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Genetic Structure, Evolutionary History, and Conservation Units of Bull Trout in the Coterminous United States
Author(s) -
Ardren William R.,
DeHaan Patrick W.,
Smith Christian T.,
Taylor Eric B.,
Leary Robb,
Kozfkay Christine C.,
Godfrey Lindsay,
Diggs Matthew,
Fredenberg Wade,
Chan Jeffrey,
Kilpatrick C. William,
Small Maureen P.,
Hawkins Denise K.
Publication year - 2011
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1080/00028487.2011.567875
Subject(s) - biology , biological dispersal , gene flow , genetic structure , trout , population , effective population size , evolutionary biology , phylogeography , ecology , isolation by distance , zoology , genetic variation , phylogenetic tree , genetics , fishery , gene , demography , fish <actinopterygii> , sociology
Abstract The bull trout Salvelinus confluentus is a broadly distributed char in northwestern North America that has undergone significant population declines. This species is currently protected under the Endangered Species Act across its range in the coterminous United States. To clarify patterns of phylogenetic structure and to assist with identification of conservation units, we examined genetic variation within and among 75 representative bull trout populations sampled throughout the USA. Genealogies from a 520‐base‐pair portion of the mitochondrially encoded NADH dehydrogenase 1 gene ( ND‐1 ) revealed reciprocal monophyly between coastal and interior lineages that differed by 1.34% in DNA sequence. The geographic distribution of the two lineages was divided by the Cascade Mountains, a pattern that likely reflects postglacial dispersal from separate glacial refugia. Analysis of microsatellite variation revealed that 76% of populations had an estimated effective population size less than 50 and indicated high divergence among populations caused by genetic drift (average genetic differentiation index F ST = 0.32) and mutation (average genetic differentiation index R ST = 0.58). Concordant phylogeographic and phylogenetic patterns observed with microsatellite and mitochondrial DNA analyses provided evidence for two to six bull trout lineages that largely reflect historic patterns of gene flow and isolation among populations. These lineages can be further subdivided into finer‐scale units due to the extremely low dispersal among populations and small effective population sizes. In fact, Bayesian analysis of population structure identified an optimal solution of 69 genetically different groups. Based on these results, we believe that conservation efforts should ideally be focused on the 118 bull trout core areas originally identified in the draft Endangered Species Act recovery plan, which are broadly defined as metapopulations. We provide examples of how other data, such as unique life history forms and ecological setting, can be used in combination with our genetic results to refine the U.S. Fish and Wildlife Service's hierarchical conservation strategy for bull trout.