Mechanisms of Constraint in the Evolutionary Radiation of a Crustacean Species Complex

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Related species share many similarities due to their common ancestry, but also differ in important ways because each may be adapted to a unique environment. The patterns of differences and similarities among species represent the "structure of biological diversity". This project seeks to understand the mechanistic details of how this structure develops over time. Specifically, the PI will examine a group of freshwater crustaceans, amphipods, whose common ancestor invaded North America approximately 8 million years ago, and has since diversified into at least three-dozen species that exist today. The PI will use DNA analysis to reconstruct the historical pattern of diversification of the species, and use statistical methods to infer how the traits of extant species arose from their ancestors. A second major component of the project will be a "selection experiment" in which the PI imposes evolutionary pressures on experimental populations of amphipods and monitors the form and rate of change in the species' traits over many generations. This project is significant because it provides an in-depth understanding of the factors that give rise to structure in biological diversity. Although we know that the course of evolutionary change is shaped by sets of constraints imposed by the genetic makeup of species, the environmental conditions experienced by species, and other factors, we do not currently have an adequate understanding of how these constraints interact to produce the structure we observe within groups of related species. This project employs complementary methodological approaches to illuminate this process.