A major area of my research is investigating the pattern and process of major habitat transitions. Much of this work has focused on transitions between marine and freshwaters in fishes.
My analysis of anchovies focused on South American lineages, and demonstrated that (in contrast to expectations based on taxonomy), Neotropical freshwater anchovies represent a monophyletic radiation with a single origin in freshwater. This work provided the first comprehensive molecular phylogeny of anchovies and supports the biome conservatism hypothesis, which states that transitions between biomes (macrohabitats) are rare events. Our data suggests that competition is the primary mechanism regulating aquatic habitat transitions, a concept that has been supported by subsequent research. This research makes important inroads, because it suggests that biotic interactions may be just as important as intrinsic constraints in determining species distribution patterns. This work also establishes anchovies as an ideal system for investigating adaptation to different macrohabitats, and the role of habitat transitions in facilitating adaptive radiation.