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New frog species pose challenge for conservation project in Panama

John Barrat — Thu, 29 Jul 2010 12:06:04 +0000

The recent discovery of what may be three new frog species by researchers in Panama illustrates the hope and fear encountered daily by the Panama Amphibian Rescue and Conservation Project. The discoveries lead to hope that project researchers can save these animals from a deadly fungus killing frogs worldwide and the fear that many species will go extinct before scientists even know they exist.

Photo right: One of the three potentially new species appears to be a robber frog, genus Craugastor, shown here. The unique skin folds on its arms and feet distinguish it from other closely related species. Robber frogs are especially susceptible to chytrid. (Photos by Brian Gratwicke, Smithsonian Conservation Biology Institute)

“It is disturbing to witness the disappearance of species that some of us only recently described and even more devastating to lose those we know are probably new species,” said Roberto Ibáñez, local director of the project and a scientist at the Smithsonian Tropical Research Institute, one of nine project partners, including the Smithsonian’s National Zoo. “Scientists are just starting to investigate the ecological impact of the loss of amphibians, and while we’re aiming to preserve some of these species, we already know it will be impossible to save them all.”

Nearly one-third of all amphibian species globally are at the risk of going extinct. The rescue project aims to save more than 20 species of frogs in Panama, which is one of the world’s last strongholds for amphibian biodiversity. While the global amphibian crisis is the result of habitat loss, climate change and pollution, the deadly amphibian chytrid fungus is likely at least partly responsible for the disappearances of 94 of the 120 frog species that are thought to have gone extinct since 1980.

Photo left: Two of the three potentially new species is a rain frog from the genus Pristimantis. The species pictured here has a bright red stomach that is uncharacteristic for rain frogs, earning it the nickname “red tomato.”

Although it can take years to determine that a species is new to science, project researchers have identified some telltale signs indicating that the three species found in eastern Panama are, indeed, new. The first two are rain frogs from the genus Pristimantis. One of these species has a bright red stomach that is uncharacteristic for rain frogs, earning it the nickname “red tomato.” The second species is much larger than any known Pristimantis in the region. The third frog species appears to be a robber frog, genus Craugastor, but unique skin folds on its arms and feet distinguish it from other closely related species. Robber frogs are especially susceptible to chytrid.

A new study by Andrew Crawford, a STRI research associate, and colleagues reveals that many frog species at a site in western Panama have gone extinct before researchers knew they existed. The project’s three potentially new species are evidence of the same story playing out right now in the mountains of eastern Panama. Researchers have brought a handful of animals of each species back to the Summit Municipal Park in Panama City, Panama, where the project has turned used shipping containers into amphibian rescue pods.

“We are doing our best to salvage what we can, but we are in urgent need of funding to build capacity in Panama to house all of these chytrid refugees,” said Brian Gratwicke, a National Zoo research biologist and the international coordinator for the Panama Amphibian Rescue and Conservation Project. “The species is the basic unit of conservation, so these discoveries are rewarding, but that comes with the daunting responsibility of deciding how we look after them. We already have a huge job, and it just gets bigger with every discovery.”

Now project scientists will use collections of frogs from the same region at the Smithsonian’s Natural History Museum and elsewhere to determine if these species are genuinely new or if they have already been discovered (or “described”) elsewhere. The project has also collected tissue sample to use DNA testing to map out the animals’ closest genetic relatives.

“Finding a new species is like discovering a new Pablo Picasso,” said Gratwicke. “Each species is a priceless creation painted with the brushstrokes of natural selection on the canvas of DNA and has something of value to offer. We might not know how they’re valuable to us right now, but if they go extinct, we lose the opportunity to learn what secrets they hold.”

The mission of the Panama Amphibian Rescue and Conservation Project is to rescue amphibian species that are in extreme danger of extinction throughout Panama. The project’s efforts and expertise are focused on establishing assurance colonies and developing methodologies to reduce the impact of the amphibian chytrid fungus so that one day captive amphibians may be re-introduced to the wild. Project participants include Africam Safari, Autoridad Nacional del Ambiente, Cheyenne Mountain Zoo, Defenders of Wildlife, El Valle Amphibian Conservation Center, Houston Zoo, Smithsonian’s National Zoological Park, Smithsonian Tropical Research Institute, Summit Municipal Park and Zoo New England.

