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.

鉴于早期发育阶段的应激可在成年后引发适应性代价，学界推测婴儿期的同胞竞争与冲突会降低窝雏与幼崽中存活低地位个体的繁殖价值（reproductive value）。我们针对蓝脚鲣鸟（Sula nebouxii）的离巢幼鸟，分析了其所在窝群中次级个体所面临的发育滞后代价：这类个体往往会遭受攻击性从属地位、食物匮乏以及皮质酮（corticosterone）水平升高的影响，但在离巢时的体型却几乎无明显缺陷。在为期最长16年的10个观测队列中，无论寿命长短，次级个体在各年龄段的繁殖成功率均未出现显著不足，该结论在同胞配对样本中同样成立。在雌性个体中，16年观测周期内次级个体的繁殖产出实际高于优势个体。但次级个体在生命最初3年内所产的后代，相较于优势个体的后代，成功招募进入繁殖种群的概率更低。此前已有研究证实，次级离巢幼鸟的存活、种群招募与竞争能力均与优势个体无异，且其终身繁殖成功率也与优势个体相当；由此可见，从属地位带来的滞后代价似乎会传递给后代，且仅局限于生命最初3年内产下的少量后代。这些相关性研究结果表明，幼崽同胞间因系统性竞争产生的发育环境差异，可通过影响其最终后代的存活能力，改变自身的繁殖价值。