November 20, 2013
In 1834, Charles Darwin discovered a strange animal during his exploration of Chile’s southern coast. The creature, a small frog, was shaped like a leaf with a pointed nose, but appeared puffed up as if had been blown full of air, like a balloon. As it turned out, those fat male frogs hadn’t been gorging themselves on too many mosquitoes, but instead were enacting duties that earn them distinction as one of nature’s best dads. They were incubating several of their squirming babies in their vocal sac.
These peculiar animals, known as Darwin’s frogs, are today divided into two species, one that occurs in northern Chile, and another that lives in southern Chile and Argentina. When a female Darwin’s frogs lay her eggs, her mate keep a careful watch until the tadpoles hatch. The eager dad then swallows his young, allowing the babies to safely grow within his vocal sac until they turn into frogs and are ready to strike out on their own. Here, you can see a dutiful papa frog seemingly vomit up his living young:
Northerly Darwin’s frogs, however, have not been spotted in the wild since 1980. Researchers are nearly certain the species is extinct. Meanwhile, their southerly cousins are in steep decline and seem to be heading down extinction’s death row as well. For once, it seems that humans are not entirely to blame for these biodiversity disasters (unlike the western black rhino, which bit the dust a couple years ago after enduring decades of poaching for its valuable but medicinally worthless horn, used as an ingredient in traditional Chinese medicine). Instead, the deadly amphibian chytrid fungus, researchers report today in PLoS One, is likely to blame.
The chytrid fungus has popped up in amphibians in North and South America, Europe and Australia. The fungus infects the animals’ skin, preventing them from absorbing water and other nutrients. The fungus can rapidly decimate amphibian populations it comes into contact with, and has been called (pdf) “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction” by the International Union for Conservation of Nature.
To identify chytrid as the likely culprit behind the Darwin’s frogs disappearance and decline, researchers from Chile, the UK and Germany conducted a bit of historical sleuthing. They dug up hundreds of archived specimens of Darwin’s frogs and closely related species dating from 1835 until 1989, and then tested them all for fungal spores (the problematic form of chytrid fungus was first recorded in the 1930s and reached epidemic-status around 1993, but researchers aren’t certain of when it first emerged). They also took around 800 skin swabs between 2008 and 2012 from 26 populations of still-living southern Darwin’s frogs and other similar frog species that live nearby.
Six of the old museum specimens, all collected between 1970 and 1978–just before the northern Darwin’s frog’s disappearance–tested positive for the disease. More than 12 percent of the living frogs tested positive for the fungal spores. In places where the Darwin’s frog has gone extinct or is experiencing drastic declines, however, rates of infection jumped to 30 percent in other amphibian species. Although these events don’t prove that the fungus killed the northern Darwin’s frogs and are now wiping out the southern species, the researchers strongly suspect that is the case.
Despite evidence that the disease has spread throughout the Darwin’s frog’s range, the researchers are not giving up on hope to save one of the world’s greatest dads from extinction. “We may have already lost one species, the Northern Darwin’s frog, but we cannot risk losing the other one,” Claudio Soto-Azat, the study’s lead author, said in a statement. ”There is still time to protect this incredible species.”
October 16, 2013
Most scientists conduct their research in a lab, or by working with calculations or simulations on computers. Some engage in field work, perhaps observing animals in the wild or excavating fossils.
Then, there’s the team of biologists from Brown University led by Henry Astley that studies the movement of animals and has been conducting some science in a decidedly less conventional atmosphere. Recently, they traveled to the Calaveras County Jumping Frog Jubilee in Angels Camp, California—the county made famous by Mark Twain’s 1865 short story—to film and analyze 3124 of the jumps and try to figure out exactly how the bullfrogs in the competition jump so far.
The idea originated, they say, with the realization that expert frog “jockeys” (annual competitors that bring their own frogs and urge them to jump with special techniques) were far better than scientists at getting the animals to clear vast distances: The longest bullfrog jump ever recorded in a lab was 4.26 feet, while frogs at the competition surpassed that figure regularly, at times jumping 6 or 7 feet.
To figure out how this was possible—in terms of biomechanics, muscle strength and other limits of physiology—the group traveled to the competition, documenting their results in a paper published today in the Journal of Experimental Biology. They caught on camera bullfrogs jumping as far as 7.2 feet, and calculated that the frogs beat the lab record of 4.26 feet 58 percent of the time.
How do these superlative bullfrogs do it? The data indicated that apparently, the jockeys’ strange-looking approach to motivating the frogs really does make a huge difference.
Jockeys take their craft seriously—beyond the $50 prize for breaking the world record, there are the immense bragging rights of winning the world’s foremost frog-jumping competition, which attracts thousands of entrants annually and dates to 1893. These jockeys, the authors write, “bring their own locally-caught frogs and are serious competitors, often working in family groups that have passed down frog jumping secrets through generations of competition.”