Japanese giant salamanders given to the National Zoo by Asa Zoological Park in Hiroshima

John Barrat — Fri, 23 Jul 2010 16:48:31 +0000

The Smithsonian’s National Zoo recently acquired Japanese giant salamanders given to the Zoo by the City of Hiroshima Asa Zoological Park. This donation will be the foundation of a new long-term breeding program in the United States and may play an important role in saving amphibians around the globe. “Our Japanese colleagues at the Asa Zoo have successfully applied decades of work and science to Japanese giant salamanders in the field and at their zoo,” said Dennis Kelly, director of the Smithsonian’s National Zoological Park. “It is an honor for the National Zoo to be entrusted with the offspring from their efforts, and we look forward to collaborating with them to save this magnificent species.”

Japanese giant salamanders live in cold, fast-flowing streams in Japan. Their numbers have been greatly reduced over the years because of agricultural development and habitat modification.

Photo left: Rick Quintero (left), the primary Japanese giant salamander keeper at the Smithsonian’s National Zoo, feeds the Zoo’s new juvenile salamanders for Japanese Ambassador Ichiro Fujisaki (right). Fujisaki was at the Zoo on July 22 to help celebrate the arrival of the salamanders, a gift from the City of Hiroshima Asa Zoological Park. (Mehgan Murphy photo)

“In conserving salamanders, we conserve the ecosystems in which they live,” said Ed Bronikowski, senior curator at the Zoo. “People share those same ecosystems, so what is good for the salamanders is good for many species, including us. We hope our visitors will learn from this generous gift to embrace our own diverse native salamander populations and protect healthy ecosystems for all.”

The National Zoo has experience caring for Japanese giant salamanders since as early as 1940, but with this gift, the Zoo hopes to become the first in the United States to successfully breed this species, which has not been bred outside of Japan in at least 100 years.

During the donation ceremony on July 22, kids from Great Falls Elementary School in Great Falls, Virginia were present to help name one male salamander. The students were asked to choice between two names selected by the ambassador – Hiro, derived from Hiroshima, the salamanders’ home in Japan and Asa, of the City of Hiroshima Asa Zoological Park. Hiro won the student’s vote! –Jessica Porter

Astronomers take the first clear look inside a turbulent stellar nursery

John Barrat — Wed, 14 Jul 2010 12:28:57 +0000

A team of scientists led by Harvard-Smithsonian Center for Astrophysics astronomer Jaime Pineda has managed to get a clearer look into the turbulent and murky environment of a stellar nursery in the constellation Perseus. The result is the first observation ever of a critical step in the creation of stars.

Understanding star formation is a key quest in astronomy. Theorists have models for the process, but as with all sciences, observations must be made to support or modify these ideas.

Image right: The Orion Nebula is the most famous stellar nursery in the northern sky. Its young stars are fully mature, while the Perseus region is still at the earliest stages of star formation. (Photo NASA/ESA)

Stars form inside relatively dense concentrations of interstellar gas and dust called molecular clouds. Within such clouds, material roils and bubbles like a boiling soup. For a time, the energy of those turbulent motions supports the cloud against gravitational collapse. Eventually, gravity begins pulling denser parts of the cloud interior together. When the material inside these clumps loses enough internal motion, they condense into cores. These cores then form into protostars.

“The dust and gas molecules have to slow down enough for gravity to begin pulling them together into a protostar,” Pineda says. “So far it has been hard to tell which cloud material is going into a protostar and which material is still too energetic.”

Since the molecular clouds do not shine in visible light, astronomers must use radio and infrared telescopes to make measurements. Using the 100-meter Byrd radio telescope in Green Bank, WV, to map temperature and motion in the cloud, Pineda and other team members have for the first time determined a sharp boundary surrounding a protostar.

“This result lets us define a zone where material inside the boundary is ‘ready to be used’ in the star formation process, while the gas outside the boundary needs to get rid of the turbulence before it can go on to form a star,” says Pineda.

Theory predicts a region around a protostar where the forming star’s gravity is slowing and capturing more and more material from the parent cloud. The actual size and shape of such a region has not been measured or accurately predicted before.

What was completely unknown was whether or not the material made a gradual or abrupt transition into what co-author Alyssa Goodman describes as “islands of calm in a more turbulent sea.”

