Data from: Optimists or realists? How ants allocate resources in making reproductive investments.

1. Parents often face an investment trade-off between either producing many small or fewer large offspring. When environments vary predictably, the fittest parental solution matches available resources by varying only number of offspring and never optimal individual size. However when mismatches occur often between parental expectations and true resource levels, dynamic models like multifaceted parental investment (MFPI) and parental optimism (PO) both predict offspring size can vary significantly. MFPI is a “realist” strategy: parents assume future environments of average richness. When resources exceed expectations and it is too late to add more offspring, the best-case solution increases investment per individual. Brood size distributions therefore track the degree of mismatch from right-skewed around an optimal size (slight underestimation of resources), to left-skewed around a maximal size (gross underestimation). Conversely, PO is an “optimist” strategy: parents assume maximally good resource futures and match numbers to that situation. Normal or lean years do not affect “core” brood as costs primarily fall on excess “marginal” siblings who die or experience stunted growth (producing left-skewed distributions). 2. Investment patterns supportive of both MFPI and PO models have been observed in nature, but studies that directly manipulate food resources in order to test predictions are lacking. Ant colonies produce many offspring per reproductive cycle, and are amenable to experimental manipulation in ways that can differentiate between MFPI and PO investment strategies. 3. Colonies in a natural population of a harvester ant (Pogonomymex salinus) were protein-supplemented over two years and mature sexual offspring were collected annually prior to their nuptial flight. 4. Several results support either MFPI or PO in terms of patterns in offspring size distributions and how protein differentially affected male and female production. Unpredicted by either model, however, is that supplementation affected distributions more strongly across years than within (e.g., small females are significantly rarer in the year after colonies receive protein). 5. Parental investment strategies in P. salinus vary dynamically across years and conditions. Finding that past conditions can more strongly affect reproductive decisions than current ones, however, is not addressed by models of parental investment.

1. 亲本通常面临一项投资权衡：要么产生大量小型后代，要么产生少量大型后代。当环境可预测变化时，最优的亲本策略仅通过改变后代数量来匹配可用资源，而不会调整最优个体大小。然而当亲本预期与实际资源水平频繁出现错配时，多维度亲本投资（multifaceted parental investment, MFPI）和亲本乐观主义（parental optimism, PO）这类动态模型均预测后代大小会出现显著变化。MFPI属于“现实主义”策略：亲本假设未来环境的资源丰度处于平均水平。当资源超出预期且已来不及增加后代数量时，最优应对方案会提升对单个后代的投资。因此，窝后代的大小分布会反映错配程度：从围绕最优大小的右偏分布（对应资源轻度低估），到围绕最大大小的左偏分布（对应资源严重低估）。与之相反，PO属于“乐观主义”策略：亲本假设未来资源条件处于最优水平，并据此匹配后代数量。正常或贫瘠年份不会影响“核心”窝后代，因为成本主要由过剩的“边缘”同胞承担——这些同胞会死亡或生长受阻，最终形成左偏分布。2. 自然界中已观测到支持MFPI和PO模型的投资模式，但目前仍缺乏通过直接调控食物资源来验证相关预测的研究。蚁群在每个繁殖周期会产生大量后代，且可通过实验操作区分其采用的MFPI或PO投资策略。3. 某自然种群的收获蚁（Pogonomymex salinus）的蚁群在两年期间接受了蛋白质补充处理，并在其婚飞前每年收集成熟的有性后代。4. 就后代大小分布模式以及蛋白质对雌雄后代生产的差异化影响而言，多项结果支持MFPI或PO模型。然而，有一项发现是两个模型均未预测到的：蛋白质补充对分布的影响在年份间强于同一蚁群内部（例如，在蚁群接受蛋白质补充后的次年，小型雌性个体的占比显著更低）。5. P. salinus的亲本投资策略会随年份和环境条件动态变化。但现有亲本投资模型并未涉及“过往环境条件对繁殖决策的影响强于当前环境条件”这一发现。