Rands Sean A, Cuthill Innes C, Houston Alasdair I
Centre for Behavioural Biology, School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.
Theor Biol Med Model. 2006 May 16;3:20. doi: 10.1186/1742-4682-3-20.
Studies of birds have a disproportionate representation in the literature on life-history evolution, because of the (apparent) ease with which the costs and benefits can be quantified and manipulated. During reproduction, birds frequently show a highly conserved pattern of mass change and changes in mass loss during breeding have been widely considered to be a valid short-term measure of the costs of reproduction. Experimental manipulations of the breeding attempts of birds usually argue that the presence of a response shows that a cost of reproduction exists, but there is little consensus as to how the size of these costs can be measured.
We model this mass loss by considering how a parent can maximise its lifetime reproductive success, using a theoretical framework that is particularly suited to modelling parental care in altricial birds. If lifetime reproductive success is taken to be the sum of a parent's current and future reproductive success, we show that the exact forms of these components will influence the optimal amount of mass a parent should lose. In particular, we demonstrate that the shape of the relationship between parental investment and chick survival will lead to differing degrees of investment between parents of different initial qualities: parents with initially high levels of energy reserves could conceivably invested a lesser, similar or greater amount of resources than parents with initially low reserves, and these initially 'heavy' parents could potentially end up being lighter than the initially 'lighter' individuals.
We argue that it is difficult to make predictions about the dependence of a parent's final mass on its initial mass, and therefore mass loss should only be used as a short-term measure of the costs of reproduction with caution. The model demonstrates that we require a better understanding of the relationship between mass loss and both current and future reproductive success of the parent, before predictions about mass loss can be made and tested. We discuss steps that could be taken to increase the accuracy of our predictions.
在关于生活史进化的文献中，鸟类研究的占比过高，这是因为（表面上）鸟类繁殖的成本和收益易于量化和操控。在繁殖过程中，鸟类常常呈现出高度保守的体重变化模式，且繁殖期间的体重减轻被广泛视为繁殖成本的有效短期衡量指标。对鸟类繁殖尝试的实验操控通常认为，出现某种反应就表明存在繁殖成本，但对于如何衡量这些成本的大小，几乎没有达成共识。
我们通过考虑亲代如何最大化其终生繁殖成功率来对这种体重减轻进行建模，使用了一个特别适合模拟晚成雏鸟类亲代抚育行为的理论框架。如果将终生繁殖成功率视为亲代当前和未来繁殖成功率的总和，我们表明这些组成部分的具体形式将影响亲代应减轻的最佳体重。特别是，我们证明亲代投资与雏鸟存活之间关系的形状会导致不同初始质量的亲代之间投资程度不同：初始能量储备水平高的亲代可能比初始储备低的亲代投入更少、相似或更多的资源，而且这些初始“较重”的亲代最终可能比初始“较轻”的个体更轻。
我们认为很难预测亲代最终体重对其初始体重的依赖性，因此体重减轻仅应谨慎用作繁殖成本的短期衡量指标。该模型表明，在能够做出并检验关于体重减轻的预测之前，我们需要更好地理解体重减轻与亲代当前和未来繁殖成功率之间的关系。我们讨论了可以采取哪些步骤来提高预测的准确性。
