Data from: Should mothers provision their offspring equally? A manipulative field test

Within-brood variation in offspring size is universal, but its causes are unclear. Theoretical explanations for within-brood variation commonly invoke bet-hedging, although alternatives consider the role of sibling competition. Despite abundant theory, empirical manipulations of within-brood variation in offspring size are rare. Using a field experiment, we investigate the consequences of unequal maternal provisioning for both maternal and offspring fitness in a marine invertebrate. We create experimental broods of siblings with identical mean, but different variance, in offspring size, and different sibling densities. Overall, more-variable broods had higher mean performance than less-variable broods, suggesting benefits of unequal provisioning that arise independently of bet-hedging. Complementarity effects drove these benefits, apparently because offspring-size variation promotes resource partitioning. We suggest that when siblings compete for the same resources, and offspring size affects niche usage, the production of more-variable broods can provide greater fitness returns given the same maternal investment; a process unanticipated by the current theory.子代体型的窝内变异普遍存在，但其成因尚未明晰。针对窝内变异的理论解释通常以波动避险（bet-hedging）假说为核心，不过也有部分理论关注同胞竞争的作用。尽管相关理论研究已较为丰富，但针对子代体型窝内变异的实验操控类研究仍较为稀缺。本研究依托野外实验，以一种海洋无脊椎动物为研究对象，探究了母体资源分配不均对母体及子代进化适合度（fitness）的影响。我们构建了同胞子代的实验窝群：各组窝群的子代体型均值保持一致，但子代体型的方差存在差异，同时同胞密度也各不相同。整体结果显示，体型变异程度更高的窝群，其平均表现优于变异程度更低的窝群，这表明资源分配不均可带来优势，且该优势并非由波动避险（bet-hedging）策略所介导。上述优势由互补效应驱动，其背后机制似乎是子代体型变异能够促进资源分区利用。我们据此提出：当同胞间竞争共享资源、且子代体型影响生态位利用时，在母体投入总量相同的前提下，产生体型变异程度更高的窝群可获得更高的进化适合度收益——这一过程是现有进化理论未曾预见的。