Evol Ecol Res 5: 1023-1036 (2003)     Full PDF if your library subscribes.

Within-population structure of competition and the dynamics of male-killing Wolbachia

John Jaenike,1,2* Kelly A. Dyer1,2 and Laura K. Reed2

1Department of Biology, University of Rochester, Rochester, NY 14627 and  2Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA

Address all correspondence to John Jaenike, Department of Biology, University of Rochester, Rochester, NY 14627, USA.
e-mail: joja@mail.rochester.edu

ABSTRACT

Males are evolutionary dead-ends for endosymbiotic bacteria that are transmitted maternally. It has been shown theoretically that male killing will enhance endosymbiont transmission if the fitness of females increases as a result of the death of their male siblings. Despite the intuitive appeal of this explanation for the spread of male-killing bacteria, it has never been examined experimentally. Here we consider how the structure of larval competition within panmictic populations affects the dynamics of a male-killing Wolbachia that infects Drosophila innubila. In populations with exclusively sib competition for larval resources, the Wolbachia infection spreads rapidly to fixation, in contrast to much less deterministic dynamics in populations where competition is unstructured. Sib competition is likely to be important if females lay eggs in clutches on individual breeding sites. Drosophila innubila, a mycophagous species, lays eggs in clutches on individual mushrooms in the laboratory, even when several mushrooms are available. The larvae of species that exploit patchy, ephemeral resources typically exhibit aggregated distributions across breeding sites, due at least in part to egg laying in clutches. These species may therefore be particularly susceptible to invasion by male killers.

Keywords: aggregation, clutch size, endosymbionts, intragenomic conflict, larval competition, population structure, sex ratio, sib competition.

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