Variability of yolk testosterone concentrations during the reproductive cycle of Japanese quail.

Deposition of yolk androgens can vary among females as well as within eggs of one female. Numerous external and internal factors can contribute to this variability. In our study, we investigated the systemic variation of yolk testosterone concentrations during the laying cycle of Japanese quail reared in stable environmental and social conditions. Testosterone was analysed in three eggs collected per female at the beginning, top and the end of a reproductive period and the extent of inter- and intra-female differences in yolk deposition of this androgen was quantified. Yolk testosterone concentrations and the yolk testosterone content decreased from the early to the latest stage of reproductive period. Testosterone concentrations in the egg yolk as well as the age-dependent pattern significantly differed among individual females. We found high repeatability of yolk testosterone among 3 eggs of individual females together with high repeatability between 3 stages of the reproductive cycle. Testosterone in the egg yolk correlated positively with eggshell weight. Our results suggest that precocial birds with long laying sequences display higher inter-female differences in yolk testosterone concentrations compared with intra-individual variability. The decreased testosterone deposition with age may influence the development and behaviour of the young hatched at different stages of the female's reproductive cycle.