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Coping with Infection

Resistance and Tolerance of Parasites in Soay Sheep

Co Authors:

Laura A. Schoenle
Office of Undergraduate Biology
Cornell University

Cynthia J. Downs
Department of Biology
Hamilton College


This interrupted case study introduces two distinct, but not mutually exclusive, strategies for defending against parasites: resistance and tolerance. Students analyze and interpret research conducted on resistance and tolerance to gastrointestinal parasites in Soay sheep (Ovis aries), and discuss the relative costs and benefits of these defense strategies. Immune responses have costs, and fighting off parasites is not always adaptive. The final part of the case study asks students to look beyond the Soay sheep example and consider how resistance and tolerance could provide insights into the management of infectious disease and antibiotic resistance. This case was designed for an upper level undergraduate vertebrate physiology course, but could also be used in courses like introductory disease ecology, ecological physiology, evolutionary medicine, or immunology.

  • Differentiate between resistance and tolerance.
  • Discuss why the costs of parasite defenses, like the immune response, could result in hosts favoring investment in tolerance.
  • Identify the relative costs and benefits of both resistance and tolerance from the perspective of the host and the parasite.
  • Explain why the advantages of resistance and tolerance vary across contexts.
  • Evaluate how both resistance and tolerance could be applied to the management of infectious disease.
Keywords: Tolerance; resistance; parasite; immunology; immunity; infection; ecoimmunology; nematode; soay sheep;
Topical Area: N/A
Educational Level: Undergraduate upper division, Graduate
Formats: PDF
Type/Method: Discussion, Interrupted
Language: English
Subject Headings: Biology (General)   Ecology   Physiology   Public Health   Science (General)   Zoology  
Date Posted: 11/29/2018
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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The following video(s) are recommended for use in association with this case study.

  Soay, The Wildest Sheep in the West
This brief video is a fun introduction to Soay sheep. Running time: 1:11 min. Produced by BBC, 2010.

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