June 22, 2006, 5:53 PM CT

Appetite And Limb Development In Frogs

Leptin, the hormone secreted by fat cells that plays an important role in food intake, has been described for the first time in a cold-blooded vertebrate, the South African clawed frog Xenopus.

As it does in humans and other mammals, leptin acts on the frog brain to suppress appetite. But the hormone also seems to play a role in the complex signaling that turns a finned tadpole into a four-legged frog, as per Robert Denver, an associate professor of biology at the University of Michigan.

Denver's team gave frogs a dose of leptin at various stages of development from tadpole to near adult and watched what happened. As in mice, the hormone is apparently a powerful appetite suppressant for these animals, causing them to give up eating even as their bodies waste away.

But the youngest tadpoles showed a different response to the hormone. Rather than going off their feed as the older frogs did, these tadpoles kept right on eating and quickly sprouted limbs.

Denver, who has studied the ability of frogs to speed up their metamorphosis in response to a drying pond, thinks that the tadpoles' feeding mechanism is stuck in the "on" position at the first stages of life, because they need to eat and grow as fast as possible to avoid being prey. For these tadpoles, the leptin signal isn't capable of turning the feeding behavior off, but it does apparently tell their bodies that they've had enough to eat now, and they can begin sprouting limbs.........

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June 22, 2006, 5:42 PM CT

future of giant panda

Researchers at Cardiff University, using a novel method to estimate population, have found that there may be a number of more giant pandas remaining in the wild than previously thought.

The giant panda is one of the world's most endangered and elusive species. It is found only in a restricted mountainous region in China with an unusual dietary dependence on bamboos found only in these mountains. This elusive nature has shielded important knowledge needed to save it from extinction, until now.

Understanding population trends for giant pandas has been a major task for conservation authorities in China for the past thirty years, during which time three national surveys were carried out. The first two revealed alarming evidence of declines numbers of giant pandas. However, the most recent survey, carried out in 2002, showed the first evidence of a recovery, thanks largely to protection measures taken by the Chinese government including a network of natural reserves and strictly enforced bans on poaching and deforestation.

However, given the variable accuracy of traditional ecological population recording methods, researchers from Cardiff's School of Biosciences working with a team in China used a novel approach to accurately estimate population size. The results are reported in the international journal Current Biology.........

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June 21, 2006, 0:09 AM CT

Can Biological Traits Predict Diversification Rates In Birds?

Why do some taxanomic families contain a number of species and others contain far fewer? There has been much debate in the scientific community over the reason for such variation, but a recent study in The American Naturalist by Albert B. Phillimore (Imperial College London, Silwood Park Campus), Robert P. Freckleton (Oxford University), C. David L. Orme (Imperial College London, Silwood Park Campus), and Ian P. F. Owens (Imperial College London, Silwood Park Campus) identifies the two biological traits in birds that account for most of the variation: dispersal and feeding generalization.

"Few studies have looked at ecological traits such as dispersal and feeding generalization as explanations for variation in rate of diversification, perhaps because these traits are challenging to quantify," says Phillimore. "Hopefully our findings may stimulate research into the role played by ecological traits in the diversification of other types of organisms."

The study found that bird families with high seasonal dispersal rates and very general feeding patterns also had the highest species diversification rates.........

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June 20, 2006, 9:13 PM CT

Eavesdropping Fringe-lipped Bats

Like a diner ordering a dessert based solely on the "oohs" and "aahs" of a customer eating the same dish the next table over, frog-eating bats learn to eat new prey by eavesdropping on their neighbors as they eat, report biologists from The University of Texas at Austin.

Rachel Page and Mike Ryan, studying fringe-lipped bats at the Smithsonian Tropical Research Institute on Barro Colorado Island in Panama, found that naïve bats quickly learned to associate a new frog call with edible prey by observing their neighbor eating, even when the call comes from a frog they wouldn't normally eat.

Page, a graduate student in Ecology, Evolution and Behavior, and Ryan, the Clark Hubbs Regents Professor in Zoology, report their findings in the June 20 issue of Current Biology.

This is the first study to show predators learning socially through acoustic, rather than visual or olfactory, prey cues.

