Free choice by female sticklebacks:: lack of preference for male dominance traits

To experimentally assess if a male sexual trait has an influence on female choice and (or) male-male competition, it is essential to separate these two evolutionary forces. Female choice may be obscured by the overriding influence of male-male competition, and it may therefore appear that female interests coincide with male dominance. We approached this problem using the threespine stickleback, Gasterosteus aculeatus, by leashing the males, allowing the female to fully interact and mate with each male, while physical interactions between the males were prevented. Our results show that in this situation, females display no preference for dominant males and no, or only a weak, preference for more colorful males. When the males could interact freely with each other, females chose the dominant and the more colorful males, but in this case the dominant male always deprived the female of the opportunity to interact with the subordinate male. When the females were separated physically from the males by glass walls, they demonstrated a preference for males with the most intense red color. This suggests that if females are given only a limited number of cues on which to base their choice (by introducing glass walls), they are attracted to the redness of the males, while in a situation involving free physical and sensory interaction, other factors become more important for females' choice if they have the possibility to make a free choice in the absence of forceful male-male interactions.