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Fish Out of (Salt) Water

Adaptation of an Ocean-Going Fish to Freshwater Environment

Co Authors:

Janna R. Willoughby
School of Forestry and Wildlife Sciences
Auburn University

Avril M. Harder
Department of Biological Sciences
Purdue University

Jaqueline M. Doyle
Department of Biological Sciences
Towson University


This interrupted case study is based on a journal article that describes the rapid adaptation of a population (in this case, steelhead trout) in response to a shift in environmental conditions despite genome‚Äźwide reductions in genetic diversity. First, students learn the basics of natural selection and explicitly link phenotype to fitness as well as fitness to changes in genotype. The discussion then shifts to the evolution of steelhead trout as a result of relocation from salt to freshwater. Students develop hypotheses of expected genomic changes and cultivate skills in interpreting genomic data. The case focuses primarily on population response to changes in habitat, and as such is appropriate for a class focused on response to local habitat changes (e.g., salinity changes in aquatic systems). The case is designed for evolution, ecology, or genomics courses primarily comprised of biology (or related discipline) majors.

  • Understand how selection influences phenotypic and genotypic frequencies.
  • Gain perspective on the ways in which populations adapt to novel conditions.
  • Improve the ability to understand and plot data graphically.
  • Understand how genomic data are interpreted and used to illustrate evolution.
Keywords: Adaptation; DNA; evolution; rainbow trout; steelhead trout; genotype; phenotype; genomic data; genetic data; salt water; species introduction; climate change;
Topical Area: N/A
Educational Level: Undergraduate lower division, Undergraduate upper division
Formats: PDF
Type/Method: Analysis (Issues), Interrupted
Language: English
Subject Headings: Biology (General)   Ecology   Genetics / Heredity   Evolutionary Biology  
Date Posted: 3/28/2019
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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