In many animal species, embryos are exposed to maternal hormones that affect their development. Maternal hormone transfer varies with environmental conditions of the mother and is often interpreted as being shaped by natural selection to adjust the offspring to prevailing environmental conditions. Such hormone transfer requires genetic variability, which has not yet been experimentally demonstrated. Our study reports direct evidence for additive genetic variance of maternal androgens through a bidirectional selection on yolk testosterone (T) levels in Japanese quail. Lines selected for high egg T (HET) and low egg T (LET) concentration differed in yolk levels of this androgen, resulting in high realized heritability (h² = 0.42)Correlated responses to selection on other gonadal hormones indicated that selection specifically targeted biologically active androgens. Eggs of HET quail contained higher androstenedione and lower estradiol concentrations than did those of LET quail, with no line differences in yolk progesterone concentration. Plasma T concentrations in adult females were not affected by selection, seriously challenging the hypothesis that transfer of maternal hormones to offspring is constrained by hormone levels in a mother's circulation. Our results suggest that transfer of maternal T represents an indirect genetic effect that has important consequences for the evolution of traits in offspring.
Okuliarová M., P. Škrobánek, M. Zeman: Effect of Increasing Yolk Testosterone Levels on Early Behaviour in Japanese Quail Hatchlings. Acta Vet. Brno 2007, 76: 325-331.The aim of our study was to investigate effects of increased testosterone content in egg yolk on early behaviour of 1-and 2-day-old Japanese quail. Three different doses of testosterone (0.25; 2.5 and 25 ng), not exceeding a physiological range, were examined in three separate experiments. Testosterone propionate dissolved in 20 ml olive oil was injected into the yolk before the onset of incubation.Behaviour of newly hatched chicks was recorded in response to both a novel environment in the open-fi eld test and manual restraining in the test of tonic immobility (TI). Behavioural consequences of embryonic exposure to elevated testosterone were observed in the open-fi eld test in all three experiments which indicated inhibition of behavioural responses in hatchlings. Birds treated with testosterone in ovo displayed longer latency to leave the start square, decreased locomotor activity, enhanced defecation and lower number of distress calls as compared to control birds. In TI test, the infl uence of treatment was manifested at the highest concentration only. Hatchlings from testosterone treated eggs expressed longer duration of TI and required less attempts to induce TI in comparison with the control group.Our results demonstrated increased fearfulness of Japanese quail chicks hatched from eggs with experimentally elevated testosterone content. The effect is specifi c for a short period after hatching since previous studies reported stimulatory effect of yolk testosterone on behaviour of Japanese quail later in ontogeny.
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