Different ornaments signal male health and MHC variation in two populations of a warbler LINDA A. WHITTINGHAM,* COREY R. FREEMAN-GALLANT, † CONOR C. TAFF ‡ and PETER O. DUNN* *Department of Biological Sciences, Behavioral and Molecular Ecology Group, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA, †Department of Biology, Skidmore College, Saratoga Springs, NY 12866, USA, ‡Department of Evolution and Ecology, University of California-Davis, Davis CA 95616, USA Abstract Male traits that signal health and vigour are used by females to choose better quality mates, but in some cases the male trait selected by females differs among populations. Multiple male traits can be maintained through female mate choice if both traits are equally honest indicators of male quality, but tests of this prediction are rare. By choosing males based on such traits, females could gain direct benefits from males (assistance with parental care), but when females choose extra-pair mates based on these traits, females gain only male sperm, and potentially indirect genetic benefits for their offspring. In common yellowthroats (Geothylpis trichas), female choice of extra- pair mates targets two different plumage ornaments: the black mask in a Wisconsin population and the yellow bib in a New York population. Previously, we found that the black mask in Wisconsin is related to greater major histocompatibility complex (MHC) class II variation, which in turn signals better survival and disease resistance. In this study, we examined the signalling function of the yellow bib in New York to test whether it signals the same aspects of male quality as the black mask in Wiscon- sin. As predicted, we found that the yellow bib in New York is most closely associated with MHC variation, which also signals survival and resistance to blood parasites. Thus, the ornament preferred by females differs between the two populations, but the different ornaments signal similar aspects of male health and genetic quality, specifi- cally information regarding MHC variation and potential indirect genetic benefits to females. Keywords: compatibility, extra-pair mating, good genes, indirect genetic benefits, malaria, sexual selection, warbler Received 26 November 2014; revision received 20 February 2015; accepted 24 February 2015 Introduction Males often display ornamental traits that signal their health and vigour and are used to attract females. How- ever, it is less clear why males appear to have more than one of these ornamental traits, because, in theory, females are expected to prefer the trait with the greatest honesty and detectability and ignore the others (Schluter & Price 1993). One hypothesis for the maintenance of multiple ornaments is that these traits signal different aspects of male quality. For example, one male trait may function in male–male competition (e.g. badges of status) and a different trait may be used by females to choose better quality mates (Pryke et al. 2001; Dunn et al. 2008). However, the trait that signals male quality to females may vary among populations. In this case, Schluter & Price (1993) predicted that females could prefer males based on two different traits, as long as both traits are equally honest indicators of male quality. Indeed, the information signalled by multiple orna- ments is known to vary temporally (Chaine & Lyon Correspondence: Linda A. Whittingham, Fax: 414 229 3926; E-mail: whitting@uwm.edu © 2015 John Wiley & Sons Ltd Molecular Ecology (2015) doi: 10.1111/mec.13130