June 12, 2013
Visit a sunny pond in a meadow, park or zoo and you’ll likely see turtles basking on logs and small lizards hanging out on warm rocks. If you’re in the south, you may even spot an alligator lazing on a bright patch of shore.
Ectotherms (better known as cold-blooded animals) such as these reptiles have to shuttle back and forth between shade and sun in order to manually regulate their body temperature. Insects, fish, amphibians and reptiles all do it. Now, new research suggests that these animals begin their temperature-regulating tasks much earlier than previously thought–while they are embryos encased in their eggs.
Previously, researchers thought of developing embryos as cut off from the outside world. But back in 2011, researchers found that Chinese soft-shelled turtle embryos could move between warmer or cooler patches in their eggs, though they lacked any feet at such an early stage of development. Some of the same Chinese and Australian researchers who published that original finding decided to investigate further to see just how deliberate these movements are.
“Do reptile embryos move away from dangerously high temperatures as well as towards warm temperatures?” the team, writing in the journal Biology Letters, wondered. “And is such embryonic movement due to active thermoregulation, or (more simply) to passive embryonic repositioning caused by local heat-induced changes in viscosity of fluids within the egg?”
In other words, are unborn reptiles purposefully moving from one spot to another within their eggs, much like an adult animal does? The team decided to investigate these questions by experimenting on turtle embryos. They incubated 125 eggs from Chinese three-keeled pond turtles. They randomly assigned each of the eggs to one of five temperature groups: constant temperature, hot on top/cool on the bottom, or at a range of heats directed towards one end of the egg.
When they began the experiment, most embryos sat in the middle of their eggs. A week after exposing them to the different temperature groups, the team again measured the baby turtles’ positioning within the eggs. At the 10-day mark, the researchers again measured the turtles’ positions, and then injected half of the eggs with a poison that euthanized those developing embryos. Finally, after another week, they took one last measurement of the developing turtles and euthanized turtles.
The turtles within the eggs held at constant temperature or those that were in the “warm on the top/cool on the bottom” group tended not to shift around in their eggs, the researchers found. Those belonging to the groups that experienced warm temperatures only on one end of their egg, however, did move around. They gravitated towards warm conditions (84-86°F), but if things heated up too extremely (91°F), they edged towards the cooler side of their egg. Crucially, the embryos that the researchers euthanized stopped moving after receiving the dose of poison. This shows that the embryos themselves, not some passive physical process, are doing the shifting.
The turtle embryos, the researchers note, behave much like adult reptiles do when thermoregulating their bodies. They warm up and cool down by moving toward or away from heat sources. For species like turtles, temperature during development plays an important part of determining the embryo’s sex. Turtle nests, which are buried in the sand, often experience a range of different temperatures, so embryos could be playing a role in determining their own gender, edging towards the cooler side of the egg if they feel like becoming a male, or the warmer side if they’re more female-inclined, the authors write.
May 13, 2013
Humans drew the short end of the toothbrush when it comes to our pearly whites’ longevity. Other animals such as reptiles and fish frequently lose and replace their teeth by growing new ones, but people are stuck with the same set of mature adult teeth their entire lives. If they lose a tooth–or all 32–dentures are usually the only option.
Oddly enough, alligators’ deadly chomps may hold a clue for how scientists could coax humans into regrowing teeth. These reptiles belong to the order Crocodilia, who, with their famous cheerful grins, caused songwriters to warn that you should never smile at a crocodile. To the bane of Captain Hook and other victims of gator and croc attacks, the large reptiles often regrow their razor teeth multiple times. Researchers think that, given time, technology may advance so that we can borrow these reptilian smiles. But first, scientists need to understand just how these animals keep their smiles toothy.
In a paper published this week in the Proceedings of the National Academy of Sciences, an international team of researchers attempted to get at the mechanisms behind the superior tooth regenerating abilities of one species of Crocodilia–the American alligator–in the hopes of applying the results to humans.
