Paternity analysis reveals opposing selection pressures on crown coloration in the blue tit (Parus caeruleus).
In socially monogamous species, extra-pair paternity can increase the variance in reproductive success and thereby the potential for sexual selection on male ornaments. We studied whether male secondary sexual ornaments are selected through within- and/or extra-pair reproductive success in the blue tit (Parus caeruleus). Male blue tits display a bright blue crown plumage, which reflects substantially in the ultraviolet (UV) and previously has been indicated to be an important sexual signal. We show that males with a more UV-shifted crown hue were less cuckolded, which probably resulted from female preference for more ornamented mates. By contrast, however, older males and males with a less UV-shifted hue sired more extra-pair young. This probably did not reflect direct female preference, since cuckolders were not less UV-ornamented than the males they cuckolded. Alternatively, a trade-off between UV ornamentation and other traits that enhance extra-pair success could explain this pattern. Our results might reflect two alternative male mating tactics, where more UV-ornamented males maximize within-pair success and less UV-ornamented males maximize extra-pair success. Since crown colour was selected in opposite directions by within-pair and extra-pair paternity, directional selection through extra-pair matings seemed weak, at least in this population and breeding season. Reduced intensity of sexual selection due to alternative mating tactics constitutes a potential mechanism maintaining additive genetic variance of male ornaments.
Delhey
Kaspar
K
Max Planck Research Centre for Ornithology, PO Box 1564, D-82305, Starnberg (Seewiesen), Germany. delhey@erl.ornithol.mpg.de
Johnsen
Arild
A
Peters
Anne
A
Andersson
Staffan
S
Kempenaers
Bart
B
D000818:Animals; D001317:Austria; D003307:Copulation / Q000502:physiology*; D005260:Female; D016014:Linear Models; D008297:Male; D010152:Pair Bond; D010858:Pigmentation / Q000502:physiology; D012641:Selection, Genetic; D012727:Sex Characteristics; D020308:Songbirds / Q000502:physiology*; D014466:Ultraviolet Rays