Am Nat. 2019 May;193(5):725-737. doi: 10.1086/702848. Epub 2019 Mar 14.
The coevolution of parental supply and offspring demand has long been thought to involve offspring need driving begging and parental care, leaving other hypotheses underexplored. In a population of wild birds, we experimentally tested whether begging serves as a negatively condition-dependent signal of need or a positively condition-dependent signal of quality. Across multiple years, we supplemented nestling house wrens with food shortly after hatching and simultaneously manipulated corticosterone levels to simulate the hunger-induced increase in glucocorticoids thought to mediate begging. This allowed us to also test whether begging is simply a proximate signal of hunger. Days after supplementation ended, food-supplemented nestlings were in better condition than nonsupplemented nestlings and begged for food at an increased rate; their parents, in turn, increased provisioning to a greater extent than parents of nonsupplemented young, as begging positively predicted provisioning. Food-supplemented nestlings therefore attained above-average condition, which predicted their recruitment as breeding adults in the local population. Glucocorticoids increased begging in the short term, but this transient effect depended on satiety. Thus, glucocorticoids promoted begging as a proximate response to hunger, whereas the longer-term changes in nestling condition, begging, and food provisioning suggest that begging ultimately signals offspring quality to elicit increased investment, thereby enhancing offspring survival.
长期以来，人们一直认为亲代供给和后代需求的共同进化涉及后代需求驱动的乞求和亲代养育，而其他假说则未得到充分探索。在一个野生鸟类种群中，我们通过实验测试了乞求是作为需要的负条件依赖信号还是作为质量的正条件依赖信号。在多年的时间里，我们在孵化后不久就给雏鸟补充食物，并同时操纵皮质酮水平，以模拟饥饿诱导的、被认为介导乞食的糖皮质激素的增加。这使我们还可以测试乞食是否只是饥饿的一个近因信号。在补充结束后的几天里，与未补充的雏鸟相比，补充食物的雏鸟状况更好，乞食的频率更高；作为回应，它们的父母比未补充的雏鸟的父母提供的食物更多，因为乞食能很好地预测父母的供给。因此，补充食物的雏鸟获得了高于平均水平的条件，这预示着它们在当地种群中作为繁殖成鸟的招募。短期的皮质酮增加了乞食，但这种短暂的效果取决于饱腹感。因此，皮质酮促进了乞食，作为对饥饿的近因反应，而雏鸟的状况、乞食和食物供给的长期变化表明，乞食最终向亲代发出了后代质量的信号，以引发更多的投资，从而提高后代的存活率。
