While carotenoid-based beak color is not the only factor female zebra finches evaluate when selecting a mate, "It is now clear that carotenoid levels are linked to sexual attractiveness and immune function," said Blount.
The next step, according to Blount, is to tease out the relative importance of the different factors that may determine the range in carotenoid-dependent signals. These include immune function, foraging efficiencies, susceptibility to and cost incurred by parasites, and the amount of energy an individual requires to convert dietary carotenoids into a usable form.
Though beak color is probably not the only factor involved in blackbird sexual signaling either, blackbirds are a relevant biological model for investigating the carotenoid-immunocompetence connection, said Faivre.
"The colored surface of the bill may rapidly signal a change in carotenoid allocation because it is continually renewed with carotenoids. This kind of information is not available from feather color, because pigments in sex-signaling plumage are only allocated to feathers once or twice a year during molt events," said Faivre.
Faivre speculated that carotenoid-based signals may have evolved because they are honest signals of individual quality.
"Once males and females started to react adaptively to carotenoid-based signals, their expression was further favored by natural selection."
'"/>
Contact: Lisa Onaga
lonaga@aaas.org
202-326-7088
American Association for the Advancement of Science
3-Apr-2003