May 1, 2012
We live in an age of alarming extinction, in which many species are lost in large part due to human activity. At the same time, the natural world is so complex that even after centuries of research, scientists are still rapidly discovering new species everywhere from mountain tops to rain forests to the ocean floor.
This paradox is aptly illustrated by an announcement made yesterday: 24 new species of lizards, known as skinks, have been discovered in the Caribbean islands. But half of them may be close to extinction, and some may already extinct in the wild.
The research was conducted by a team led by Blair Hedges, a biologist at Penn State University and one of the world’s foremost experts at identifying new forms of life. Previously, Hedges has been involved with the discovery of what were then the world’s smallest snake, lizard and frog. The two dozen species named in this paper, published in the journal Zootaxa, constitute one of the largest mass discoveries of lizards in centuries.
To identify the many species of skinks (formally, members of the family Scincidae), Hedges and his team examined specimens housed at zoos and conservation centers around the world. By comparing taxonomic features of the lizards (such as the shapes of scales) and using DNA analysis, they determined that there are a total of 39 distinct species of skinks that live in the Caribbean—6 species that were previously recognized, 9 that had been named long ago but had been considered invalid and the 24 entirely new ones.
“Now, one of the smallest groups of lizards in this region of the world has become one of the largest groups,” Hedges said in a press release. “We were completely surprised to find what amounts to a new fauna, with co-occurring species and different ecological types.” He has determined that the skinks came to the Americas roughly 18 million years ago, likely arriving from Africa on floating rafts of vegetation.
How did the skinks go unnoticed for so long? Hedges speculates that because large numbers of skinks had already disappeared by the start of the 20th century, scientists, tourists and local residents have been much less likely to encounter them in the years since. Additionally, many of the characteristics that distinguish the species from one another have been overlooked or weren’t detectable until now, especially those indicated by DNA analysis.
The researchers determined that the skinks have long been most threatened by an exotic intruder: the mongoose, introduced from India to Cuba in 1872 with the intention of reducing rat populations in sugarcane fields. Rat populations were partially controlled, but by 1900, nearly half of the islands to which the mongoose had spread were also without skinks, and the remaining lizards have dwindled in population ever since. Additionally, the researchers note, current human activities such as forest removal are likely contributing to the skinks’ endangered status. The research team hopes that their data will be used to plan future conservation efforts.
Theoretically, if you’re in the U.S. Virgin Islands, Trinidad and Tobago, or Martinique, you might try looking for a skink. But because each of the species is remarkably rare—with even the non-endangered ones qualifying as vulnerable—it’ll certainly be difficult. Above all, if you do want to find one, hurry up: there may not be much time left.
February 1, 2012
American cane toads (Rhinella marina), native to Central and South America, are an invasive species in Australia. These toads contain a substance called “bufotoxin” that makes a lot of predators ill, sometimes fatally. (Warning: This is very poisonous stuff. Do not even lick a cane toad!)
Australian animals that eat this toad are typically poisoned by it, but one animal, the bluetongue skink (Tiliqua scincoides), appears to be able to eat the toad with few or no ill effects. Or, more exactly, some bluetongue skinks can eat the cane toads, depending on where they live.
Many animals and plants produce complex molecules (like bufotoxin) that have been shaped by natural selection to be toxic to predators. Some of our favorite spices, such as basil, chili peppers and other aromatic plants, owe their culinary properties to these molecular adaptations to herbivory. Only a few mammals produce molecular toxins, but many frogs and toads do.
If a weapon evolves in nature, there is a certain chance that a counter-weapon will also evolve. Many insects that feed on toxic plants have evolved the ability to sequester the poisonous molecules produced by those plants, rendering them harmless to the insect, and in some cases concentrating the undesirable substance in the insect’s own body to be used as a defense against insect-eating animals (usually other insects). Many mammals have enzymes in their digestive tract that detoxify plants that would otherwise be harmful. The evolution of toxicity and the evolution of anti-toxin strategies is considered an arms race between the eaten and the eaters.
So, it would be reasonable to suspect that the bluetongue skink has evolved a physiological mechanism to combat the bufotoxin produced by the cane toads. But it turns out that the explanation for the ability of some skinks to snack on the toxic toads is a little more complicated.
Another invasive species found in Ausralia is the ornamental “mother-of-millions” plant, a Bryophyllum from Madagascar. This plant produces a toxin that is chemically similar to bufotoxin. Why is it chemically similar to bufotoxin? This is probably a coincidence. If you have a large number of animals and plants producing toxins, sometimes there are going to be accidental similarities.
The mother-of-millions plant is invasive and found in the wild in certain areas of Australia, but it is not common everywhere. Bluetongue skinks that live where mother-of-millions is common appear to have adapted to eating them, and as such posses the ability to neutralize bufotoxin-like molecules. When these skinks encounter cane toads, they eat them without consequence. In fact, the skinks living in these area regularly eat both the mother-of-millions plants and the cane toads.
