Global late Quaternary [132,000 to 1,000 years ago] Megafauna Extinctions linked to humans, not climate change
Christopher Sandom, Søren Faurby, Brody Sandel and Jens-Christian Svenning (Department of Bioscience, Aarhus University, Denmark)
— Proceedings of the Royal Society / Biological Sciences, 22 July 2014
Abstract The late Quaternary megafauna extinction was a severe global-scale event. Two factors, climate change and modern humans, have received broad support as the primary drivers, but their absolute and relative importance remains controversial. …
We present, to our knowledge, the first global analysis of this extinction based on comprehensive country-level data on the geographical distribution of all large mammal species (more than or equal to 10 kg) that have gone globally or continentally extinct between the beginning of the Last Interglacial at 132 000 years BP and the late Holocene 1000 years BP, testing the relative roles played by glacial–interglacial climate change and humans.
We show that the severity of extinction is strongly tied to hominin palaeobiogeography, with at most a weak, Eurasia-specific link to climate change. …
IMAGE Global maps of late Quaternary [a, b] large mammal extinction severity, [c] hominin palaeobiogeography, [d] temperature anomaly and [e] precipitation velocity. [More detail here …]
Global late Quaternary megafauna extinctions linked to humans, not climate change is an open access article.
STRUCTURE OF CHIKUNGUNYA VIRUS-LIKE PARTICLES
Modeled Using X-ray Crystallography and Electron Cryo-microscopy
Chikungunya, a mosquito-borne virus discovered in 1955 by two scientists in Tanzania, has been a health problem in Africa and southern Asia for decades. It made its way to the Caribbean in late 2013.
Research article: Siyang Sun et al: “Structural analyses at pseudo atomic resolution of Chikungunya virus and antibodies show mechanisms of neutralization” || April 2, 2013 || eLife 2013;2:e00435 [an open access peer reviewed journal]
The Chikungunya virus is carried by mosquitos and can cause a number of diseases in humans including encephalitis, which can be fatal in some cases, and severe arthritis.
Chikungunya virus has a single-stranded RNA genome that codes for four non-structural proteins and five structural proteins. …
A recent mutation in the E1 protein of the virus has allowed it to efficiently reproduce in a different species of mosquitos, leading to a Chikungunya epidemic in Réunion Island in 2005 and the subsequent infection of millions of individuals in Africa and Asia. The virus [has already spread to] the Americas.
[Recently, researchers from Purdue University and several other US institutions, led by Siyang Sun] used two techniques – X-ray crystallography and electron cryo-microscopy – to determine the structure of Chikungunya virus-like particles, and to obtain new insights into the interactions of these particles with four related antibodies.
Electron cryo-microscopy was used to figure out the structure of the particles at near atomic resolution, and X-ray crystallography was used to determine the atomic resolution structures of two of the four Fab [fragment antigen-binding] antibodies that neutralize the Chikungunya virus.
Electron cryo-microscopy was also used to probe the complex formed by the interactions between the virus-like particles and the antibodies.
Continue reading at eLife…
TOP: Structure of the Chikungunya virion ||| BOTTOM: (A) Surface-shaded figure of ectodomain (left) and surface-shaded figure of nucleocapsid (right), colored according to the radial distance from the center of the virus. White triangles indicate one icosahedral asymmetric unit. (B) Cross-section of the virus showing density above 1.5 σ also colored according to the radial distance from the center of the virus. (C) Resolution of β-strands in the E1 [protein] domain III. [DOI: http://dx.doi.org/10.7554/eLife.00435.003]
Structure of an Ebola Virus
A diagnosis of prostate cancer can be an “uh oh” moment. After skin cancer, it’s the most common cancer in American men, with more than 238,000 new cases diagnosed each year and almost 30,000 deaths.
However, the confocal micrograph above, produced by Xiaochen Lu and C. Chase Bolt at the University of Illinois at Urbana-Champaign, is not an uh-oh moment. Rather, it may be an “ah-hah!”
Mouse models of prostate cancer are widely used, in part because the disease is often very slow progressing in humans and typically not detected in men until their 60s or older.
The hummingbird has long been admired for its ability to hover in flight. The key to this behavior is the bird’s capability to produce lift on both its downstroke and its upstroke. The animation above shows a simulation of hovering hummingbird. The kinematics of the bird’s flapping—the figure-8 motion and the twist of the wings through each cycle—are based on high-speed video of actual hummingbirds. These data were then used to construct a digital model of a hummingbird, about which scientists simulated airflow. About 70% of the lift each cycle is generated by the downstroke, much of it coming from the leading-edge vortex that develops on the wing. The remainder of the lift is creating during the upstroke as the bird pulls its wings back. During this part of the cycle, the flexible hummingbird twists its wings to a very high angle of attack, which is necessary to generate and maintain a leading-edge vortex on the upstroke. The full-scale animation is here. (Image credit: J. Song et al.; via Wired; submitted by averagegrdy)
Sapria poilanei - a rare parasitic plant
As the other species in Rafflesiaceae Family, Sapria poilanei (Malpighiales - Rafflesiaceae) is a parasitic flowering plant, that lacks of chlorophyll and rely upon their host plant for both water and nutrients, emerging from the host only as ephemeral flowers during sexual reproduction.
