Negotiation over investment in biparental birds

当父母双方都照顾相同的后代时，从进化的角度来看，如果父母双方都能以牺牲配偶为代价减少自己的努力，那么父母双方的表现就会更好。因此，在双亲照顾的物种中，在每个父母应该努力喂养他们的幼崽的问题上存在性别冲突。理论研究假设父母通过谈判(在进化或行为时间尺度上)来确定每个父母的努力，这样的模型得出结论，只有当父母双方都不完全补偿其伴侣的任何努力变化时，稳定的双亲照顾才能实现(即，如果父母一方减少努力，伴侣应该增加自己的努力，但不足以弥补不足)。在大多数鸟类中，父母双方都照顾自己的幼鸟，因此，鸟类被证明是关于双亲照料的性别冲突理论的肥沃试验场。许多研究已经在实验中减少了对父母一方的照顾，并监测了其伴侣的行为反应，预测了不完全补偿。然而，这些研究的结果是模棱两可的。在某些情况下，伴侣进行了不完全的补偿，但在许多其他情况下，研究人员发现要么没有反应，要么完全补偿，甚至是匹配的反应(即与被操纵的父母方向相同的变化)。为什么实证研究为这一强大的理论体系提供了如此支离破碎的支持？最近的一个模型为这个问题提供了一个潜在的答案。以前的谈判模型假设父母可以评估子女的需要或价值；例如，父母一方的努力增加会导致一窝雏鸟乞讨减少，从而向伴侣发出更低要求的信号。然而，如果父母不能直接评估子女的需要，他们可能会注意到子女需要的其他潜在信号，例如他们伴侣的工作效率。父母对子女的需求或价值存在不确定性这一观点最近在“信息模型”中得到了形式化。该模型预测，伴侣可能表现出广泛的适应性反应，从补偿(当有关于筑巢需求的准确信息时)到匹配反应(当有部分信息可用时)，在某个中间信息水平上没有净反应。个体父母评估雏鸟需求的能力可能因物种不同而不同，在整个养育期内也可能不同，或者在不同的父母之间也不同。本研究的目的是使用长尾山雀作为模型系统来检验信息模型的预测能力。当一只幼鸟独自在巢中时，它会通过广播乞讨电话来增加一只幼鸟的关爱力度，并监测其伴侣的反应。在双亲都能评估幼鸟需要的情况下，当双亲都有部分信息时，以及当信息不对称时，即一个父母有好的信息，另一个父母信息差的情况下，该模型的预测将通过进行实验来检验。来自后代和伴侣的信息整合过程也将进行实验研究。“这将是对这一假说的首次经验性检验，这一假说扩大了我们对进化论的一个重要组成部分的理解，即关于父母投资的性冲突。”这一发现将引起研究进化生物学、动物行为和生态学的研究人员的普遍兴趣。

When both parents provide care for the same offspring, each parent does better, in evolutionary terms, if it can reduce its own effort at the expense of its partner. Thus, in species with biparental care there is sexual conflict over how hard each parent should work at feeding their young. Theoretical studies assume that parents negotiate (over evolutionary or behavioural time scales) to determine each parent's effort, and such models conclude that stable biparental care is achieved only when each parent compensates incompletely for any change in effort by their partner (i.e. if one parent reduces its effort, the partner should increase its own effort but not sufficiently to make up the shortfall). In most bird species both parents care for their chicks and birds have therefore proved to be a fertile testing ground for theories of sexual conflict over biparental care. Many studies have experimentally reduced the care of one parent and monitored the behavioural response of its partner, predicting incomplete compensation. However, the results of such studies are equivocal. In some cases, the partner has compensated incompletely, but in many others researchers have found either no response, complete compensation, or even a matching response (i.e. a change in the same direction as the manipulated parent). Why have empirical studies provided such a patchy support for this robust body of theory? A recent model provides a potential answer to this question. Previous negotiation models have assumed that parents can assess the need or value of the offspring being fed; for example, an increase in the effort of one parent will result in a brood of nestlings begging less and hence signaling lower demand to the partner. However, if parents are not able to directly assess the need of their brood, they may pay attention to other potential signals of offspring need, such as the work rate of their partner. This idea that there is parental uncertainty over offspring need or value has recently been formalized in the 'information model'. This model predicts that a partner may exhibit a wide range of adaptive responses from compensation (when accurate information on nestling need is available) through to a matching response (when partial information is available) via no net response at some intermediate level of information. The ability of individual parents to assess nestling need may vary between species, within species through the rearing period, or between parents. The aim of this study is to use the long-tailed tit as a model system to test predictions of the information model. The caring effort of one parent will be increased by broadcasting begging calls to just that parent when it is alone at the nest during the nestling period and the response of its partner will be monitored. The predictions of the model will be tested by conducting this experiment in situations where both parents can assess nestling need, when both parents have partial information and when information is asymmetric, i.e. one parent has good information and the other poor information. The process of integration of information from offspring and from a partner will also be investigated experimentally. `This will be the first empirical test of a hypothesis that extends our understanding of an important component of evolutionary theory, i.e. sexual conflict over parental investment. The findings will be of general interest to researchers studying evolutionary biology, animal behaviour and ecology.