Within- and between-population variation for Wolbachia-induced reproductive incompatibility in a haplodiploid mite.
Wolbachia pipientis is a bacterium that induces cytoplasmic incompatibility (CI), the phenomenon in which infected males are reproductively incompatible with uninfected females. CI spreads in a population of hosts because it reduces the fitness of uninfected females relative to infected females. CI encompasses two steps: modification (mod) of sperm of infected males and rescuing (resc) of these chromosomes by Wolbachia in the egg. Infections associated with CI have mod+ resa+ phenotypes. However, mod- resc+ phenotypes also exist; these do not result in CI. Assuming mod/resc phenotypes are properties of the symbiont, theory predicts that mod- resc+ infections can only spread in a host population where a mod+ resc+ infection already occurs. A mod- resc+ infection spreads if the cost it imposes on the infected females is lower than the cost inflicted by the resident (mod+ resc+) infection. Furthermore, introduction of a mod- Wolbachia eventually drives infection to extinction. The uninfected population that results can be recolonized by a CI-causing Wolbachia. Here, we investigated whether variability for induction of CI was present in two Tetranychus urticae populations. In one population all isofemale lines tested were mod-. In the other, mod+ resc+ and mod- resc+ isofemale lines coexisted. We found no evidence for a cost difference to females expressing either type (mod-/-). Infections in the two populations could not be distinguished based on sequences of two Wolbachia genes. We consider the possibility that mod- is a host effect through a population dynamics model. A mod- host allele leads to infection extinction in the absence of fecundity differences. Furthermore, the uninfected population that results is immune to reestablishment of the (same) CI-causing Wolbachia.
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands. f.vala@ucl.ac.uk
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F
Vala
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A
Weeks
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D
Claessen
J A J
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Breeuwer
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MW
Sabelis
D000818:Animals; D003593:Cytoplasm / Q000382:microbiology* / Q000502:physiology; D014644:Genetic Variation; D008297:Male; D008925:Mites / Q000382:microbiology* / Q000502:physiology; D008962:Models, Theoretical; D012098:Reproduction / Q000502:physiology; D020577:Wolbachia / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*