May 30, 2013
Think of an ecosystem as a Jenga pillar. Each piece–microbes, birds, trees, insects, animals, fungi–comes together to form the larger, intertwined structure. Maybe you can knock out a Jenga block or two, but tamper with those components enough and the system will collapse. As ecologists well know, small changes in the environment–cutting down a few patches of forest, causing a local species to go extinct–can create cascading and potentially disastrous effects on the broader environment.
Like a teetering Jenga tower, predicting which of those changes will most significantly reverberate in the complex natural world is nearly impossible. So we wait to see the consequences. Today, an international team of researchers just identified a pointed example of one such fatal tinkering. In Brazil’s damaged Atlantic forest, the absence of large birds has caused seeds to shrink and become weaker, in turn threatening the forest’s future.
The story began more than a century ago, they found. Local people began hacking away at the Atlantic forest, which once covered more than 400,000 square miles of Brazil’s coast. Agricultural and livestock fields, as well as growing urban centers, divided swaths of jungle, creating isolated patches of green. By the time people realized there was value in keeping the forest around, nearly 90 percent of it had been lost. Much of what remains today occurs in isolated, random pockets, though those patches still represent some of the world’s most biodiverse forests.
When a forest becomes divided, like the Atlantic forest did, wildlife often loses its ability to disperse from one patch of trees to another. Larger species may not be able to survive in some of the smaller, resource-scarce patches, and hunters can more easily track down animals if they’re confined to a smaller area. This turned out to be the case for some large birds that once made their home throughout the Atlantic forest, including toucans and toucanets–prized for their brilliant plumage, the birds are a favorite of hunters.
Significantly, these birds’ big beaks–which open up more than half an inch, on average–make them key players in distributing larger seeds throughout the jungle. Smaller birds can’t swallow or fit those big seeds into their beaks, meaning the toucans and toucanets carry nearly sole responsibility for regenerating the jungle with new seedlings of several plant species.
The authors of this new study, published in Science, compared the size of more than 9,000 seeds from 22 palm plant populations–a major tree type in the Atlantic forest, several species of which are threatened. Some of the seeds came from robust patches of forest with lots of large birds, while others came from smaller patches where those birds have long been missing. In those smaller patches, they found, seeds of palm plants were significantly smaller.
The researchers also used statistical models to independently evaluate 13 different environmental variables, including soil type and climate, to find out whether they could have driven the size difference seen in the seeds instead. None of the other factors could explain the difference, suggesting birds–the primary transport mechanism for large seeds–as the most likely culprit. Additional genetic analyses indicated that, in the smaller forest patches, seeds most likely began shrinking about 100 years ago, or right around the time that coffee and sugar cane plantations began to boom. Human activities a century ago, the authors conclude, likely drove a rapid evolutionary change in the forest palms’ seed size.
When the birds disappear, the larger seeds do not get distributed throughout the forest. Only the smaller ones wind up in new plots of earth, which in turn sprout into more trees that produce smaller seeds. Gradually, the forest becomes dominated by smaller seed-producing trees.
Shrinking seed size is no small detail for forest palms. The larger the seed, the more nutrients that are packed in to give the seedling the best possible chances of survival in the tough jungle ecosystem. Prior research has found that forest palms that began life as smaller seeds are smaller on average after a year of growth than those that came from larger seeds, meaning that the runty plants are more likely to lose out to competition with other species. Smaller seeds are also more prone to drying out. Given that climate models predict hotter temperatures and longer periods of drought for South America in the coming years, this could be a serious problem for smaller-seeded forest palms’ survival.
If palms start dying out throughout the Atlantic forest, researchers have no idea what will happen to the tens of thousands of species that take shelter in the ecological web the plants help to maintain–a web that includes more than 11,000 threatened plants and animals. For those smaller jungle patches, the authors speculate, the choices long-dead humans made may lead to complete collapse of some of the world’s most diverse sections of rainforest. Like a real-life game of Jenga, those birds could prove to be the key piece that causes the entire jungle system to fall down.
April 24, 2013
Pop quiz: Why are flamingos pink?
