June 25, 2009, 6:05 PM CT

How piranhas got their teeth

How did piranhas the legendary freshwater fish with the razor bite get their telltale teeth? Scientists from Argentina, the United States and Venezuela have uncovered the jawbone of a striking transitional fossil that sheds light on this question. Named Megapiranha paranensis, this previously unknown fossil fish bridges the evolutionary gap between flesh-eating piranhas and their plant-eating cousins.

Present-day piranhas have a single row of triangular teeth, like the blade on a saw, explained the researchers. But their closest relatives a group of fishes usually known as pacus have two rows of square teeth, presumably for crushing fruits and seeds. "In modern piranhas the teeth are arranged in a single file," said Wasila Dahdul, a visiting scientist at the National Evolutionary Synthesis Center in North Carolina. "But in the relatives of piranhas which tend to be herbivorous fishes the teeth are in two rows," said Dahdul.

Megapiranha shows an intermediate pattern: it's teeth are arranged in a zig-zag row. This suggests that the two rows in pacus were compressed to form a single row in piranhas. "It almost looks like the teeth are migrating from the second row into the first row," said John Lundberg, curator at the Academy of Natural Sciences in Philadelphia and a co-author of the study......... Posted by: Kelly      Read more         Source

June 23, 2009, 5:00 PM CT

Prairie dogs and plants?

Prairie dogs may seem like harmless little creatures, but they can inflict serious injury on plants simply by snacking on them. Plants cannot flee from their furry predators, so how do they avoid becoming a prairie dog's lunch?.

Dr. John Freeman and his colleagues explore the role of metal hyperaccumulation in plant defense in the June 2009 issue of the American Journal of Botany Certain plants species growing on soils with high metal content (such as arsenic, copper, selenium, and lead) accumulate large quantities of metals in their leaves and stems. The purpose of this metal hyperaccumulation is not fully known, but metal hyperaccumulation may increase a plant's ability to respond to drought, compete with other plants, or provide a defense against bacteria, viruses, and animals.

"It is interesting to think about the effect of the prairie dog, which was an amazing ecosystem engineer on a very large scale here in North America," said Dr. Freeman, Colorado State University. "From their prehistoric ancestors the ground squirrel to the modern prairie dog, these animals may have driven the evolution of selenium hyperaccumulation as an elemental defense against herbivory in a number of different plant species".

Dr. Freeman's research focused on the role of selenium hyperaccumulation in Stanleya pinnata (prince's plume), a wildflower correlation to mustard plants. Eventhough low levels of selenium are essential for a number of animals, consumption of high levels is toxic. But just because an overdose of selenium is toxic to animals does not mean that the presence of high levels in leaves deters animals from eating the plants; prairie dogs may not know to avoid S. pinnata until it is too late. Few studies have addressed this question and whether metal hyperaccumulation actually acts as a deterrent......... Posted by: Kelly      Read more         Source

June 21, 2009, 8:48 PM CT

Dino-not-so-soaring

The largest animals ever to have walked the face of the earth may not have been as big as previously thought, reveals a paper published recently in the Zoological Society of London's Journal of Zoology

Scientists have discovered that the original statistical model used to calculate dinosaur mass is flawed, suggesting dinosaurs have been oversized.

Widely cited estimates for the mass of Apatosaurus louisae, one of the largest of the dinosaurs, may be double that of its actual mass (38 tonnes vs. 18 tonnes).

"Paleontologists have for 25 years used a published statistical model to estimate body weight of giant dinosaurs and other extraordinarily large animals in extinct lineages. By re-examining data in the original reference sample, we show that the statistical model is seriously flawed and that the giant dinosaurs probably were only about half as heavy as is generally believed" says Gary Packard from Colorado State University.

The new predictions have implications for numerous theories about the biology of dinosaurs, ranging from their energy metabolism to their food requirements and to their modes of locomotion......... Posted by: Kelly      Read more         Source

June 12, 2009, 5:16 AM CT

Zebra mussels hang on while quagga mussels take over

The zebra mussels that have wreaked ecological havoc on the Great Lakes are harder to find these days not because they are dying off, but because they are being replaced by a cousin, the quagga mussel. But zebra mussels still dominate in fast-moving streams and rivers.

