Showing papers by "Peter Arcese published in 2005"
TL;DR: It is shown that in song sparrows, Melospiza melodia, a male's song repertoire size, a secondary sexual trait, increased with his cell-mediated immune response (CMI) to an experimental challenge, and this phenotypic correlation could be explained because both repertoire size and CMI declined with amale's inbreeding level.
Abstract: Hamilton and Zuk’s influential hypothesis of parasite-mediated sexual selection proposes that exaggerated secondary sexual ornaments indicate a male’s additive genetic immunity to parasites. However, genetic correlates of ornamentation and immunity have rarely been explicitly identified. Evidence supporting Hamilton and Zuk’s hypothesis has instead been gathered by looking for positive phenotypic correlations between ornamentation and immunity; such correlations are assumed to reflect causal, additive relationships between these traits. We show that in song sparrows, Melospiza melodia, a male’s song repertoire size, a secondary sexual trait, increased with his cell-mediated immune response (CMI) to an experimental challenge. However, this phenotypic correlation could be explained because both repertoire size and CMI declined with a male’s inbreeding level. Repertoire size therefore primarily indicated a male’s relative heterozygosity, a non-additive genetic predictor of immunity. Caution may therefore be required when interpreting phenotypic correlations as support for Hamilton and Zuk’s additive model of sexual selection. However, our results suggest that female song sparrows choosing males with large repertoires would on average acquire more outbred and therefore more heterozygous mates. Such genetic dominance effects on ornamentation are likely to influence evolutionary trajectories of female choice, and should be explicitly incorporated into genetic models of sexual selection.
132 citations
TL;DR: Song sparrows inhabiting Mandarte Island, British Columbia, Canada, used 20 years of data to test whether a male’s song repertoire size, a secondary sexual trait, predicted overall measures of male or offspring fitness, and suggest that female song sp Sparrows would gain immediate and intergenerational fitness benefits by pairing with males with large song repertoires.
Abstract: Models of sexual selection propose that exaggerated secondary sexual ornaments indicate a male’s own fitness and the fitness of his offspring. These hypotheses have rarely been thoroughly tested in free‐living individuals because overall fitness, as opposed to fitness components, is difficult to measure. We used 20 years of data from song sparrows (Melospiza melodia) inhabiting Mandarte Island, British Columbia, Canada, to test whether a male’s song repertoire size, a secondary sexual trait, predicted overall measures of male or offspring fitness. Males with larger song repertoires contributed more independent and recruited offspring, and independent and recruited grandoffspring, to Mandarte’s population. This was because these males lived longer and reared a greater proportion of hatched chicks to independence from parental care, not because females mated to males with larger repertoires laid or hatched more eggs. Furthermore, independent offspring of males with larger repertoires were more lik...
89 citations