These plants lack vegetative parts and grow as strands of cells embedded within the stem and root tissues of their host. The aerial portions of the plant consist only of solitary red flowers with 10 lobes.
Sapria poilanei is only found in a small area of Cambodia rainforests.
Photo credit: ©Jeremy Holden
Locality: Cardamom Mountains, Cambodia
A very sad news:
Mississippi Child Thought Cured Of HIV Shows Signs Of Infection
A baby who generated great excitement last year because it appeared she had been cured of HIV is infected with the virus after all, health officials say. The news from Mississippi generated a lot of optimism. But Dr. Hannah Gay, who had treated the baby at the University of Mississippi Medical Center, remained on the lookout for HIV infection. “Ever since we discovered this case in 2012, we’ve known that was a possibility,” she said in a conference call yesterday.
The baby was not put back on anti-HIV drugs, but doctors kept checking her for signs of infection every six to eight weeks. More than two years elapsed with no sign of the virus.
"So, last week was one of those regularly scheduled visits," Gay said. "The child came; she had no abnormalities on physical exam." But blood tests showed that the baby had an active HIV infection. The virus had emerged from some mysterious hiding place in her body.
Read more (via npr.org)
Hershey and Chase Experiment
Biologists have known that DNA exists since 1869, but until the 1950s, they didn’t know it carried the genetic information of the cell—they thought proteins held that honour, since they seemed to be so much more complex. An early, incorrect experiment proposed that the nucleotides in DNA are arranged in a repeating sequence instead of unique codes, which supported the idea that they were simpler molecules.
But in 1953, Alfred Hershey and Martha Chase showed for sure that the genetic material was not, in fact, proteins. Like many fundamental experiments in the field of biology, theirs was beautifully simple.
The key component was a virus called bacteriophage. As its name suggests, it infects bacteria, taking over their replication processes in order to make copies of itself—usually, so many replicates are made that eventually the host bacteria bursts, spreading the virus to other cells. A bacteriophage achieves this by attaching to the bacteria’s surface and injecting genetic material down into the core to start the replication process. Hershey and Chase worked with T2 bacteriophage and E. coli bacteria.
Since bacteriophages are simply composed of a protein “shell” that encloses their DNA or RNA genome, they were perfect for the experiment—all Hershey and Chase had to do was see whether protein or DNA was injected into the bacteria.
However, they had to uniquely label the two components so they could tell which was where. For this, they used their knowledge of the structure of protein and DNA: sulphur is contained in proteins but not DNA, and phosphorous is contained in DNA but not protein. So Hershey and Chase began to conduct two experiments side by side: one where they grew protein in radioactive sulphur-35 and used normal DNA, and one where they used normal protein and grew DNA in radioactive phosphorous-32.
Here’s how the rest went down:
- Introduce bacteria to the two different bacteriophages.
- The bacteriophages get to work. The shells remain on the outside of the bacteria, while its genetic material is injected into the bacteria.
- Hershey and Chase centrifuged the mixtures to separate the bits out by density—a centrifuge is essentially a ultra-fast, ultra-cool blender. The lighter shells are shaken away from the denser bacteria cores, which still contain the genetic material.
- Use a Geiger counter to check which part is radioactive, the shell or the material in the bacteria.
And as you might have guessed, here’s what they found:
- In the experiment where protein was radioactive, the shells were found to be radioactive while the infected bacteria were not.
- In the experiment where DNA was radioactive, the infected bacteria were found to be radioactive while the shells were not.
Therefore, Hershey and Chase concluded that DNA was injected into the bacteria and used to make copies of the phage, so DNA must be the genetic material.
Note for those interested: Hershey received a Nobel Prize for his efforts, but Chase did not, possibly because she was a lab technician (or, of course, a woman).
13 July 2014
Slime-forming proteins called mucins are tethered to the surfaces of your body to block bacteria that would happily chomp their way into your organs and tissues. To understand more about these front-line defenders, cells from the cornea – the surface of the eye – were genetically modified and grown in the lab, each deficient in a particular type of mucin. Scientists discovered that the lack of a mucin called MUC16 weakened the surface barrier and, surprisingly, disrupted the ability of the cells beneath to form the tight junctions between neighbours (here stained light green) that are normally free of gaps to stop anything slipping through. The absence of another mucin, MUC1, didn’t reduce the barrier function, suggesting that different types of mucin work together to create the barrier. Understanding more about our natural defences could help us develop new anti-infective drugs as existing antibiotics become less effective.
Written by Mick Warwicker