"Scientists have hypothesized that a male bird's sexual ornaments signal his individual ability to cope with parasite infections and diseases. However, no study, to our knowledge, has directly shown the trade-off between immune activation and the expression level of sexual ornaments," said Faivre.
Carotenoids can be considered the "biological currency" of the two beak color studies. One study elevated the birds' carotenoid levels with deposits while the other reported carotenoid withdrawals.
The scientists from the United Kingdom supplemented the diet of one group of male zebra finches with carotenoid pigments and measured the effects of their elevated carotenoid levels on immune function, beak color, and sexual interest from female finches.
They found that elevating the level of carotenoids in the bloodstreams of zebra finches enhanced immune defenses and reddened beak color. These males were also more attractive to prospective mates.
The French researchers approached carotenoids and immune function from a different direction. They started with a baseline carotenoid balance based on the blackbirds' beak color. When they taxed the blackbird immune systems, their beak color dulled due to carotenoid declines.
"In Blackbirds, dynamic reallocations of carotenoids from the beak to the immune system appear to convey a continual update on male health," said Frank Czilly, co-author on the Faivre paper and professor at Universit de Bourgogne in Dijon, France. "Reallocations of carotenoids were observed in three weeks time. We didn't think the answer could be so quick."
Blount's group also fou
Contact: Lisa Onaga
American Association for the Advancement of Science