“The identification of this sharp transition is a major breakthrough in understanding the star formation process,” says Pineda. “Our measurements now give a strong constraint on how these protostellar cores form.”

Because this is the first observation of such a marked transition, it had not previously been described in theory. “Now theorists will need to reproduce our observations in order to keep their models viable,” Pineda says. –Dan Brocious

Tropical tree study shows interactions with neighbors plays an important role in tree survival

John Barrat — Thu, 08 Jul 2010 11:29:16 +0000

Home to jaguars, harpy eagles and red-eyed tree frogs, tropical forests support some of the rarest species on the planet and are the most biodiverse ecosystems on land. Understanding why some species are common while others are exceedingly rare has been a challenge in these mega-diverse forests. New results from a massive study at the Smithsonian Tropical Research Institute show that interactions among community members play an important role in determining which organisms thrive.

“Based on information about the survival of more than 30,000 seedlings of 180 species of tropical trees, we found that seedlings of rare species are much more sensitive to the presence of neighbors of their own species than seedlings of common species are,” said Liza Comita, the primary author on the study and now a postdoctoral fellow at the U.S. National Center for Ecological Analysis and Synthesis. “Not only does this tell us where to look for the mechanisms that explain why certain species are rare, but it also provides potential clues about how to conserve rare species that are most vulnerable to extinction.”

Photo left: Botanist Liza Comita measures the stem diameter of a seedling on the Smithsonian Tropical Research Institute’s Barro Colorado Island in the Panama Canal. (Christian Zieglar photo)

The lowland tropical forest on Panama’s Barro Colorado Island is the site of a huge long-term study focusing on plant diversity: more than 400,000 individual trees and shrubs of more than 300 species have been marked, mapped and measured every five years for the past 30 years. A unique window on climate change and other large-scale processes, the experiment was originally set up because two ecologists, Robin Foster, now at Chicago’s Field Museum, and Stephen Hubbell at UCLA, a co-author on this paper, had an argument about how life organizes itself.

What determines the members of a community? The study site—a patch of forest the size of nearly 100 football fields—is large enough to include individuals of many rare species that would not be present in smaller studies. After realizing that many of the processes that shape diversity happen early in a tree’s life, researchers decided to expand the study to include an annual survey of seedlings growing in the forest understory. This study of seedlings, led by Comita, Hubbell and Panamanian botanist and co-author Salomón Aguilar, has now been going for nearly a decade and has yielded new insights into this diverse forest.

For years, researchers have noticed that individual plants surrounded by neighbors of the same species do not grow and survive as well as individual plants surrounded by other species. Some evidence suggests that this is either because pests and pathogens move more readily among individuals of the same species or because they are competing with each other for the same resources.

“It became clear with this seedling survival survey that even though neighbors can be shaded out by individuals of the same or of other species, there are real differences in the survival of different species depending on how many of their neighbors are the same species,” said Helene Muller-Landau, staff scientist at the Smithsonian and adjunct professor at the University of Minnesota. “Some of our colleagues are working on the specific mechanisms that explain these differences, and we look forward to seeing their results, which will be published soon.” –Beth King

Scientists find excess nitrogen favors plants that respond poorly to rising CO2

John Barrat — Wed, 30 Jun 2010 17:09:21 +0000

As atmospheric carbon dioxide levels rise, so does the pressure on the plant kingdom. The hope among policymakers, scientists and concerned citizens is that plants will absorb some of the extra CO2 and mitigate the impacts of climate change. For a few decades now, researchers have hypothesized about one major roadblock: nitrogen.

Photo right: Scientist Adam Langley sprays plants in a test chamber with nitrogen. The additional nutrients changed the composition of the plants inside the chamber, spurring the growth of grasses that respond weakly to elevated levels of CO2.

Plants build their tissue primarily with the CO2 they take up from the atmosphere. The more they get, the faster they tend to grow—a phenomenon known as the “CO2 fertilization effect.” However, plants that photosynthesize greater amounts of CO2 will also need higher doses of other key building blocks, especially nitrogen. The general consensus has been that if plants get more nitrogen, there will be a larger CO2 fertilization effect. Not necessarily so, says a new paper published in the July 1 issue of Nature.

