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Speciation and the Threespine Stickleback

Co Authors:

Joan Sharp
Department of Biological Sciences
Simon Fraser University

Erin Barley
Department of Biological Sciences
Simon Fraser University

Kevin K.-W. Lam
Department of Biological Sciences
Simon Fraser University

Suraaj Aulakh

Simon Fraser University

Allison Cornell
Department of Biological Sciences
Cedar Crest College

Kathleen A. Fitzpatrick
Department of Biological Sciences
Simon Fraser University


This case study teaches students about allopatric speciation through an investigation of the benthic and limnetic sticklebacks of Paxton Lake, which are among the youngest species on Earth, diverging from each other after the Pleistocene glaciers melted and the Gulf Islands formed. Researchers at the University of British Columbia have carried out a variety of fascinating studies on these hardy little fish. Results from this research (formatted as data sheets included in the teaching notes) are provided to students who design experiments and then compare actual data to investigate why benthic and limnetic sticklebacks seldom interbreed in Paxton Lake. Developed for a first-year biology course for majors organized around the general theme of evolution and the history of life on Earth, this case study is an updated version of another case in the collection, “Something’s Fishy in Paxton Lake” (Sharp, 2001). The current version is especially suited for a flipped classroom in which students prepare for class ahead of time with a reading assignment that also involves the viewing of a video by the case authors that introduces the mechanisms of allopatric speciation.

  • Apply the mechanisms of allopatric speciation to a real life situation.
  • Explain how natural selection may act to favor divergent morphologies as incipient species adapt to different ecological roles.
  • Explain how natural selection acts to favor the evolution of reproductive isolating mechanisms.
  • Design experiments to test hypotheses about speciation.
  • Interpret data and understand how they may be used to support or reject hypotheses.
  • Discuss the status of benthic and limnetic stickleback fish as distinct species, with reference to different species concepts (biological, morphological, ecological).
Keywords: Allopatric speciation; species; founder effect; genetic drift; mutation; natural selection; character displacement; dispersal; vicariance; stickleback; Gasterosteus aculeatus; lake zonation; causation; assortative mating; predation risk; foraging success
Topical Area: N/A
Educational Level: Undergraduate lower division
Formats: PDF
Type/Method: Discussion, Flipped, Interrupted
Language: English
Subject Headings: Biology (General)   Evolutionary Biology   Wildlife Management   Zoology  
Date Posted: 1/3/2019
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.

Teaching Notes

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Answer Key

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The following video(s) are recommended for use in association with this case study.

  Allopatric Speciation
This video by the case study authors reviews the four mechanisms of allopatric speciation: founder effect, genetic drift, mutation, natural selection. Running time: 13:32 min.

  An Interview with Dr. Dolph Schluter
This optional video by the case study authors introduces students to the researcher who led much of the research on which the case study is based. Running time: 4:52 min.

  Uncovering the Behaviour of the Three-Spined Stickleback—University of Leicester
This segment from an episode of the BBC’s The One Show shows stickleback behaviors including nest building, courtship, and reproduction. Running time: 4:35 min. Produced by BBC, 2013.

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