Wednesday, November 14, 2007

Bluer eggs mean fitter young

Spanish researchers, reported in New Scientist, have found that the intensity of the colour of Spotless Starling eggs is related to the body condition and strength of the female. The weaker and more stressed the female, the paler the egg. So what you may think - seems obvious. However, this case of apparent sexual ornamentation in females affects the male insofar that he then tends to feed offspring from darker eggs 1.5 fold more often than young from paler eggs.

The study, performed on a clutch by clutch basis, seems to indicate that males alter their parental investment according to an indirect signal from their offspring – i.e. the colour of their egg.

How does the colour represent female fitness? Well more healthy females are thought to forage more, consume more insects that contain high levels of biliverdin, a bluish antioxidant that helps to protect cells against damage from reactive compounds, and so produce bluer eggs. The young from these bluer eggs are then found to have a more active immune system giving then a survival advantage over young from pale eggs.

The complete study will be published in the American Naturalist in Feb 2008: http://www.journals.uchicago.edu/AN/

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