These authors contributed equally to the work.
SEX RATIO EVOLUTION UNDER PROBABILISTIC SEX DETERMINATION
Version of Record online: 19 MAR 2011
© 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.
Volume 65, Issue 7, pages 2050–2060, July 2011
How to Cite
Paixão, T., Phadke, S. S., Azevedo, R. B. R. and Zufall, R. A. (2011), SEX RATIO EVOLUTION UNDER PROBABILISTIC SEX DETERMINATION. Evolution, 65: 2050–2060. doi: 10.1111/j.1558-5646.2011.01266.x
- Issue online: 5 JUL 2011
- Version of Record online: 19 MAR 2011
- Accepted manuscript online: 1 MAR 2011 06:34AM EST
- Received June 15, 2010, Accepted February 2, 2011
- Bet hedging;
- biased sex ratios;
- frequency-dependent selection;
- genetic drift;
- mixed strategies;
- sex allocation;
- Tetrahymena thermophila
Sex allocation theory has been remarkably successful at explaining the prevalence of even sex ratios in natural populations and at identifying specific conditions that can result in biased sex ratios. Much of this theory focuses on parental sex determination (SD) strategies. Here, we consider instead the evolutionary causes and consequences of mixed offspring SD strategies, in which the genotype of an individual determines not its sex, but the probability of developing one of multiple sexes. We find that alleles specifying mixed offspring SD strategies can generally outcompete alleles that specify pure strategies, but generate constraints that may prevent a population from reaching an even sex ratio. We use our model to analyze sex ratios in natural populations of Tetrahymena thermophila, a ciliate with seven sexes determined by mixed SD alleles. We show that probabilistic SD is sufficient to account for the occurrence of skewed sex ratios in natural populations of T. thermophila, provided that their effective population sizes are small. Our results highlight the importance of genetic drift in sex ratio evolution and suggest that mixed offspring SD strategies should be more common than currently thought.