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.
June 24, 2013
If, somehow, you were magically transported back 255 million years in time to the middle of the vast desert that likely lay at the center of the supercontinent Pangea, you might come face to face with a cow-sized reptile called Bunostegos akokanensis. But no need to fear!
Despite its frighteningly bumpy-faced appearance, the creature was a confirmed vegetarian.
Ongoing excavations in Niger and elsewhere in Africa are allowing paleontologists to learn more about the extinct animals that roamed this ancient desert, and several newly discovered Bunostegos skull fossils provides one of the first looks at this admittedly unusual-looking creature. The reptile, described in an article published today in the Journal of Vertebrate Paleontology, truly lives up to the name of its genus: Bunostegos translates literally as knobby skull roof.
Detailed analysis of the fossils, led by Linda Tsuji of the University of Washington, allowed the researchers to produce a rendering of what the reptile would have looked like alive. At a best guess, the creature’s face was dotted with skin-covered bulbous protrusions, similar to the bumps on a giraffe’s head. “Imagine a cow-sized, plant-eating reptile with a knobby skull and bony armor down its back,” Tsuji said in a press statement, describing the creature.
The reptile belongs to the Pareiasaur group, made up of relatively large herbivores that lived during the Permian period, which lasted from 298 to 252 million years ago. Many other Pareisaurs also sported knobs on their heads, though not nearly as large as Bunostegos’. As a result, researchers had previously assumed that Bunostegos was a particularly advanced Pareiasaur, evolutionarily speaking—it had been part of the broader group for its entire evolutionary history and then evolved further.
This new analysis, though, showed that the Bunostegos also retained a number of relatively primitive characteristics—such as the shape and number of its teeth—that were found in older reptiles but not other Pareisaurs. As a result, the researchers conclude that the Bunostegos actually split off from the other creatures in its group much earlier on, and independently evolved the bony knobs on its head.
This sort of analysis also helps researchers make broader conclusions about the environment Bunostegos lived in. If Bunostegos underwent an extended period of independent evolution, there’d need to be some feature of the landscape that prevented members of the species from mingling and interbreeding with closely related reptiles in the meantime.
That feature, the researchers say, is a long-speculated enormous desert at the center of Pangea. Geological evidence supports the idea that the area—located in what is now Central and Northern Africa—was extremely dry during the late Permian, 266 to 252 million years ago, and other fossils found there show patterns of speciation that suggest long-term isolation.
Sometime soon after this period, though, Bunostegos—along with most Pareisaurs as a whole and 83% of all genera—were lost in a mass extinction event due to reasons we still don’t fully understand. Some scientists, though, believe that modern-day turtles are the direct descendants of Pareisaurs—so learning more about the anatomy and evolutionary history of this group of reptiles could help us better understand the diversity of life currently on our planet.
The key to finding out more, they say, is simple: keep digging. “It is important to continue research in these under-explored areas,” Tsuji said in the statement. “The study of fossils from places like northern Niger paints a more comprehensive picture of the ecosystem during the Permian era.”
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.”