One of the fundamental challenges facing biologists is to define the processes by which biodiversity is created. Adaptive radiations, which occur through a rapid series of speciation events that produce organisms differing in ecologically important traits, are a primary source of biodiversity. Exploration of speciation mechanisms can therefore provide great insight into the processes by which biodiversity is created. To examine speciation we will be using the remarkable adaptive radiation of the threespine stickleback, Gasterosteus aculeatus. In recently de-glaciated areas, such as our research site in Alaska, freshwater stickleback populations have diverged from a common marine ancestor in a remarkably short period of time. The freshwater populations have evolved many different types of organismal traits, and often show a correlated divergence in those traits. We will investigate how change in one trait can set the stage for changes in other traits, a process known as a 'trait' or 'character cascade'. Specifically, we will examine whether an initial divergence in stickleback ecology can cause a cascade of character changes that eventually leads to a divergence in mating preferences, an initial step in speciation. Because of the correlated evolution of many characters in recently formed populations, threespine stickleback provide a model system for studying how cascades of character change can lead to the formation of new species.
