This project uses a powerful approach for studying species invasion by combining methods of evolutionary genetics and physiological ecology. The focus is on the invasion of freshwater habitats by a marine and estuarine planktonic copepod, Eurytemora affinis. Two alternative hypotheses could account for its invasion of freshwater habitats. Freshwater colonizations have been (A) multiple independent events, or (B) rare events followed by dispersal among similar habitats. The goals of this project are (1) to test these hypotheses by reconstructing the history of colonization, (2) to determine changes in physiological traits during habitat transitions, and (3) to determine whether habitat transitions occur through genetic adaptation or acclimation. The history and geographic pathway of colonization will be determined by constructing a phylogeny of 12 populations of copepods from different salinities using DNA sequences from two genes. Breadth of salinity tolerance will be determined for 6 populations, then mapped onto the phylogeny to determine how physiological traits change during habitat transitions. Response to changes in salinity will be measured to determine whether habitat transitions involve genetic adaptation of populations or individual acclimation. The introduction of exotic species into aquatic habitats is an issue of major environmental concern. This research will reveal important processes involved in habitat transitions, and contribute to our understanding of habitat invasions, local adaptation, as well as intraspecific genetic and physiological diversity.