If you answered that it’s because of what they eat—namely shrimp—you’re right. But there’s more to the story than you might think.
naturally synthesize a pigment called melanin, which determines the color of their eyes, fur (or feathers) and skin. Pigments are chemical compounds that create color in animals by absorbing certain wavelengths of light while reflecting others. Many animals can’t create pigments other than melanin on their own. Plant life, on the other hand, can produce a variety of them, and if a large quantity is ingested, those pigments can sometimes mask the melanin produced by the animal. Thus, some animals are often colored by the flowers, roots, seeds and fruits they consume
Flamingos are born with gray plumage. They get their rosy hue pink by ingesting a type of organic pigment called a carotenoid. They obtain this through their main food source, brine shrimp, which feast on microscopic algae that
naturally produce carotenoids. Enzymes in the flamingos’ liver break down the compounds into pink and orange pigment molecules, which are then deposited into the birds’ feathers, legs and beaks. If flamingos didn’t feed on brine shrimp, their blushing plumage would eventually fade.
In captivity, the birds’ diets are supplemented with carotenoids such as beta-carotene and and canthaxanthin. Beta-carotene, responsible for the orange of carrots, pumpkins and sweet potatoes, is converted in the body to vitamin A. Canthaxanthin is responsible for the color of apples, peaches, strawberries and many flowers.
Shrimp can’t produce these compounds either, so they too depend on their diet to color their tiny bodies. Flamingos, though, are arguably the best-known examples of animals dyed by what they eat. What others species get pigment from their food? Here’s a quick list:
Northern cardinals and yellow goldfinches: When these birds consume berries from the dogwood tree, they metabolize carotenoids found inside the seeds of the fruit. The red, orange and yellow pigments contribute to the birds’ vibrant red and gold plumage, which would fade in intensity with each molt if cardinals were fed a carotenoid-free diet.
Salmon: Wild salmon consume small fish and crustaceans that feed on carotenoid-producing algae, accumulating enough of the chemical compounds to turn pink. Farmed salmon are fed color additives to achieve a deeper shades of red and pink.
Nudibranchs: These shell-less mollusks absorb the pigments of their food sources into their normally white bodies, reflecting the bright colors of sponges and cnidarians, which include jellyfish and corals.
Canaries: The birds’ normal diet doesn’t alter the color of its yellow feathers, but they can turn a deep orange if they regularly consume paprika, cayenne or red pepper. These spices each contain multiple carotenoids responsible for creating and red and yellow.
Ghost ants: There’s not much more than meets the eye with ghost ants: these tropical insects get their name from their transparent abdomens. Feed them water mixed with food coloring and watch their tiny, translucent lower halves fill up with brilliantly colored liquid.
Humans: Believe it or not, if a person eats large quantities of carrots, pumpkin or anything else with tons of carotenoids, his or her skin will turn yellow-orange. In fact, the help book Baby 411 includes this question and answer:
Q: My six-month-old started solids and now his skin is turning yellow. HELP!
A: You are what you eat! Babies are often first introduced to a series of yellow vegetables (carrots, squash, sweet potatoes). All these vegetables are rich in vitamin A (carotene). This vitamin has a pigment that can collect harmlessly on the skin, producing a condition called carotinemia.
How to tell that yellow-orange skin isn’t an indication of jaundice? The National Institutes of Health explain that “If the whites of your eyes are not yellow, you may not have jaundice.”
March 18, 2013
Some scientists investigate the universe’s biggest mysteries, like the Higgs boson, the mysterious particle that endows all other subatomic particles with mass.
Other researchers look into questions that are, well, a bit humbler—like the age-old puzzle of whether roosters simply crow when they see light of any kind, or if they truly know to crow when the morning sun arrives.
Lofty or not, it’s the goal of science to answer all questions that arise from the natural world, from roosters to bosons and everything in between. And a new study by Japanese researchers published today in Current Biology resolves the rooster question once and for all: The birds truly do have an inner circadian rhythm that tells when to crow.
The research team, from Nagoya University, investigated via a fairly straightforward route: They put several groups of four roosters in a room for weeks at a time, turned the lights off, and let a video camera running. Although roosters can occasionally crow at any time of day, the majority of their crowing was like clockwork, peaking in frequency at time intervals roughly 24 hours apart—the time their bodies knew to be morning based on the sunlight they’d last seen before entering the experiment.