This research was was carried out by scientists at the Richard Shine Lab at the University of Sidney.
Price-Rees, Samantha J. Gregory P. Brown, Richard Shine, 2012. Interacting Impacts of Invasive Plants and Invasive Toads on Native Lizards. Natural History Editor: Craig W. Benkman. Published online Jan 25, 2012
January 30, 2012
Ed. note: We welcome back guest blogger Greg Laden for a two-week blogging tour on Surprising Science.
This is a story of snakes, islands and students. Let’s start with the snakes.
Among the many different kinds of snakes are the constrictors: boas and pythons. They are close relatives that diverged millions of years ago. Pythons are found in the Old World (Africa and Asia) as well as Australia. Boas (family Boidae) are found in the New World (North, Central and South America including some Caribbean islands). All of them kill their prey by wrapping around it and squeezing it to death.
Among the boas there is an island-dwelling form in Belize that is the subject of interest to conservationists, ecologists and, lately, behavioral biologists. This is the miniature boa of Snake Cayes, a group of islands off the coast of southern Belize. When I say “miniature” I mean that they range in length from 30 cm to about 2 meters (1 to 6 feet). This is small compared to the mainland boas of the same species, which can reach 4 meters (13 feet) in length.
It is common for animal populations that live on islands to exhibit differences in size from those on the mainland. Medium and larger mammals like deer tend to be smaller on islands, small mammals like rodents tend to be larger. Something like this may happen with snakes as well.
Scott Boback is an expert on these animals, and from the time he was a graduate student at Auburn University, he’s been trying to answer the question “how and why are these snakes small?”
The most likely explanations for size differences would seem to be either diet or other features of the environment, or genetics. Perhaps there is a limited food supply on the islands, so snakes grow slowly, and thus there are few or no large ones. It would take them so long reach a large size that somewhere along the line they would have met their demise. Alternatively, it could be that snakes that grow slowly or nearly stop growing as they approach a certain size survive longer or reproduce more effectively (probably owing to food supply being limited). If so, the genes involved in growth would be shaped by natural selection and over time the island snakes would be small because they are genetically different. You can easily imagine how the two processes would work together, perhaps with environmental effects working initially but genetic changes accruing over time.
Boback did eventually come to a conclusion about the small size of the island boas. He recently told me, “we determined that there is some genetic component to dwarfism on islands. However, we believe that it is actually a combination of genetic and environmental effects that ultimately determine island boa size. That is, growth rates are different between island and mainland boas and this appears to be determined partly by genetics.” (See below for the reference to his paper on this research.)
More recently, Boback and his students at Dickinson College have been addressing a different question about boas: How do they know when to stop squeezing their prey? This is an interesting question because, as you might imagine, contracting the majority of muscles in one’s body for an extended period of time is energetically costly, but letting go of prey before it is fully dead may cause the loss of a meal. As an informal experiment, I asked five different people this question over the past two days, after reading of Boback’s research, and everyone gave approximately the same answer: The snakes let go when the prey is dead and stops struggling.
Well, it turns out that we do science to prove ourselves wrong, because that is not the answer. Suspecting a particular mechanism, Boback his students, who maintain a colony of these boas in their lab at Dickinson, devised a brilliant experiment. They took a number of dead rats that would normally be fed to the snakes, and installed robotic “hearts” in them. When the snakes constricted the rats, the hearts were allowed to beat for a while, then they were turned off. Soon after, the snakes loosened their grip, then let go.
It turns out that boas have the ability to detect a heartbeat in the prey, and they use this information to determine how much pressure to apply. Snakes that had never killed or eaten live prey acted the same as snakes with experience with live prey, suggesting that this behavior is innate and not learned.
“Many of us think of snakes as audacious killers, incapable of the complex functions we typically reserve for higher vertebrates,” says Boback. “We found otherwise and suggest that this remarkable sensitivity was a key advancement that forged the success of the entire snake group.”
One of the neat things about this project is that it involved the efforts of undergraduate researchers. The undergraduates not only participated in the research, but they helped produce the peer reviewed paper and are listed as authors. Katelyn McCann, who was a student on this project and now works as a clinical-research coordinator at Children’s Hospital in Boston, notes, “I got to experience the true collaborative nature of research as well as the hours of independent work that go into the final product. Now, working in research I feel like I truly understand the scientific method and what goes into any study.” Boback adds, “student-faculty research at Dickinson is an opportunity for students to experience science in action. It is the most fundamental level of learning in science as the student actively participates in the process of discovery.”
Boback, S., Hall, A., McCann, K., Hayes, A., Forrester, J., & Zwemer, C. (2012). Snake modulates constriction in response to prey’s heartbeat Biology Letters DOI: 10.1098/rsbl.2011.1105
Boback, S. M. and D. M. Carpenter. 2007. Body size and head shape in island boas (Boa constrictor) in Belize: Environmental versus genetic contributions. Pages 102-116 in R. W. Henderson and R. Powell, editors. Biology of the boas, pythons, and related taxa. Eagle Mountain Publishing, Eagle Mountain, UT.
