Parasite intensity and the evolution of migratory behavior

Laurinne J. Balstad, Sandra A. Binning, Meggan E. Craft, Marlene Zuk, Allison K. Shaw

Research output: Contribution to journalArticlepeer-review


Migration can allow individuals to escape parasite infection, which can lead to a lower infection probability (prevalence) in a population and/or fewer parasites per individual (intensity). Because individuals with more parasites often have lower survival and/or fecundity, infection intensity shapes the life-history trade-offs determining when migration is favored as a strategy to escape infection. Yet, most theory relies on susceptible-infected (SI) modeling frameworks, defining individuals as either healthy or infected, ignoring details of infection intensity. Here, we develop a novel modeling approach that captures infection intensity as a spectrum, and ask under what conditions migration evolves as function of how infection intensity changes over time. We show that relative timescales of migration and infection accumulation determine when migration is favored. We also find that population-level heterogeneity in infection intensity can lead to partial migration, where less-infected individuals migrate while more infected individuals remain resident. Our model is one of the first to consider how infection intensity can lead to migration. Our results frame migratory escape in light of infection intensity rather than prevalence, thus demonstrating that decreased infection intensity should be considered a benefit of migration, alongside other typical drivers of migration.

Original languageEnglish (US)
Article numbere03229
Issue number2
StatePublished - Feb 2021

Bibliographical note

Funding Information:
We thank members of the Shaw and Craft labs for useful discussions, and two anonymous reviewers for helpful feedback. This material is based in part upon work supported by the National Science Foundation under grant DEB 1654609. SAB is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Research Chair program. SAB, MEC, MZ, and AKS secured funding for the work. AKS conceived of the specific project. LJB and AKS designed the model with input from all authors. LJB analyzed the model with help from AKS. LJB and AKS wrote the paper with input from all authors.

Publisher Copyright:
© 2020 by the Ecological Society of America


  • heterogeneity
  • mathematical model
  • matrix population model
  • migratory escape
  • partial migration
  • pathogen

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.


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