Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
Proc Biol Sci. 2013 Aug 7;280(1768):20131297. doi: 10.1098/rspb.2013.1297. Print 2013 Oct 7.
Reproductive cooperation in social animals has been the focus of intensive research, yet the role of environmental factors in promoting such cooperation remains uncertain. A recent global analysis suggested that cooperative breeding in birds is a 'bet-hedging' strategy associated with climatic uncertainty, but it is unclear whether this mechanism applies generally or is restricted to the insectivorous passerines that predominate as cooperative breeders at the global scale. Here, we use a phylogenetic framework to assess the effect of climate on the evolution of cooperation in hornbills (Bucerotidae), an avian family characterized by frugivory and carnivory. We show that, in contrast to the global pattern, cooperative reproduction is positively associated with both inter- and intra-annual climatic stability. This reversed relationship implies that hornbills are relatively insensitive to climatic fluctuations, perhaps because of their dietary niche or increased body mass, both of which may remove the need for bet-hedging. We conclude that the relationship between climatic variability and cooperative breeding is inconsistent across taxa, and potentially mediated by life-history variation. These findings help to explain the mixed results of previous studies and highlight the likely shortcomings of global datasets inherently biased towards particular categories.
在社会性动物中，繁殖合作一直是密集研究的焦点，但环境因素在促进这种合作方面的作用仍不确定。最近的一项全球分析表明，鸟类的合作繁殖是一种与气候不确定性相关的“风险分摊”策略，但尚不清楚这种机制是否普遍适用，还是仅限于在全球范围内占主导地位的食虫雀形目鸟类。在这里，我们使用系统发育框架来评估气候对犀鸟（Bucerotidae）合作进化的影响，犀鸟是一种以水果和肉类为食的鸟类家族。我们表明，与全球模式相反，合作繁殖与年际和年内气候稳定性呈正相关。这种相反的关系意味着犀鸟对气候波动相对不敏感，这可能是由于它们的饮食生态位或增加的体重，这两者都可能消除风险分摊的需要。我们得出结论，气候变异性与合作繁殖之间的关系在不同类群中不一致，并且可能受到生活史变异的调节。这些发现有助于解释先前研究的混合结果，并强调了全球数据集固有的偏向特定类别的可能缺陷。
