Abstract
Background Wolbachia bacteria have invaded many arthropod species by inducing Cytoplasmic Incompatibility (CI). These symbionts represent fascinating objects of study for evolutionary biologists, but also powerful potential biocontrol agents. Here, we assess the density dynamics of Wolbachia infections in males and females of the mosquito Aedes albopitcus, an important vector of human pathogens, and interpret the results within an evolutionary framework.Methodology/Principal Findings Wolbachia densities were measured in natural populations and in age controlled mosquitoes using quantitative PCR. We show that the density dynamics of the wAlbA Wolbachia strain infecting Aedes albopictus drastically differ between males and females, with a very rapid decay of infection in males only.Conclusions/SignificanceTheory predicts that Wolbachia and its hosts should cooperate to improve the transmission of infection to offspring, because only infected eggs are protected from the effects of CI. However, incompatible matings effectively lower the fertility of infected males, so that selection acting on the host genome should tend to reduce the expression of CI in males, for example, by reducing infection density in males before sexual maturation. The rapid decay of one Wolbachia infection in Aedes albopictus males, but not in females, is consistent with this prediction. We suggest that the commonly observed reduction in CI intensity with male age reflects a similar evolutionary process. Our results also highlight the importance of monitoring infection density dynamics in both males and females to assess the efficiency of Wolbachia-based control strategies.
Highlights
Wolbachia are maternally inherited bacteria that optimize their own fitness by manipulating the reproduction of their host [1]
This hypothesis was substantiated by a standard PCR assay using wAlbA-wsp specific primers [7] which revealed that 4 out of 5 specimens characterised as negative for wAlbA with the previously described PCR primers [11] were positive
The presence of Wolbachia is crucial to the survival of infected females’ offspring, as only these bacteria can restore the functionality of the sperm ‘‘modified’’ by the paternal Wolbachia
Summary
Wolbachia are maternally inherited bacteria that optimize their own fitness by manipulating the reproduction of their host [1]. Similar embryonic mortality is seen in crosses between males and females harbouring different, incompatible, Wolbachia variants [2] This pattern produces two consequences of interest for the present study. The lethal effect of infected males’ sperm expressed in crosses with incompatible females is detrimental to the transmission of the host nuclear genes. For this reason, theory predicts that selection acting on host nuclear genes should tend to prevent this effect, for example by reducing the density of infection in males before they become sexually mature [4,5]. Wolbachia bacteria have invaded many arthropod species by inducing Cytoplasmic Incompatibility (CI) These symbionts represent fascinating objects of study for evolutionary biologists, and powerful potential biocontrol agents. We assess the density dynamics of Wolbachia infections in males and females of the mosquito Aedes albopitcus, an important vector of human pathogens, and interpret the results within an evolutionary framework
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