Research conducted by Suzanne Peyer, a doctoral candidate in the University of Wisconsin-Madison Department of Zoology, shows that physiological differences between the two species might determine which mollusk dominates in either calm or fast-moving waters.

"Zebra mussels quite rapidly colonized rivers close to the Great Lakes right after their introduction, within a year or two," Peyer explains. "Quagga mussels were introduced in the Great Lakes around 20 years ago, but they are not yet found in the rivers or tend to be present in low numbers".

The mussels are similar in a number of ways. Their habitats overlap, and both are suspension feeders that filter water to extract their food. But the cousin species are different in a number of ways, too. Zebra mussels prefer to attach to a hard surface, while quagga mussels can live on soft bottoms, such as sand or silt. Zebra mussels also prefer warmer water temperatures and do not grow as big as quagga mussels.

Peyer's research focused on the ability of the mussels to attach to underlying material. Both species attach to rocks, sand, silt or each other by producing tiny but strong "byssal" threads, string-like strands of protein. These threads act as an adhesive that enable the mussels to attach to surfaces, regardless of how slippery the surface is. Byssal threads are the reason mussels are so difficult to remove from boats or water intake pipes......... Posted by: Kelly      Read more         Source

June 10, 2009, 8:56 PM CT

The Secret of a Snake's Slither

Snake locomotion may seem simple in comparison to walking or galloping. But in reality, it's no easy task to move without legs. Prior research has assumed that snakes move by pushing off of rocks and debris around them. But a study published this week in the Proceedings of the National Academy of Sciences says that it's all in their design--specifically, their scales.

Overlapping belly scales provide friction with the ground that gives snakes a preferred direction of motion, like the motion of wheels or ice skates. Like wheels and ice skates, sliding forward for snakes takes less work than sliding sideways.

In addition, snakes aren't lying completely flat against the ground as they slither. They redistribute their weight as they move, concentrating it in areas where their bodies can get the most friction with the ground and therefore maximize thrust. In this way, snake slithering is not unlike human walking--we, too, shift our weight from left to right to enable us to move.

See the video........ Posted by: Kelly      Read more         Source

June 10, 2009, 8:50 PM CT

Evolution can occur in less than 10 years

How fast can evolution take place? In just a few years, as per a newly released study on guppies led by UC Riverside's Swanne Gordon, a graduate student in biology.

Gordon and her colleagues studied guppies small fresh-water fish biologists have studied for long from the Yarra River, Trinidad. They introduced the guppies into the nearby Damier River, in a section above a barrier waterfall that excluded all predators. The guppies and their descendents also colonized the lower portion of the stream, below the barrier waterfall, that contained natural predators.

Eight years later (less than 30 guppy generations), the scientists observed that the guppies in the low-predation environment above the barrier waterfall had adapted to their new environment by producing larger and fewer offspring with each reproductive cycle. No such adaptation was seen in the guppies that colonized the high-predation environment below the barrier waterfall.

"High-predation females invest more resources into current reproduction because a high rate of mortality, driven by predators, means these females may not get another chance to reproduce," explained Gordon, who works in the lab of David Reznick, a professor of biology. "Low-predation females, conversely, produce larger embryos because the larger babies are more competitive in the resource-limited environments typical of low-predation sites. Moreover, low-predation females produce fewer embryos not only because they have larger embryos but also because they invest fewer resources in current reproduction"......... Posted by: Kelly      Read more         Source

June 8, 2009, 10:19 PM CT

Complexity of animal mating choices

When female tiger salamanders choose a mate, it turns out that size does matter - tail size that is - and that's not the only factor they weigh.

Findings of a Purdue University study show that animals make more complex decisions about choosing mates than once thought. The results of Andrew DeWoody's study, released Monday (June 8) in the journal Molecular Ecology, refute a theory that animals use major histocompatibility complex (MHC) genes as the sole basis for mate choice. Immunologists have long known that MHC genes play key roles in the immune response, but more recently behavioral ecologists have postulated that animal mate choice is often based on MHC-type because of the function of those genes.

"Our data indicate that mate-choice decisions aren't solely dependent on MHC, tail length, body size or any other single factor," said DeWoody, a professor of genetics. "Mate choice is a complex process that takes a number of factors into account".

