Abstract:
Sexual selection often involves female preference for males of a certain age, and a body of theory predicts
preference for old males. We measured a comprehensive set of traits from the acoustic sexual display of
male field crickets, Gryllus bimaculatus, and found that nearly all song traits changed predictably as males
aged, involving a general slowing down of the wing movements during song production. Our female
preference experiments indicated a strong and repeatable preference for the songs of young males,
contradicting the existing literature, which argues that female crickets prefer older males on the basis of
changes in song carrier frequency. Rather, female preference for young male song was determined by its
high energetic quality. We develop the ‘old flight muscle’ hypothesis, arguing that age-related degradation
of stridulatory muscle performance is likely to result in the observed changes with age. Secondary sexual
characters may be subject to oxidative somatic degradation suggesting that, when males provide only
sperm, females should prefer the sexual displays of young males. Our results support new modelling
approaches and a growing body of empirical evidence suggesting that old males are not always preferred
by females.
