Male-trait-specific variation in female mate preferences

Empirical studies identifying the causes of variation in mate preference are needed to assist in determining when variation is adaptive. We examined the strength of female preference in the swordtail fish Xiphophorus multilineatus for two sexually selected male traits (body size and symmetrical bar number) across variation in both embryonic and postembryonic environments. We measured brood size, then split fry from each brood into high- and low-quality diet treatments. Once females reached sexual maturity, we tested their mate preferences using dummies in dichotomous choice tests. Both the embryonic (brood size) and postembryonic (diet) environment influenced females' strength of preference for symmetrical bar number; females from smaller broods as well as females raised on high-quality diets had a stronger preference for symmetrical bars. However, only the postembryonic environment influenced preference for male size, with females on the low-quality diet having a stronger preference for larger males. There was no relationship between the strength of preference for the two traits across females. Our results demonstrate that plasticity in mate preferences can depend on the specific traits being assessed. We hypothesize that at least one of the preferences may be tracking the conditions that influence signal reliability of the preferred trait. In addition, we demonstrate an influence of the embryonic environment on mate preference, which is rarely considered or controlled for in studies of adaptive variation in mate preferences.