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.
In the summer of 2010, husband-and-wife paleobiologist team Z. Jack Tseng and Juan Liu traveled to the Zanda Basin in western Tibet with a group of colleagues. The remote area, a week’s drive from Beijing and near the border of Pakistan and China, is “basically badlands everywhere, with deeply cut valleys throughout,” Tseng says.
To explore the valleys, the team drove up dirt trail after dirt trail before coming upon a dense patch of fossils sticking out of the ground halfway up a hill. “In the little concentration of fossils, there were lots of limb bones from antelopes and horses obscuring everything else,” says Tseng, who was then a graduate student at USC and is now with the American Museum of Natural History. “It wasn’t until we started lifting things up, one by one, that we saw the top of a skull, and we thought, from the shape, that it looked something like a cat.”
After a few years of analysis, Tseng’s team has discovered that the skull doesn’t belong to any old cat. As they’ve documented in a study published today in Proceedings of the Royal Society B, the skull and six associated fossilized jawbone fragments are the first evidence of a newly discovered species, which they’ve called Panthera blytheae. The discovery represents the oldest “big cat” (a group that includes large predatory cats like lions, jaguars, tigers and leopards) ever found by a wide margin.
The sediments that make up the basin as a whole range from 6 million to 400,000 years in age, so the group dated the fossil by analyzing the age of the particular rock layers it was buried in. This involved using techniques of magnetostratigraphy, in which scientists analyze the magnetic orientation of the rocks and compare it to known reversals of the Earth’s magnetic field. This method can only provide rough estimates for an item’s age, but it revealed that the skull is between 4.10 and 5.95 million years old. Previously, the oldest known big cat fossils—a number of tooth fragments found in Tanzania—were 3.6 million years old.
The new find fills a gap in the evolutionary record of big cats. By analyzing the DNA of living species, scientists had previously estimated that big cats had split from the Felinae subfamily—which includes smaller wild cats, like cougars, lynxes, along with domestic cats—about 6.37 million years ago. The very existence of P. blytheae confirms that the split happened prior to when this big cat roamed.
But how much earlier? The find could suggest, Tsang says, that big cats branched off from smaller cats much farther back than thought. By comparing the skull’s characteristics with fossils from other extinct big cats, the anatomy of living cat species, and DNA samples taken from both living cats and a few recently extinct, Ice Age-era species (known as cave lions), the researchers assembled a new evolutionary family tree for all big cats. Using known rates of anatomical changes over time and the observed anatomy of P. blytheae, they projected backwards, and estimated that the earliest big cats likely branched off from the Felinae subfamily between 10 and 11 million years ago.
The new fossil also solves a geological mystery. Previously, using DNA analysis of all living big cats and mapping the the fossils excavated from various sites around the world, researchers had determined it was most likely that their common ancestor had lived in Asia. The oldest known specimens, however, were found in Africa. The new species provides the first direct evidence that central Asia was indeed the big cats’ ancestral home, at least as far back as the current fossil record currently goes.
From the fragmented fossils, it’s hard to know much about the extinct species’ behavior and lifestyle, but the researchers were able to make some basic extrapolations from the skull’s anatomy. “It’s not a huge cat, like a lion or a tiger, but closer to a leopard,” Tsang says. The creature’s habitat was likely similar to the current Tibetan plateau, so Tseng speculates that, like the snow leopards that currently live in the area, this species did not hunt on the open plains, but rather cliffs and valleys. Tooth wear patterns also suggest similarities with current snow leopards—the rear teeth, likely used for cutting soft tissue, remain sharp, whereas the front teeth are heavily worn, perhaps reflecting their use in prying open carcasses and picking meat off bones.
Tseng says that he and colleagues plan to return to the area to search for more fossils that could help enlighten us on the evolutionary history of big cats. “The gap still isn’t completely filled yet,” he says. “We need to find older big cats to put the picture together.”
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.
November 5, 2013
In October 2012, a Duke University biologist named a newly discovered genus of ferns after Lady Gaga. Then, in December, Brazilian scientists named a new bee species Euglossa bazinga, after a catch phrase from a TV show.
“The specific epithet [bazinga] honors the clever, funny, captivating “nerd” character Sheldon Cooper, brilliantly portrayed by the North American actor James Joseph “Jim” Parsons on the CBS TV show ‘The Big Bang Theory,’” they wrote [PDF]. Scientists weren’t done honoring dear old Sheldon: This past August, he also got a new species of jellyfish, Bazinga rieki, and was previously heralded with an asteroid.
These organisms and astronomical entities are far from the first to be given cute pop culture-inspired names. The tradition goes back at least a few decades, with bacteria named after plot elements from Star Wars, a spider named for Frank Zappa and a beetle named after Roy Orbison.
