1 1Department of Biological Sciences, Ohio University, Athens, OH 45701, USA
2 2Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA
3 3Departamento de Biología Evolutiva, Instituto de Ecología, A.C. Km 2.5 Carretera antigua a Coatepec No. 351, Ap. Postal 63, Congregación El Haya, Xalapa 91070, México;, Email: firstname.lastname@example.org
Female mimicry is commonly considered in the context of alternative mating tactics as mimics can avoid male–male competition to gain increased access to females. We describe a case where one of the benefits to being a female mimic could be the increase in size of a sexually selected trait that should eventually decrease the mimics' ability to fool males. In the swordtail fish Xiphophorus nezahualcoyotl, a small percentage of males have a permanent pigment pattern known as 'false brood spot' (FBS), express a horizontal bar pigment pattern common for females, and yet have longer swords (a sexually selected trait) for their body size. FBS males did not use more 'coercive' behaviours in the field, and females do not appear to distinguish between males based on whether or not they have FBS in the laboratory. However, in the field males with FBS were chased less by other males, spent significantly more time feeding, and those that expressed the horizontal bar had greater access to females. We suggest that FBS males with swords can still fool other males into thinking they are females because the true brood spot remains informative as long as the frequency of FBS males (mimics) remains low.