This consistency continued for about 2 weeks, then gradually began to die out. The roosters were left in the room for 4 weeks in total, and during the second half of the experiment, their crowing began occurring less regularly, at any time of day, suggesting that they do need to see the sun on a regular basis for their circadian rhythms to function properly.
In the experiment’s second part, the researchers also subjected the roosters to alternating periods of 12 hours of light and 12 hours of darkness, while using bright flashes of light and the recorded crowing of roosters (since crowing is known to be contagious) to induce crowing at different times of day. When they activated these stimuli near at or near the dawn of the roosters’ 12-hour day, crowing rates increased significantly. At other times of day, though, exposing them to sudden flashes of light or playing the sound of crowing had virtually no effect, showing that the underlying circadian cycle played a role in the birds’ response to the stimuli.
Of course, many people who live in close proximity to roosters note that they often crow in response to a random light source turning on, like a car’s headlights, no matter what time of day it is. While this may be true, the experiment shows that the odds of a rooster responding to a car’s headlights depend on how close the current time is to dawn—at some level, the rooster’s body knows whether it should be crowing or not, and responding to artificial stimuli based on this rhythm.
For the research team, all this is merely a prelude to their bigger, more complex questions: Why do roosters have a biological clock that controls crowing in the first place, and how does it work? They see the simple crowing patterns of the rooster as an entry point into better understanding the vocalizations of a range of animals. “We still do not know why a dog says ‘bow-wow’ and a cat says ‘meow,’” Takashi Yoshimura, one of the co-authors, said in a press statement. “We are interested in the mechanism of this genetically controlled behavior and believe that chickens provide an excellent model.”
March 14, 2013
Roughly 150 million years ago, birds began to evolve. The winged creatures we see in the skies today descended from a group of dinosaurs called theropods, which included tyrannosaurs, during a 54-million-year chunk of time known as the Jurassic period. Why the ability to fly evolved in some species is a difficult question to answer, but scientists agree that wings came to be because they must have been useful: they might have helped land-based animals leap into the air, or helped gliding creatures who flapped their arms produce thrust.
As researchers continue to probe the origin of flight, studies of fossils have shown that theropods–particularly coelurosaurian dinosaurs, which closely resemble modern birds—had large feathers on both their fore limbs and hind limbs. However, extensive evidence for these leg feathers didn’t exist in the earliest birds. But now, a new examination of fossils reported today in the journal Science reveals several examples of this four-winged anatomy in modern birds’ oldest common ancestors.
Modern birds have two types of feathers: vaned feathers that cover the outside of the body, and the down feathers that grow underneath them. Researchers studying the approximately 120 million-year-old fossils of 11 primitive birds from the Shandong Tianyu Museum of Natural History in China found that one type of vaned plumage, also known as pennaceous feathers, was neatly preserved in skeletal fossils of these specimens, along each creatures’ hind limbs. After this find, the researchers must have been flying high: The feathers of birds’ wings, known as flight feathers, are long, stiff and asymmetrically shaped pennaceous feathers, similar to those found in the fossils. When fanned together, pennaceous feathers form the broad surfaces of birds’ wingspans—without these surfaces, birds cannot stay aloft.
Pennaceous feathers, which are composed of many flattened barbs, existed in some winged dinosaurs. Finding them on the hind legs of early birds suggests that before birds used two wings to fly, they may have depended on four. Over millions of years, however, birds gradually lost the feathers on this extra set of wings.
The study adds to existing theories that suggest the first birds flew with four wings. Examination of a primitive bird fossil from the Archaeopteryx genus in 2004 revealed long feathers on the animal’s back and legs, which would have aided its gliding ability. Two years later, another study of the crow-sized animal, which lived about 150 million years ago, reported that the prehistoric bird’s feathers resembled those on modern birds’ flight wings.
One of the more complete skeletons examined in today’s study actually showed hind-limb pennaceous feathers along the bone of each leg. The longest feather stretched almost two inches, which is remarkable considering that the legs they covered were between one inch and two and a half inches long. In fact, specimens from a group of birds called Enantiornithes, which externally resemble modern birds, showed symmetrically paired large feathers preserved along their hind leg bones. Such feather arrangement is present in modern birds’ wings.