Additional information for this story came from Dr. Scott Boback, and a press release from Dickinson College.
January 23, 2012
Around the world, people are celebrating the Chinese New Year and the start to the Year of the Dragon. This got us wondering: Where did the myth of the dragon come from in the first place? Scholars say that belief in dragons probably evolved independently in both Europe and China, and perhaps in the Americas and Australia as well. How could this happen? Many have speculated about which real-life animals inspired the first legends. Here’s our run-down of the likeliest suspects.
Dinosaurs. Ancient people may have discovered dinosaur fossils and understandably misinterpreted them as the remains of dragons. Chang Qu, a Chinese historian from the 4th century B.C., mislabeled such a fossil in what is now Sichuan Province. Take a look at a fossilized stegosaurus, for example, and you might see why: The giant beasts averaged 30 feet in length, were typically 14 feet tall and were covered in armored plates and spikes for defense.
The Nile Crocodile. Native to sub-Saharan Africa, Nile crocodiles may have had a more extensive range in ancient times, perhaps inspiring European dragon legends by swimming across the Mediterranean to Italy or Greece. They are among the largest of all crocodile species, with mature individuals reaching up to 18 feet in length—and unlike most others, they are capable of a movement called the “high walk,” in which the trunk is elevated off the ground. A giant, lumbering croc? Might be easy to mistake for a dragon.
The Goanna. Australia is home to a number of species of monitor lizards, also referred to as Goannas. The large, predatory animals have razor-sharp teeth and claws, and they are important figures in traditional Aboriginal folklore. Recent studies even indicate that Goannas may produce venom that causes bite victims’ wounds to develop infections after an attack. At least in Australia, these creatures may be responsible for the dragon myth.
Whales. Others argue that the discovery of megafauna such as whales prompted stories of dragons. Ancient humans encountering whale bones would have no way of knowing that the animals were sea-based, and the idea of such gargantuan creatures might well have led people to assume that whales were predatory. Because live whales spend up to 90 percent of their time underwater, they were poorly understood for most of human history.
The Human Brain. The most fascinating explanation involves an unexpected animal: the human. In his book An Instinct for Dragons, anthropologist David E. Jones argues that belief in dragons is so widespread among ancient cultures because evolution embedded an innate fear of predators in the human mind. Just as monkeys have been shown to exhibit a fear of snakes and large cats, Jones hypothesizes that the trait of fearing large predators—such as pythons, birds of prey and elephants—has been selected for in hominids. In more recent times, he argues, these universal fears have been frequently combined in folklore and created the myth of the dragon.
October 26, 2011
Side-blotched lizards (Uta stansburiana) are a small lizard species found in many states in the American West and Mexico. Males come in three varieties, each with a different throat color: orange, yellow or blue. Those throat colors announce to the lizard world what mating strategy a male will use. Orange-throated males are bigger and more aggressive, and they have large territories with several females. Blue-throated males have smaller territories with only one female, and they cooperate with other blues for defense. Yellow-throated males, whose markings and behaviors mimic those of females, are known as “sneakers”; they don’t keep a territory but instead cluster around and sneak into the territories of other males to mate with their females.
And like a big game of rock-paper-scissors, each variety has its pluses and minuses in the mating game. The result is that once every few years, the original study in Nature found, the dominant variety changes.
If we start with the orange males, they have the advantage over blues in terms of territory size and numbers of females they control. But with more territory controlled by orange males, the more opportunities for sneaky yellow males to mate, and then the yellow population begins to grow. But the yellows are vulnerable to the blues, who can easily defend their females because they cooperate with other blues, so then they take over. But then oranges mate with more females and grow in numbers again. Orange is most successful when blues are greater in number; yellows are most successful when oranges are greater in number; blues are most successful when yellows are greater in number. The result is a cycle that has persisted for millions of years.
But not everywhere. Further research into this species, published in PNAS, has found that there are many populations of this species that have lost one or two of the color varieties. The yellows were always the first to go; something (not yet known) had changed the game’s rules so that they no longer had any advantages over orange or blue. Some places had also lost their oranges and others had also lost their blues. And that loss of a color variety or two had further consequences: It was accompanied by rapid changes in traits like body size in the remaining lizard types, changes that could lead to the evolution of new species.
These lizards came up in a conversation among some of my friends earlier this year (a mathematician in the group told me about the lizards, which, along with the rock-paper-scissor game, have been studied in game theory). One of them was wearing a rock-paper-scissors-lizard-Spock T-shirt, illustrating that lesser-known variant of the game. I am disappointed to report, however, that I was unable to find any link between it and the discovery of the lizards’ mating strategy.