ORIGINAL PAPER UV wavelengths make female three-spined sticklebacks (Gasterosteus aculeatus) more attractive for males Ingolf P. Rick & Theo C. M. Bakker Received: 19 December 2006 / Revised: 9 July 2007 / Accepted: 23 August 2007 / Published online: 13 September 2007 # Springer-Verlag 2007 Abstract Numerous fishes possess UV vision and show UV patterns, which often play a role in social communi- cation, especially during courtship. UV light is scattered strongly in water and thus might be used for intra-specific close-range communication without being detected by predators. In addition to the red-belly colouration and blue-coloured iris, male three-spined sticklebacks possess UV reflectance on their skin, and females prefer males presented with UV light rather than without. To investigate whether UV also influences male visual preference for females in this species, we used a dichotomous mate choice design in which one female could be viewed by a male in two visual conditions. Courting male sticklebacks preferred females that were presented in full-spectrum conditions including UV to the same females presented in conditions lacking this light component. Furthermore, control trials with neutral-density filters indicated that male preference in the UV treatment was not affected by a difference in achromatic brightness between the UV+ and UV- stimuli. Reflectance measurements of gravid females suggest an enhanced UV contrast between the dark bar pattern, which is characteristic of gravid females, and silvery body parts. Keywords Male choice . Spectral reflectance . Stickleback . UV vision Introduction UV colour signals (300–400 nm) are of recent interest in studies on social signalling, especially in the context of sexual selection. In several species, there is a UV component to female mate choice (in birds: Bennett et al. 1996, 1997; Andersson and Amundsen 1997; in fish: Smith et al. 2002; Macias Garcia and Burt de Perera 2002; Boulcott et al. 2005; Rick et al. 2006) and male contests (Alonso-Alvarez et al. 2004; Siebeck 2004; Stapley and Whiting 2006). However, only two studies have considered a potential influence of female trait variation in the UV on male mating decisions (Hunt et al. 1999; LeBas and Marshall 2000). Nevertheless, female ornaments can be sexually selected through male mate choice or female– female competition (reviewed by Amundsen 2000), al- though data are limited to human-visible wavelengths (400–700 nm). In the three-spined stickleback, females often develop nuptial colouration in the form of a dark, bar-like pattern on their dorsum, upper flanks and tail stem (Rowland et al. 1991). Courting stickleback males preferred dummies of a gravid female with a bar pattern to gravid, uncoloured ones (Rowland et al. 1991). Rowland et al. hypothesized that female nuptial colours might enable males to quickly find a receptive partner and hence increase the females’ chances of being courted. Males also preferred dummies of gravid females in head-up courtship posture to horizontal ones (Bakker and Rowland 1995). Furthermore, in female sticklebacks, fecundity correlates with body size (Baker 1994), and when presented with two dummy females, which differed in abdominal distension, males preferen- tially courted the more distended (more fecund) one (Rowland 1989). Accordingly, Kraak and Bakker (1998) demonstrated that more attractive stickleback males pre- Behav Ecol Sociobiol (2008) 62:439–445 DOI 10.1007/s00265-007-0471-6 Communicated by I. Cuthill I. P. Rick (*) : T. C. M. Bakker Institut für Evolutionsbiologie und Ökologie, University of Bonn, An der Immenburg 1, 53121 Bonn, Germany e-mail: irick@evolution.uni-bonn.de