Environmental gradients are an inescapable consequence of living on earth, with altitudinal gradients being one of the most extreme examples. For instance, the distance from the base of the Sierra Nevada to the peak of Mount Dana (3,979 m, Yosemite Park, CA) is a mere 60 miles. Yet, the average temperature drops approximately 24 degree Celsius - the equivalent of traversing over 3,700 miles in latitude. These changes in air temperature are accompanied by a 37% decrease in air density and dramatic changes in resources, ultraviolet exposure, humidity, and predators. High altitude conditions are challenging; and not surprisingly, species diversity decreases precipitously above moderate altitudes. Flying insects may be particularly challenged at altitude because their ability to fly will be compromised by both cold temperatures and thin air. This research investigates how altitudinal gradients impact insect physiology and evolution. To accomplish this goal, the fruit fly, Drosophila pseudoobscura will be collected from a range of altitudes in Yosemite Park, CA to determine: 1) the direct and interactive effects of temperature and air density on development, fitness, and flight ability, 2) the relative contributions of "beneficial acclimation" and "localized adaptation" to this species' success across a wide range of altitudes, and 3) whether local adaptations are evolutionarily maintained along the altitudinal gradient despite extensive gene flow due to the presence of chromosomal inversions. This research will promote a better understanding of how air density and temperature interactively affect insect locomotion and fitness, potentially facilitating the development of more accurate models to predict the impacts of environmental change. In addition, it will help clarify the antagonistic relationship between natural selection and gene flow along environmental gradients.