In humans, organs such as hair, scales, nails and teeth “are at the interface between an organism and its external environment and therefore, face constant wear and tear,” the researchers write. But alligators have evolved ways to deal with these challenges. The carnivores can replace any of their 80 teeth up to 50 times throughout their 35 to 75-year lives. Small replacement teeth grow under each mature alligator tooth, ready to spring into action the moment a gator loses a tooth.
To figure out the molecules and cells responsible for replacement, the researchers used X-rays and small tissue samples from alligator embryos, hatchlings and 3-year old juveniles’ developing teeth. They also grew tooth cells in the laboratory and created computer models of the process. Alligator teeth appear to cycle continuously, they write, but in fact the animals’ teeth seem to go through three distinct phases: pre-initiation, initiation and growth.
Once an alligator loses a tooth, these three phases kick off. The dental lamina, or a band of tissue associated with the initial stages of tooth formation in many animals, begins to bulge. This triggers stem cells and an array of signaling molecules that direct the process of forming a new tooth.
These results may be applicable to humans’ pearly whites. Alligators’ flesh-chomping incisors are surprisingly similar to well-organized, complex vertebrate teeth such as ours. In humans, a remnant of the dental lamina–the structure crucial to tooth formation–still exists and sometimes wrongly activates and begins forming toothy tumors. If the researchers could better tease out the molecular signaling pathways behind alligator tooth replacement, they reason, they they may be able to induce those same chemical instructions in humans to coax the body into forming a new tooth after one gets kicked out in a soccer game or has to be removed after becoming infected.
Alternatively, doctors may be able to shut off the molecules responsible for conditions that cause uncontrolled tooth formation. Individuals suffering from cleidocranial dysplasia syndrome grow many unusually shaped, peg-like teeth, for example, and people with Gardner syndrome also grow supernumerary, or extra, teeth.
While the researchers still need to clarify more molecular details behind alligator tooth growth, this initial study does hint that doctors and dentists may someday be able to selectively bestow patients with the reptiles’ tooth-regenerating abilities.
“Based on our study, it may be possible to identify the regulatory network for tooth cycling,” the researchers conclude. “This knowledge will enable us to either arouse latent stem cells in the human dental lamina remnant to restart a normal renewal process in adults who have lost teeth or stop uncontrolled tooth generation in patients with supernumerary teeth.”
Either way, they note that “Nature is a rich resource from which to learn how to engineer stem cells for application to regenerative medicine.”
April 11, 2013
Visitors to Guam’s forests find them quiet–eerily so: No chirping of birds can be heard overhead. But slithering in the shadows on the ground are snakes, each some six feet long. Brown tree snakes made their debut on Guam, the southernmost island in the Mariana Archipelago, when islanders were rebuilding after World War II. Most likely, they were stowaways in lumber shipments heading north through the Pacific Ocean from New Guinea. They quickly began feasting on the birds and small lizards they discovered in Guam’s dense forests, and–free to slither through the mountainous terrain without predators of their own–they completed an invasion of the island at a pace of one mile per year. By the late 1940s, the forests had largely fallen silent, and now, all of Guam’s native bird species are history.
Last fall, scientists from Rice University and the University of Guam published one of the first studies of the island’s extinct forest birds, which include species such as the Mariana fruit dove, Guam flycatcher and Rufous fantail. They focused on how the absence of birds has caused a spike in the spider population, which is 40 times greater on Guam than nearby islands.
Now, the researchers are turning their attention to the issue of Guam’s thinning forests—a consequence, they also believe, of the bird deficit. This summer they’ll launch a four-year study of 16 tree species, looking at how the loss of birds, which scatter seeds, is affecting tree distribution.
The study has its roots in an a-ha moment that lead scientist Haldre Rogers recently had while conducting another seed-dispersal study in Guam’s forests. “I noticed that there seemed to be a lot of gaps [in the trees] and that the pioneer tree species–such as papaya and sumak–were difficult to find on Guam, compared to nearby islands,” she explained to Surprising Science. She discovered that there were in fact twice as many such gaps on Guam per unit area of forest.
