Prenatal environmental conditions underlie alternative reproductive tactics that drive the formation of a mixed-kin cooperative society

Although animal societies often evolve due to limited natal dispersal that
results in kin clustering and facilitates cooperation among relatives,
many species form cooperative groups with low kin structure. Such groups
often comprise residents and immigrants of the same sex that compete for
breeding opportunities. To understand how such mixed-kin societies form,
we investigated the causes and fitness consequences of dispersal decisions
in male cooperatively breeding superb starlings (Lamprotornis superbus)
inhabiting a climatically unpredictable environment. We show that the two
alternative reproductive tactics—natal dispersal or philopatry—exhibit
reproductive tradeoffs resulting in equal lifetime inclusive fitness.
Surprisingly, an individual’s tactic is determined by the prenatal
environment its parents experience prior to laying rather than the
environment it experiences as a juvenile. Individuals that adopt the
tactic not predicted by prenatal environmental conditions have lower
fitness. Ultimately, climate-driven oscillating selection appears to
stabilize mixed-kin societies despite the potential for social conflict.

尽管动物社会的演化通常源于有限的出生扩散（natal dispersal），该过程可形成亲缘聚类并促进亲属间的合作，但诸多物种仍会构建亲缘结构松散的合作群体。这类群体通常由同性的定居者与迁入者构成，二者会为繁殖机会展开竞争。为阐明这类混合亲缘社会（mixed-kin societies）的形成机制，我们针对栖息于气候不可预测环境中的合作繁殖雄性华丽椋鸟（*Lamprotornis superbus*），研究了其扩散决策的成因与适合度后果。研究结果显示，两种备选繁殖策略——出生扩散（natal dispersal）与留居（philopatry）——存在繁殖权衡，二者的终身广义适合度（inclusive fitness）完全相等。令人意外的是，个体的繁殖策略并非由其幼年所处的环境决定，而是由双亲在产卵前经历的产前环境所决定。未按照产前环境条件选择对应繁殖策略的个体，其适合度更低。最终，尽管存在社会冲突的潜在可能，由气候驱动的波动选择似乎稳定了这类混合亲缘社会。