Data from: Incest avoidance, extrapair paternity, and territory quality drive divorce in a year-round territorial bird.

Divorce can be an important behavioral strategy to improve fitness. This is particularly relevant for species that are territorial year-round with continuous partnerships, where individuals face constraints on partner choice due to limited vacancies and dispersal opportunities. We tested several hypotheses for divorce in such a species, the cooperatively breeding bird Malurus coronatus. Based on 9 years of detailed information on dispersal and survival of 317 breeding pairs, we tested whether divorce is driven by inbreeding avoidance, by a better partner or territory, or by social variables (number of subordinates and fidelity of partners). We found that divorce is important to escape incest: incestuous pairs were substantially more likely to divorce (64%) than non-incestuous pairs (14%). However, incestuous pair bonds lasted up to a year, highlighting constraints on breeder dispersal. Non-incestuous pairs also divorced, but here the only predictor for divorce was the presence of extrapair offspring in a previous brood. Although reproductive failure did not trigger divorce, and reproductive success did not improve in the year following divorce, females that dispersed after divorce obtained higher quality territories, unlike females that dispersed after their partner died. Thus, divorce may be a strategy to improve long-term benefits associated with better territories. Some divorces appeared to be forced evictions by older females, although direct evidence for this is limited. Taken together, our findings demonstrate the complexity of factors that affect the occurrence of divorce when partner choice is constrained.

配偶离异（divorce）可作为提升适合度的重要行为策略。这一点对于全年维持领域性且伴侣关系稳定的物种尤为关键，这类物种的个体因可获得的繁殖空位有限、扩散机会匮乏，在配偶选择上存在诸多限制。我们针对这类物种——合作繁殖鸟类华丽细尾鹩莺（Malurus coronatus）——中的配偶离异行为检验了多项假说，即配偶离异是否由近交回避、寻求更优质的配偶或领域，亦或是社会变量（辅助繁殖者数量与配偶忠贞度）所驱动。我们基于针对317个繁殖对的9年详细扩散与存活监测数据开展了检验。研究发现，配偶离异是规避近交的重要手段：近交繁殖对的离异概率（64%）显著高于非近交繁殖对（14%）。但近交繁殖的配偶关系最长可维持一年，这凸显了繁殖者扩散所面临的限制。非近交繁殖对同样会发生配偶离异，但此类情况下唯一可预测离异发生的因素是前一窝雏鸟存在婚外子代。尽管繁殖失败并不会触发配偶离异，且离异后当年的繁殖成功率也未得到提升，但与配偶死亡后扩散的雌性不同，离异后扩散的雌性能够获得质量更优的领域。由此可见，配偶离异或许是一种通过获取更优质领域来提升长期适合度收益的策略。部分配偶离异事件似乎是由年长雌性主动驱逐配偶所致，不过相关直接证据较为有限。综合来看，当配偶选择受到限制时，影响配偶离异发生的因素兼具复杂性，我们的研究结果也印证了这一点。