Data from: Trade-off between carotenoid-based sexual ornamentation and sperm resistance to oxidative challenge

It has been hypothesized that carotenoid-based sexual ornamentation signals male fertility and sperm competitive ability as both ornamentation and sperm traits may be co-affected by oxidative stress, resulting in positive covariation (the 'redox-based phenotype-linked fertility hypothesis'; redox-based PLFH). On the other hand, the 'sperm competition theory' (SCT) predicts a trade-off between precopulatory and postcopulatory traits. Here, we manipulate oxidative status (using diquat dibromide) and carotenoid availability in adult zebra finch (Taeniopygia guttata) males in order to test whether carotenoid-based beak ornamentation signals, or is traded off against, sperm resistance to oxidative challenge. Initial beak colouration, but not its change during the experiment, was associated with effect of oxidative challenge on sperm velocity, such that more intense colouration predicted an increase in sperm velocity under control conditions but a decline under oxidative challenge. This suggests a long-term trade-off between ornament expression and sperm resistance to oxidative challenge. Shortening of the sperm midpiece following oxidative challenge further suggests that redox homeostasis may constrain sperm morphometry. Carotenoid supplementation resulted in fewer sperm abnormalities but had no effect on other sperm traits. Overall, our data challenge the redox-based PLFH, partially support the SCT and highlight the importance of carotenoids for normal sperm morphology.有假说提出，基于类胡萝卜素（carotenoid）的性饰特征可传递雄性生育力与精子竞争能力——由于性饰特征与精子性状均可能受氧化应激（oxidative stress）共同影响，进而产生正协变关系，该假说即“基于氧化还原的表型关联生育力假说（redox-based PLFH）”。另一方面，“精子竞争理论（SCT）”则预测交配前与交配后性状间存在权衡关系。本研究通过敌草快二溴盐（diquat dibromide）操控成年雄性斑胸草雀（Taeniopygia guttata）的氧化状态，并调控其类胡萝卜素可获得性，以此检验基于类胡萝卜素的喙部饰色是否可传递精子抗氧化应激能力，抑或二者间存在权衡。初始喙部颜色（而非实验期间的颜色变化）与氧化应激对精子速度的影响相关联：在对照组条件下，喙部颜色越浓郁，精子速度越高；而在氧化应激条件下，精子速度则随喙部颜色加深而降低。这一结果提示，饰特征表达与精子抗氧化应激能力间存在长期权衡。氧化应激后精子中段缩短的现象进一步表明，氧化还原稳态（redox homeostasis）可能会限制精子形态计量学（sperm morphometry）特征。类胡萝卜素补充可减少精子畸形，但对其他精子性状无显著影响。综上，本研究数据对基于氧化还原的PLFH提出了挑战，部分支持了SCT，并凸显了类胡萝卜素对正常精子形态的重要性。