2009
Evolution in Extreme Environments
November 13, 2009
Educational Resources online CD
The focus for 2009's symposium is evolution in four distinct extreme environments: high altitude, extreme cold, darkness, and high pressure. How organisms survive, and even thrive, under these conditions is fascinating, but understanding adaptations that allow life under extreme conditions also provides insight about physiological systems that have evolved in more commonly encountered, moderate conditions. Our four speakers this year provided examples of how evolution yields organisms adapted to these harsh environmental conditions. Their presentations are available below. Educational resources relevant to each presentation are available through the online version of the symposium CD here. We would appreciate your feedback on the CD.
Speakers
Cynthia Beall - Human Evolution and Adaptation to High Altitude
Steve Haddock - Life in the Deep Sea: Only the Fragile Survive
William Jeffery - Cavefish: Evolution in the Dark
Jody Deming - Arctic Winter Sea Ice: A Biological Museum or Evolutionary Playground?
Cynthia Beall - Case Western Reserve University, OH
Human Evolution and Adaptation to High-altitude
During the past 100,000 – 200,000 years, humans have moved out of Africa to an enormous range of environments including the world's high plateaus in the Andes, Tibet, and East Africa. The environmental stress at high altitude is clear: lower barometric pressure results in fewer than normal oxygen molecules in every breath, and therefore in circulation. Lowlanders traveling to high altitudes respond to acute hypoxia - or oxygen deficiency - with homeostatic responses of the lung, heart, blood vessels, and blood. However, native residents of the world’s three high plateaus deliver oxygen more effectively, which is hypothesized to be the result of evolution by natural selection over thousands of years of high-altitude residence. Furthermore, the physiology in these populations differs, which suggests that three replications of the same natural experiment of moving from low to high altitude had different outcomes. There is also evidence of ongoing natural selection – differential survival of genotypes – in the Tibetan population. Strikingly, the degree of physiological hypoxia of healthy high-altitude natives on these plateaus is in the range considered pathological at low altitudes where it is routinely treated with oxygen therapy. Study of adaptations in healthy hypoxic people may suggest new therapies and interventions for patients with hypoxia at all altitudes.
Educational resources from the CD
Updates
May, 2010 ActionBioScience Interview with Cynthia Beall
June 2010 Cynthia Beall's research into how Tibetans handle low oxygen levels
Steve Haddock - Monterey Bay Aquarium Research Institute, CA
Life in the Deep Sea: Only the Fragile Survive
The deep ocean is the largest living space on Earth, abundant with diverse alien-looking life forms despite the fact that it is dark, cold, has limited resources and exerts high pressures. In response to these environmental challenges and unique ecological constraints, organisms have evolved a variety of forms and functions including transparent dome eye covers, cloaks of invisibility, and the ability to communicate by making bioluminescent light. Because there are few surfaces, morphologies have diversified in unconstrained manner resulting in 40-meter long jellies and diaphanous comb jellies that propel themselves with eyelash-like cilia. Many of these deep-sea species are not yet described, and current research involves understanding the diversity and relationships of these animals, as well as the genetic underpinnings of their unique bio-optical properties. Although they are obscure even to marine biologists and live in some of most unexplored habitats on the planet, these animals actually can occur as close as a few kilometers from a large city. This paradox underscores how much we have yet to learn about life on this planet.
Educational resources from the CD
William Jeffery - University of Maryland, MD
Cavefish: Evolution in the Dark
Cave animals have adapted to the challenges of life in perpetual darkness by losing their eyes and pigmentation and enhancing other sensory systems, such as taste, smell, and tactile senses. Although the sensory gains are easily explained by natural selection, the losses are more difficult to explain because they seem to have no immediate benefits. Recent studies in the Mexican cavefish (Astyanax mexicanus) show that eye degeneration is developmentally linked to adaptive gains in the gustatory system via evolutionary changes in a pleiotropic gene called "sonic hedgehog." Thus, cavefish may illustrate a general phenomenon in biology in which pleiotropy and indirect selection guide the course and extent of evolution. Another benefit for cavefish living in dark caves is the absence of predators, which promotes survival by evolving an unusual suite of feeding behaviors. These behaviors would be risky in more complex, well-lit environments, such as exist on the Earth’s surface, illustrating the importance of environmental complexity as a driving force in evolution.
Educational resources from the CD
Jody Deming - University of Washington, WA
Arctic Winter Sea Ice: A Biological Museum or Evolutionary Playground?
During winter, the sea ice cover in the high Arctic grows and thickens, entrapping small organisms into its interior pore spaces. As temperatures drop, these spaces shrink in size as more pure water freezes, leaving behind high concentrations of sea salts that depress the freezing point and keep the sea-ice pores filled with liquid. Only single-celled microorganisms remain in this micrometer scale subzero salty habitat. There they are free of all grazers -- except viruses. Under conditions of environmental stress, viruses often fail to kill their hosts upon infection, instead incorporating as new DNA into their hosts' genomes. In the process, they can bring new genes from former hosts into the DNA of their new hosts. This striking form of horizontal gene transfer can be an adaptive boon for the microbes. The thick sea ice in the darkness of Arctic winter that has long appeared to Arctic explorers as a frozen museum for any life entrapped within it may in fact be an evolutionary playground where microbes and viruses interact in positive ways to bring new adaptations into the realm of oceanic microbes. Given the astronomical numbers of microbes that are trapped in the polar ice cap each year, returning to the ocean when the ice melts in summer, this form of evolution may contribute substantially to the ability of microbes to run the major biogeochemical cycles of the ocean.
Educational resources from the CD
To complement the AIBS/NESCent Evolution Symposium Friday morning, we offer a teacher workshop exploring the remarkable ability of some plants to undergo desiccation and revive with the addition of water. This ability is ancient, and modern day descendants of the earliest land plants, such as mosses, retain this ability. Vascular plants have lost desiccation tolerance in all tissues (with the exception of seeds, pollen and spores), but it has re-evolved in a few species. This workshop explores a problem space in which we can compare gene expression patterns in desiccation tolerant and sensitive plants and examine the evolutionary relationships of genes involved in desiccation tolerance. Resources from Understanding Evolution that support the basic evolutionary concepts of this problem space are linked throughout the workshop.