Adam Langley and Pat Megonigal, two ecologists at the Smithsonian Environmental Research Center, conducted a four-year study on plants growing in a brackish Chesapeake Bay marsh. In 2006 they began feeding sedge-dominated plots a diet rich in CO2 and nitrogen. Just as atmospheric CO2 levels are rising, so is nitrogen pollution in estuaries due farming, wastewater treatment and other activities. Because the sedge has previously shown a large CO2 fertilization effect, Langley and Megonigal expected that adding nitrogen could only enhance it.

Photo left: The Smithsonian’s Global Change Research Marsh is a tidal system. It sits on the western shore of the Chesapeake Bay in Edgewater, Maryland.

The sedge, Schoenoplectus americanus, initially reacted as expected. However, after the first year something unanticipated happened. Two grass species that had been relatively rare in the plots, Spartina patens and Distichlis spicata, began to respond vigorously to the excess nitrogen. Eventually the grasses became much more abundant. Unlike sedges, grasses respond weakly to extra CO2 and do not grow faster. Thus, the nitrogen ultimately changed the composition of the ecosystem as well as its capacity to store carbon.

The experiment unfolded on the Smithsonian Global Change Research Wetland, located on the Chesapeake’s western shore in Maryland. The Smithsonian site has a history of climate change research that dates back to the 1980s. For this study, Megonigal and Langley placed 20 open-top chambers over random plots of plants. The chambers were 6 feet in diameter and had 5-foot-tall transparent plastic walls.

Photo right: Open-top plastic chambers allow Smithsonian researchers to control and measure the amount of carbon dioxide and nitrogen that the plants receive.

The large, plastic pods allowed the scientists to manipulate CO2 concentrations in the air and nitrogen levels in the soil. Half of the plots grew with normal, background CO2 levels; the other half were raised in an environment with CO2 concentrations roughly double that amount. Similarly, half of the chambers were fertilized with nitrogen and the other half were untreated.

Langley and Megonigal began and ended each growing season with a census of the plants in each chamber. They noted the individual plant species, measured the above-ground biomass and the root growth. In the chambers that received the high-nitrogen diet, the plant composition changed dramatically; it went from 95 percent sedge in 2005 to roughly half grass in 2009. “It’s a fact that not all plants will be able to respond optimally to all changes,” said Megonigal. “The things they do respond to reflects their strategy for making a living in the environment.”

“The study underscores the importance of considering the mix of species when you’re trying to predict how terrestrial ecosystems will react to global climate change factors,” said Langley. Rising CO2 levels will favor some plants and excess nitrogen will favor others. This lesson will be important to understand as scientists consider additional global change factors such as precipitation, temperature and, in tidal wetlands, sea-level rise. The plant species that gain a competitive edge under these evolving conditions will determine how ecosystems respond to global change.

This study was supported by the U.S. Geological Survey and U.S. Department of Energy. The Smithsonian scientists recently received funding from the National Science Foundation that will sustain the research for another 10 years. Langley and Megonigal’s paper, “Ecosystem Response to Elevated CO2 Limited by
Nitrogen-Induced Plant Species Shift,” can be accessed on Nature’s website http://www.nature.com/nature/journal/v466/n7302/full/nature09176.html.

“Death Star” Shreds, Swallows Dwarf Planet

John Barrat — Tue, 22 Jun 2010 11:23:55 +0000

In the movie “Star Wars,” the Death Star uses a futuristic weapon to blast apart the planet Alderaan. It seems the stuff of science fiction, but astronomers have found a real-life “Death Star” that shredded a rocky planet and is swallowing the dusty remains.

The star in question is known as a white dwarf. When a sun-like star reaches the end of its life, it swells to form a red giant. Its outer layers then puff off, leaving behind a hot core of carbon and oxygen. This white dwarf is very dense, cramming half a sun’s worth of material into a sphere the size of Earth. A teaspoon of white dwarf would weigh more than a ton.

Image right: This artist’s concept shows a white dwarf star surrounded by the bits and pieces of a disintegrating asteroid. Astronomers have found a white dwarf that shredded and gulped down an object the size of Ceres. (NASA/JPL-Caltech/T. Pyle )

An international team of astronomers examined thousands of white dwarfs to look for ones with unusual chemical compositions. They followed up their strangest target with the MMT Observatory in Arizona. This target is located about 440 light-years away in the direction of the constellation Gemini. (A light-year is 6 trillion miles.)

