Diet-dependent female choice for males with ‘good genes’ in a soil predatory mite

Female choice for mates with ‘good genes’ presupposes that some males have better genes than others1. However, the resulting selection against inferior males causes such genetic variability to disappear. This paradox may be resolved when substantial variability is maintained at a balance between selection and mutation2. Alternatively, populations may exhibit genetic polymorphisms maintained by frequency-dependent selection or hybrid vigour3,4,5,6,7,8,9. Here we show that a local population of soil predatory mites exhibits genetic variation in preference for two prey species. We find that hybrids between selected preference lines are superior or inferior in population growth rate, depending on the composition of the diet. Finally, we show that females in this population mate disassortatively when hybrids are superior, but switch to assortative mating otherwise. Thus, mate choice varies with diet and is tuned to incorporate ‘good genes’ in the offspring, that is, genes that promote the population growth rate of the offspring on the same diet as that experienced by the parents. In this way, hybrid success and mate choice act together in maintaining or eliminating genetic polymorphism in local populations.