Data from: Why does offspring size affect performance? Integrating metabolic scaling with life-history theory

Within species, larger offspring typically outperform smaller offspring. While the relationship between offspring size and performance is ubiquitous, the cause of this relationship remains elusive. By linking metabolic and life-history theory, we provide a general explanation for why larger offspring perform better than smaller offspring. Using high-throughput respirometry arrays, we link metabolic rate to offspring size in two species of marine bryozoan. We found that metabolism scales allometrically with offspring size in both species: while larger offspring utilise absolutely more energy than smaller offspring, larger offspring use proportionally less of their maternally-derived energy throughout the dependent, non-feeding phase. The increased metabolic efficiency of larger offspring while dependent on maternal investment may explain offspring size effects –larger offspring reach nutritional independence (feed for themselves) with a higher proportion of energy relative to structure than smaller offspring. These findings offer a potentially universal explanation for why larger offspring tend to perform better than smaller offspring but studies on other taxa are needed.

在同一物种内，体型更大的后代通常表现优于体型更小的后代。尽管后代体型与表现之间的关联普遍存在，但该关联背后的成因仍难以厘清。本研究将代谢理论（metabolic theory）与生活史理论（life-history theory）相结合，为体型更大的后代为何表现更优提供了一般性解释。我们借助高通量呼吸测定阵列（high-throughput respirometry arrays），在两种海洋苔藓虫（marine bryozoan）中建立了代谢速率与后代体型之间的关联。研究发现，两种苔藓虫的代谢均随后代体型呈现异速生长缩放：尽管体型更大的后代绝对能耗高于体型更小的后代，但在依赖母体的非摄食阶段，体型更大的后代消耗的母体供给能量占比更低。体型更大的后代在依赖母体供给期间代谢效率的提升，或可解释后代体型效应——相较于体型更小的后代，体型更大的后代在达到营养独立（自行摄食）时，其体内能量相较于躯体结构的占比更高。本研究结果为“体型更大的后代通常表现更优”这一现象提供了潜在的普适性解释，但仍需针对其他动物类群开展相关研究予以验证。