Aims: Female birds deposit variable amounts of androgens in their eggs, and research shows that these hormones can influence several aspects of offspring development and phenotype. Some evidence suggests that yolk androgen deposition may be a costly investment for the female bird. We studied the relationship between female expression of a male ornament and yolk androgen deposition in the pied flycatcher (Ficedula hypoleuca). In this species, some females present a white forehead patch, which is an ornament typically restricted to males. Female expression of this trait has previously been found to be associated with older age and low levels of blood parasites. We predicted that, if yolk androgen deposition is costly, eggs from females displaying a white forehead patch should contain higher concentrations of yolk androgens that those laid by females lacking that ornament.
Location: La Hiruela, central Spain.
Methods: We measured testosterone (T) and androstenedione (A4) levels in 10 pied flycatcher broods, after an ether extraction, following a radioimmunoassay method.
Results and Conclusions: We found that yolk T and A4concentrations increased with laying order. However, the increase in A4 with laying order was steeper for females without a forehead patch than for those expressing it. Also, and contrary to expectations, we found a marginally significant trend for females with white foreheads to have lower yolk-T levels. We discuss these results with reference to the adaptive function of hatching asynchrony.
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