Species Conceptualization and Delimitation: A Framework for the Taxonomic Revision of Cutthr
Sierra M. Love Stowell, Jessica L. Metcalf, Douglas F. Markle, and Andrew P. Martin
Abstract.—One objective of systematics is to recognize species in a manner that minimizes the disparity between species as real entities in nature and species as a Linnaean category. Reconciliation requires a conceptualization of species consistent with evolutionary processes that yields predictive delimitation criteria. Here we review the unified species concept (USC) and its associated delimitation criteria as a prelude to revising the taxonomy of Cutthroat Trout Oncorhynchus clarkii. Additionally, in the context of the conceptualizing species as a separately evolving metapopulation, we briefly review how climate change may have influenced the connectivity and isolation of Cutthroat Trout within and among river basins, with a focus mainly on the Cutthroat Trout of the Southern Rocky Mountains. We summarize evidence based on delimitation criteria that distinguishes Rainbow Trout O. mykiss and Cutthroat Trout, Gila Trout O. gilae and Rainbow Trout, and blue lineage and green lineage Cutthroat Trout from the Southern Rocky Mountains. We advocate adopting the USC as a guide for taxonomic revision of Cutthroat Trout, recommend eliminating subspecies as a valid taxonomic designation, and expect—based on our evaluation of three pairs of species—that the taxonomy of Cutthroat Trout will be revised in ways that elevate some recognized subspecies to species status.