This white dwarf showed strong signs of chemical elements like silicon, magnesium, calcium, and iron – all of which are abundant in rocky planets like Earth. Since a white dwarf’s gravity is so strong (100 thousand times Earth’s gravity), these heavy elements should have sunk out of sight below the surface. Since we can see them, they must have been deposited there relatively recently (in an astronomical sense).

The most likely source is a rocky planet that wandered too close to the white dwarf and got torn apart by tidal forces. The debris settled into a disk around the white dwarf and is raining down onto the star’s surface. Observations from the Gemini Observatory in Hawaii detected this debris disk, confirming the astronomers’ theory.

Judging from the amount of material on the white dwarf and surrounding it, the hapless planet was about the size of Ceres, the largest asteroid in our solar system.

Photo left: The Multiple Mirror Telescope. (Photo by: Howard Lester)

The team also noted that the amount of hydrogen the white dwarf has swallowed is much less than expected. (In our solar system, Ceres contains a significant amount of ice, which would split into hydrogen and oxygen if consumed by a white dwarf.) This suggests that any water or ice the dwarf planet possessed was boiled off long ago by the red giant’s heat.

“There are now more than 450 extrasolar planets known, all of them bigger than Earth, and we don’t really know much about their compositions. Here we’re seeing the remnants of an extrasolar dwarf planet, which gives us a chance to learn about the chemistry of worlds in distant planetary systems,” said Mukremin Kilic of the Smithsonian Astrophysical Observatory.

“White dwarf science is telling us that there are many small planets similar to those in our solar system out there. Since it is not possible to detect such small objects in orbit around other stars with our current technology, studies such as this one offer a unique opportunity to learn about other planetary systems,” added lead author Patrick Dufour of the University of Montreal. –Christine Pulliam

Scientists find ultrasonic calls of bats also serve a social function

John Barrat — Thu, 17 Jun 2010 18:10:20 +0000

To find flying insects and navigate in the dark, bats emit ultrasonic cries and then listen to the echoes that are reflected back to them. Now, a new study by scientists from the Smithsonian Tropical Research Institute, the Leibniz Institute for Zoo and Wildlife Research, and other research organizations suggest that echolocation calls also serve a social function for bats. Namely, bats listen to the ultrasonic calls of other bats to identify roost mates, bats of the same species, members of the opposite sex and intruders to their territory.

Images: Lesser bulldog bats from Panama that were used in this study. (Photos courtesy Silke Voigt-Heucke)

To test the idea that echolocation calls can communicate social information for bats, the scientists recorded the ultrasonic echolocation calls emitted by lesser bulldog bats (Noctilio albiventris) and bats of other species, and then played them back to bulldog bats held in temporary captivity. They observed that captive bats reacted differently to calls made by bats of their same species than they did to calls by bats of another species. They also observed the bats respond differently to calls from bats which shared their roosts and to the calls of unfamiliar bats. The experiments were conducted in Panama. Ultrasonic white noise was used as a control in the experiment.

This video shows a lesser bulldog bat in a holding container responding to the ultrasonic calls of one of its roost mates. The audible chirps heard in this video is the bat’s non-ultrasonic voice. (Video courtesy Silke Voigt-Heucke)

“We were able to show that bats respond with a set of social behaviors [crawling, nodding, wing stretching, etc.] to the playback of echolocation calls,” the scientists write in a recent article in the journal “Animal Behaviour.” They conclude that N. albiventris can indeed distinguish between the ultrasonic calls of bats of their same species and bats of a different species, and between the calls of familiar and unfamiliar bats.

Our results demonstrate that echolocation calls are not only “perceived and processed by the individual producing the sound,” the scientists write, but that “other individuals may obtain information about species identity and group affiliation by listening to echolocation calls.” Authors of the paper are Silke L. Voigt-Heucke of the Leibniz Institute for Zoo and Wildlife Research; Michael Taborsky of the University of Bern, Switzerland, and Dina K.N. Denchmann, a research associate at the Smithsonian Tropical Research Institute in Panama.

