vol. 168, no. 6 the american naturalist december 2006  Manipulating Lek Size and Composition Using Decoys: An Experimental Investigation of Lek Evolution Models Fre ´de ´ric Jiguet 1,2,* and Vincent Bretagnolle 2,† 1. Centre de Recherches sur la Biologie des Populations d’Oiseaux, Unite ´ Mixte de Recherche 5173, Conservation des Espe `ces, Restauration et Suivi des Populations, Muse ´um National d’Histoire Naturelle, 55 rue Buffon, Case Postale 51, 75005 Paris, France; 2. Centre d’Etudes Biologiques de Chize ´, Centre National de la Recherche Scientifique, 79360 Villiers-en-Bois, France Submitted December 14, 2005; Accepted July 3, 2006; Electronically published October 12, 2006 Online enhancements: appendix figures and table. abstract: Four theoretical models have been proposed to account for the origin and maintenance of leks: hotspot, female preference, hotshot, and black hole models. Each has been validated in par- ticular cases, and most are not mutually exclusive; therefore, it has been difficult to contrast and separate them, empirically and ex- perimentally. By using decoys to mimic natural leks in the little bustard, artificial leks attracted wild birds. Then, by manipulating artificial lek size and structure (sex ratio, male phenotype), the study of responses of wild males and females allowed us to test specific predictions derived from the four classical models of lek evolution. The hotspot model was not supported because female decoys did not attract wild males. Conversely, hotshot males do exist in this species (attracting both wild females and males), as does a female preference for a particular lek size (four males). Finally, males aggressive toward decoys attracted fewer females, consistent with one of the mechanisms by which the black hole model may work. Therefore, three models of lek evolution were partly or fully supported by our experimental results: hotshot, fe- male preference, and black hole models. We suggest that these models actually fit within each other, ensuring the evolution, func- tioning, and long-term maintenance of leks. Keywords: black hole, exploded lek, female preference, hotshot, hot- spot, little bustard. * Corresponding author; e-mail: fjiguet@mnhn.fr. † E-mail: breta@cebc.cnrs.fr. Am. Nat. 2006. Vol. 168, pp. 758–768.  2006 by The University of Chicago. 0003-0147/2006/16806-41494$15.00. All rights reserved. The lek is a rare mating system (Ho ¨glund and Alatalo 1995; see also Jiguet et al. 2000 for an updated review in birds) and remains perhaps one of the most controversial evolutionary puzzles. A lek consists of clustered male ter- ritories that females visit strictly for the purpose of mating (there is no male parental care in lekking species; review in Ho ¨glund and Alatalo 1995). Male territories therefore do not hold resources attractive to females other than the males themselves. Leks are characterized by (i) male clus- tering; (ii) extreme bias in female choice, resulting in skewed male mating success; and, in many cases, (iii) sta- bility of lek location over time (Ho ¨glund and Alatalo 1995). In comparison with other territorial mating sys- tems, the extreme clustering of lekking male territories raises the ultimate question of the benefits of this aggre- gative behavior in contrast to its associated costs such as competition (Bradbury and Gibson 1983; Wiley 1991; Is- varan and St. Mary 2003). Local clustering of males may facilitate the apparent unanimity of female choice for par- ticular males (Bradbury et al. 1985; Wiley 1991), which may be explained either by independent female choice or by copying as a strategy to reduce the costs of mate as- sessment (Bradbury and Gibson 1983; Ho ¨glund et al. 1990, 1995; Uehara et al. 2005 for a modeling approach). Sta- bility of lek location might result from the different sex roles (Emlen and Oring 1977); that is, leks may settle through male initiation at locations with a high probability of encountering females (Bradbury 1981; Bradbury et al. 1986) or as a response to predation risk (Aspbury and Gibson 2004; Boyko et al. 2004). Much interest has also centered on the possibility that leks may be driven by female choice (Bradbury 1981; Gibson 1992). Finally, in black grouse and mannakins, males are related to each other in a lek, so those who do not mate still gain inclusive fitness by increasing lek size and the mating success of the dominant male (Shorey 2002). Four main models have been proposed to account for the origin and maintenance of leks (reviewed in Sutherland 1996; see also Isvaran and St. Mary 2003), although they may not be mutually exclusive. The hotspot model is the only one that assumes that males are the driving force of