Behaviors of cavefish offer insight into developmental evolution

Abstract

Many developmental processes have evolved through natural selection, yet in only a few cases do we understand if and how a change of developmental process produces a benefit. For example, many studies in evolutionary biology have investigated the developmental mechanisms that lead to novel structures in an animal, but only a few have addressed if these structures actually benefit the animal at the behavioral level of prey hunting and mating. As such, this review discusses an animal's behavior as the integrated functional output of its evolved morphological and physiological traits. Specifically, we focus on recent findings about the blind Mexican cavefish, Astyanax mexicanus, for which clear relationships exist between its physical traits and ecosystem. This species includes two morphotypes: an eyed surface dweller versus many conspecific types of blind cave dwellers, some of which evolved independently; all of the blind subtypes derived from eyed surface dwellers. The blind cavefish evolved under clear selection pressures: food is sparse and darkness is perpetual. Simulating the major aspects of a cave ecosystem in the laboratory is relatively easy, so we can use this species to begin resolving the relationships between evolved traits and selection pressures-relationships which are more complex for other animals models. This review discusses the recent advances in cavefish research that have helped us establish some key relationships between morphological evolution and environmental shifts.