Researchers speculate that the second set of wings might have provided extra lift or created drag in the air. They might also have helped birds maneuver their airborne bodies.
If these hind wings indeed served a functional purpose in fight, they will earn an important place in bird evolution.
Bird movement is characterized by a combination of feathered arms for flight and legs for walking on land. This study suggests that if walking legs, present in birds today, developed after these feathered hind legs, then the loss of feathers on the back legs—and thus an extra pair of wings—reflects a period of change during which the arms became specialized for flight and the legs, for locomotion.
Today, leg feathers are less well developed than wing feathers—they are usually much smaller and fluffy—and they serve as protection and insulation for the leg. These fluffy bits are sparse too—instead, the legs are covered in scales, which form only if feather growth is inhibited. Studies of modern birds show how this works. As chicks develop from embryos and grow into adults, feathered legs can be transformed into scaled legs, or vice versa, by altering how certain genes are expressed.
The recent revelation about feathers on birds’ hind legs suggest that a similar genetic, and more permanent, change might have occurred early in bird evolution, according to lead researchers. This shift triggered the loss of birds’ hind wings, pushing the creatures down an evolutionary path that would allow them to fly with just two.
March 5, 2013
Antarctica, as you might expect, gets pretty darn cold: Temperatures as low as -40 degrees Fahrenheit are often recorded during the winter. For the creatures who live there, this extreme cold demands innovative survival strategies that enable the loss of as little heat as possible.
Scientists recently discovered that Emperor Penguins—one of Antarctica’s most celebrated species—employ a particularly unusual technique for surviving the daily chill. As detailed in an article published today in the journal Biology Letters, the birds minimize heat loss by keeping the outer surface of their plumage below the temperature of the surrounding air.
At the same time, the penguins’ thick plumage insulates their body and keeps it toasty. A team of scientists from Scotland and France recently came to the finding by analyzing thermal images (below) of penguins taken at a coastal Emperor breeding colony in Adélie Land, an area of Antarctica claimed by France.
The researchers analyzed thermographic images like this one taken over roughly a month during June 2008. During that period, the average air temperature was 0.32 degrees Fahreinheit. At the same time, the majority of the plumage covering the penguins’ bodies was even colder: the surface of their warmest body part, their feet, was an average 1.76 degrees Fahrenheit, but the plumage on their heads, chests and backs were -1.84, -7.24 and -9.76 degrees Fahrenheit respectively. Overall, nearly the entire outer surface of the penguins’ bodies was below freezing at all times, except for their eyes and beaks.
The scientists also used a computer simulation to determine how much heat was lost or gained from each part of the body—and discovered that by keeping their outer surface below air temperature, the birds might paradoxically be able to draw very slight amounts of heat from the air around them. The key to their trick is the difference between two different types of heat transfer: radiation and convection.
The penguins do lose internal body heat to the surrounding air through thermal radiation, just as our bodies do on a cold day. Because their bodies (but not surface plumage) are warmer than the surrounding air, heat gradually radiates outward over time, moving from a warmer material to a colder one. To maintain body temperature while losing heat, penguins, like all warm-blooded animals, rely on the metabolism of food.
The penguins, though, have an additional strategy. Since their outer plumage is even colder than the air, the simulation showed that they might gain back a little of this heat through thermal convection—the transfer of heat via the movement of a fluid (in this case, the air). As the cold Antarctic air cycles around their bodies, slightly warmer air comes into contact with the plumage and donates minute amounts of heat back to the penguins, then cycles away at a slightly colder temperature.
Most of this heat, the researchers note, probably doesn’t make it all the way through the plumage and back to the penguins’ bodies, but it could make a slight difference. At the very least, the method by which a penguin’s plumage wicks heat from the bitterly cold air that surrounds it helps to cancel out some of the heat that’s radiating from its interior.
And given the Emperors’ unusually demanding breeding cycle (celebrated in the documentary March of the Penguins), every bit of warmth counts. Each winter, they trek from
inland coastal locations to the coast inland—walking as far as 75 miles—where they breed and incubate their eggs. After the females lay eggs, the males incubate them by balancing them on top of their feet in a pouch for roughly 64 days. Since they don’t eat anything during this entire period, conserving calories by giving up as little heat as possible is absolutely crucial.