Super sensitive telescope will detect “killer” asteroids and comets on collision course with Earth

John Barrat — Thu, 17 Jun 2010 14:02:55 +0000

Astronomers announced on June 16, 2010, that the first Pan-STARRS (Panoramic Survey Telescope & Rapid Response System) telescope, PS1, is fully operational. This innovative facility will be at the front line of Earth defense by searching for “killer” asteroids and comets. It will map large portions of the sky nightly, making it an efficient sleuth for not just asteroids but also supernovae and other variable objects.

Image right: Asteroids that cross Earth’s orbit, like the one shown in this artist’s conception, threaten to impact our planet. The new Pan-STARRS observatory offers our first line of defense, surveying huge swaths of the sky every night looking for moving objects. (Artwork by David A. Aguilar)

Pan-STARRS is an all-purpose machine,” said Harvard astronomer Edo Berger. “Having a dedicated telescope repeatedly surveying large areas opens up a lot of new opportunities.”

PS1 has been taking science-quality data for six months, but now we are doing it dusk-to-dawn every night,” says Dr. Nick Kaiser (University of Hawaii Institute for Astronomy, or IfA), the principal investigator of the Pan-STARRS project.

Pan-STARRS will map one-sixth of the sky every month. By casting a wide net, it is expected to catch many moving objects within our solar system. Frequent follow-up observations will allow astronomers to track those objects and calculate their orbits, identifying any potential threats to Earth. PS1 also will spot many small, faint bodies in the outer solar system that hid from previous surveys.

“PS1 will discover an unprecedented variety of Centaurs [minor planets between Jupiter and Neptune], trans-Neptunian objects, and comets. The system has the capability to detect planet-size bodies on the outer fringes of our solar system,” said Smithsonian astronomer Matthew Holman.

Pan-STARRS features the world’s largest digital camera–a 1,400-megapixel (1.4 gigapixel) monster. With it, astronomers can photograph an area of the sky as large as 36 full moons in a single exposure. In comparison, a picture from the Hubble Space Telescope’s WFC3 camera spans an area only one-hundredth the size of the full moon (albeit at very high resolution).

Photograph left: Pan-STARRS PS1 Observatory just before sunrise on Haleakala, Maui. (Photo by Rob Ratkowski)

Its sensitive digital camera was rated as one of the “20 marvels of modern engineering” by Gizmo Watch in 2008. Inventor Dr. John Tonry (IfA) said, “We played as close to the bleeding edge of technology as you can without getting cut!”

Each image, if printed out as a 300-dpi photograph, would cover half a basketball court, and PS1 takes an image every 30 seconds. The amount of data PS1 produces every night would fill 1,000 DVDs.

“As soon as Pan-STARRS turned on, we felt like we were drinking from a fire hose!” said Berger. He added that they are finding several hundred transient objects a month, which would have taken a couple of years with previous facilities.

Located atop the dormant volcano Haleakala, Pan-STARRS exploits the unique combination of superb observing sites and technical and scientific expertise available in Hawaii. Funding for the development of the observing system was provided by the U.S. Air Force.

The PS1 Surveys have been made possible through contributions of the PS1 Science Consortium (PS1SC): IfA; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, Germany and the Max Planck Institute for Extraterrestrial Physics, Garching, Germany; the Johns Hopkins University; the University of Durham; the University of Edinburgh; the Queen’s University Belfast; the Harvard-Smithsonian Center for Astrophysics; the Los Cumbres Observatory Global Telescope Network, Inc.; and the National Central University of Taiwan.Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Killing of methane-producing megafauna may have caused cooling 13,000 years ago

John Barrat — Fri, 04 Jun 2010 14:42:06 +0000

The mechanisms for global warming are relatively well understood, but what does it take to cool the planet? According to new research, a taste for large game by the prehistoric inhabitants of the Americas may have caused the Earth to cool some 13,000 years ago.

Image right: Mastadon, painting by Charles R. Knight

As reported in the June issue of the journal Nature Geoscience, ancient settlers to North and South America may have significantly reduced atmospheric levels of methane – a much more problematic greenhouse gas than carbon dioxide – by relentlessly hunting large herbivores of their day. “This may be the first measurable impact of humans on the greater environment,” says S. Kathleen Lyons, co-author and researcher in paleobiology at the Smithsonian’s National Museum of Natural History.

Image left: Prehistoric megafauna, painting by Jay Matternes.

