Müller Wendt, Vergauwen Jonas, Eens Marcel
Department of Biology-Ethology, University of Antwerp, Antwerp, Wilrijk, Belgium.
Horm Behav. 2008 Jun;54(1):125-33. doi: 10.1016/j.yhbeh.2008.02.005. Epub 2008 Mar 10.
Avian eggs contain substantial amounts of maternal yolk androgens, which have been shown to modulate offspring phenotype. The first studies on the functional consequences of maternal yolk androgens have focused on early life stages and their role in sibling competition. However, recent longitudinal studies reported long-lasting effects of maternal yolk androgens on offspring phenotype, mostly concerning traits that are sensitive to androgens. This suggests that maternal yolk androgens could play an important role in sexual selection, since the expression of many male sexual characters is testosterone-dependent. Using male canaries as a model, we examined the consequences of an experimental elevation of yolk testosterone concentrations on early development as well as long-lasting effects particularly on song, which is one of the most important sexual characters in male songbirds. Elevated yolk testosterone concentrations inhibited male growth, possibly in interaction with an existent ectoparasite exposure. Males hatched from testosterone-treated eggs (T-males) did not have enhanced competitive skills, in contrast to previous studies. The elevation of yolk testosterone concentrations delayed song development but did not affect adult song phenotype. This is intriguing, as yolk testosterone possibly induced developmental stress, which is known to reduce song quality. We hypothesize that yolk testosterone has either no direct effect on adult song phenotype, or that positive effects are merged by the negative effects of developmental stress. Finally, females mated with T-males invested more in their clutch indicating that females either assess T-males as more attractive (differential allocation hypothesis) or compensated for lower offspring viability (compensation hypothesis).
鸟类的卵含有大量母体来源的卵黄雄激素，研究表明这些雄激素能够调节后代的表型。最初关于母体卵黄雄激素功能影响的研究主要集中在生命早期阶段及其在同胞竞争中的作用。然而，最近的纵向研究报告了母体卵黄雄激素对后代表型具有持久影响，主要涉及对雄激素敏感的性状。这表明母体卵黄雄激素可能在性选择中发挥重要作用，因为许多雄性性征的表达都依赖于睾酮。我们以雄性金丝雀为模型，研究了实验性提高卵黄睾酮浓度对早期发育的影响以及对长期影响，特别是对鸣叫的影响，鸣叫是雄性鸣禽最重要的性征之一。卵黄睾酮浓度升高抑制了雄性的生长，这可能与现存的体外寄生虫感染相互作用有关。与之前的研究相反，从经睾酮处理的卵孵化出的雄性（T - 雄性）并没有增强的竞争技能。卵黄睾酮浓度的升高延迟了鸣叫发育，但并未影响成年后的鸣叫表型。这很有趣，因为卵黄睾酮可能诱发了发育应激，而发育应激已知会降低鸣叫质量。我们推测，卵黄睾酮要么对成年后的鸣叫表型没有直接影响，要么其积极影响被发育应激的负面影响所抵消。最后，与T - 雄性交配的雌性在其窝卵数上投入更多，这表明雌性要么认为T - 雄性更具吸引力（差异分配假说），要么是为了补偿较低的后代生存能力（补偿假说）。
