Sexual Selection, Multiple Male Ornaments, and Age- and Condition-dependent Signaling in the Common Yellowthroat
In many animals, sexual selection has resulted in complex signaling systems in which males advertise aspects of their phenotypic or genetic quality through elaborate ornamentation and display behaviors. Different ornaments might convey different information or be directed at different receivers, but they might also be redundant signals of quality that function reliably at different times (ages) or in different contexts. We explored sexual selection and age- and condition-dependent signaling in the common yellowthroat (Geothlypis trichas), a sexually dichromatic warbler with two prominent plumage ornaments--a melanin-based, black facial "mask" and carotenoid-based, UV-yellow "bib." In a three-year study, variance among males in the number of social (M(w)) and extra-pair (M(e)) mates generated strong sexual selection on mask and bib attributes. Some traits (mask size, bib yellow brightness) were correlated with male age and did not experience selection beyond age-related increases in M(w) and M(e). Other traits showed age-specific (bib size) or age-reversed (ultraviolet brightness) patterns of selection that paralleled changes in the information-content of each ornament. The components of male fitness generating selection in young versus old males were distinct, reflecting different sources of variation in male fertilization success. Age- and context-dependent changes in the strength, direction, and target of selection may help explain the maintenance of multiple ornaments in this and other species.