Pioneer trees, which are the first to appear after a disruption to the ecosystem and thrive in the full sunlight of open spaces in the forest, have small seeds that are consumed by small birds. “Without birds to move their seeds to these sunny spots in the forest, these quick-growing trees may be less likely to germinate or grow to their full size,” Rogers hypothesized.
The problem with such thinning is that it could change the structure of Guam’s forests. “There’s a concern that [they] may become filled with open areas and start to look more like Swiss cheese than a closed canopy forest,” Rogers said. In other words, what were once cool, dark forests could transform into hot, open sunny ones.
There are other possible explanations for the tree-thinning: An undiscovered forest disease could be targeting pioneer species, or mammals like pigs and deer might have a strong taste for the trees. But according to Rogers, there isn’t strong evidence to support either of these scenarios. The upcoming study will attempt to determine the cause definitively.
To that end, the researchers will cut down individual trees in various spots within Guam’s forests, creating new gaps in the forest. They’ll also remove trees from locations on two nearby islands that are still brimming with birds. Then they’ll monitor how long it takes the spaces to fill in and take note of which seedlings thrive on Guam versus on the other islands. It may seem that to get their results they’re destroying what they’re trying to study, but in actuality they’re taking down a tiny percentage of the island’s trees–20 total.
Guam’s situation is similar to that of tropical regions worldwide. “Animals involved in seed-dispersal are in decline in a lot of tropical forests around the world right now,” the co-principal investigator of the study, Amy Dunham, said in a statement. “It’s very important to understand the implications of those declines.” So far scientists have looked into the role of endangered mammals like lemurs, giant tortoises (PDF) and African forest elephants (PDF) in seed dispersal, but the upcoming study will be one of the first to focus on endangered birds.
It’s also the rare study to examine what happens when seed dispersal completely ceases–Guam being the only place in the world to experience whole-island forest bird loss in modern times. “The situation on Guam–which is tragic–provides us with a unique opportunity to see what happens when all seed-dispersal services provided by animals are lost from an entire ecosystem,” Dunham said.
The snakes, meanwhile, continue to dominate the island of Guam. The U.S. Department of Agriculture traps approximately 6,000 brown tree snakes each year, and yet there are still nearly two million slithering around the island. The snakiest patches contain 14,000 of the reptiles per square mile–one of the highest snake concentrations in the world.
In February, the Department of Agriculture embarked on a new tactic for tackling the snake problem: dropping dead mice laced with acetaminophen, which is fatal to them, into the jungle. ”We are taking this to a new phase,” Daniel Vice of the Department of Agriculture’s branch that focuses on wildlife services in Hawaii, Guam and other U.S. held Pacific Islands, said in a recent interview. “There really is no other place in the world with a snake problem like Guam.”
April 1, 2013
Anyone who lives in or has visited a tropical country is likely familiar with the chipper chirping of the gecko. These friendly little lizards inhabit homes and jungles stretching from Indonesia to Tanzania to the Dominican Republic. They emerge after sunset, taking advantage of their night vision eyesight—which is 350 times more powerful than a human’s—and are welcome guests in homes and hotels since they gobble up mosquitoes and other insect pests.
In addition to the locals, scientists also love these colorful lizards. Geckos possess the unique ability among lizards to run up flat walls and scamper across ceilings, even if the surface is very smooth. Researchers have been puzzling over this ability for years, and dozens of labs have tested gecko adhesion in the hopes of harnessing this superpower for potential use in everything from robotics to space technology to medicine to “gecko tape.”
Gecko toes, it turns out, contain hair-like structures that form a multicontact interface, meaning geckos grip with thousands of tiny adhesive structures rather than what appears to be a single uniform foot.
Gaps remain, however, in researchers’ understanding of how gecko feet interact with surfaces in their natural environment, especially in dry versus wet conditions. Scientists know that gecko toe pads are superhydrophobic, or water repelling, yet geckos lose their ability to cling to glass when it becomes wet. Why don’t they just repel the water and cling to the glass surface below? Similarly, scientists wonder how geckos deal with wet leaves in the forest during rain storms.
