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，双亲应调整对雄性与雌性后代的投入，以提升自身的亲本适合度（parental fitness）。该理论已在多个物种与选择情境中得到验证。然而，同一物种内的季节性性比变异及其潜在成因仍鲜为人知。本研究以红褐林蚁（Formica pratensis）为对象，探究其性分配变异规律。由于单倍二倍体（haplodiploidy）遗传与亲缘不对称性（relatedness asymmetries），工蚁与蚁后对雌雄后代的投入偏好存在差异，该物种因此存在社群性比冲突。在蚁属（Formica）蚂蚁中，该物种尤为特殊：其每季可产生两批独立的有性后代群。我们预测，早期批次的性比更趋近于蚁后最优值，而后期批次的性比则更偏向雌性，且更接近工蚁最优值。这是因为工蚁调控社群性比的能力，会随二倍体卵（diploid eggs）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，我们发现后期后代批次的性比始终更偏向雌性，这一结果明确支持了我们的预测。这一在蚁后与工蚁最优性比间交替的季节性性比格局，首次证实了理解性比调控的约束机制，可有效提升我们预测性比变异的能力。