Male Mating Tactics in the Northern Mountain Swordtail Fish (Xiphophorus nezahualcoyotl): Coaxing and Coercing Females to Mate


Molly R. Morris, Department of Biological Sciences, Ohio University, Athens, OH 45701, USA. E-mail:


Our understanding of the evolution of alternative male mating tactics would benefit greatly from more comparative studies; however, descriptions of the variation in mating behaviors are often lacking or reported in ways that consider only the role of male–male competition. Here we examine the mating behavior of the swordtail fish Xiphophorus nezahualcoyotl in relation to male size across different competitive contexts and in relation to coaxing vs. coercing females to mate. We also compare these results with reports for four other species of northern swordtails. The mating behaviors displayed by X. nezahualcoyotl males were correlated with male size, and were ranked in order from most coaxing to most coercive (a new behavior ‘headstand’, frontal displays, backing and fast chase) based on the probability that a behavior was followed by an attempted forced copulation. The largest males never used the most coercive behavior in the laboratory setting, even in the context of a larger competitor, and the smallest males never used the most coaxing behavior, even when alone with females. We argue, however, that changing the competitive context may not be the best way to expose the full range of behaviors a male may use if circumventing female mate choice is also driving the evolution of the alternative tactics. Finally, when we compared the mating behaviors of X. nezahualcoyotl males to those of the males of four other species of northern swordtails, they were not most similar to males of the closely related species X. continens. In X. continens, all males are small and have no morphological traits or behaviors that coax females to mate, where as even the smallest X. nezahualcoyotl males had both morphological and behavioral traits that could coax females to mate.