Manipulating carer number versus brood size: complementary but not equivalent ways of quantifying carer effects on offspring.
Manipulating carer number versus brood size: complementary but not equivalent ways of quantifying carer effects on offspring.
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DOI：
10.1093/beheco/arw038
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发表时间：
2016-07
期刊：
影响因子：
--
通讯作者：
Russell AF
中科院分区：
文献类型：
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作者：
Liebl AL;Browning LE;Russell AF
为了理解合作照料系统的进化，需要测量照料者数量增加对后代成功的因果影响。在这里，我们用两种实验技术在澳大利亚内陆的栗色冠牙牙鹦鹉身上做到了这一点。看护人的移除和幼崽数量的操纵都表明了帮助者对后代食物获取的因果影响。然而，结果并不相同，即使在控制了相似的看护人与后代的比例之后，雏鸟也会在孵化规模操纵后获得更多的食物。在合作繁殖系统中，旨在量化照顾者数量增加对后代照顾水平的影响的实验很少，在合作繁殖系统中，后代是由繁殖对之外的个体抚养的。这种缺乏可能源于对阐明这些影响所必需的最适当的操作的分歧。本研究对合作繁殖的栗冠咿呀学语者（Pomatostomus ruficeps）进行了看护人去除和幼崽增加实验，以检验看护人数量和看护人与幼崽比例对哺育率的影响。移除护理员导致整体育雏率呈线性下降。进一步的分析未能提供证据，证明这种影响受到领土质量的影响，或因迁徙而导致的群体动态中断。同样，将雏鸟添加到巢中导致雏鸟供给率线性增加，这表明照顾者对不断增加的后代需求做出了反应。然而，这两项实验并没有产生数量上相同的结果：尽管两项实验中看护人与后代的比例相当，但每只雏鸟在控制雏鸟数量后得到的食物都比移除看护人后得到的食物多。为了打破孵化前母体效应和孵化后乞讨模式之间的任何联系，我们在孵化时进行了分离设计交叉培育操作，发现在控制饥饿指标后，大窝的乞讨强度增加了。这些发现表明，当乞食强度受到争夺竞争的影响时，对雏鸟大小的操纵本身就会影响雏鸟的供给率。我们强调，照顾者数量和育雏规模的操作是互补的，但不是等效的；同时采用这两种方法可以更全面地了解合作育种系统中的照料者效应。
Measuring the causal effects of increasing carer number on offspring success is required to understand the evolution of cooperative care systems. Here, we did so using 2 experimental techniques in the chestnut-crowned babbler from outback Australia. Both carer removal and brood size manipulations indicate causal effects of helpers on offspring food acquisition. However, the results were not equivalent, with nestlings receiving more food following brood size manipulations, even after controlling for similar carer to offspring ratios. Experiments designed to quantify the effects of increasing numbers of carers on levels of offspring care are rare in cooperative breeding systems, where offspring are reared by individuals additional to the breeding pair. This paucity might stem from disagreement over the most appropriate manipulations necessary to elucidate these effects. Here, we perform both carer removal and brood enhancement experiments to test the effects of numbers of carers and carer:offspring ratios on provisioning rates in the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps). Removing carers caused linear reductions in overall brood provisioning rates. Further analyses failed to provide evidence that this effect was influenced by territory quality or disruption of group dynamics stemming from the removals. Likewise, adding nestlings to broods caused linear increases in brood provisioning rates, suggesting carers are responsive to increasing offspring demand. However, the 2 experiments did not generate quantitatively equivalent results: Each nestling received more food following brood size manipulation than carer removal, despite comparable carer:offspring ratios in each. Following an at-hatching split-design cross-fostering manipulation to break any links between prehatching maternal effects and posthatching begging patterns, we found that begging intensity increased in larger broods after controlling for metrics of hunger. These findings suggest that manipulation of brood size can, in itself, influence nestling provisioning rates when begging intensity is affected by scramble competition. We highlight that carer number and brood size manipulations are complimentary but not equivalent; adopting both can yield greater overall insight into carer effects in cooperative breeding systems.