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Population dynamics of the Wolbachia infection causing cytoplasmic incompatibility in Drosophila melanogaster
A A Hoffmann1, M Hercus, H Dagher
1School of Genetics and Human Variation, La Trobe University, Bundoora, Victoria, Australia. genaah@gen.latrobe.edu.au
Abstract:
Field populations of Drosophila melanogaster are often infected with Wolbachia, a vertically transmitted microorganism. Under laboratory conditions the infection causes partial incompatibility in crosses between infected males and uninfected females. Here we examine factors influencing the distribution of the infection in natural populations. We show that the level of incompatibility under field conditions was much weaker than in the laboratory. The infection was not transmitted with complete fidelity under field conditions, while field males did not transmit the infection to uninfected females and Wolbachia did not influence sperm competition. There was no association between field fitness as measured by fluctuating asymmetry and the infection status of adults. Infected field females were smaller than uninfecteds in some collections from a subtropical location, but not in other collections from the same location. Laboratory cage studies showed that the infection did not change in frequency when populations were maintained at a low larval density, but it decreased in frequency at a high larval density. Monitoring of infection frequencies in natural populations indicated stable frequencies in some populations but marked fluctuations in others. Simple models suggest that the infection probably provides a fitness benefit for the host in order to persist in populations. The exact nature of this benefit remains elusive.
Insights
Field populations of Drosophila melanogaster commonly host Wolbachia bacteria. This study found weaker reproductive incompatibility and variable transmission in natural settings, suggesting an elusive host fitness benefit for Wolbachia persistence.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genetics
Background:
- Wolbachia are intracellular bacteria vertically transmitted in insects.
- In laboratory settings, Wolbachia infections can cause reproductive incompatibilities.
- Understanding Wolbachia's ecological role in natural populations is crucial.
Purpose of the Study:
- To investigate factors influencing Wolbachia distribution in natural Drosophila melanogaster populations.
- To assess the impact of Wolbachia on host fitness and reproductive success under field conditions.
- To explore the dynamics of Wolbachia infection frequency in natural populations.
Main Methods:
- Field surveys of Drosophila melanogaster populations to assess Wolbachia infection prevalence.
- Laboratory experiments to quantify reproductive incompatibility and transmission fidelity.
- Measurement of host fitness parameters, including fluctuating asymmetry and body size.
- Population cage studies to model infection frequency dynamics under varying larval densities.
Main Results:
- Wolbachia-induced reproductive incompatibility was significantly weaker in field conditions compared to laboratory settings.
- Infection transmission fidelity was incomplete under field conditions; males did not transmit to uninfected females.
- No association was found between Wolbachia infection status and host fitness (fluctuating asymmetry).
- Infection frequency decreased at high larval densities in laboratory populations but remained stable at low densities.
- Natural populations exhibited stable or fluctuating Wolbachia infection frequencies.
Conclusions:
- Wolbachia infection dynamics in natural populations are complex and differ from laboratory observations.
- The persistence of Wolbachia suggests a potential, yet unidentified, fitness benefit for the host.
- Further research is needed to elucidate the precise nature of the host-symbiont fitness interactions in the field.