Something’s Fishy in Paxton Lake
Speciation in Sticklebacks
Department of Biological Sciences
Simon Fraser University
In this interrupted case study, students explore the mechanisms of speciation while working in groups to design a series of experiments to determine whether two populations of sticklebacks in Paxton Lake in British Columbia represent separate species or not. As the case progresses, the instructor and teaching assistants move from group to group, prompting students to consider the biological species concept in designing these experiments and encouraging them to think carefully about what data they need. As students design their lab experiments and plan their field data collection, they are supplied with appropriate data (a set of 11 data sheets for this purpose is included in the teaching notes). Due to the open-ended nature of the activity, there is no separate answer key for this case. This 60–90 minute activity was designed for use in the final week of a general biology course organized around the general theme of evolutionary mechanisms and the history of life on earth. [For an updated, flipped version of this case study, see “Speciation and the Threespine Stickleback,” also in this case collection.]
- Use the biological species concept to decide whether two populations represent separate species.
- Apply the mechanisms of speciation to a real life case.
- Explain how prezygotic and postzygotic reproductive isolating mechanisms reduce genetic exchange between incipient species.
- Explain how natural selection may act to favor divergent morphologies, as incipient species adapt to different ecological roles, and favor the evolution of reproductive isolating mechanisms.
- Design experiments to test hypotheses.
- Interpret data and understand how they may be used to support or reject hypotheses.
Keywordsspeciation; stickleback; biological species concept; reproductive isolation; Gasterosteus aculeatus; benthic; limnetic; gene flow; hybrid; British Columbia
Educational LevelUndergraduate lower division, Undergraduate upper division
Type / MethodsInterrupted
Subject HeadingsBiology (General) | Evolutionary Biology |