Evolution? How?

Never give up Mr Red, there are readers here who find you entertaining. I just don't happen to be one of them.

They're all RR! How'd you do that? Let me guess. With God's help.

The Early Bird Caught the Fish: Fossils Depict Aquatic Origins of Near-Modern Birds 115 Million Years Ago
June 15, 2006

PHILADELPHIA -- Five fossil specimens of a near-modern bird found in the Gansu Province of northwestern China show that early birds likely evolved in an aquatic environment, according to a study reported today in the journal Science. Their findings suggest that these early modern birds were much like the ducks or loons found today. Gansus yumenesis, which lived some 105 to 115 million years ago during the Early Cretaceous period, took modern birds through a watery path out of the dinosaur lineage.

The report was co-authored by Peter Dodson of the University of Pennsylvania and his former students Hai-lu You of the Chinese Academy of Geological Sciences, Jerald Harris of Dixie State College of Utah and Matthew Lamanna of Carnegie Natural History Museum in Pittsburgh.

"Gansus is very close to a modern bird and helps fill in the big gap between clearly non-modern birds and the explosion of early birds that marked the Cretaceous period, the final era of the Dinosaur Age," said Peter Dodson, professor of anatomy at Penns School of Veterinary Medicine and professor in Penns Department of Earth and Environmental Sciences. "Gansus is the oldest example of the nearly modern birds that branched off of the trunk of the family tree that began with the famous proto-bird Archaeopteryx."

Gansus yumenensis takes its name from the Gansu region, where it was found, and the nearby city of Yumen. According to Dodson, Gansus is something of a lost species, originally described from a fossil leg found in 1983, but since largely ignored by science. The five specimens described by Dodson and his colleagues had many of the anatomical traits of modern birds, including feathers, bone structure and webbed feet, although every specimen lacked a skull.

"It appears that the early ancestors of modern birds lived lifestyles that today we would stereotype as being duck-like, heron-like, stork-like, loon-like, etc.," said Jerald Harris, director of paleontology at Dixie Sate College of Utah. "Gansus likely behaved much like its modern relatives, probably eating fish, insects and the occasional plan. We won't have a definitive dietary answer until we find a skull."

The skeletons, headless as they are, offer plenty of evidence for a life on the water. Its upper body structure offers evidence that Gansus could take flight from the water, like a modern duck, and the webbed feet and bony knees are clear signs that Gansus swam.

"Webbed feet is an adaptation that has evolved repeatedly in widely separate groups of animals, such as sea turtles, whales and manatees, and would only hinder climbing or landing in trees," Harris said. "The big bony crest that sticks off the knee-end of their lower leg bones are similar to structures seen in loons and grebes. These crests anchor powerful muscles needed for diving under water and swimming."

According to Harris, these adaptations all demonstrate how the Gansus branch of the family tree, the structurally modern birds called ornithuromorphs, split from the enantiornitheans (or "opposite birds"). Enantiornitheans were among the feathered fossils found in northeastern China during the 1990s.

"The enantiornitheans had the best adaptations for perching, so they were able to dominate the ecological niche that we would associate with songbirds, cuckoos, woodpeckers or birds of prey," Harris said. "Gansus appears to have had adaptations for a lifestyle centered around water, based on things like the proportions of the leg and foot bones."

While the enantiornitheans are now long gone, their perching lifestyle has now been taken over by the descendents of birds like Gansus. What remains a mystery for now, according to the researchers, is how the amphibious lifestyle of birds like Gansus helped enable them to survive the cataclysmic end of the dinosaurs 65 million years ago.

Funding was provided by the Discovery Channel (Quest program) and the Science Channel, the Carnegie Museum of Natural History, Dixie State College, the Chinese Geological Survey of the Ministry of Land and Resources of China and the Gansu Bureau of Geology and Mineral Resources.

While the enantiornitheans are now long gone, their perching lifestyle has now been taken over by the descendents of birds like Gansus. What remains a mystery for now, according to the researchers, is how the amphibious lifestyle of birds like Gansus helped enable them to survive the cataclysmic end of the dinosaurs 65 million years ago.

