title: Parasite-mediated disruptive selection in a natural Daphnia population.
abstract: BACKGROUND
  A mismatch has emerged between models and data of host-parasite evolution. Theory readily predicts that parasites can promote host diversity through mechanisms such as disruptive selection. Yet, despite these predictions, empirical evidence for parasite-mediated increases in host diversity remains surprisingly scant.
  
  
  RESULTS
  Here, we document parasite-mediated disruptive selection on a natural Daphnia population during a parasite epidemic. The mean susceptibility of clones collected from the population before and after the epidemic did not differ, but clonal variance and broad-sense heritability of post-epidemic clones were significantly greater, indicating disruptive selection and rapid evolution. A maximum likelihood method that we developed for detecting selection on natural populations also suggests disruptive selection during the epidemic: the distribution of susceptibilities in the population shifted from unimodal prior to the epidemic to bimodal after the epidemic. Interestingly, this same bimodal distribution was retained after a generation of sexual reproduction.
  
  
  CONCLUSIONS
  These results provide rare empirical support for parasite-driven increases in host genetic diversity, and suggest that this increase can occur rapidly.
authors.affiliation: W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060, USA. meghan.duffy@biology.gatech.edu
authors.forename: Meghan A
authors.initials: MA
authors.lastname: Duffy
authors.forename: Chad E
authors.initials: CE
authors.lastname: Brassil
authors.forename: Spencer R
authors.initials: SR
authors.lastname: Hall
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Tessier
authors.forename: Carla E
authors.initials: CE
authors.lastname: Cáceres
authors.forename: Jeffrey K
authors.initials: JK
authors.lastname: Conner
mesh_terms: D000818:Animals; D003621:Daphnia / Q000235:genetics* / Q000382:microbiology*; D014644:Genetic Variation; D054884:Host-Pathogen Interactions; D004718:Saccharomycetales / Q000502:physiology*; D012641:Selection, Genetic