Competition promotes the evolution of host generalists in obligate parasites

Kevin P. Johnson, Jael R. Malenke, Dale H. Clayton

Research output: Contribution to journalArticlepeer-review


Ecological theory traditionally predicts that interspecific competition selects for an increase in ecological specialization. Specialization, in turn, is often thought to be an evolutionary 'dead end,' with specialist lineages unlikely to evolve into generalist lineages. In host-parasite systems, this specialization can take the form of host specificity, with more specialized parasites using fewer hosts. We tested the hypothesis that specialists are evolutionarily more derived, and whether competition favours specialization, using the ectoparasitic feather lice of doves. Phylogenetic analyses revealed that complete host specificity is actually the ancestral condition, with generalists repeatedly evolving from specialist ancestors. These multiple origins of generalists are correlated with the presence of potentially competing species of the same genus. A competition experiment with captive doves and lice confirmed that congeneric species of lice do, in fact, have the potential to compete in ecological time. Taken together, these results suggest that interspecific competition can favour the evolution of host generalists, not specialists, over macroevolutionary time.

Original languageEnglish (US)
Pages (from-to)3921-3926
Number of pages6
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1675
StatePublished - Nov 22 2009


  • Birds
  • Coevolution
  • Comparative methods
  • Lice
  • Specialization

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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