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Abstract:
Avian eggs contain variable levels of several maternal androgens that may all be important in adjusting offspring phenotype at the individual or brood level. Most studies have focused on experimental manipulations of testosterone (T), and the other yolk androgens such as androstenedione (A(4)) and 5-alpha-dihydrotestosterone (DHT) were so far neglected. However, in species where the amount of A(4) in the yolk much exceeds that of the other androgens, A(4) could represent the dominant agent of androgen-mediated maternal effects, in which case manipulations of T would be misdirected. We conducted our study in a species with high yolk A(4) and relatively low T and DHT levels, the Japanese quail Coturnix japonica. We injected unincubated eggs with a physiological dose of either A(4), T, or DHT, and measured hatchling growth, as well as behaviour in an open field test. T treatment non-significantly increased social reinstatement behaviour in the open field test, but it seemed to significantly suppress early skeletal growth and mass gain. The A(4) and DHT treatments, in contrast, significantly increased reinstatement behaviour, but did not affect mass and size growth. These results suggest that future investigations should view yolk androgens as integrated components of the complex yolk steroid environment.
