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（包括配偶选择投入）的生理机制之一。本研究以褐鲣鸟（Sula leucogaster）——一种具有长期双亲育幼行为的长寿命海鸟——为研究对象，探讨氧化应激是否通过作为繁殖的代价或约束因素，来影响其繁殖决策。研究发现，在求偶期，雌雄个体的脂质过氧化（lipid peroxidation, LP）水平与喉囊皮肤颜色呈正相关，而该性状被认为在配偶选择中发挥作用；同时，随着产卵临近以及早期繁殖配对的个体，其活性氧（reactive oxygen species, ROS）水平更高。雌性氧化应激的约束效应可由以下现象佐证：求偶期活性氧水平更高的雌性，其所产首枚卵更小，雏鸟的体质量增长速率更低；而雌性较高的脂质过氧化水平则与更低的后代抚育时长相关。未发现亲本繁殖投入存在氧化代价的相关证据：从求偶期到育幼期，雌雄个体的活性氧水平均有所下降，而脂质过氧化水平的变化无统计学显著性。最后，通过交叉抚育实验（cross-fostering experiment），我们发现后代的活性氧水平与抚育亲本及遗传亲本的活性氧水平均无关联。值得注意的是，后代的脂质过氧化水平与抚育亲本以及遗传父亲在求偶期的脂质过氧化水平均呈正相关，这表明后代的脂质过氧化水平可能同时受遗传和环境因素的影响。因此，在褐鲣鸟中，氧化应激可能是产卵前繁殖性状投入的代价，并约束雌性在产卵及双亲育幼方面的投入。