• environmental fluctuations;
  • evolution;
  • evolution of sex;
  • population genetics;
  • theoretical biology

Fluctuating selection is often thought to be ineffective in maintaining a genetic polymorphism except when generations overlap, for example when a seed bank causes a storage effect. Here, I demonstrate that fluctuating selection on sex-limited traits automatically includes such a ‘storage effect’ because sex-limited alleles are shielded from selection in the sex where they are not expressed. With analytical calculations and numerical simulations I show that fluctuating selection can maintain a genetic polymorphism in sex-limited traits. Such a protected polymorphism can reduce the cost of sex when female-limited traits are involved. But, this effect will probably be small compared to the two-fold advantage of asexual reproduction unless many polymorphic loci interact or exceptionally strong environmental fluctuations are present. It is argued that genetic polymorphisms maintained by fluctuating selection on sex-limited traits may partly explain the large genetic variance of traits under strong sexual selection.