Data from: Within-female plasticity in sex allocation is associated with a behavioral polyphenism in house wrens

Sex allocation theory assumes individual plasticity in maternal strategies, but few studies have investigated within-individual changes across environments. In house wrens, differences between nests in the degree of hatching synchrony of eggs represent a behavioural polyphenism in females, and its expression varies with seasonal changes in the environment. Between-nest differences in hatching asynchrony also create different environments for offspring, and sons are more strongly affected than daughters by sibling competition when hatching occurs asynchronously over several days. Here, we examined variation in hatching asynchrony and sex allocation, and its consequences for offspring fitness. The number and condition of fledglings declined seasonally, and the frequency of asynchronous hatching increased. In broods hatched asynchronously, sons, which are over-represented in the earlier-laid eggs, were in better condition than daughters, which are over-represented in the later-laid eggs. Nonetheless, asynchronous broods were more productive later within seasons. The proportion of sons in asynchronous broods increased seasonally, whereas there was a seasonal increase in the production of daughters by mothers hatching their eggs synchronously, which was characterized by within-female changes in offspring sex and not by sex-biased mortality. As adults, sons from asynchronous broods were in better condition and produced more broods of their own than males from synchronous broods, and both males and females from asynchronous broods had higher lifetime reproductive success than those from synchronous broods. In conclusion, hatching patterns are under maternal control, representing distinct strategies for allocating offspring within broods, and are associated with offspring sex ratios and differences in offspring reproductive success.

性别分配理论假定母方策略存在个体可塑性，但目前鲜有研究探讨单个个体在不同环境下的内部变化。在家鹪鹩（House Wren）中，不同巢穴间卵的孵化同步性程度差异体现了雌性的行为多型现象，且该多型的表达随环境的季节性变化而改变。孵化异步性的巢间差异也会为后代营造各异的生长环境，当孵化持续数日呈现异步模式时，雄性后代比雌性更易受到同胞竞争的负面影响。本研究探讨了孵化异步性与性别分配的变异及其对后代适合度的影响。离巢幼鸟的数量与身体状况随季节推移逐渐下降，而异步孵化的发生频率则随之升高。在异步孵化的雏窝中，前期产出的卵中雄性占比偏高，此类雄性幼鸟的身体状况优于后期产出卵中占比偏高的雌性幼鸟。尽管如此，季节后期的异步孵化雏窝繁殖成效更高。异步孵化雏窝中的雄性比例随季节升高，而采用同步孵化的雌性所产雌性后代的数量随季节增加；该现象源于雌性个体自身后代性别的个体内变化，而非性别偏倚性死亡所致。作为成体时，异步孵化雏窝产出的雄性个体身体状况更佳，且自身繁殖的窝卵数多于同步孵化雏窝的雄性个体；此外，异步孵化雏窝产出的雌雄个体终生繁殖成功率均高于同步孵化雏窝的个体。综上，孵化模式受母方调控，代表了窝内后代分配的差异化策略，且与后代性别比例及后代繁殖成功率的差异密切相关。