarily isolated,” says Martin Mendez, a molecular ecologist at the American Museum of Natural History and lead author of the dolphin paper. “The key is that all the evidence–mitochondrial DNA, nuclear DNA and morphology–exhibited concordant patterns of distinct units,” he continues, which are “usually a must for species proposals.”
The genetic data the team collected does not have enough resolution to reveal how long ago the humpback dolphins diverged, and the team has yet to examine the drivers that fueled those speciation events. But Mendez and his colleagues have found that, in some dolphin populations, environmental factors such as currents and temperature play a role in separating populations and encouraging speciation. Different behaviors can help reinforce that separation, too. Most likely, however, geographic isolation plays a significant role in this case. “For populations living a couple hundred kilometers from one another, it’s perfectly possible for them to meet,” Mendez says. “But the distance from Africa to Australia is so great, it’s difficult to imagine those populations would ever be linked.”
Dolphins, Mendez and his colleagues are finding, evolve relatively quickly once isolated from parent populations. New cryptic–or hidden–species have similarly turned up in waters near South America. There may very well be other species of dolphins–or any type of animal, in fact–lurking undetected within an already-discovered species. ”This really applies to most taxa,” Mendez says. Across the board, “we’re adding many more species by looking at genetic data.”
While cryptic species almost certainly await discovery and will increase the head-counts of some organisms, in the case of ancient human ancestors, on the other hand, researchers now suspect that we’ve been too quick to pull the species card. An extremely well-preserved, approximately 1.8 million year-old Homo erectus skull discovered in Georgia alerted scientists to the potential revision. The skull’s odd proportions–large, but with a small brain case–prompted researchers to analyze variation between modern human and chimpanzee skulls, and compare those variations with other known human ancestor species. As the Guardian reports:
They concluded that the variation among them was no greater than that seen at Dmanisi. Rather than being separate species, the human ancestors found in Africa from the same period may simply be normal variants of H erectus.
If the scientists are right, it would trim the base of the human evolutionary tree and spell the end for names such as H rudolfensis, H gautengensis, H ergaster and possibly H habilis.
Ancient humans, of course, are no longer around for us to study their behaviors and mating tendencies, so anatomy has to do. For now, researchers are calling for more specimens to determine where that line will fall.
The line distinguishing two species may be a fuzzy one, but in the case of the dolphins, it is a big deal in terms of conservation. Australia, for example, is planning to design protective legislation for its new dolphin species, and Mendez hopes other countries will do the same.
Nonetheless, pondering the speciation of humans in dolphins in light of these two findings raises lots of questions: Are we fractally subdividing genetic information and brain cavity size to group and regroup organisms, or is there vast genetic diversity in even familiar species that we’ve yet to uncover? What does it mean for a species to gain or lose members of its family tree? The world and its organisms await more research.