Abstract
Theory suggests that genetic conflicts drive turnovers between sex-determining mechanisms, yet these studies only apply to cases where sex allocation is independent of environment or condition. Here, we model parent–offspring conflict in the presence of condition-dependent sex allocation, where the environment has sex-specific fitness consequences. Additionally, one sex is assumed to be more costly to produce than the other, which leads offspring to favor a sex ratio less biased toward the cheaper sex in comparison to the sex ratio favored by mothers. The scope for parent–offspring conflict depends on the relative frequency of both environments: when one environment is less common than the other, parent–offspring conflict can be reduced or even entirely absent, despite a biased population sex ratio. The model shows that conflict-driven invasions of condition-independent sex factors (e.g., sex chromosomes) result either in the loss of condition-dependent sex allocation, or, interestingly, lead to stable mixtures of condition-dependent and condition-independent sex factors. The latter outcome corresponds to empirical observations in which sex chromosomes are present in organisms with environment-dependent sex determination. Finally, conflict can also favor errors in environmental perception, potentially resulting in the loss of condition-dependent sex allocation without genetic changes to sex-determining loci.
Highlights
Condition-dependent sex allocation—where investment in one sex versus the other is dependent on the environment or an individual’s condition—provides an adaptation to environments that have different fitness consequences for males and females (Trivers and Willard 1973; Charnov and Bull 1977)
INVASION BY CONDITION-INDEPENDENT SEX FACTORS We assess whether parent–offspring conflict favors invasion by condition-independent sex factors, which could potentially lead to the replacement of condition-dependent sex allocation by sex-determining mechanisms that are independent of condition
We first assess the extent of parent–offspring conflict over the sex ratio when sex allocation is independent of the environment or condition
Summary
Monogamous sexual population with discrete generations. Similar to the seminal Charnov–Bull model (e.g., Charnov and Bull 1977; Schwanz et al 2006), we assume that environmental variation has different fitness consequences to each sex. Note that the timing of male dispersal may affect the evolution of condition-dependent sex allocation: in case male dispersal occurs after mating, males achieve all their reproductive success in their natal environment, after which they disperse but have no further reproductive opportunities In this case, conditiondependent sex allocation will not evolve (see Section S1 of the Supporting Information). Conditiondependent sex allocation will not evolve (see Section S1 of the Supporting Information) This is because an individual male’s reproductive success will always be affected by a single environment (the natal environment), which eliminates one of the basic assumptions of the Charnov–Bull model, namely that any individual is likely to experience a certain variation in environmental conditions (Charnov and Bull 1977)
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