Ever since Darwin's discovery of natural selection, we expect traits to evolve to increase organisms' fitness. As a result, we can use optimization models to make a priori predictions of phenotypic variation, even when selection is frequency-dependent. A notable example is the prediction of female-biased sex ratios resulting from local mate competition (LMC) and inbreeding. LMC models incorporate the effects of LMC and inbreeding. Fig wasp sex ratio adjustments fit LMC predictions well. However, the appropriateness of LMC models to fig wasps has been questioned, and the role that a coincidental by-product plays in creating the apparent fit has been clearly illustrated. Here, we show that the sex ratio adjustments of a fig wasp are the result of a dual mechanism. It consists of a standard facultative LMC response favoured by natural selection, as well as a mechanism that may be the result of selection, but that could also be a coincidental by-product. If it is a by-product, the fitness increase is coincidental and natural selection's role was limited to fine-tuning it for higher fitness returns. We further document a case of an apparent fitness-reducing sex ratio adjustment. We conclude that the use of the adaptationist approach demands that our understanding of traits must be remodelled continually to rectify spurious assumptions.

中文翻译：

---

自然选择在无花果黄蜂物种中产生最佳性别比例调整的功效

自从达尔文发现自然选择以来，我们就期望通过进化来增加生物体的适应性。因此，我们可以使用优化模型对表型变异进行先验预测，即使选择是频率相关的。一个显着的例子是预测由本地配偶竞争 (LMC) 和近亲繁殖导致的偏向女性的性别比例。LMC 模型结合了 LMC 和近亲繁殖的影响。无花果黄蜂性别比例调整与 LMC 预测非常吻合。然而，LMC 模型对无花果黄蜂的适用性受到质疑，并且已经清楚地说明了巧合的副产品在产生明显的配合方面所起的作用。在这里，我们表明无花果黄蜂的性别比例调整是双重机制的结果。它包括受自然选择青睐的标准兼性 LMC 反应，以及可能是选择结果但也可能是巧合的副产品的机制。如果它是副产品，则适应度增加是巧合，自然选择的作用仅限于对其进行微调以获得更高的适应度回报。我们进一步记录了一个明显降低适应性的性别比例调整的案例。我们得出的结论是，适应主义方法的使用要求我们必须不断重塑对特征的理解，以纠正虚假假设。我们进一步记录了一个明显降低适应性的性别比例调整的案例。我们得出的结论是，适应主义方法的使用要求我们必须不断重塑对特征的理解，以纠正虚假假设。我们进一步记录了一个明显降低适应性的性别比例调整的案例。我们得出的结论是，适应主义方法的使用要求我们必须不断重塑对特征的理解，以纠正虚假假设。