The rules dictate that each competitor’s frog is allowed three jumps in a row, and the distance of each jump is combined for the total score. The current record, set in 1986 by “Rosie the Ribiter” and jockey Lee Giudici, is 21 feet, 5 3/4 inches: 7.16 feet per jump. On average, the scientists observed that at the recent Jubilee, the jockeys’ frogs jumped nearly 5 feet per attempt.
But the researchers were gratified to find that they weren’t alone in being outclassed by the jockeys. The Jubilee’s “rental” frogs—which are available for amateurs to rent so they can enter the competition themselves—only averaged 3.6 feet per jump, similar to those in the lab.
Part of the explanation for this discrepancy was made apparent in the scientists’ calculations, which they made after they digitized each filmed jump so they could conduct a detailed analysis. These showed that, compared to rental frogs, the jockeys’ had a greater take-off velocity, jumped at a higher angle compared to the ground and performed more work with their leg muscles as they sprang off the ground.
What’s the underlying reason for this superior performance, though? The jockeys are required to use the exact same species of frogs as the amateurs, and the researchers reported that, outwardly, they didn’t look all that different.
They surmised that the difference was what Astley calls “the will of the jockey.” He explains, in a press statement: “The frog senses whether you are a scientist hoping it’s going to jump well, or a deadly reptilian-like predator who is going to eat it.”
To resemble this deadly predator, jockeys follow a ritualized strategy that’s been honed over the past few decades. Crouching, they rub the frogs’ hind legs, then drop them a short distance to the ground. A moment after the frog lands, they chase after it head-first, either shouting at it or blowing at it from behind. Apparently, this behavior powerfully triggers the frogs’ flight instincts, leading them to jump the greatest possible distance.
For the researchers, this led to an interesting question: Do the Jubilee-winning 7-foot jumps represent the pinnacle of sheer bullfrog ability? Their theoretical calculations, based on our knowledge of the frogs’ muscle strength, energy, jump velocity and angle, indicate that the answer is yes—the frogs probably can’t jump any farther than this length.
This answer is supported by historical trends in the competition. For the first few decades in which figures were kept, the record repeatedly shot up by leaps and bounds, going from roughly 12 feet (for 3 combined jumps) in 1930 to nearly 17 feet in 1953 to 20 feet in 1976. Since then, it’s been relatively stagnant, only creeping past 21 feet in 1986 and remaining unbroken in the years since.
This sort of trend indicates that jockeys figured out the best method by trial-and-error, then hit the bullfrogs’ physiological wall—and that when it comes to frog-jumping Jubilees, it’s jockeys, not frogs, that win championships.
March 25, 2013
As Easter draws near, we begin to notice signs of nature’s very own annual resurrection event. Warming weather begins “breeding lilacs out of the dead land,” as T.S. Elliot noted, and “stirring dull roots with spring rain.” Where a black and white wintery landscape just stood, now technicolor crocus buds peak through the earth and green shoots brighten up the azalea bushes.
Aside from this grand show of rebirth, however, nature offers several cases of even more overtly stunning resurrections. From frozen animals jumping back into action during spring thaws to life blooming from seemingly desolate desert sands, these creatures put a new spin on nature’s capacity for revival.
As its name suggests, during a drought the resurrection fern shrivels up and appears dead, but with a little water the plant will burst back into vibrant life. It can morph from a crackled, desiccated brown into a lush, vibrant green in just 24 hours.
The fern doesn’t actually die, but it can lose up to 97 percent of its water content during an extreme dry spell. In comparison, other plants will usually crumble into dust if they lose more than 10 percent of their water content. Resurrection ferns achieve this feat by synthesizing proteins called dehydrins, which allow their cell walls to fold and reverse back to juicy fullness later.
Resurrection ferns are found as far north as New York and as far west as Texas. The ferns needs another plant to cling to in order to grow, and in the south it’s often found dramatically blanketing oak trees. A fallen oak branch covered in resurrection ferns are common features in southern gardens, though the ferns have also turned up in more uncanny locales: in 1997, astronauts took resurrection fern specimens onto the Space Shuttle Discovery to study how the plant resurrects in zero gravity. As investigators write (PDF), the fern “proved to be a hardy space traveler and exhibited regeneration patterns unaltered by its orbital adventure.” This earned it the title of “first fern in space.”
Brine shrimp, clam shrimp and tadpole shrimp
In the deserts of the western U.S., from seemingly life-barren rocks and sands, life blooms by just adding a little rain water. So-called ephemeral pools or “potholes” form tiny ecosystems ranging from just a few millimeters across to several meters deep. The ponds can reach up to 140 degrees Fahrenheit in the summer sun or drop below freezing during winter nights. They can evaporate nearly as quickly as they appeared, or linger on for days or weeks. As such, the animals that live there all have special adaptations for allowing them to thrive in these extreme conditions.
