Does a trade-off exist between sexual ornamentation and ecological plasticity? Sexual dichromatism and occupied elevational range in finches

Secondary sexual traits are thought to be costly to produce and maintain, and the allocation of energy to sexual traits could result in reduced investment in traits associated with growth and basic maintenance. It has been suggested that the trade-off between sexual traits and growth and maintenance traits should manifest itself in the correlation between development of sexual traits and resistance to environmental variability. Interspecifically, this hypothesis predicts that species with greater sexual ornamentation and dimorphism should be able to tolerate a narrower width of environmental condition compared to related species with less developed sexual traits. We tested this prediction by examining whether sexual dimorphism in cardueline finches was negatively associated with the width of elevational range occupied during breeding. We assumed that the range in elevations where breeding can occur represents a measure of tolerance of environmental variability. We found a positive rather than a negative relationship between breeding range and sexual dimorphism. Finches that were capable of breeding over a large range of elevations were also more dimorphic in plumage. Possible explanations for the observed relationship between sexual dichromatism and ecological breadth could include interspecific differences in food availability and foraging ability, as well as variation in energy required for baseline metabolism.