Data from: Sex differences in the drivers of reproductive skew in a cooperative breeder

Many cooperatively breeding societies are characterized by high
reproductive skew, such that some socially dominant individuals breed,
while socially subordinate individuals provide help. Inbreeding avoidance
serves as a source of reproductive skew in many high-skew societies, but
few empirical studies have examined sources of skew operating alongside
inbreeding avoidance, or compared individual attempts to reproduce
(reproductive competition) with individual reproductive success. Here we
use long-term genetic and observational data to examine factors affecting
reproductive skew in the high-skew cooperatively breeding southern pied
babbler (Turdoides bicolor). When subordinates can breed, skew remains
high, suggesting factors additional to inbreeding avoidance drive skew.
Subordinate females are more likely to compete to breed when older or when
ecological constraints on dispersal are high, but heavy subordinate
females are more likely to successfully breed. Subordinate males are more
likely to compete when they are older, during high ecological constraints,
or when they are related to the dominant male, but only the presence of
within-group unrelated subordinate females predicts subordinate male
breeding success. Reproductive skew is not driven by reproductive effort,
but by forces such as intrinsic physical limitations and intra-sexual
conflict (for females), or female mate choice, male mate-guarding and
potentially reproductive restraint (for males). Ecological conditions or
‘outside options’ affect the occurrence of reproductive conflict,
supporting predictions of recent synthetic skew models. Inbreeding
avoidance together with competition for access to reproduction may
generate high skew in animal societies, and disparate processes may be
operating to maintain male vs. female reproductive skew in the same
species.

诸多合作繁殖社群均以显著的生殖偏倚（reproductive skew）为典型特征：部分具有社会优势地位的个体拥有繁殖权，而社会从属个体则提供抚育帮助。在诸多高偏倚的合作繁殖社群中，近交回避（inbreeding avoidance）是生殖偏倚的重要成因之一，但目前鲜有实证研究探讨与近交回避共同作用的其他生殖偏倚驱动因素，也鲜有研究将个体的繁殖尝试（即繁殖竞争（reproductive competition））与个体繁殖成功率进行对比分析。本研究借助长期遗传与观测数据，针对高生殖偏倚的合作繁殖物种——南非斑鸫鹛（Turdoides bicolor），探讨影响其生殖偏倚的各类因素。当从属个体拥有繁殖机会时，种群仍维持较高的生殖偏倚，这表明除近交回避外，还存在其他驱动生殖偏倚的因素。从属雌性在年龄更大或扩散面临的生态限制更强时，更倾向于参与繁殖竞争；而体型较重的从属雌性则更易成功获得繁殖权。从属雄性则在年龄更大、扩散生态限制较强，或与优势雄性存在亲缘关系时，更易参与繁殖竞争；但仅当社群内存在无亲缘关系的从属雌性时，从属雄性才能成功获得繁殖机会。生殖偏倚并非由繁殖投入所驱动，而是受以下因素影响：对于雌性而言，主要为内在生理限制与性内冲突；对于雄性而言，则主要为雌性配偶选择、雄性配偶守卫，以及潜在的繁殖克制行为。生态条件或“外部选择权”会影响繁殖冲突的发生，这一结果验证了近期综合偏倚模型的相关预测。在动物社群中，近交回避与繁殖资源竞争的共同作用或许会催生高生殖偏倚；而同一物种种群中，维持雄性与雌性生殖偏倚的内在机制可能存在显著差异。