DeWoody and David Bos, a former postdoctoral assistant who is now a continuing lecturer at Purdue, set out to see how much MHC genes affected mate choice in wild animals. Most previous research showed that an animal would choose a mate with MHC that is the most divergent from its own so that offspring will have more effective immune systems......... Posted by: Kelly      Read more         Source

June 5, 2009, 4:57 AM CT

Bats recognize the individual voices of other bats

Bats can use the characteristics of other bats' voices to recognize each other, as per a research studyby scientists from the University of Tuebingen, Gera number of and the University of Applied Sciences in Konstanz, Gera number of. The study, published June 5 in the open-access journal PLoS Computational Biology, explains how bats use echolocation for more than just spatial knowledge.

The scientists first tested the ability of four greater mouse-eared bats to distinguish between the echolocation calls of other bats. After observing that the bats learned to discriminate the voices of other bats, they then programmed a computer model that reproduces the recognition behaviour of the bats. Analysis of the model suggests that the spectral energy distribution in the signals contains individual-specific information that allows one bat to recognize another.

Animals must recognize each other in order to engage in social behaviour. Vocal communication signals are helpful for recognizing individuals, particularly in nocturnal organisms such as bats. Little is known about how bats perform strenuous social tasks, such as remaining in a group when flying at high speeds in darkness, or avoiding interference between echolocation calls. The finding that bats can recognize other bats within their own species based on their echolocation calls may therefore have some significant implications......... Posted by: Kelly      Read more         Source

June 5, 2009, 4:47 AM CT

Different genes cause loss of body parts

New research shows that when two species of stickleback fish evolved and lost their pelvises and body armor, the changes were caused by different genes in each species.

That surprised researchers, who expected the same genes would control the same changes in both related fish.

Results of the study, funded by the National Science Foundation (NSF)'s Divisions of Environmental Biology and Integrative Organismal Systems, are published online today in the journal Current Biology

"Earth's climate and biosphere are changing rapidly and in unpredictable ways," says Penny Firth, deputy director of NSF's Division of Environmental Biology. "A major challenge for biology is understanding the connections among evolving genomes, evolving populations and changing ecosystems. This research takes an important step by illuminating the genetic basis of evolutionary change in long-separated lineages".

Biologists knew that in a number of cases of evolution, "the same gene has been used over and over again--even in different species--to result in the same anatomy," says Mike Shapiro, first author of the paper and a biologist at the University of Utah. "What we are finding now is that different genes can have similar effects".

The findings shed new light on how evolution produces diversity in nature, and on the evolution of limb loss--and not just the loss of the pelvis and leg-like pelvic spines in certain sticklebacks......... Posted by: Kelly      Read more         Source

June 1, 2009, 7:17 PM CT

Coryphodon

Ancestors of tapirs and ancient cousins of rhinos living above the Arctic Circle 53 million years ago endured six months of darkness each year in a far milder climate than today that featured lush, swampy forests, as per a newly released study led by the University of Colorado at Boulder.

CU-Boulder Assistant Professor Jaelyn Eberle said the study shows several varieties of prehistoric mammals as heavy as 1,000 pounds each lived on what is today Ellesmere Island near Greenland on a summer diet of flowering plants, deciduous leaves and aquatic vegetation. But in winter's twilight they apparently switched over to foods like twigs, leaf litter, evergreen needles and fungi, said Eberle, curator of fossil vertebrates at the University of Colorado Museum of Natural History and chief study author.

The study has implications for the dispersal of early mammals across polar land bridges into North America and for modern mammals that likely will begin moving north if Earth's climate continues to warm. A paper on the subject co-authored by Henry Fricke of Colorado College in Colorado Springs and John Humphrey of the Colorado School of Mines in Golden appears in the recent issue of Geology

The team used an analysis of carbon and oxygen isotopes extracted from the fossil teeth of three varieties of mammals from Ellesmere Island -- a hippo-like, semi-aquatic creature known as Coryphodon, a second, smaller ancestor of today's tapirs and a third rhino-like mammal known as brontothere. Animal teeth are among the most valuable fossils in the high Arctic because they are extremely hard and better able to survive the harsh freeze-thaw cycles that occur each year, Eberle said......... Posted by: Kelly      Read more         Source