title: Mortality selection during the 2003 European heat wave in three-spined sticklebacks: effects of parasites and MHC genotype.
abstract: BACKGROUND
  Ecological interaction strength may increase under environmental stress including temperature. How such stress enhances and interacts with parasite selection is almost unknown. We studied the importance of resistance genes of the major histocompatibility complex (MHC) class II in 14 families of three-spined sticklebacks Gasterosteus aculeatus exposed to their natural macroparasites in field enclosures in the extreme summer of 2003.
  
  
  RESULTS
  After a mass die-off during the 2003-European heat wave killing 78% of 277 experimental fish, we found strong differences in survival among and within families. In families with higher average parasite load fewer individuals survived. Multivariate analysis revealed that the composition of the infecting parasite fauna was family specific. Within families, individuals with an intermediate number of MHC class IIB sequence variants survived best and had the lowest parasite load among survivors, suggesting a direct functional link between MHC diversity and fitness. The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important.
  
  
  CONCLUSIONS
  The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003. Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.
authors.affiliation: Department of Integrative Biology (IBZ), Experimental Ecology, ETH Zürich, Universitätstrasse 16, CH - 8092 Zürich, Switzerland. mathias.wegner@env.ethz.ch
authors.forename: K Mathias
authors.initials: KM
authors.lastname: Wegner
authors.forename: Martin
authors.initials: M
authors.lastname: Kalbe
authors.forename: Manfred
authors.initials: M
authors.lastname: Milinski
authors.forename: Thorsten Bh
authors.initials: TB
authors.lastname: Reusch
mesh_terms: D000818:Animals; D017753:Ecosystem; D005060:Europe; D005802:Genes, MHC Class II; D014644:Genetic Variation; D006790:Host-Parasite Interactions; D006358:Hot Temperature; D008285:Major Histocompatibility Complex; D012641:Selection, Genetic; D023701:Smegmamorpha / Q000235:genetics* / Q000469:parasitology* / Q000502:physiology; D016019:Survival Analysis