Largest & Strongest Spider Web

An approximately three-foot-wide (meter-wide) Darwin's bark spider web hangs above a river in Madagascar.Though the new species' webs are overall the world's largest, other spiders might exist that create larger orbs—the spiral at the center of the web—according to study co-author Todd Blackledge, a biologist at the University of Akron in Ohio.

Despite spinning webs of Spider-Man-like size and strength, the Darwin's bark spider uses them to feed mainly on small fry—insects such as mayflies and dragonflies, the team found.

Animal Evolution : Lizard From Laying Egg to Live Birth

A yellow-bellied three-toed skink carrying embryos, visible as light orbs inside its body, instead of laying eggs.

Evolution has been caught in the act, according to scientists who are decoding how a species of Australian lizard is abandoning egg-laying in favor of live birth.

Along the warm coastal lowlands of New South Wales, the yellow-bellied three-toed skink lays eggs to reproduce. But individuals of the same species living in the state's higher, colder mountains are almost all giving birth to live young.

Only two other modern reptiles—another skink species and a European lizard—use both types of reproduction.

Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.

But modern reptiles that have live young provide only a single snapshot on a long evolutionary time line, said study co-author James Stewart, a biologist at East Tennessee State University. The dual behavior of the yellow-bellied three-toed skink therefore offers scientists a rare opportunity.

"By studying differences among populations that are in different stages of this process, you can begin to put together what looks like the transition from one [birth style] to the other."

Eggs-to-Baby Switch Creates Nutrient Problem

One of the mysteries of how reptiles switch from eggs to live babies is how the young get their nourishment before birth.

In mammals a highly specialized placenta connects the fetus to the ovary wall, allowing the baby to take up oxygen and nutrients from the mother's blood and pass back waste.

In egg-laying species, the embryo gets nourishment from the yolk, but calcium absorbed from the porous shell is also an important nutrient source.

Some fish and reptiles, meanwhile, use a mix of both birthing styles. The mother forms eggs, but then retains them inside her body until the very last stages of embryonic development.

The shells of these eggs thin dramatically so that the embryos can breathe, until live babies are born covered with only thin membranes—all that remains of the shells.

This adaptation presents a potential nourishment problem: A thinner shell has less calcium, which could cause deficiencies for the young reptiles.

Stewart and colleagues, who have studied skinks for years, decided to look for clues to the nutrient problem in the structure and chemistry of the yellow-bellied three-toed skink's uterus.

"Now we can see that the uterus secretes calcium that becomes incorporated into the embryo—it's basically the early stages of the evolution of a placenta in reptiles," Stewart explained.

Evolutionary Transition Surprisingly Simple

Both birthing styles come with evolutionary tradeoffs: Eggs are more vulnerable to external threats, such as extreme weather and predators, but internal fetuses can be more taxing for the mother.

For the skinks, moms in balmier climates may opt to conserve their own bodies' resources by depositing eggs on the ground for the final week or so of development. Moms in harsh mountain climates, by contrast, might find that it's more efficient to protect their young by keeping them longer inside their bodies.

In general, the results suggest the move from egg-laying to live birth in reptiles is fairly common—at least in historic terms—because it's relatively easy to make the switch, Stewart said.

"We tend to think of this as a very complex transition," he said, "but it's looking like it might be much simpler in some cases than we thought."

The skink-evolution research was published online August 16 by the Journal of Morphology.


Reference: http://news.nationalgeographic.com/news/2010/09/100901-science-animals-evolution-australia-lizard-skink-live-birth-eggs/

Largest Ancient Seabird

Boasting a 17-foot (5.2-meter) wingspan and sharp, spiny "pseudoteeth," this ancient seabird is one of the largest flying birds known, according to a study released Wednesday.

Soaring above the oceans and mountains of what's now Chile between five and ten million years ago, the newly discovered species, named Pelagornis chilensis, was part of a prehistoric group known as the bony-toothed birds. The hollow spikes on the birds' beaks allowed the predators to grab slippery squid and fish from the ocean.

P. chilensis was identified based on an "exquisitely and exceptionally preserved" fossil skeleton that was found to be 70 percent complete, said study co-author David Rubilar of the Museo Nacional de Historia Natural in Chile.

The specimen includes the largest and most complete fossil bird wing yet excavated. Previous bony-toothed bird fossils included wings dug up in pieces, if it all, making it harder to accurately establish wingspan.

—Rachel Kaufman

New giant bird species study appears in the Journal of Vertebrate Paleontology.

Reference: http://news.nationalgeographic.com/news/2010/09/photogalleries/100915-giant-bird-wingspan-science-chilensis-teeth-pictures/

Cockroach Brains May Hold New Antibiotics?

Cockroaches may make your skin crawl, but the insects—or, to be exact, their brains—could one day save your life.

That's because the central nervous systems of American cockroaches produce natural antibiotics that can kill off bacteria often deadly to humans, such as methicillin-resistant Staphylococcus aureus (MRSA) and toxic strains of Escherichia coli, scientists said this week.

Two species of locust tested so far also have the same bacteria-killing molecules in their tiny heads.

The findings suggest that the inset world—which makes up 80 percent of all animals on Earth—may be teeming with new antibiotics, said study co-author Simon Lee of the University of Nottingham in the U.K.

Such a discovery is crucial, because scientists are scrambling to combat strains of several infectious diseases, including MRSA and E. coli, that are resistant to traditional antibiotics, Lee said.

"It's a promising new lead. We are looking in an unusual place, and to my knowledge no one else is looking there," Lee said.

"That's what we need in terms of [finding new] antibiotics, because all the usual places"—such as soil microbes, fungi, and purely synthetic molecules—"have been exhausted."

Insect Brains Have "Clever Defense" Against Bacteria

Lee and colleagues dissected the tissues and brains of cockroaches—which "smell as bad as they look," Lee said—and locusts in the lab.

The team tested nine separate types of antibacterial molecules found in the insects' brains and discovered that each molecule is specialized to kill a different type of bacteria.

This "very clever defense mechanism" allows the bugs to survive in the most dirty of domains, Lee said.

The scientists found the bugs had antibiotics only in their brain tissue, the most essential part of the body, he added.

A bug might live with an infected leg, for instance, but a brain infection would almost certainly be fatal.

Insect-brain drugs for humans are still years away, Lee said, but there's one hopeful glimmer: When the team added the insect antibiotics to human cells in the lab, there were no toxic effects.

Preliminary findings on antibiotics in bug brains were presented at the Society for General Microbiology meeting held this week at the University of Nottingham.

Reference: National Geographic http://news.nationalgeographic.com/news/2010/09/100909-cockroach-brains-mrsa-ecoli-antibiotics-science-health/