title: Genetic conflicts over sex ratio: mite-endosymbiont interactions.
abstract: Nucleocytoplasmic genetic conflicts arise as a result of asymmetric transmission of cytoplasmic and nuclear genes. Spread of a cytoplasmic element promoting female-biased sex ratios creates selection on nuclear genes for mechanisms that decrease the bias. Here we investigate the conflict over sex ratio between the cytoplasmic bacterium Wolbachia and the two-spotted spider mite Tetranychus urticae Koch. We show that, first, infected females produce significantly more female-biased sex ratios than uninfected (cured) females. Second, this effect is not due to parthenogenesis, male killing, or feminization, phenotypes commonly associated with infection by Wolbachia. Third, sex ratio is a trait with a heritable component in this species; thus, it can evolve under selection. Fourth, the sex ratio produced by uninfected (cured) females changes over time, approaching the sex ratio produced by females from the infected culture. On the basis of these results, we suggest that after sex ratio manipulation by Wolbachia, a host compensatory mechanism evolved that allows infected females to produce the sex ratio favored by nuclear genes. We discuss the evolution of "mutualism" with respect to the evolution of host mechanisms that compensate for effects induced by vertically transmitted "parasites."
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, Section of Population Biology, University of Amsterdam, P.O. Box 94084, Amsterdam 1090 GB, The Netherlands. f.vala@ucl.ac.uk
authors.forename: Filipa
authors.initials: F
authors.lastname: Vala
authors.forename: Tim
authors.initials: T
authors.lastname: Van Opijnen
authors.forename: Johannes A J
authors.initials: JA
authors.lastname: Breeuwer
authors.forename: Maurice W
authors.initials: MW
authors.lastname: Sabelis
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D006790:Host-Parasite Interactions; D008098:Litter Size; D008297:Male; D012098:Reproduction; D012744:Sex Ratio; D013559:Symbiosis; D040102:Tetranychidae / Q000235:genetics / Q000382:microbiology* / Q000502:physiology*; D020577:Wolbachia / Q000502:physiology*