New world megafauna such as mammoths, bison and camelids that were alive at the end of the Pleistocene epoch (some 13,000 years ago) would have produced massive amounts of methane-rich flatulence and belching, thanks to the cellulose-digesting microbes in their guts. Human hunting activities likely made a sizable dent–anywhere from 12.5 to 100 percent–in the level of atmospheric methane at that time. As a result, a cooling in transregional temperatures of the Younger Dryas period may be attributable in part to the rapid eradication of some 100 herbivorous species.

“The timing of the extinction aligns perfectly with the arrival of humans in the Americas,” Lyons says, “and their hunting may have contributed to this famous cool-down.” A drop of 9 to 12 degrees Celsius is believed to have occurred within the Younger Dryas stadial, or the “Big Freeze,” which came between the Pleistocene and Holocene epochs.

Chart right: The extinction of megafauna (indicated by red shaded region) closely coincides with an abrupt drop in atmospheric methane concentration at the onset of the Younger Dryas (indicated by blue shaded region). Time is given in kiloannum. Scientists estimate that prior to the extinction event, large-bodied herbivores in the Americas released about 9.6 Tg of methane to the atmosphere annually. The loss of these species could be responsible for 12.5 to 100% of the overall methane decline. Atmospheric methane concentrations during the past 15,000 years are derived from the Greenland ice core samples.

Ice core samples and fossil and archaeological records, combined with body mass and gut size calculations of these ancient animals, informed the methane estimates derived by the authors.

The research team, which was led by Felisa A. Smith of the University of New Mexico, and assisted by Scott M. Elliott of Los Alamos National Laboratory and Lyons, also found the Intergovernmental Panel on Climate Change is likely undervaluing the amount of methane emitted by non-domesticated animals.

As a result of their findings, the authors propose that the beginning of the ‘Anthropocene’ be recalibrated to 13,400 years ago instead of 8,000 years ago when ancient farmers are known to have cleared forests to grow crops. –Brian Ireley

Tiny, new brains prove just as adept as large, mature brains among tropical orb-web spiders

John Barrat — Wed, 02 Jun 2010 19:18:24 +0000

When it comes to brains, is bigger better? For instance, can the tiny brain of a newly hatched spiderling handle problems as adeptly as the brain of a larger adult spider? One theory, known as the size limitation hypothesis, predicts that the miniscule brains of tiny creatures contain fewer neurons and thus have less capacity, making these creatures more prone to mistakes.

Photo right: An adult Nephila clavipes on its web with an insect it has captured.

To test this theory, Thomas Hesselberg of the Smithsonian Tropical Research Institute in Panama, recently examined and compared the designs of webs woven by newly hatched, mid-size and adult orb-web spiders of the species Nephila clavipes and Eustala illicita. (Nephila grow explosively and an adult can weigh up to 500 times more than it did when newly hatched.) He collected a number of spiders from each age group, induced them to weave webs on square frames in a laboratory and then took careful measurements of each web. He also conducted observations of the webs of both species in the wild. A paper on Hesselberg’s work was published recently in the scientific journal “Ethology.”

Photo left: An N. clavipes resting at the hub of its laboratory web.

Orb-web spiders have a fixed reserve of sticky capture spiral silk inside their bodies prior to web building. This reserve is thought to be entirely used up as the web is completed. “As orb spiders build the capture spiral from the outer periphery towards the hub [or center of the web], they need to match web size to silk reserves,” Hesselberg writes. Younger spiders that haven’t mastered this behavior, he reasoned, should have a larger area free of silk at their web’s center hub. Or, to cover for a miscalculation, a young spider may increase the distance between the spirals of its capture silk spun out nearer to the web’s hub.

In his observations of the different webs, he found no evidence that adult Nephila or Eustala spiders have any more brain power or build webs any more effectively than newly-hatched spiderlings. “Neither species showed clear signs of being behaviorally limited or more prone to committing errors as spiderlings than were older juveniles or adults,” Hesselberg concluded.

Photo right: The web of an E. illicita spider in the wild. (Photos by Thomas Hesselberg).

One miscalculation may lie, Hesselberg adds, in the human assumption that “the orb web is the result of a demanding computational behavioral process. Theoretical models suggest that the construction of the orb web might be achieved by following a few simple rules of thumb and thus not pose any significant computational challenge for the spider.”

–John Barrat