Evolution of female preference for old mates

Costly female choice for mate quality is a phenomenon that is difficult to account for in the theory of sexual selection. We present a model to determine whether a specific case of mate choice - preference for old mates - can be justified by viability selection in mutation-selection balance only, or whether biotic interactions or random variations in the environment are necessary to maintain the preference if the age of the male does not yield any direct benefit for the female. The results of the model, considering multiple polygenic viability-related traits, show that choosiness will be favoured with any positive mutation rate, but the advantage will be slightly reduced rather than enhanced in the case of a Red Queen type process. Hence, observations of old-age preference indicate a far more important role for viability indicators based on mutation-selection balance alone than previously assessed. Because using age as a choice criterion is also less accountable as a Fisherian mating advantage, the result implies confidence in viability indicators ('good genes' models) as an explanation for female preferences in general.