jueves, 7 de agosto de 2008

Selección del Complexity Digest - Junio- Julio

Why Do Mountains Support So Many Species Of Birds?, Ecography

Excerpt: Although topographic complexity is often associated with high bird diversity at broad geographic scales, little is known about the relative contributions of geomorphologic heterogeneity and altitudinal climatic gradients found in mountains. We analysed the birds in the western mountains of the New World to examine the two-fold effect of topography on species richness patterns, (...).We conclude that bird diversity gradients in mountains primarily reflect local climatic gradients. Widespread (lowland) species and narrow-ranged (montane) species respond similarly to changes in the environment, differing only in that the richness of lowland species correlates better with broad-scale climatic effects (...).
  1. Scientists Confirm That Parts Of Earliest Genetic Material May Have Come From The Stars, Innovations-report

    Excerpts: Scientists have confirmed for the first time that an important component of early genetic material which has been found in meteorite fragments is extraterrestrial in origin, in a paper (...). The finding suggests that parts of the raw materials to make the first molecules of DNA and RNA may have come from the stars. The scientists, (...) provides evidence that life's raw materials came from sources beyond the Earth. The materials they have found include the molecules uracil and xanthine, which are precursors to the molecules that make up DNA and RNA, and are known as nucleobases. (...)

    1. Genetic Building Blocks May Have Formed In Space, NewScientist.com

      Excerpts: Some fundamental building blocks of our genetic code might have come from outer space, according to a controversial new meteorite study.

      The study suggests that some organic compounds associated with genetic material might have formed in a meteorite called Murchison before it landed in Australia in 1969. The chemicals are two kinds of nucleobases, ring-like carbon molecules that are essential for the creation of nucleic acids like DNA and RNA.

  2. Scientists Close to Reconstructing First Living Cell, Scientific American

    THE FIRST CELL?: Scientists at Harvard Medical School have designed what they think is a reasonable model for the first cell on Earth, some 3.5 to four billion years ago.
    Researchers get genetic material to copy itself in a recreation of a simple protocell that could have existed eons ago

    Harvard Medical School researchers report in Nature that they have built a model of what they believe the very first living cell may have looked like, which contains a strip of genetic material surrounded by a fatty membrane. The membranes of modern cells consist of a double layer of fatty acids known as phospholipids.

Bacteria Make Major Evolutionary Shift In The Lab, New Scientist

But sometime around the 31,500th generation, something dramatic happened in just one of the populations - the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use.

Indeed, the inability to use citrate is one of the traits by which bacteriologists distinguish E. coli from other species. The citrate-using mutants increased in population size and diversity.

"It's the most profound change we have seen during the experiment.(...)".

Change Lifestyle, Change Genes - 3 Months On Ornish Diet Changes 500 Genes, Many With Anticancer Effects, WebMD Health News

Excerpts: WebMD Health News More than 500 genes changed the way they worked. Genes with beneficial effects, including some tumor-suppression genes, became more active. Genes with deleterious effects, including some cancer-promoting genes, were switched off.

Complex Food Webs Prevent Competitive Exclusion Among Producer Species, Proc. Biol. Sc.

Excerpts: Herbivorous top-down forces and bottom-up competition for nutrients determine the coexistence and relative biomass patterns of producer species. Combining models of predator-prey and producer-nutrient interactions with a structural model of complex food webs, I investigated these two aspects in a dynamic food-web model. While competitive exclusion leads to persistence of only one producer species in 99.7% of the simulated simple producer communities without consumers, embedding the same producer communities in complex food webs generally yields producer coexistence. (...) This negative feedback loop regulates the coexistence and biomass patterns of the producers by balancing biomass increases of producers and biomass fluxes to herbivores, (...).

How The Snake Got Its Fangs, Science News

By observing gene activity in snake embryos, a team revealed that, on the evolutionary tree, fangs sprang from one source. Pictured is the 18-day-old embryo of an African night adder. (...)
Credit: F. Vonk and M. Richardson
It likely all started when the back of the mouth left the front. (...)

Dagger-sharp frontal fangs allow cobras and vipers to prey on feisty mammals such as the large desert rat. Garter snakes, corn snakes and others that hunt less volatile creatures do just fine with fangs in the back of their mouth. What confused biologists, however, was learning that the front-fanged snakes don't fall into a neat group. In the snake tree of life, rear-fanged snakes are scattered on evolutionary branches in between the cobras and the more recently evolved vipers, which indicates that fangs evolved at least a couple of times on separate branches leading to front-fanged snakes.

Genetics: Simple Sleepers, Science

Excerpts: Classic genetic model organisms--fruit flies, zebrafish, and roundworms--are popular newcomers in sleep research laboratories, although debate continues about how much their dozing relates to human slumber.(...)

When birds and mammals sleep, their brains generate characteristic electrical patterns that denote deep sleep and dreaming. Since discovering this phenomenon in 1953 using electroencephalogram recordings of human brains, scientists have incorporated EEG patterns into the definition of sleep. But the simpler brains of flies, worms, and even reptiles don't produce those patterns, and no one was certain these animals even sleep.

China: Where Have All The Flowers Gone?, Nature

Excerpts: At least 117 boys were being born for every 100 girls at the beginning of this century in China. (...)

In 1982 the average male-to-female ratio at birth in China was 1.07 (as opposed to the normal level of 1.03-1.06); by 2000, various estimates put it at 1.17-1.21. And according to even official figures, the female-to-male infant mortality ratio rose during this period from around 0.95 to 1.46. The timing seems to imply a direct link to the one-child policy, although Guilmoto points out that the sex ratio has also increased in recent times in countries where no such restrictions apply, such as India and South Korea.

Scientists Hope To Gain Insight Into Fossil Record By Studying Current Size Ranges, The New Mexican

Excerpts: That more recent fossil record, they think, can help scientists better understand the size differences between animals in a group - like mammals or lizards or dinosaurs - from times much further back than 50 million years, such as the time of the dinosaurs, which ended 65 million years ago, Clauset said.

"This model may give us a way of estimating what we're missing in the fossil record," Clauset said.

That could be useful because fossils from the time of the dinosaurs, for instance, can be very deceptive.

  1. The Evolution and Distribution of Species Body Size, Science

    Excerpts: The distribution of species body size within taxonomic groups exhibits a heavy right tail extending over many orders of magnitude, where most species are much larger than the smallest species. We provide a simple model of cladogenetic diffusion over evolutionary time that omits explicit mechanisms for interspecific competition and other microevolutionary processes, yet fully explains the shape of this distribution. We estimate the model's parameters from fossil data and find that it robustly reproduces the distribution of 4002 mammal species from the late Quaternary.

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