Data from: Evolution of displays within the pair bond

Although sexual selection is an important cause of display evolution, in socially monogamous species (e.g. many birds), displays continue after formation of the pair bond. Here, we consider that these displays evolve because they stimulate the partner to increase investment in offspring. Our study is motivated by elaborate mutual displays in species that are largely monomorphic and have long-term pair bonds (e.g. the great crested grebe, Podiceps cristatus) and by many empirical results evidencing that display manipulation affects parental investment. Using population genetic models, we show that a necessary condition for the permanent establishment of mutual displays in the pair bond is that the benefit of investment by the pair is more than twice that resulting from investment by a single individual. Pre-existing biases to respond to displays by increased investment are a necessary component of display evolution. We also consider examples where one sex (e.g. males) stimulates increased investment in offspring by the other sex. Here, display and additional investment cannot evolve permanently, but can increase and linger at high frequency for a long time before loss. We discuss how such transient effects may lead to the evolution of permanent displays as a result of evolution at additional loci.尽管性选择（sexual selection）是驱动展示行为演化的重要动因，但在社会一夫一妻制物种（如多数鸟类）中，配偶联结形成后，展示行为仍会持续上演。本研究的动机源于两类观察：其一为诸多形态单型且具有长期配偶联结的物种（如凤头䴙䴘，Podiceps cristatus）所展现的精巧相互展示行为；其二为大量实证研究证实，对展示行为的干预会显著影响亲本投资（parental investment）水平。我们借助种群遗传模型开展研究，结果显示：配偶联结中相互展示行为得以永久确立的必要条件是，双亲共同抚育后代所带来的收益需超过单亲抚育收益的两倍。此外，个体因回应展示行为而提升抚育投资的预先存在的偏好，是展示行为演化的必要构成要素。我们还探讨了单一性别（例如雄性）促使另一性别增加后代抚育投资的场景。在此类情形下，展示行为与额外抚育投资无法实现永久演化，但可在较长时期内以较高频率维持并存续，直至最终消亡。我们进一步讨论了此类暂时性效应如何通过其他基因座的演化，最终促成永久性展示行为的出现。