Multiple traits predict reproductive success and assortative mating in mutually ornamented Campo flickers ( Colaptes campestris campestris )

Cooperative species have provided extensive evidence on the evolution of cooperation and kin selection mechanisms, but they have been poorly studied in terms of sexual selection. Assortative mating has been recorded in several taxonomic groups and has significant implications for population genetics. In this study, we investigated the occurrence of sex differences, assortative mating, and the relationship between ornaments and fitness in the campo flicker ( Colaptes campestris campestris ). Campo flickers are facultative cooperative breeders with a complex social and reproductive system. Both males and females are ornamented in the species. Our results demonstrate that males and females are almost entirely alike, and that they mate assortatively for neck and throat coloration. Moreover, individuals possessing larger crowns and a lighter yellow neck coloration were more likely to reproduce. Surprisingly, more homozygous individuals were also more likely to reproduce. Our results support at least two possibilities. The first possibility is that same-sex competition within and between social units may be intense and likely to influence territory occupation, within-group hierarchy, and, ultimately, reproductive success. Alternatively, variation in reproductive success may be associated with mutual sex preferences. The association between fitness and lower heterozygosity may be related to some level of inbreeding, although it does not seem to be impacting campo flicker population numbers. Significance statement In this study, we investigated the extent to which morphometric traits and plumage coloration predict sex, body condition, and breeding probability in the facultative cooperative breeder Campo Flicker ( Colaptes campestris campestris ). Our results showed that only body mass differed significantly between males and females, with males being heavier. Males and females are almost entirely alike in terms of coloration. Interestingly, we found that larger crowns and a lighter yellow neck coloration were positively associated with breeding probability, while heterozygosity was negatively associated. These findings advance our understanding of the role of sexual selection in cooperative breeders and provide valuable insights into the impact of competition and mate preferences in ornament evolution and population genetics of social species.