LAUSR

Significance Ornaments are thought to signal the genetic quality of males to females choosing mates, but the qualities they signal and why they sometimes vary between populations are poorly understood. Here, we show, within a single warbler species, that two plumage ornaments signal similar aspects of male quality (e.g., immunity and oxidative balance) at the level of genetic functions, even though the ornament preferred by females differs between populations, involves different body parts, and is produced by different pigments (melanins and carotenoids). This parallelism at the functional level provides the flexibility for different types of ornaments to be used as signals of similar aspects of male quality, allowing for switches in female preferences between ornaments and potentially facilitating divergence and speciation. Extravagant ornaments are thought to signal male quality to females choosing mates, but the evidence linking ornament size to male quality is controversial, particularly in cases in which females prefer different ornaments in different populations. Here, we use whole-genome sequencing and transcriptomics to determine the genetic basis of ornament size in two populations of a widespread warbler, the common yellowthroat (Geothlypis trichas). Within a single subspecies, females in a Wisconsin population prefer males with larger black masks as mates, while females in a New York population prefer males with larger yellow bibs. Despite being produced by different pigments in different patches on the body, the size of the ornament preferred by females in each population was linked to numerous genes that function in many of the same core aspects of male quality (e.g., immunity and oxidative balance). These relationships confirm recent hypotheses linking the signaling function of ornaments to male quality. Furthermore, the parallelism in signaling function provides the flexibility for different types of ornaments to be used as signals of similar aspects of male quality. This could facilitate switches in female preference for different ornaments, a potentially important step in the early stages of divergence among populations.