Female preference for dynamic traits in the green swordtail, Xiphophorus helleri

Analyses of the relationship between female preference and male behaviour have been complicated by correlated variation in factors such as male size and appearance. This study examined the effects of systematically manipulating male behaviour, while holding male morphology constant. Female green swordtails were shown video-recorded sequences of the same male engaging in an active courtship display, performing similar levels of feeding activity, and remaining inactive. Control sequences of moving food particles and of an empty aquarium were also presented. Female responsiveness was significantly different across time intervals (before, during and after the stimulus) for the three stimuli showing a male, but not for the two controls. Analyses of female behaviour patterns during the stimulus presentations revealed that they preferred sequences of courting males to all other stimuli. Females did not respond differently to the feeding and inactive sequences. These results indicate that female interest depends upon a specific set of motor patterns, and suggest that male behaviour and morphology may act synergistically to determine female preference. Video stimuli should prove useful in future experiments seeking to identify the role of specific courtship motor patterns in mate choice. ? 1996 The Association for the Study of Animal Behaviour Recent models of sexual selection have considered the role of perceptual mechanisms in the evolution of sexually dimorphic traits. Ryan (1990) proposed that secondary sexual characteristics can evolve to exploit pre-existing sensory biases within individuals of the opposite sex, and Endler (1992) examined the evolution of male morphology in terms of constraints imposed by environmental parameters and predator pressures. Support for these models has been found in a variety of systems involving both visual signals (Basolo 1990a; Proctor 1991; Endler 1992) and acoustic signals (Ryan 1991). Most studies of the interaction between sexual signals and sensory systems, like most studies of sexual selection in general, have concentrated on single traits. Considerable evidence suggests, however, that mate choice decisions are typically dependent upon the integration of information from a number of characters. Burley (1981) showed that preference by female pigeons, Columba livia, could be expressed as a function of male coloration, rank order and prior sexual experience. Female red jungle fowl, Gallus gallus, attend to several male traits, including tail length, hackle feather colour, comb length and colour, and courtship display (Zuk et al. 1992). Similarly, female great tits, Parus major, select males on the basis of both song repertoire size and stripe size (Baker et al. 1986). Female guppies, Poecilia reticulata, attend to tail size (Bischoff et al. 1985), display rate (Farr 1980), colour contrast (Endler 1980), brightness (Kodric-Brown 1985), and orange coloration (Houde 1987). Evaluation of multiple male ornaments may yield a more accurate estimate of a male’s current physical condition, as well as provide a degree of redundancy that reduces the likelihood of erroneous rejection based on one character alone (Zuk et al. 1992). Studies of the auditory basis of female mate choice suggest that it is useful to categorize traits as either ‘static’ or ‘dynamic’, depending on the level of within-male variability during a calling Correspondence: G. G. Rosenthal, Department of Zoology, University of Texas, Austin, TX 78712, U.S.A. (email: [email protected]). C. S. Evans is at the Department of Psychology, School of Behavioural Sciences, Macquarie University, Sydney, NSW 2109, Australia. W. L. Miller is at the Center for Neuroscience, University of California, Davis, CA 95616, U.S.A. 0003–3472/96/040811+10 $18.00/0 ? 1996 The Association for the Study of Animal Behaviour