Parasitism shapes selection by drastically reducing host fitness and increasing host fitness variation

Adam Z. Hasik, Adam M. Siepielski

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Determining the effects of parasites on host reproduction is key to understanding how parasites affect the underpinnings of selection on hosts. Although infection is expected to be costly, reducing mean fitness, infection could also increase variation in fitness costs among hosts, both of which determine the potential for selection on hosts. To test these ideas, we used a phylogenetically informed meta-analysis of 118 studies to examine how changes in the mean and variance in the outcome of reproduction differed between parasitized and non-parasitized hosts. We found that parasites had severe negative effects on mean fitness, with parasitized hosts suffering reductions in fecundity, viability and mating success. Parasite infection also increased variance in reproduction, particularly fecundity and offspring viability. Surprisingly, parasites had similar effects on viability when either the male or female was parasitized. These results not only provide the first synthetic, comparative, and quantitative summary of the strong deleterious effects of parasites on host reproductive fitness, but also reveal a consistent role for parasites in shaping the opportunity for selection.

Original languageEnglish
Article number20220323
JournalBiology Letters
Issue number11
StatePublished - 2 Nov 2022
Externally publishedYes


  • fitness components
  • host-parasite
  • meta-analysis
  • reproduction
  • sexual selection
  • variance

ASJC Scopus subject areas

  • General Agricultural and Biological Sciences
  • Agricultural and Biological Sciences (miscellaneous)


Dive into the research topics of 'Parasitism shapes selection by drastically reducing host fitness and increasing host fitness variation'. Together they form a unique fingerprint.

Cite this