Sexual Selection in Black Morph Girardinus metallicus (Pisces: Poeciliidae): Females Can Spot a Winner (But We Cannot)

Male-male competition may interfere with the ability of females to choose mates by interrupting courtship or by favoring highly aggressive males who may damage females during mating attempts. Alternatively, females may benefit by mating with dominant males, and female choice and male-male competition may therefore act in unison. The same traits, including aggressiveness, may indicate male quality to females and to rivals. We investigated sexual selection in the black morph of the endemic Cuban poeciliid fish, Girardinus metallicus, to ascertain the links between morphological and behavioral traits and success in intra- and intersexual selection. Males conspicuously exhibit their black ventral surface and gonopodium to females during courtship. Dichotomous choice tests revealed female association preferences for certain males, and those same males were more successful in monopolizing access to females when the fish were allowed to directly interact. Dominant males followed, courted, and copulated with females more than subordinate males within a pair, and it appears that females could either assess dominance based on cues we did not measure, or could influence subsequent mating success by their behavior during the dichotomous choice trials. There was an interaction between black status (i.e., whether the male in each pair had more or less ventral black coloration than the other male in that pair) and dominance, such that low-black dominant males courted early and then shifted to following females, whereas high-black dominant males courted far more later in the observation period. These results hint at the importance for sexual selection of the interplay between a static morphological trait (black coloration) and a dynamic behavioral trait (aggressiveness), but the functional significance of the courtship display remains a mystery