Higher cortisol in muscle correlates with weaker strength of female mate preference in the swordtail fish Xiphophorus multilineatus

Abstract

Understanding the physiological factors that contribute to variation in female mate preference can provide valuable insights into factors that can influence the strength of sexual selection as well as the costs and benefits of being choosy. We asked whether the hormone cortisol could be involved in regulating variation in female mate preference in the swordtail fish Xiphophorus multilineatus . On average, females prefer to mate with larger males from the reproductive tactic that courts females (courters) as compared to the tactic that uses coercive mating behaviours (sneakers), but the strength of this preference varies with sexual experience and female size. We measured cortisol concentrations from muscle tissue across females after measuring their mate preferences between courter and sneaker males, taking into consideration female size, sexual experience and lineage (courter or sneaker fathers/grandfathers). We found that females with stronger preferences for courter males had lower cortisol concentrations, suggesting cortisol may be involved in regulating variation in preference. The relationship between cortisol and preference was not influenced by female's size, sexual experience or lineage. Our results suggest that cortisol may not be involved in a female's interest in mating, as cortisol was not related to the total time a female spent with males. Finally, intraspecific variation in cortisol was best explained by a female's lineage, suggesting that further study of known differences between the male tactics (i.e. growth rates, cognition) may provide insights into adaptive variation in female mate preferences. Further investigation of the role of cortisol in relation to female mate preferences has the potential to provide new insights into both adaptive variation and environmental influences on the strength of sexual selection. • Cortisol could be a mechanism behind variation in female mating behaviour. • Female X. multilineatus typically prefer larger males that court. • Females with higher muscle concentrations of cortisol did not prefer larger males. • Variation in female mate preference may maintain multiple male mating strategies.