Data from: Oxidative stress during courtship affects male and female reproductive effort differentially in a wild bird with biparental care

Oxidative stress has been suggested as one of the physiological mechanisms modulating reproductive effort, including investment in mate choice. Here, we evaluated whether oxidative stress influences breeding decisions by acting as a cost of or constraint on reproduction in the brown booby (Sula leucogaster), a long-lived seabird with prolonged biparental care. We found that during courtship, levels of lipid peroxidation (LP) of males and females were positively associated with gular skin color, a trait presumably used in mate choice, while levels of reactive oxygen species (ROS) were higher as laying approached and in early breeding pairs. Evidence of a constraining effect of oxidative stress for females was suggested by the fact that females with higher ROS during courtship laid smaller first eggs and had chicks with lower rates of body mass gain, and higher female LP was associated with lower offspring attendance time. No evidence of an oxidative cost of parental effort was found; from courtship to parental care male and female' ROS decreased, and changes in LP levels were non-significant. Finally, using a cross-fostering experiment we found that offspring ROS was unrelated to rearing and genetic parents' ROS. Interestingly, offspring LP was positively associated with the LP during courtship of both the rearing parents and the genetic father, suggesting that offspring LP might have both a genetic and an environmental component. Hence, in the brown booby oxidative stress may be a cost of investment in reproductive traits before egg laying and constrain females' investment in eggs and parental care.

氧化应激（oxidative stress）被认为是调控繁殖投入的生理机制之一，其中涵盖择偶投入。本研究以褐鲣鸟（Sula leucogaster）——一种具备长期双亲抚育行为的长寿海鸟——为研究对象，旨在探究氧化应激是否通过充当繁殖的代价或约束因子，影响其繁殖决策。

研究结果显示，在求偶阶段，雌雄个体的脂质过氧化（lipid peroxidation, LP）水平与喉囊皮肤颜色呈显著正相关，而该性状被推测在择偶过程中发挥作用；与此同时，活性氧（reactive oxygen species, ROS）水平随着产卵日期临近以及早期繁殖配对个体的出现而升高。

关于雌性氧化应激的约束效应，相关证据体现为：求偶期ROS水平更高的雌性，其产下的首枚卵卵重更小，且雏鸟的体质量增长速率更低；而雌性LP水平较高则与后代抚育时长缩短存在关联。本研究未发现亲本繁殖投入存在氧化代价的相关证据：从求偶期至育雏阶段，雌雄个体的ROS水平均有所下降，且LP水平的变化无统计学显著性。

最后，通过交叉抚育实验，我们发现后代的ROS水平与抚育亲本及遗传亲本的ROS水平均无关联。值得关注的是，后代的LP水平与抚育双亲以及遗传父亲在求偶期的LP水平均呈正相关，这表明后代的LP可能同时兼具遗传与环境组分。

综上，在褐鲣鸟中，氧化应激可能是产卵前繁殖性状投入的代价，并会限制雌性在产卵以及亲本抚育方面的投入。