9781934874509-ch1

Cutthroat Trout: Evolutionary Biology and Taxonomy

A Special Workshop on the Taxonomy and Evolutionary Biology of Cutthroat Trout

Patrick Trotter, Peter Bisson, Brett Roper, Luke Schultz, Carl Ferraris, Gerald R. Smith, and Ralph F. Stearley

doi: https://doi.org/10.47886/9781934874509.ch1

Abstract.—Cutthroat Trout Oncorhynchus clarkii are currently considered a single, widespread species composed of many subspecies following the classification system proposed by Robert J. Behnke in 1979. More recently, molecular genetic and geological evidence has yielded results that are inconsistent with Behnke’s classification, which suggests that a re-evaluation of the existing phylogenetic tree is timely. Additionally, several varieties of Cutthroat Trout are either listed under the U.S. Endangered Species Act or are considered to be at risk by the states in which they reside, making it important that the classification and evolutionary relationships among Cutthroat Trout be based on the best available scientific evidence. In 2015, the Western Division of the American Fisheries Society convened a special workshop in which a panel of experts was asked to weigh carefully evidence on Cutthroat Trout phylogeny and classification, from the oldest published studies to the most recent and answer two questions: (1) does Behnke’s 14-subspecies classification remain scientifically tenable and defensible given all available evidence, and (2) if not, what taxonomic classification does satisfy this array of evidence? From new information, the panel concluded that the existing classification system is no longer supported by existing evidence; however, the panel was unable to reach consensus on what a new phylogeny and classification system should be. In the interim, we suggest that the four major evolutionary lineages of Cutthroat Trout be elevated to full species designation and that several uniquely identifiable evolutionary units receive additional investigation to elucidate additional evolutionary structure. This chapter provides the background and context for topics that are covered in the following chapters and suggests fruitful lines of investigation that should help resolve outstanding questions.