ORIGINAL ARTICLE Elevation affects extra-pair paternity but not a sexually selected plumage trait in dark-eyed juncos Katie LaBarbera 1 & Kia R. R. Hayes 1,2 & Kelley E. Langhans 3 & Eileen A. Lacey 1 Received: 28 February 2019 /Revised: 6 May 2019 /Accepted: 13 May 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Differences in environmental conditions are expected to generate distinct selective pressures favoring different phenotypes. For example, environmental conditions that affect the timing of breeding may influence opportunities for extra-pair copulations and thus the strength of sexual selection on males. To explore these relationships quantitatively, we compared breeding synchrony, rates of extra-pair paternity, and expression of a sexually selected plumage trait (the amount of white on the tail feathers) in populations of dark-eyed junco (Junco hyemalis) breeding at elevations from 1960 to 2660 m in California. Microsatellite parentage analysis revealed that extra-pair paternity rates varied by elevation, with intermediate elevations having the highest rate. Differences in breeding synchrony could not explain this variation. Extra-pair males had more tail white than the social males they cuckolded, consistent with tail white being a sexually selected trait. Although the observed differences in rates of extra-pair paternity suggested that sexually selected traits should also vary with elevation, there were no differences among elevations in the amount of white on male tails or in the correlation between tail white and proxies for male condition. Multiple factors may have contributed to this result, including persistent gene flow among elevations, which may counter the effects of local differences in selective pressures. These findings demonstrate the complexity of interactions among environmental conditions, selective pressures, and variation in phenotypic traits, and underscore the importance of assessing the impacts of sexual selection in the larger context of population genetic structure. Significance statement Environmental differences, such as those occurring along elevation gradients, can lead to differences in sexual selection. We found that juncos at mid elevations had higher rates of extra-pair paternity than juncos at high and low elevations. Our results also provide evidence that male tail plumage is sexually selected, as females preferred to copulate with males with more white on their tail plumage than the females’ social mates. This suggests that male tail white should differ among elevations, as the reproductive rewards of having an attractive tail would be greater at mid elevations. However, we found no differences in male tail white among elevations. This may be due to the birds breeding freely across elevations, as evidenced by a lack of genetic structure, i.e., gene flow swamping out any differences that might otherwise form. Keywords Breeding synchrony . Dark-eyed junco . Elevation . Extra-pair paternity . Sexual selection Introduction The selective forces operating on a trait reflect the environ- ment. Accordingly, changes in environmental variables may produce changes in the strength and direction of selection (Grant and Grant 1993; Chaine and Lyon 2008; Gosden and Svensson 2008; Punzalan et al. 2010). Like other forms of selection, sexual selection—the selection resulting from com- petition for mates (Webster et al. 1995)—is affected by the environment (Emlen and Oring 1977; Clutton-Brock et al. 1997; Kwiatkowski and Sullivan 2002; Candolin et al. 2007; Robinson et al. 2008; Candolin and Vlieger 2013; Taff et al. Communicated by K. McGraw Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00265-019-2698-4) contains supplementary material, which is available to authorized users. * Katie LaBarbera klabarbera@berkeley.edu 1 Museum of Vertebrate Zoology, University of California - Berkeley, Berkeley, CA 94720, USA 2 Present address: Institute of Environmental and Human Health, Box 41163, Lubbock, TX 79409, USA 3 Department of Biology, Stanford University, Stanford, CA 94305, USA Behavioral Ecology and Sociobiology (2019) 73:82 https://doi.org/10.1007/s00265-019-2698-4