All of which makes an observer of science wonder: Why do we keep naming species after figures from movies, music and TV shows?
“Mostly, when you publish research about termite gut microbes, you don’t get much interest—even most of the people in the field don’t really give a crap,” says David Roy Smith, a scientist at University of Western Ontario who studies these and other types of microorganisms for a living. Recently, though, he saw firsthand that this doesn’t always have to be the case: His colleagues discovered two new species of protists that lived inside termite guts and helped them digest wood, and the group named them Cthulhu macrofasciculumque and Cthylla microfasciculumque, after the mythical creature Chtulhu, created by influential science fiction writer H.P. Lovecraft.
“I remember Erick James, who was the lead author on the study, telling us that he’d named it something cool right before we submitted it, but we didn’t really pay him much attention,” Smith says. “Then, afterwards, day after day, he kept coming into the lab telling us he’d seen an article on the species on one site, then another. By the second week, we were getting phone calls from the Los Angeles Times.” Eventually, James was invited to present work on the protists at an annual conference of H.P. Lovecraft fans, and a search for Cthulhu macrofasciculumque now yields nearly 3,000 results.
The episode prompted Smith to take silly scientific names seriously for the first time—so much so that he wrote an article about the phenomenon [PDF] in the journal BioScience last month. For him, a scientist’s incentive in giving a new discovery this sort of name is obvious. “Science is a competitive field, if you can get your work out there, it’s only going to help you,” he says. Mainstream press attention for an esoteric scientific discovery, he feels, can also garner increased citations from specialists in the field: A microbe researcher is likely to notice a Cthulhu headline on a popular news site, then think of it when she’s writing her next paper.
But is naming species after sci-fi villains and TV catch phrases good for science as a whole? Smith argues that it is. “Scientists are perceived to be serious and stiff,” he says. “When you put some entertainment and fun into your work, the general public gets a kick out of it, and appreciates it a little more.” In an age when public funding for science is drying up, garnering every bit of support can make a difference in the long-term.
There are critics who take issue with the idea, though. It’s easy to imagine, for instance, that the vast majority of the people who shared articles about Lady Gaga’s fern focused mostly on the pop star, rather than the botanical discovery.
Moreover, species names are forever. “The media interest will subside, but the name Cthulhu will stay and plague the biologists who deal with this organism, tomorrow and 200 years from now. It’s difficult to spell and pronounce and utterly mysterious in meaning for people who don’t know Lovecraft,” Juan Saldarriaga, a research fellow at the University of British Columbia, told Smith for his BioScience article. “And for what? People saw the name on their Twitter account, smiled, said ‘Cool,’ and then went on with their lives.”
For his part, Smith feels that all species names inspired by pop culture are not created equal. The Cthulhu microbe, for example, is named after a legendary character with legions of fans nearly a century after its creation; moreover, the protist itself, with a tentacle-like head and movements resembling an octopus, calls to mind Lovecraft’s original Cthulhu character. This is a far cry from, say, a bee, jellyfish and asteroid all named for a catch phrase from a current (and likely to be eventually forgotten) primetime sitcom. “You can do it tactfully, and artfully,” Smith says. “Other times, people might be reaching, and just desperately want to give something a popular name.”
It’s also worth remembering one of the earliest instances of naming a discovery after heroes from contemporary culture: the planets, which the ancient Greeks named after their gods–for example, the gods of war and love. The planets were later rebranded by the Romans—and nowadays, the average person might have no idea that Mars and Venus were gods in the first place—but their names live on.
This blogger’s opinion? Long live Cthulhu.
November 1, 2013
For the first few decades of his career, Emory neuroscientist Gregory Berns studied the human mind. Using fMRI technology, which tracks the flow of blood to different areas of the brain, he sought to find correlations between people’s internal mental patterns and their real-world behaviors, decisions and preferences.
Then, in 2011, he took on a new object of neuroscientific study: Canis lupus familiaris, otherwise known as the domesticated dog. Instead of merely studying canine behavior, as has been done for years, he and his colleagues began scrutinizing the internal architecture and patterns of dogs’ brains, using the same tools they rely on to better understand the brains of humans.
“I’ve always been a dog person, and when my dog died, a pug named Newton, it planted a seed in my mind,” says Berns, who published a new book on his recent work, How Dogs Love Us, last week. “It got me wondering about how dogs view their relationship with us—if he had loved me the same way I had loved him.”
