Long-term effect of yolk carotenoid levels on testis size in a precocial bird

Conditions experienced during prenatal development can have long-lasting organizational effects on offspring. Maternal carotenoids deposited in the eggs of birds and other oviparous species play an important role during fast embryonic growth and chick development through their antioxidant properties. However, the long-term consequences of variation in maternal carotenoid transfer for the offspring have seldom been considered. Since plasma carotenoid levels at adulthood are known to influence testis size and yolk carotenoid levels influence the ability to extract carotenoids later in life, we hypothesized that maternally transmitted carotenoids might influence gonad size at adulthood. Here, we showed that male Japanese quail (Coturnix japonica) originating from a carotenoid-enriched egg had smaller testes than control individuals at adulthood. This result shows that yolk carotenoids have long-term organizational effects. In addition, given that carotenoid intake at sexual maturity increases sperm quality and that a decreased testis size is associated with a lower sperm production, we propose that carotenoid exposure during embryo development might influence a trade-off between ejaculate size and sperm quality.

产前发育阶段经历的环境条件，可对子代产生持久的组织调控效应。母体沉积于鸟类及其他卵生动物（oviparous species）卵内的类胡萝卜素（carotenoids），凭借其抗氧化特性，在胚胎快速生长与雏鸟发育过程中发挥重要作用。然而，母体类胡萝卜素传递量差异对子代造成的长期影响，迄今鲜有研究被纳入考量。已知成年个体的血浆类胡萝卜素水平会影响睾丸大小，而卵黄类胡萝卜素水平则会影响生物体后期获取类胡萝卜素的能力，据此我们提出假说：母体传递的类胡萝卜素可能会影响成年个体的性腺大小。本研究证实，源自类胡萝卜素富集卵的雄性日本鹌鹑（Coturnix japonica），在成年后的睾丸体积显著小于对照组个体。这一结果表明，卵黄类胡萝卜素具备长期组织调控效应。此外，鉴于性成熟阶段摄入类胡萝卜素可提升精子质量，而睾丸体积减小往往伴随精子生成量降低，我们据此推测：胚胎发育阶段的类胡萝卜素暴露，可能会影响射精量与精子质量之间的权衡关系。