"It is stunning that these bats show such rapid changes in their responses to prey cues, to the extent that they will respond to a stimulus that they should be under strong selective pressure to avoid in the wild," said Page. "This result is very unexpected and shows an extreme degree of flexibility."

Through the bats' ability to learn socially, the new correlation between a frog call and the presence of food can quickly spread through the tight-knit bat colony.........

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June 20, 2006, 8:54 PM CT

Showing Off Your Weapons

In a paper from the recent issue of The American Naturalist, Kristopher Lappin (Northern Arizona University), Yoni Brandt (University of Toronto), Jerry Husak (Oklahoma State University), Joe Macedonia (Arizona State University), and Darrell Kemp (James Cook University), demonstrate that a threat display can provide accurate information about the performance of a weapon.

Working at the Wichita Mountains National Wildlife Refuge in Oklahoma, the scientists showed that when an adult male lizard gapes his jaws at a rival male during an intense territorial interaction, information is made available to his opponent about how hard he can bite - indeed, the lizard's jaw muscles become clearly visible. Further, some lizards have evolved bright patches that reflect ultraviolet light, which lizards can see, to delineate the jaw muscles.

Lappin and his colleagues point out that the information about bite force provided by the display does not correspond to body or head size because males of similar size can vary substantially in how hard they can bite. The display thus provides unique and honest information about weapon quality, as well as a mechanism for making the decision to fight or to back down. Adult male collared lizards (the species examined in this study) are larger than the females, have hypertrophied jaw muscles, and are highly territorial toward other males. All of this relates to males having evolved the ability to bite with great force, which means that they can seriously wound rivals in fights.........

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June 20, 2006, 8:31 PM CT

Bronx Zoo Sends Gators Home

A dozen rare Chinese alligators hatched and raised in the U.S. are about to get in touch with their roots. The toothy twelvesome were donated by Disney's Animal Kingdom, St. Augustine Farm Zoological Park, and the Wildlife Conservation Society's Bronx Zoo for relocation to China.

Beginning their journey at the Bronx Zoo, the alligators took off from New York's JFK airport on May 17, bound for Shanghai. A team of WCS veterinarians oversaw the shipment to ensure that the travelers were healthy and comfortable. Once the alligators touched down in China, they were moved to a holding facility. Eventually, they will be released in a wetlands reserve near the mouth of the Yangtze River.

"We are delighted that the Chinese government will receive these twelve alligators in an effort to help bolster numbers of the critically endangered species," said WCS conservationist Dr. John Thorbjarnarson, who is helping oversee the program. "Given the chance, these animals will grow in number and roam in areas where they haven't been seen in many years".

Human communities of the Yangtze River valley should fear not-Chinese alligators are smaller than their American cousins and relatively timid animals, preferring small fish and aquatic birds to people.

The Chinese alligator is one of just two alligator species in the world. While the formerly endangered American alligator has recovered thanks to conservation efforts, Chinese alligators have been virtually eliminated from their native habitat. Large-scale conversion of wetlands into farmland over the past several thousand years has left only a few dozen remaining in the wild.........

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June 19, 2006, 11:56 PM CT

How Dorsophilia genome was sequenced

In this small and charming book, Won for All, Michael Ashburner gives us a glittering account of the sequencing of the Drosophila genome by a public-private partnership between government-funded laboratories and Celera Genomics. He portrays both the working life and the good life of science, with neat character sketches set off by Lewis Miller's excellent portraits. Michael's flair for detail and inveterate name-dropping, albeit of restaurants rather than people, lends itself nicely to re-creating the time and place of key events in this collaboration. The original fast-paced manuscript, which I liked so well when I first saw a draft in 2001, has been updated and provided with extensive footnotes that inform without interrupting the narrative. Technical background is given in two excellent postscripts: a fly primer from Scott Hawley, and an overview of fly functional genomics from Ethan Bier.

Michael and I have been orbiting around Cambridge (the original one, as he puts it) for a number of years. Our paths intersect occasionally and pleasantly, but never so forcibly as over genomics-in keeping with Maurice Wilkins' remark to Horace Judson that: "DNA, you know, is Midas' gold. Everyone who touches it goes mad" [1]. It has indeed proved so in the age of sequencing genomes.........