Just looking inside inside the canine brain, however, posed a formidable challenge: Getting an accurate fMRI reading means that the subject has to stay almost perfectly still, moving less than a millimeter from one moment to the next. Using anesthesia or restraining the dogs would ruin the experiments, producing an image of an unconscious or anxious dog instead of a comfortable, alert one.
To solve the problem, Berns recruited dogs from the local community—starting with a dog he adopted after Newtown died—and gradually trained them to climb up a series of steps into a table, rest their head on a pad inside the fMRI’s inner tunnel and sit still for 30 seconds at a time as the machine does its work. To deal with the device’s noise (which can surpass 95 decibels, equivalent to the sound of a jackhammer 50 feet away), they taped earmuffs to the dogs’ heads and piped in ambient noise over loudspeakers, so instead of the machine’s sound beginning abruptly, it gradually arrived over background noises.
In total, they’ve successfully trained about a dozen dogs to voluntarily participate in their studies. The research is still in its preliminary stages, but as Berns’ team begins to scratch the surface of the canine brain, they’re finding something surprising—in several ways, its activity mirrors that of the human brain to a much greater extent than expected.
As part of their first paper published on the work in 2012, they trained dogs to recognize two different hand signals: one that meant the animal would be given a piece of hot dog imminently, and one that meant no hot dog. As they hypothesized, the first signal triggered elevated activity in an area called the caudate nucleus, which is rich in receptors for dopamine (a neurotransmitter involved in the sensation of pleasure). In humans—and in dogs, the research indicated—caudate activity is related to the desire to have something that causes pleasure, and the satisfaction involved in obtaining it.
Subsequent work revealed more unexpected findings. As part of a second experiment, they had dogs sit in the scanner and exposed them to smells of humans (from either their owners or strangers) and other dogs (from either dogs they lived with or unfamiliar dogs). “We wanted to understand how dogs recognize other people and dogs in their households,” Berns says. Again, they saw increased activity in the caudate, but only as a result of one of the scents. “In this case, the reward system only seems to activate in response to the smell of a familiar human, which is pretty amazing,” he says.
To further probe how the dogs’ brain activity correlates with the actions of humans they know well, they put the dogs in the fMRI and had their owners leave the room, then walk back in. This, too, triggered activation in the caudate.
Berns interprets these results as indications that, in some ways, the mental processes of dogs may not be so different from those of humans. They’re close enough, he suggests, that we can safely describe them with words we don’t often apply to animals: the mental activity represents emotions, and perhaps even constitute love. “At some fundamental level, we believe the dogs are experiencing emotions something like we do,” Berns says.
He admits that the idea is controversial. But, he points out, the research suggests that the human brain and canine brain aren’t as radically different as we might have imagined.
“Obviously, dog brains are much smaller, and they don’t have as much cortex as we do, but some of the core areas around the brainstem—the basal ganglia, which the caudate nucleus is part of—look very much like those in humans,” he says. Dogs might not have the hardware necessary for complex thoughts and higher-level reasoning, the thinking goes, but they do have the relevant structures for basic emotions.
This also makes sense from an evolutionary perspective: We evolved the heavily folded cortex necessary for high-level thinking after we diverged from all other animal species, but areas like the basal ganglia developed beforehand, so it follows that our ability to feel emotions produced by those areas existed way back in our evolutionary history, in ancestors that we share with many other mammals, including dogs.
Dog lovers mind find these ideas obvious, but Berns’ work has attracted a fair amount of criticism. One of the biggest complaints is against his use of words like emotion and love for dogs—their attachment to us is simply a result of conditioning, some say, entirely based on the desire for food, rather than the deeper emotional connections we feel for other humans.
But Berns hopes to respond with future fMRI work, which will compare brain activity in dogs being fed by automated mechanisms with that of dogs being fed by humans. He hopes to show that dogs do develop qualitatively different relationships with humans, underscoring the strength of those attachments.
He took his ideas to what some might call as a rather extreme conclusion earlier this month in the New York Times, in an op-ed he penned with a provocative headline: Dogs Are People, Too. If animals truly are capable of emotions we normally consider characteristically human, he argued, they should no longer be treated as mere objects, or property, but instead be given some of the rights we associate with personhood—namely, a respect for their preferences and well-being that would lead to the abolition of things like puppy mills and dog racing.
There’s obviously a long way to go—both in terms of scientific evidence and policy changes—before dogs are treated anything like people. But Berns cites a recent Supreme Court decision that invoked neuroscientific evidence (specifically, the finding that the juvenile brain is less developed than a mature adult’s, and thus should not be subject to the same punishments) as an indication that our laws will inevitably follow the science. The next step, then, is for he and his colleagues to keep peering into the minds of dogs, finding out how deeply the mental similarities truly go.