RESEARCH PAPER Sexual Selection in Black Morph Girardinus metallicus (Pisces: Poeciliidae): Females Can Spot a Winner (But We Cannot) Gita R. Kolluru* 1 , Crystal Castillo*, Michele Hendrickson*, Meghan Hughes*, Paris Krause*, Krista LePiane*, Colleen McCann*, Emily Pavia*, Colin Porter*, Rodet Rodriguez†, Tomas Rodriguez-Cabrera‡, Ellen Scott*, McCall Willrodt* & Susan M. Bertram§ 1 * Biological Sciences Department, California Polytechnic State University, San Luis Obispo, CA, USA † Instituto de Ecolog  ıa y Sistem atica, La Habana, Cuba ‡ Jard  ın Bot anico de Cienfuegos, Cienfuegos, Cuba § Biology Department, Carleton University, Ottawa, ON, Canada Correspondence Susan M. Bertram, Biology Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6. E-mail: Sue.Bertram@carleton.ca Received: June 5, 2015 Initial acceptance: August 17, 2015 Final acceptance: September 17, 2015 (E. Hebets) doi: 10.1111/eth.12434 Keywords: male–male competition, female choice, Poeciliidae, Girardinus, coloration 1 These authors contributed equally; lead authorship was determined by coin toss. Abstract 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 court- ship. 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 mea- sure, 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 ven- tral 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 impor- tance for sexual selection of the interplay between a static morphologi- cal trait (black coloration) and a dynamic behavioral trait (aggressiveness), but the functional significance of the courtship display remains a mystery. Introduction Sexual selection operates when members of one sex (typically males) compete for access to the opposite sex by intimidating, deterring, or defeating rivals (intrasexual selection) and when members of one sex (typically females) select among potential mates (in- tersexual selection; Darwin 1859, 1871). Male–male competition and female mate choice have historically been viewed as separate, sometimes complementary (Berglund et al. 1996; Wiley & Poston 1996) and sometimes opposing (Moore & Moore 1999), forces Ethology 121 (2015) 1–13 © 2015 Blackwell Verlag GmbH 1 Ethology ethology international journal of behavioural biology