Cave animals hold a fascination both bacause of the strange habitat in which they live, and the modifications that they've undergone for life in darkness. The purpose of the present study is to unravel the cause of the morphological changes that accompany life in caves, which serves as a model system to understand the evolutionary loss or reduction of structures such as the appendix in humans. The principal investigators will investigate the cause of the reduction of eyes in cave populations of a small shrimp-like animal, Gammarus minus. Eye loss may happen either because animals with eyes are at some disadvantage in the cave, perhaps because of wasted energy; or eye loss may occur simply due to the random accumulation of mutations that reduce the eyes. Using a variety of statistical techniques, the principal investigators will determine whether animals with small eyes have any advantage over animals with large eyes in the cave environment, and whether animals with large eyes have any advantage over animals with small eyes in the spring environment. Preliminary results indicate that natural selection plays a critical role in the loss of eyes. Using techniques of molecular genetics that provide an estimate of the genetic differences among population, the PI's will also determine if invasion and isolation in caves, with its predictable morphological consequences, has been frequent. Field work for this project will be done in a series of caves and springs in West Virginia and Virginia.
