Data from: Offspring size and reproductive allocation in harvester ants

A fundamental decision that an organism must make is how to allocate resources to offspring, both with respect to size and to number. The two major theoretical approaches to this problem, optimal offspring size and optimistic brood size models, make different predictions that may be reconciled by including how offspring fitness is related to size. We extended the reasoning of Trivers and Willard (1973) to derive a general model of how parents should allocate additional resources with respect to the number of males and females produced, and among individuals of each sex, based on the fitness payoffs of each. We then predicted how harvester ant colonies should invest additional resources, and tested three hypotheses derived from our model, using data from three years of food supplementation bracketed by six years without food addition. All major results were predicted by our model: Food supplementation increased the number of reproductives produced. Male, but not female,
size increased with food addition; the greatest increases in male size occurred in colonies that made small females. We discuss how use of a fitness landscape improves quantitative predictions about allocation decisions. When parents can invest differentially in offspring of different types, the best strategy will depend on parental state as well as the effect of investment on offspring fitness.

生物体必须作出的一项基础性决策，是如何在后代的体型与数量两个维度上分配自身资源。针对该问题的两大主流理论范式——最优后代体型模型与乐观窝群规模模型——作出了迥异的预测，若纳入后代适合度（offspring fitness）与体型的关联机制，则可实现二者的理论调和。我们拓展了特里弗斯（Trivers）与威拉德（Willard）1973年的推理框架，基于不同性别个体的适合度收益（fitness payoffs），推导出一套普适性模型，用以阐明亲本应如何根据产出的雌雄个体数量，以及每一性别内的个体情况，分配额外资源。随后我们预测了收获蚁（harvester ant）群落应如何分配额外资源，并利用为期三年的食物补充实验数据（该实验周期被六年无食物添加的对照时段所环绕），检验了基于本模型提出的三项假说。本模型成功预测了全部核心实验结果：食物补充提升了繁殖型个体的产出总量；雄性后代的体型随食物补充量增加而增大，雌性后代则无显著变化；雄性体型增幅最为显著的群落，正是培育小型雌性后代的群落。我们还探讨了运用适合度景观（fitness landscape）可如何提升资源分配决策的定量预测精度。当亲本能够对不同类型的后代实施差异化投入时，最优策略将同时取决于亲本自身的生理状态，以及资源投入对后代适合度的影响效应。