Pair-bond strength is consistent and related to partner responsiveness in a wild corvid

The need to maintain strong social bonds is widely thought to be a key driver of cognitive evolution. Cognitive abilities to track and respond to information about social partners may be favoured by selection if they vary within populations and confer fitness benefits. Here we evaluate four key assumptions of this argument in wild jackdaws (<i>Corvus monedula</i>), corvids whose long-term pair-bonds exemplify one of the putative social drivers of cognitive evolution in birds. Combining observational and experimental behavioural data with long-term breeding records, we found support for three assumptions: (1) pair-bond strength varies across the population, (2) is consistent within pairs over time, and (3) is positively associated with a measure of socio-cognitive performance. However, (4) we did not find clear evidence that stronger pair-bonds lead to better fitness outcomes. Strongly bonded pairs were better able to adjust hatching synchrony to environmental conditions, but did not fledge more or higher quality offspring. Together, these findings suggest that maintaining strong pair-bonds is linked to socio-cognitive performance and may facilitate effective coordination between partners. However, they also imply that these benefits are insufficient to explain how selection acts on social cognition. We argue that evaluating how animals navigate trade-offs between investing in long-term relationships versus optimising interactions in their wider social networks will be a crucial avenue for future research.

维持牢固的社会联结被广泛认为是认知演化的核心驱动力之一。若针对社会伙伴的信息追踪与响应认知能力在种群内存在变异且可带来适合度（fitness）收益，自然选择便会青睐这类认知能力。本研究以野生寒鸦（*Corvus monedula*）为研究对象——该鸦科物种的长期配对联结（pair-bond）堪称鸟类认知演化的推定社会驱动力之一——检验了该论证的四项核心假设。我们将观测与实验行为数据与长期繁殖记录相结合，分析结果支持其中三项假设：（1）配对联结强度在种群中存在个体变异；（2）同一配对内的联结强度随时间保持稳定；（3）联结强度与社会认知性能（socio-cognitive performance）指标呈显著正相关。然而，（4）本研究未发现明确证据表明更强的配对联结能够带来更优的适合度结果。联结牢固的配对能够更好地根据环境条件调整孵化同步性（hatching synchrony），但并未育出更多或质量更高的后代。综合来看，上述研究结果表明，维持牢固的配对联结与社会认知性能存在关联，或可促进配对双方间的有效协作。但同时也意味着，这类收益不足以解释自然选择如何作用于社会认知。我们认为，探究动物如何权衡长期关系投入与更广社交网络中的互动优化策略，将是未来相关研究的关键方向。