Some of the potholes’ most captivating critters include brine shrimp (of sea monkey fame!), clam shrimp and tadpole shrimp. These crustaceans practice a peculiar form of drought tolerance: In a process known as cryptobiosis, they can lose up to 92 percent of their body water, then pop back into fully-functional action within an hour of a new rain’s arrival. To do this, the tiny animals keep their neural command center hydrated but use sugar molecules instead of water to keep the rest of their cells intact throughout the drought. Like resurrection ferns, brine shrimp, too, have been taken into space–they were successfully hatched even after being carried outside of the spacecraft.
Most of these animals only live for about ten days, allowing them to complete their entire life cycle (hopefully) before their pool dries up. Their dried eggs are triggered to hatch not only when they’re hydrated again but also when oxygen content, temperature, salinity and other factors are just right. Some researchers, such as this zoologist quoted in a 1955 newspaper article, think that the eggs can remain dormant for several centuries and still hatch when conditions are right.
Some amphibians undergo their own sort of extreme hibernation in order to survive freezing winter temperatures. This suspended animation-like state allows them to slow down or stop their life processes–including breathing and heartbeat–just to the brink of death, but not quite. Wood frogs, for example, may encounter freezing conditions on the forest floor in winter. Their bodies may contain 50 to 60 percent ice, their breathing completely stops and their heartbeat is undetectable. They may stay like this for days, or even weeks.
They achieve this through a specially evolved biological trick. When the frogs encounter the first signs of freezing, their bodies pull moisture away from its central organs, padding them in a layer of water which then turns into ice. Before it freezes, the frog also floods its circulatory system with sugar molecules, which act as an antifreeze. When conditions warm up again, they can make a complete recovery within a day, which researchers call “spontaneous resumption of function.” Here, Robert Krulwich explains the process:
As seen through these examples, some creatures really do come back from the brink of death to thrive!
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
June 20, 2011
When I started working on this frog blog post (inspired by the adorable yet deadly poison dart frogs at the National Zoo), my knowledge of frogs was limited to Mr. Toad from The Wind in the Willows and Kermit. Obviously, I had a lot to learn. I have since discovered many amazing, surprising, disgusting and flat-out weird facts about frogs, and have collected the 14 best to share here with you:
1 ) One gram of the toxin produced by the skin of the golden poison dart frog could kill 100,000 people.
2 ) The female Surinam toad lays up to 100 eggs, which are then distributed over her back. Her skin swells around the eggs until they become embedded in a honeycomb-like structure. After 12 to 20 weeks, fully formed young toads emerge by pushing out through the membrane covering the toad’s back.
3 ) A frog completely sheds its skin about once a week. After it pulls off the old, dead skin, the frog usually eats it.
4 ) When Darwin’s frog tadpoles hatch, a male frog swallows the tadpoles. He keeps the tiny amphibians in his vocal sac for about 60 days to allow them to grow. He then proceeds to cough up tiny, fully formed frogs.
5 ) When a frog swallows its prey, it blinks, which pushes its eyeballs down on top of the mouth to help push the food down its throat.
6 ) The wood frog of North America actually freezes in the winter and is reanimated in the spring. When temperatures fall, the wood frog’s body begins to shut down, and its breathing, heartbeat and muscle movements stop. The water in the frog’s cells freezes and is replaced with glucose and urea to keep cells from collapsing. When there’s a thaw, the frog’s warms up, its body functions resume and it hops off like nothing ever happened.
7 ) A group of birds is called a flock, a group of cattle is called a herd, but a group of frogs is called an army.
8 ) The glass frog has translucent skin, so you can see its internal organs, bones and muscles through its skin. You can even observe its heart beating and its stomach digesting food.
9 ) There is a frog in Indonesia that has no lungs – it breathes entirely through its skin.
10 ) The waxy monkey frog secretes a wax from its neck and uses its legs to rub that wax all over its body. The wax prevents the skin of the frog from drying out in sunlight.
11 ) Most frogs have teeth, although usually only on their upper jaw. The teeth are used to hold prey in place until the frog can swallow it.
12 ) The biggest frog in the world is the Goliath frog. It lives in West Africa and can measure more than a foot in length and weigh more than 7 pounds – as much as a newborn baby.
13 ) There’s a type of poison dart frog called the blue-jeans frog; it has a red body with blue legs. It is also sometimes called the strawberry dart frog.
14 ) The red-eyed tree frog lays it eggs on the underside of leaves that hang over water. When the eggs hatch, the tadpoles fall into the water below.