Data from: Sex allocation conflict between queens and workers in Formica pratensis wood ants predicts seasonal sex ratio variation

Sex allocation theory predicts parents should adjust their investment in male and female offspring in a way that increases parental fitness. This has been shown in several species and selective contexts. Yet, seasonal sex ratio variation within species and its underlying causes are poorly understood. Here we study sex allocation variation in the wood ant Formica pratensis. This species displays conflict over colony sex ratio as workers and queens prefer different investment in male and female offspring, owing to haplodiploidy and relatedness asymmetries. It is unique among Formica ants because it produces two separate sexual offspring cohorts per season. We predict sex ratios to be closer to queen optimum in the early cohort but more female-biased and closer to worker optimum in the later one. This is because the power of workers to manipulate colony sex ratio varies seasonally with the availability of diploid eggs. Consistently more female-biased sex ratios in the later offspring cohort over a three-year sampling period from 93 colonies clearly support our prediction. The resulting seasonal alternation of sex ratios between queen and worker optima is a novel demonstration how understanding constraints of sex ratio adjustment increases our ability to predict sex ratio variation.性分配理论（Sex allocation theory）预测，亲本应调整对雄性和雌性后代的投入，以提升亲本适合度。这一结论已在多个物种及选择情境中得到验证。然而，物种内的季节性性比变异及其潜在成因仍鲜少被深入阐明。本研究以草原木蚁（Formica pratensis）为对象，探究其性分配变异规律。由于单倍二倍性（haplodiploidy）与亲缘不对称性（relatedness asymmetries）的存在，该物种的工蚁与蚁后对雌雄后代的投入偏好存在差异，进而引发种群性比冲突。该蚁在蚁属（Formica）蚂蚁中独具一格，因其每个繁殖季会产生两批独立的有性后代批次。我们提出如下预测：早期批次的后代其性比更接近蚁后的最优策略，而后期批次的性比则更偏向雌性，且更贴合工蚁的最优策略。这一预测的依据是，工蚁调控种群性比的能力，会随二倍体卵的可获得性呈现季节性变化。通过对93个蚁群开展为期三年的采样调查，我们发现后期后代批次的性比始终更偏向雌性，这一结果明确支撑了我们的预测。最终实现的蚁后与工蚁最优策略间的季节性性比交替，为"理解性比调控的限制因素能够提升性比变异预测能力"这一论点提供了全新的实证支撑。