A Repository of Useful Links/URLs Under the Subject of Evolution

[hexo]

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it's too late to apologize, it's too late.
it's too late to apologize yeah.

[gareb]

^^ Still waiting for the moderators to merged it to other thread.

as requested

[orcgod]

NOVA | Evolution Down Under

The animal kingdom as developed in Australia presents us with anomalies and peculiarities perhaps even more remarkable than are exhibited by the plants. Alfred Russel Wallace, Australasia, 1893

Australia, the smallest of the seven continents, is the world capital of two of the three types of mammal on Earth: the marsupials, like the kangaroo and koala, which nourish their young in pouches, and the monotremes, featuring the platypus and the echidnas, which nourish their young in eggs. (The third variety, placentals, include all the rest of us—from mice to whales to people—which nourish their young in an advanced placenta.)

How did this happen? Why did Australia get a preponderance of pouched and egg-laying mammals? And, at the same time, precious few of the kind of mammal that dominates every other land in the world?

The story is a long one—say, 100 million years or more—and for decades was missing key sections. Only in recent years have paleontologists succeeded in filling in some of those gaps to their satisfaction, enabling them to draw a reasonably detailed portrait of Australia's unique evolutionary history.


Mammals with pouches, like this red kangaroo, didn't originate in Australia, but they have prospered there like nowhere else on the planet.

Tooth Be Told

Two long-standing questions were answered, remarkably enough, by a single fossil tooth. Or two single fossil teeth actually, unearthed on opposite sides of the globe, both in 1992.

Until sometime in the Cretaceous Period (146 to 65 million years ago), Australia, Antarctica, and South America all abutted one another in the southern supercontinent Gondwana. While they were attached, experts believe a single belt of forest likely stretched from southeastern Australia, through Antarctica, and into southern South America, and they know that early versions of all three mammal models existed at the time. Yet today no monotremes exist outside of Australia (and New Guinea), and no placental mammals that didn't fly or swim there—for example, bats or dugongs—exist in Australia except for rodents (which arrived only about five million years ago) and mammals that were introduced by people (who arrived by 60,000 years ago).

Why didn't monotremes use the connection to leave Australia? And why didn't placentals use it to enter Australia?

One of the teeth, uncovered in Argentina from deposits 63 to 61 million years old, answered the first question. Monotremes had lived elsewhere, for paleontologists determined that the tooth belonged to a platypus, an extinct species now known as the Patagonian platypus. (Which way the monotremes originally crossed the Antarctic bridge—from or to Australia—remains a mystery.) The second tooth, meanwhile, answered the second question. Placentals had come to Australia, for some experts believe the tooth, dug out of Queensland deposits radiometrically dated to at least 55 million years ago, belonged to a primitive, nonflying placental known as a condylarth. More recent discoveries hint that other early placentals lived in Australia, even before marsupials turn up in the fossil record.

But the monotremes in South America, and the placentals in Australia, didn't last.

(more info on the link)
NOVA | Evolution Down Under

[orcgod]

Studying bat skulls, evolutionary biologists discover how species evolve

Studying Bat Skulls, Evolutionary Biologists Discover How Species Evolve

ScienceDaily (Nov. 23, 2011) — A new study involving bat skulls, bite force measurements and scat samples collected by an international team of evolutionary biologists is helping to solve a nagging question of evolution: Why some groups of animals develop scores of different species over time while others evolve only a few. Their findings appear in the current issue of Proceedings of the Royal Society B: Biological Sciences.



To answer this question, Elizabeth Dumont at the University of Massachusetts Amherst and Liliana Dávalos of Stony Brook University together with colleagues at UCLA and the Leibniz Institute for Zoo and Wildlife Research, Berlin, compiled large amounts of data on the diet, bite force and skull shape in a family of New World bats, and took advantage of new statistical techniques to date and document changes in the rate of evolution of these traits and the number of species over time.

They investigated why there are so many more species of New World Leaf-Nosed bats, nearly 200, while their closest relatives produced only 10 species over the same period of time. Most bats are insect feeders, while the New World Leaf-Nosed bats eat nectar, fruit, frogs, lizards and even blood.

One hypothesis is that the evolution of a trait, such as head shape, that gives access to new resources can lead to the rapid evolution of many new species. As Dumont and D?valos explain, connecting changes in body structure to an ecological opportunity requires showing that a significant increase in the number of species occurred in tandem with the appearance of new anatomical traits, and that those traits are associated with enhanced resource use.

"If the availability of fruit provided the ecological opportunity that, in the presence of anatomical innovations that allowed eating the fruit, led to a significant increase in the birth of new species, then skull morphology should predict both diet and bite force" they said. They found support for these predictions by analyzing thousands of evolutionary trees of more than 150 species, measuring over 600 individual bat skulls of 85 species, testing bite force in over 500 individual bats from 39 species in the field and examining thousands of scat samples to identify the bats' diets.

They found that the emergence of a new skull shape in New World Leaf-Nosed bats about 15 million years ago led to an explosion of many new bat species. The new shape was a low, broad skull that allowed even small bats to produce the strong bite needed to eat hard fruits. The rate of birth of new species jumped as this new shape evolved, and this group of bats quickly increased the proportion of fruit in their diet. Change in shape slowed once this new skull had evolved.

It can be difficult for evolutionary biologists to demonstrate that traits related to anatomical changes, also called "morphological innovations" such as a new skull shape, give certain groups a survival advantage when new food sources, such as hard fruits, become available.

"This study conducted during the International Year of the Bat offers a clear example of how the evolution of new traits, in this case a skull with a new shape, allowed animals to use new resources and eventually, to rapidly evolve into many new species," Dumont says. "We found that when a new ecological niche opened up with an opportunity for bats that could eat hard fruits, they shifted their diet significantly, which in turn led to the evolution of new species."



http://www.sciencedaily.com/releases...0114173923.htm
Bats Evolve from Genetically mutated Mice.

ScienceDaily (Jan. 14, 200 — A research team led by Dr. Richard Behringer at MD Anderson Cancer Center reports that they have successfully switched the mouse Prx1 gene regulatory element with the Prx1 gene regulatory region from a bat -- and although these two species are separated by millions of years of evolution -- the resulting transgenic mice displayed abnormally long forelimbs.



While forelimb length is just one of several key morphological changes that occurred during the evolution of the bat wing, this unprecedented finding demonstrates that evolution can be driven by changes in the patterns of gene expression, rather than solely by changes in the genes, themselves.

Prx1 is a paired-box homeodomain transcription factor, with an established role in limb bone growth. Dr. Behringer and colleagues identified a conserved Prx1 enhancer domain, which regulates expression of Prx1 in the developing forelimb.

To study the evolutionary contribution of the Prx1 enhancer to the morphological differences between the bat and mouse forelimb, Dr. Behringer and colleagues replaced the endogenous mouse Prx1 enhancer with that of the bat. The transgenic mice showed higher expression levels of Prx1 in the perichondrium, increased chondrocyte proliferation, and ultimately, longer forelimbs.

Dr. Behringer describes the significance of his finding as such: "Darwin suggested that "successive slight modifications" would ultimately result in the evolution of diverse limb morphologies, like a hand, wing, or fin. The genetic change we engineered in mice may be one of those "slight modifications" to evolve a mammalian wing."

This research was published In the January 15th issue of Genes and Development.