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STABILIZING SELECTION AND VARIANCE IN FIG WASP SEX RATIOS
1Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama.
Summary
Phenotypic variance in fig wasp offspring sex ratios is lower when single foundress broods occur more frequently. This supports the theory that traits under stabilizing selection show less variance as their fitness impact increases.
Area of Science:
- Evolutionary Biology
- Behavioral Ecology
- Population Genetics
Background:
- Theoretical models predict a negative correlation between phenotypic variance of a trait and its fitness impact under stabilizing selection.
- This relationship has been infrequently tested empirically, particularly in natural populations.
- Pollinating fig wasp foundress offspring sex ratios are a model trait for studying stabilizing selection due to fitness consequences of extreme ratios.
Purpose of the Study:
- To empirically test the theoretical prediction of a negative correlation between phenotypic variance and fitness impact for single foundress sex ratios.
- To investigate if the frequency of single foundress broods influences the intensity of stabilizing selection on sex ratios.
- To examine this relationship across multiple species of pollinating fig wasps.
Main Methods:
- Studied 16 species of Panamanian pollinating fig wasps.
- Quantified the phenotypic variance in single foundress sex ratios for each species.
- Assessed the natural frequency of single foundress brood production per species.
- Performed comparative analyses using species as independent data points and accounting for phylogenetic relationships.
Main Results:
- A significant negative correlation was found between the phenotypic variance of single foundress sex ratios and the frequency of encountering single foundress broods.
- Species with more frequent single foundress broods exhibited lower phenotypic variance in their sex ratios.
- Phylogenetic comparative analysis confirmed the results obtained using species as independent data points.
Conclusions:
- The findings support the theory that phenotypic variance decreases as the fitness impact of a trait under stabilizing selection increases.
- The frequency of encountering single foundress broods acts as a proxy for the intensity of stabilizing selection on sex ratios in these wasps.
- This study provides strong empirical evidence for the relationship between selection intensity and phenotypic variance in a natural system.
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