title: Is host-schistosome coevolution going anywhere?
abstract: BACKGROUND
  That pathogens and hosts coevolve is a powerful concept with broad theoretical and applied implications spanning from genetic theory to the medical and veterinary sciences, particularly in the context of infectious disease epidemiology. A substantial body of theory has been developed to explore the likelihood and consequences of coevolution, but few empirical studies have been conducted to test these theories, particularly for indirectly-transmitted pathogen-host systems. We initiated replicate longitudinal host-schistosome co-selection trials under different host genotype combinations: Schistosoma mansoni parasite lines were co-selected with populations of either previously resistant-selected Biomphalaria glabrata host genotypes, or unselected susceptible B. glabrata genotypes, or a mixed population of the two. All parasite lines were also passaged through their obligatory mammalian definitive host at each generation.
  
  
  RESULTS
  We demonstrated variation in, and a reciprocal impact on, the fitness of both host and pathogen phenotype and genotype, an outcome dependent on the combinations of genotypes involved, and evidence of change over time. Most apparent was the observation that parasites appeared to rapidly adapt to those intermediate hosts previously selected for resistance.
  
  
  CONCLUSIONS
  Our results illustrate the potential for host-schistosome coevolution and, in particular, suggest that host resistance may be a temporary phenomenon in nature due, in part, to rapid counter-adaptations by parasites.
authors.affiliation: Department of Zoology, University of Oxford, Oxford, UK. joanne.webster@imperial.ac.uk
authors.forename: Joanne P
authors.initials: JP
authors.lastname: Webster
authors.forename: Jaya
authors.initials: J
authors.lastname: Shrivastava
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Johnson
authors.forename: Lynsey
authors.initials: L
authors.lastname: Blair
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000818:Animals; D005075:Biological Evolution; D001700:Biomphalaria / Q000235:genetics / Q000469:parasitology*; D003433:Crosses, Genetic; D019143:Evolution, Molecular; D017238:Genes, Helminth; D005828:Genetics, Population; D005838:Genotype; D006790:Host-Parasite Interactions / Q000235:genetics; D007113:Immunity, Innate; D051379:Mice; D008808:Mice, Inbred CBA; D010641:Phenotype; D012550:Schistosoma mansoni / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D012641:Selection, Genetic; D014774:Virulence