Data from: Is offspring dispersal related to male mating status? An experiment with the facultatively polygynous spotless starling

Patterns of natal dispersal are generally sex-biased in vertebrates, i.e. female-biased in birds and male-biased in mammals. Interphyletic comparisons in mammals suggest that male-biased dispersal occurs in polygynous and promiscuous species where local mate competition among males exceeds local resource competition among females. However, few studies have analysed sex-biased patterns of dispersal at the individual level, and facultatively polygynous species might offer this opportunity. In the spotless starling, polygynous males exhibit their mating status during courtship carrying higher amounts of green plants to nests than monogamous males. We experimentally incorporated green plants to nests during four years to analyse long-term consequences on breeding success and offspring recruitment rates. We unexpectedly found that experimental sons recruited farther than experimental daughters, while control daughters recruited farther than control sons. A similar pattern was found using observational information from eight years. We discuss this result in the context of local competition hypothesis and speculate that sons dispersed farther from nests controlled by polygynous males to avoid competition with relatives. The amount of green plants in nests affects female perception of male attractiveness and degree of polygyny, although little is known about proximate mechanisms linking this process with the offspring dispersal behaviour. Our results support the idea that male-biased dispersal is related to polygyny in a facultatively polygynous bird.

脊椎动物的出生扩散（natal dispersal）模式普遍存在性别偏倚特征：鸟类多为雌性偏倚型，哺乳类则多为雄性偏倚型。针对哺乳类的跨类群比较研究表明，雄性偏倚的出生扩散多见于一雄多雌制（polygynous）与混交制（promiscuous）物种，这类物种中雄性的局部配偶竞争强度高于雌性的局部资源竞争强度。然而，鲜有研究在个体层面解析扩散的性别偏倚模式，而兼性一雄多雌制（facultatively polygynous）物种恰好为该类研究提供了可行路径。在纯色椋鸟（spotless starling）中，一雄多雌制的雄鸟在求偶阶段会比单配偶制雄鸟向巢内搬运更多绿色植物，以此彰显自身的交配状态。本研究历时四年开展巢内添加绿色植物的操控实验，以分析其对繁殖成功率与后代招募率的长期影响。研究意外发现：实验组子代雄鸟的扩散距离显著大于实验组子代雌鸟，而对照组子代雌鸟的扩散距离则显著大于对照组子代雄鸟。基于八年的长期观测数据也得到了一致的结果模式。本研究结合局部竞争假说（local competition hypothesis）对上述结果展开讨论，并推测雄鸟会远离由一雄多雌制雄鸟掌控的巢区进行扩散，以此避免与亲缘个体产生竞争。巢内绿色植物的数量会影响雌鸟对雄鸟吸引力以及一雄多雌制程度的判断，但目前学界对连接该过程与后代扩散行为的直接机制仍知之甚少。本研究结果证实，在兼性一雄多雌制鸟类中，雄性偏倚的出生扩散与一雄多雌制存在显著关联。