A new paper published in Proceedings of the National Academy of Sciences investigates these mysteries. The authors decided to test gecko grip on a range of wet and dry materials that both attract and repel water. To perform their experiments, they outfitted six tokay geckos with gecko-sized harnesses. They placed the geckos onto four different types of materials, such as glass, plastic and a substance designed to mimic waxy tropical leaves. After giving the lizards some time to adjust to their new surroundings, the researchers applied a uniform tugging pressure onto the geckos’ harnesses, pulling in the opposite direction of where the animals were walking. Eventually, the geckos could cling no longer and lost their grip. This allowed the team to measure the adhesive force required to displace the animals. They repeated the same experiments under very wet conditions, too.
The authors found that materials that are more “wettable”—an indication of the degree to which a surface attracts water molecules—the less force it took to disrupt the clinging geckos’ grips. Glass had the highest wettability of the surfaces the researchers tested, and geckos easily slipped from wet glass compared to dry glass. When that material gets wet, water forms a thin, attractive film that prevents the gecko’s tiny toe hairs from coming into contact with the surface.
The low wettability properties of waxy leaves, on the other hand, allow geckos to establish a sturdy grip, even in rain storms, because leaves actively repel water. Geckos performed equally well in wet and dry conditions on the leaf-mimicking surface, the researchers found.
How the geckos interact with surfaces depends upon a thermodynamic theory of adhesion, the authors conclude. These features are dictated by Van der Waals force, or the sum of attractive and repulsive interactions between gecko toes and the characteristics of the surfaces they come into contact with. So long as those attractive forces jibe, geckos are in luck for getting a grip on whatever surface they come into contact with, regardless of whether it’s wet or dry.
Using our whole-animal adhesion results, we found that wet surfaces that are even weakly [water repulsive] allow the gecko adhesive system to remain functional for clinging and likely locomotion as well.
Our findings suggest a level of versatility in the gecko adhesive system that previously was not accounted for and calls into question interesting evolutionary, ecological, and behavioral predictions.
In addition to shedding light on how gecko adaptations help the lizards cope with their natural environment, the authors think their findings may contribute to designing new synthetic gecko robots that may overcome real-life geckos’ wet glass Achilles’ heel, useful perhaps for cleaning skyscraper windows, spying on suspected terrorists, or simply changing a hard-to-reach light bulb.
March 21, 2013
Designing a robot that can easily move across loose terrain—say, a rover meant to traverse the surface of Mars—poses a unique engineering challenge: Wheels commonly sink into what engineers call “flowable ground” (mixtures of sand, soil, mud and grass).
Given the many biologically-inspired innovations in robotics, a team of researchers from Georgia Tech had an idea—to base a design on desert creatures such as zebra-tailed lizards that are able to scramble across a loose, sandy surface without slowing down. Their efforts allowed them to create this small six-legged device, presented in an article published today in Science, which can run across a granular surface in a way uncannily reminiscent of a reptile.
The research team, led by Chen Li, designed the device after studying the locomotion of various creatures and mathematically simulating the performance of different types of legs (varying in number, shape and length) in several distinct environments. They hope their research will spur the development of a field they’ve termed “terradynamics”—just as aerodynamics is concerned with the performance of winged vehicles in air, their field will study the motion of legged vehicles on granular surfaces.
To design their robot, they used these simulations to determine the exact leg lengths, movement speeds and levels of force that would propel devices across a loose surface without causing them to sink in too deeply. They then printed a variety of leg types with a 3D printer, and built robots to test them in the lab.
One of their most interesting findings is that the same types of design principles apply for locomotion on a variety of granular surfaces, including poppy seeds, glass beads and natural sand. Their simulations and real-world experiments revealed that C-shaped legs generally worked best, but that any type of bow-shaped limbs worked relatively well because they spread out the weight of the device over long (albeit narrow) leg surfaces as the legs come into contact with the ground over the course of a stride.
The applications of this kind research are broad: This particular robot, the researchers say, could be developed into a useful search-and-rescue or scouting device, while the principles derived from the field of terradynamics could be useful in designing probes to explore other planets in the future. They could also help biologists to better understand the how life forms here on earth have evolved to move across our planet’s surface.