Darwin, Meet Frankenstein
Category: Evolution
Posted on: June 14, 2006 1:00 PM, by

Scientists have figured out many ways to study the origin of species. They can build evoluitonary trees, to see how species descend from a common ancestor. They can survey islands or mountains or lakes to see how ecological conditions foster the rise of new species. They can look for fossils that offer clues to how long ago species branched off from one another, and how their ranges spread or shrank. Now comes a new trick in tomorrow's issue of the journal Nature: to test their ideas about how a new species of butterfly came to be, they essentially recreated it in their lab.



The new species in question was a graceful little butterfly called Heliconius heurippa. It lives in a small region of Columbia, just east of the Andes. Many other Heliconius (or passion-vine) butterflies live in South and Central America. Of particular interest is H. melpomene. Its wide range includes that of H. heurippa. The two butterflies have the same hindwing color, and they also share an orange streak across the forewing.

Scientists were also struck by the similarity between H. heurippa and another species, H. cydno. These two species share the same white streak across the wing. It does not live alongside H. heurippa, though. Its range stops at the western side of the Andes.

H. heurippa almost looks like a simple combination of the other two species. A team of scientists who study the butterfly wondered if that indeed was the case. Perhaps, they speculated, a population of H. cydno became isolated on the eastern side of the Andes from the other butterflies of its species. The isolated butterflies mated with the H. melpomene around them. Instead of merging with the other species, the butterflies became distinctive hybrids with an appearance all their own. They were attracted to their own appearance, while the original two species continued to be attracted to theirs. The hybrids became a new species: H. heurippa.

This was a provocative idea. Mathematical models had suggested that new species formed from hybrids should be very rare. It's hard for hybrids to become reproductively isolated from their pure-bred parents, particularly when they live side by side. As I wrote in the New York Times a couple weeks ago, interbreeding may be able to cause two newly diverged species to collapse back into a single hybrid swarm. The best example of new species from hybrids come from plants--in particular, sunflowers. The evidence from animals has been suggestive, but it couldn't rule out the possibility that another process had produced the same patterns. Instead of forming a new hybrid species, the animals might have first split into two new species, and then only interbred later, mixing some of their genes.

To try to rule out these sorts of alternative explanations, the scientists looked at H. heurippa from many angles. They compared its DNA to that of the other two species. All three butterfly species are closely related, but their genes belong to three distinct clusters. H. heurippa is not just some isolated race of either of the more widespread species.

On the other hand, the scientists could identify certain genes in H. heurippa that were most similar to the corresponding in genes in one of the two other species--just as you'd expect from hybrids.

Then the scientists did a Frankenstein-meets-Darwin experiment. They tried to recreate H. heurippa all over again. They mated H. melpomene and H. cydno, and produced hybrids. In the first generation, the female hybrids were all sterile--a common result of interbreeding. But this did not mean the experiment was over. The male hybrids could still breed with the females of the original species. After a few generations of interbreeding this way, the scientists produced butterflies that looked remarkably like H. heurippa and could now breed among themselves. While fertile hybrids are also familiar to biologists, they tend to produce a jumble of offspring, many of which look more like their pure-bred ancestors. Not so for the new butterflies. They consistently produced offspring that also looked like H. heurippa.

Even if hybrids can produce a stable line of offspring like themselves, they may not actually do so. If the hybrids are willing to mate with their parental species, they may simply merge back together. In the final part of their study, the scientists showed that this was not happening in H. heurippa. They observed how likely butterflies from each species would be to mate with other species. All three showed a strong preference for their own. The key to their preference seems to be those beautiful bands on their wings. The scientists covered over each of the bands on female butterflies to see how the new look affected how males decided to court. Removing either the red or yellow bands made male H. heurippa less likely to try to woo a female.

This research is intriguing on a lot of levels (more details appear in a paper in the Journal of Evolutionary Biology). The researchers propose a path to the origin of species from hybrids, one that the theorists haven't thought about before. And who knows how many other species might have formed that way. As I wrote here, the human and chimpanzee genomes contain hints that our ancestors may have interbred millions of years ago. Did they create some new hybrid species? It's possible that mate choice in primates is just too different from that in butterflies. We may not be so easily controlled by visual cues like colored stripes.

But I cringed when I looked at the map in the paper showing the distribution of the three species. H. heurippa exists in only in one stretch of Andean foothills and nowhere else in the world. Passion-vine butterflies can only lay their eggs on a single species of passion vine, because they have evolved defenses against that particular plant and can't feed on other passion vines. If its habitat or host plant should disappear, this wonderful natural experiment in evolution may will disappear as well.