Data from: Costs of growing up as a subordinate sibling are passed to the next generation in blue-footed boobies

As stresses in early development may generate costs in adult life, sibling competition and conflict in infancy are expected to diminish the reproductive value of surviving low-status members of broods and litters. We analysed delayed costs to blue-footed booby fledglings, Sula nebouxii, of junior status in the brood, which involves aggressive subordination, food deprivation and elevated corticosterone, but little or no deficit in size at fledging. In ten cohorts observed for up to 16 years, juniors showed no deficit in breeding success at any age, independent of lifespan, including in a sample of sibling pairs. Among females, juniors actually outreproduced seniors across the 16-year span. However, offspring produced by juniors in the first 3 years of life were less likely to recruit into the breeding population than offspring of seniors. Since junior fledglings survive, recruit and compete as well as seniors (shown earlier), and breed as successfully as seniors across the lifespan, it appears the delayed cost of subordination is passed to offspring, and only to those few offspring produced in the first 3 years of life. These correlational results indicate that systematic competition-related differences in developmental conditions of infant siblings can alter their reproductive value by affecting the viability of their eventual offspring.

由于早期发育阶段的压力可能会在成年后带来适应性代价，因此幼年期的同胞竞争与冲突，预计会降低雏群与同窝幼崽中存活下来的低地位个体的繁殖价值。我们针对蓝脚鲣鸟（blue-footed booby, *Sula nebouxii*）雏鸟分析了其在窝群中处于幼次地位所带来的延迟性代价：这类地位会伴随攻击性从属行为、食物剥夺与皮质酮（corticosterone）水平升高，但出飞时的体型几乎无任何缺陷。在共计长达16年观测的10个研究队列中，无论寿命长短，幼次个体在各年龄段的繁殖成功率均无缺陷，这一结果在同胞配对样本中同样成立。在雌性个体中，16年观测周期内幼次个体的繁殖产出实际上优于年长个体。然而，幼次个体在出生前3年内所产的后代，相较于年长个体的后代，更难成功招募进入繁殖种群。鉴于此前研究已表明，幼次雏鸟的存活、繁殖招募与竞争能力均与年长个体无异，且终身繁殖成功率也与年长个体相当，因此从属地位带来的延迟代价似乎会传递给后代，且仅局限于其出生前3年内产下的少数后代。这些相关性研究结果表明，幼年期同胞间因竞争产生的系统性发育环境差异，可通过影响其最终后代的生存能力，改变自身的繁殖价值。