Conspicuous female ornamentation and male mate preference of Threespine Sticklebacks (Gasterosteus aculeatus)

Abstract

Sexual selection drives the evolution of exaggerated male ornaments (traits showing little function outside social interactions) in many animal species. Female ornamentation is now acknowledged also to be common but is generally less well understood. One example is the recently documented red female throat coloration in some threespine stickleback (Gasterosteus aculeatus) populations. Although female sticklebacks often exhibit a preference for red male throat coloration, the possibility of sexual selection on females has been little studied. Moreover, in those species in which female ornaments have been examined, research has often been limited to a single trait. Ornamented female threespine sticklebacks provide an excellent opportunity to examine male preference on multiple traits and the correlations between those traits. Using a combination of sequential and simultaneous mate choice trials, male-mating preferences for female throat color (as well as other traits) is examined using wild-captured male and female threespine sticklebacks from the Little Campbell River, British Columbia. In sequential and simultaneous choice tests, males do not exhibit a preference for female throat and pelvic spine color. Surprisingly, males also lack a preference for female standard length. Using mixed modeling, males were tested for differences in the slopes of their preferences for female traits and their mean responsiveness. Results showed that males did not differ in their preference slopes but differed significantly in their mean responsiveness to females. Additionally, when presented with a conspecific male in sequential choice tests, males responded differently than to females and male response decreased as conspecific male body size and throat coloration increased, showing that males can discriminate conspecific traits in the experimental setting. Mean response rates of experimental males toward females had significant, positive correlations with individual throat and pelvic spine coloration, as well as overall male condition. Male condition, however, lacks any correlation with throat or spine coloration. The results presented here are the first to explicitly address male preference for female throat color as well as documenting the relationship between male pelvic spine color and responsiveness.