Biology
Dartmouth biology prof links environmental conditions & sexual dimorphism size
Dartmouth professor Ryan Calsbeek and postdoctoral researcher Robert Cox recently found that intraspecific variation in sexual size dimorphism (SSD) in brown anole lizard (Anolis sagrei) can be attributed to underlying sex differences in response to local variation of environmental conditions, rather than solely to natural selection. The finding was published in the International Journal of Organic Evolution.
Sexual size dimorphism describes the phenomenon in which males and females of a species differ in body size. The researchers studied two geographically distinct populations of A. sagrei located on Great Exuma and Eleutheqra, two separate islands in the Bahamas. They found that the magnitude of SSD differs considerably between the two island populations—a difference primarily driven by variation in the size of the males. Viability selection favored male-biased SSD on both islands though adult males grew more slowly on Eleuthera than on Exuma. While both sexes exhibited poorer body condition on Eleuthera than on Exuma, the growth of females did not differ between islands.
The study suggested that intraspecific variation in SSD in A. sagrei reflects both environmental variation in the energetic potential for rapid growth and sex-specific phenotypic plasticity in growth and body size.
The brown anole lizard is an example of how local environmental conditions can affect sexual size dimorphism
Tracing the molecular roots of vision
Davide Pisani, professor of evolutionary biology at The National University of Ireland, described the evolutionary basis of vertebrate vision in a biology department seminar at Dartmouth last fall.
Arthropods and vertebrates possess distinct visual pathways, but they are evolutionarily related by their use of visual pigments known as opsins. There are animals still alive today that have opsins not used for vision, such as the lancet and sea squirt. These animals use opsin-1. This fact not only links all of these animals genetically in reference to visual proteins, but also demonstrates that the genetic divergence event most likely involved a transition from non-visually capable opsins to visually-capable opsins.
What all of this genetic interconnectivity implies is that visual abilities reach far back into the Lower Cambrian period 745 to 520 million years ago, to a distinct protein family that allowed for advanced bright-light vision. This research is an enormous improvement over the extremely sparse fossil record of vision in the distant pre-Cambrian past.
Photosynthesizing fish
Pamela Silver, professor of systems biology at Harvard University, asserted that bioengineering will play a key role in the future of biology and medicine in a Jones Seminar lecture on October 2nd.
A major recent development in bioengineering has been the ability to manipulate the “memory” of cells. By developing a “switch” that causes cells to change color upon contact with specific molecules, engineers are able to track their exposure to different cellular elements. Silver has used this technique to channel photosynthesis to produce hydrogen in cells by introducing a specific enzyme to the photosystems of the chloroplast, the cell’s photosynthesizing organelle. The enzyme, called PFOR, steals electrons excited by sunlight in the photosystems and uses them to reduce hydrogen to its gaseous form. The released hydrogen could be a future alternative power source.
In Silver’s latest project, she isolated and transplanted the sugar- producing elements of the plant Calvin cycle into zebra fish. The research is ongoing, and the still-young fish have yet to eat. Ideally, Silver says, they won’t have to at all.
Medicine
DMS research team makes suggestions on health care delivery reform
In the midst of the U.S. health insurance debate, a research team led by Elliott Fisher at Dartmouth Medical School has asserted that reform of the health care delivery system should include two important components: the patient-centered medical home (PCMH) and the accountable-care organization (ACO). The team published their findings in the New England Journal of Medicine last October.
The PCMH model focuses on expanding the role of primary care. Substantial evidence has shown that the expansion would reduce costs by limiting medical spending in unnecessary specialty operations and treatments, while improving general quality of care.
The ACO is a broader model aimed at integrating health care through holding primary care physicians, specialists, and hospitals responsible as an organization for patients’ overall medical outcomes. This would distribute costs and benefits among health care providers, and better ensure patient accountability through the efficiency of networked health providers.
Fisher’s team thus concluded that the PCMH and ACO are complementary to each other. ACO requires strong primary care organization which PCMH provides, and PCMH needs a broader medical infrastructure which ACO provides. An effective delivery system reform thus relies on the successful integration of the two models. In conjunction with insurance reform, delivery system reform will help realize the sought-after changes in U.S. health care.
Physics
“Relativity First” in physics?
Dartmouth professor emeritus Elisha Huggins presented his award-winning program as a tool for teaching physics and talked about his convictions on how to teach contemporary physics at a colloquium conducted by the physics department at Dartmouth College on October 23rd.
Huggins, a long-time professor of physics, emphasized the importance of beginning each physics class with the principle of relativity, which he calls “weird science.” Although special relativity, the principle that there is no way to determine uniform motion, is commonly perceived as a very complicated concept of advanced theory, Huggins believes that it can be taught understandably to make sense of the rest of the course material.
Huggins emphasized that physics teachers can use 20th century topics in any standard course to make the rest of the subject matter relevant and fun. From music to magnetism, and probability to time compression, special relativity takes an important role in understanding almost all concepts in physics.
At the end of his presentation, Huggins beseeched all of the educators in the room to start week one with special relativity. He said, “It only takes four hours of fun stuff in the beginning, to make everything else fun.”
Frank Oppenheimer: Uncle of the atomic bomb, father of the Exploratorium
Dartmouth College’s department of physics and astronomy hosted a public lecture last fall that featured K.C. Cole, a science journalist who has written over a thousand articles for various publications. Cole gave a presentation titled, “The Uncle of the Atom Bomb: Frank Oppenheimer and the World He Made Up.”
Frank Oppenheimer was the brother of Robert Oppenheimer, the father of the atomic bomb. They grew up in a wealthy, intellectual and artistic family in New York, and both brothers excelled in science even as children. They eventually teamed up to develop the atomic bomb in hopes of creating the weapon that would end all wars.
Oppenheimer later opened up the first Exploratorium in San Francisco in the old Palace of Fine Arts, merging science and art to promote learning. He designed and built his Exploratorium on his belief in play and intuitive learning—education that cannot be measured or tested. He placed art and science on the same level, believing aesthetics were just as important in reflecting human senses and behavior. He called scientists and artists the “noticers” of society and often argued that the discoveries artists made could be validated just like scientific hypotheses.
When others pointed out the constraints of the real world, Frank would dismiss the notion and reply that there is no real world, but “a world we made up.” When asked to sum up Frank Oppenheimer, Cole said, “Frank believed that if we stop trying to understand things, we’ll all be sunk. He thought we needed really new and radical ideas to deal with the world’s problems.”
Chemistry
Dartmouth chemistry prof sheds light on fluorocarbons’ unique chemical behavior
Dartmouth professor emeritus David Lemal recently discovered new pathways for cycloaddition reactions of o-fluoranil, a highly reactive and versatile electrophile. The finding, which was published in The Journal of Organic Chemistry, could lead to important applications in daily life.
According to Lemal, “It [o-fluoranil] has been difficult to synthesize, and as a result has received very little attention in the chemical literature. Our interest in it is twofold. We want to learn about and understand its chemical reactivity in detail, and to demonstrate its usefulness as a building block in the synthesis of more complex organic molecules.”
The research team discovered that there is a preference for one specific orientation in the reaction. The two components of the reaction, the diene and the dienophile, may approach each other in two distinct orientations: the substituent on the dienophile may be directed away from the diene (exo approach) or towards it (endo approach). Lemal found that for o-fluoranil, the endo addition configuration was preferred to the exo configuration.
“An important reason for our interest in the Diels-Alder chemistry of the quinone is its ability to serve as a synthetic building block. We have already carried out a few reaction sequences of this type, and will flesh out this facet of our o-fluoranil research in the future,” Lemal said.