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June 19, 2006, 11:51 PM CT

Winged Sharpshooter Eats With Friends

Like a celebrity living on mineral water, the glassy-winged sharpshooter consumes only the dilute sap of woody plants-including grapevines in California , which is feverishly working to prevent the insect's flight into prized vineyards. Now, in a surprising study reported in the June 6 issue of Public Library of Science Biology (PLoS Biology), scientists at The Institute for Genomic Research (TIGR), the University of Arizona , and their colleagues have discovered that the sharpshooter's deprivation diet is sneakily supplemented by not one, but two co-dependent bacteria living inside its cells.

Eventhough insect-bacteria symbiosis is common, this is the first genomic analysis of three partners. In the study, a team of researchers led by TIGR microbiologist Jonathan Eisen, now at the University of California , Davis , uncovered an intimate metabolic co-dependency among the glassy-winged sharpshooter ( Homalodisca coagulata ) and two bacteria, Baumannia cicadellinicola and Sulcia muelleri. The sharpshooter channels the sweets from sap to the bacteria, which in turn feed the insect vitamins, cofactors, and essential amino acids.

"Much as mosquitoes transmit malaria, the sharpshooter transmits plant disease, including Pierce's disease, which threatens vineyards," Eisen says. "In order to design methods to fight the insect, we've got to understand how it works and its weaknesses. We knew symbionts were doing something for this insect--but until this study, we had no clue what that was".........

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June 18, 2006, 6:37 PM CT

Arctic Warming And Plight Of Polar Bears

A climate scientist at the University of Chicago and 30 of her colleagues from across North America and Europe are urging the U.S. Fish and Wildlife Service to list the polar bear as a threatened species because global warming is melting its sea-ice habitat.

"As researchers engaged in research on climate change, we are deeply concerned about the effect of Arctic warming on the polar bear habitat," said a letter submitted to the Fish and Wildlife Service on June 15. "Biologists have determined that sea-ice is critical in the life cycle of the polar bear and the survival of the polar bear as a species.

Under the Endangered Species Act, the Fish and Wildlife Service is mandatory to list a species for protection if it is in danger of extinction or threatened by possible extinction in all or a significant portion of its range. The ongoing and projected increased loss of sea-ice in the warming Arctic poses a significant threat to the polar bear."

The letter was not a petition, said Pamela Martin, Assistant Professor in Geophysical Sciences at the University of Chicago, who organized the effort. "Rather, it was a letter summarizing some key aspects of the best available science on global warming and, in particular, Arctic warming.

"The polar bear listing petition is really illustrative of the challenge in addressing a number of environmental problems encountered us as a global community. These problems don't fit squarely within a single scientific discipline--they not only require researchers to talk across disciplines, such as the geophysical and biological sciences as in the case of the polar bear, but also across the larger divide that separates researchers from policy makers."........

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June 18, 2006, 4:39 PM CT

Orb-weaver spider

The orb-weaver spiders (family Araneidae) are the familiar builders of spiral wheel-shaped webs often found in gardens, fields and forests. The family is a large one, including over 2800 species in over 160 genera worldwide, making it the third largest family of spiders known (behind Salticidae and Linyphiidae). The oldest known orb-weaving spider is Mesozygiella dunlopi, with specimens in amber dating from the Early Cretaceous.

Generally, orb-weaving spiders are three-clawed builders of flat webs with sticky spiral capture silk. The web has always been thought of as an engineering marvel. In building it, the spider starts with a line, floated on the wind to another surface. The spider secures the line and then drops another line from the center, making a "Y". The rest of the scaffolding follows with a number of radii of non-sticky silk being constructed before a final spiral of sticky capture silk. The third claw is used to walk on the non-sticky part of the web. Characteristically, the prey insect that blunders into the sticky lines is stunned by a quick bite and then wrapped in silk. If the prey is a venomous insect, such as a wasp, wrapping may precede biting.

Some "orb-weavers" do not build webs at all. Members of the genera Mastophora in the Americas and Dicrostichus in Australia produce sticky globules, which contain a pheromone analog. The globule is hung from a silken thread dangled by the spider from its front legs. The pheromone analog attracts male moths of only a few species. These get stuck on the globule and are reeled in to be eaten. Interestingly, both types of "bolas" spiders are highly camouflaged and difficult to locate.........

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