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Assessing Differences in Sperm Competitive Ability in Drosophila
Published on: August 22, 2013
Factors affecting the distribution of cytoplasmic incompatibility in Drosophila simulans
A A Hoffmann1, M Turelli, L G Harshman
1Department of Genetics and Human Variation, La Trobe University, Bundoora, Australia.
Abstract:
In Drosophila simulans a Wolbachia-like microorganism is responsible for reduced egg-hatch when infected males mate with uninfected females. Both incompatibility types have previously been found in North America, Europe and Africa. Some California populations have remained polymorphic for over two years, and the infection is apparently spreading in central California. Egg hatch proportions for wild-caught females from polymorphic populations show that the incompatibility system acts in nature, but egg mortality rates are apparently lower than observed in laboratory populations. Although infected females maintained under various laboratory conditions never produce uninfected offspring, some wild-caught infected females produce both infected and uninfected progeny. This helps explain the persistence of a low frequency of uninfected flies in predominantly infected populations and may also explain the other polymorphisms observed. Fitness comparisons of infected and uninfected stocks, including both larval and adult fitness components, indicate that fecundity may be the component most affected. Infected females suffer a fecundity reduction of 10-20% in the laboratory, but the reduction seems to be smaller in nature. A theoretical analysis provides some insight into the population biology of the infection.
Insights
In Drosophila simulans, a Wolbachia-like microorganism causes reduced egg hatch in crosses between infected males and uninfected females. This reproductive incompatibility system is spreading in California, impacting natural populations.
Area of Science:
- Evolutionary Biology
- Microbiology
- Genetics
Background:
- Wolbachia-like microorganisms can cause reproductive incompatibility in Drosophila simulans.
- This phenomenon, known as cytoplasmic incompatibility, affects egg hatch rates when infected males mate with uninfected females.
- Previous studies have documented these incompatibility types across North America, Europe, and Africa.
Purpose of the Study:
- To investigate the prevalence and dynamics of Wolbachia-induced reproductive incompatibility in California Drosophila simulans populations.
- To assess the effects of this incompatibility system on natural populations and compare them to laboratory observations.
- To analyze the fitness consequences of Wolbachia infection on host flies.
Main Methods:
- Field observations of polymorphic populations in California, monitoring infection spread and egg hatch rates.
- Laboratory experiments with infected and uninfected Drosophila simulans strains under controlled conditions.
- Fitness component analysis, including fecundity and larval survival, for both infected and uninfected flies.
- Theoretical modeling to understand the population biology of the infection.
Main Results:
- California populations exhibit polymorphism for Wolbachia infection, with evidence of spread in central regions.
- Incompatibility acts in nature, but with lower egg mortality than observed in laboratory settings.
- Infected females can produce both infected and uninfected offspring in the wild, explaining polymorphism persistence.
- Fecundity reduction (10-20% in the lab) appears to be the primary fitness cost for infected females, potentially lower in nature.
Conclusions:
- The Wolbachia-like microorganism significantly influences Drosophila simulans population dynamics in California.
- Natural selection and host-parasite interactions are shaped by reproductive incompatibility and varying fitness costs.
- Understanding these dynamics is crucial for predicting the spread and impact of Wolbachia infections in insect populations.
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