title: High Wolbachia density correlates with cost of infection for insecticide resistant Culex pipiens mosquitoes.
abstract: In the mosquito Culex pipiens, insecticide resistance genes alter many life-history traits and incur a fitness cost. Resistance to organophosphate insecticides involves two loci, with each locus coding for a different mechanism of resistance (degradation vs. insensitivity to insecticides). The density of intracellular Wolbachia bacteria has been found to be higher in resistant mosquitoes, regardless of the mechanism involved. To discriminate between costs of resistance due to resistance genes from those associated with elevated Wolbachia densities, we compared strains of mosquito sharing the same genetic background but differing in their resistance alleles and Wolbachia infection status. Life-history traits measured included strength of insecticide resistance, larval mortality, adult female size, fecundity, predation avoidance, mating competition, and strength of cytoplasmic incompatibility (CI). We found that: (1) when Wolbachia are removed, insecticide resistance genes still affect some life-history traits; (2) Wolbachia are capable of modifying the cost of resistance; (3) the cost of Wolbachia infections increases with their density; (4) different interactions occurred depending on the resistance alleles involved; and (5) high densities of Wolbachia do not increase the strength of CI or maternal transmission efficiency relative to low Wolbachia densities. Insecticide resistance genes generated variation in the costs of Wolbachia infections and provided an interesting opportunity to study how these costs evolve, a process generally operating when Wolbachia colonizes a new host.
authors.affiliation: Team Genetics of Adaptation, Laboratoire Génétique et Environnement, Institut des Sciences de l'Evolution (UMR CNRS 5554), Université de Montpellier II (C.C. 065), F-34095 Montpellier 05, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Duron
authors.forename: Pierrick
authors.initials: P
authors.lastname: Labbé
authors.forename: Claire
authors.initials: C
authors.lastname: Berticat
authors.forename: François
authors.initials: F
authors.lastname: Rousset
authors.forename: Sylvain
authors.initials: S
authors.lastname: Guillot
authors.forename: Michel
authors.initials: M
authors.lastname: Raymond
authors.forename: Mylène
authors.initials: M
authors.lastname: Weill
mesh_terms: D000818:Animals; D004390:Chlorpyrifos / Q000494:pharmacology*; D003465:Culex / Q000187:drug effects* / Q000235:genetics / Q000382:microbiology* / Q000502:physiology; D005260:Female; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology; D008297:Male; D001074:Propoxur / Q000494:pharmacology*; D012098:Reproduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D020577:Wolbachia / Q000502:physiology*
chemical_list: D007306:Insecticides; D001074:Propoxur; D004390:Chlorpyrifos