Sumatran orangutan mothers differ in the extent and trajectory of their expression of maternal behaviour

Mothers play a crucial role in the early development and survival of
mammalian offspring, and differences in maternal care may differentially
affect offspring’s development. Whereas previous research has primarily
focused on biological and socioecological factors to understand
population-level variation in maternal behaviour, the individual as a
source of variation remains understudied. We investigated
between-individual variation in the average expression of, and plasticity
in, six maternal behaviours in Sumatran orangutans, using 15 years of
behavioural data. We found that mothers differed substantially in the
average expression of four maternal behaviours, even after controlling for
socioecological conditions, biological state characteristics, and the
offspring’s influence on these behaviours. Furthermore, not controlling
for these confounding effects exaggerated or masked between-individual
variation. Mothers also substantially differed in how they adjusted three
of the maternal behaviours during offspring development, meaning that
mothers differed in behavioural plasticity. Our results suggest that
Sumatran orangutan mothers are constrained in the average expression of
maternal behaviours and their plastic responses, potentially resulting in
consistent differences among mothers, otherwise called maternal
personality. Our findings highlight that individual variation around the
population mean in maternal behaviour is more than noise and presents
opportunities to study novel evolutionary processes that shape maternal
behaviour.

母兽在哺乳动物后代的早期发育与存活过程中扮演着至关重要的角色，而母育照料的差异则可能对后代发育产生差异化影响。尽管既往研究多聚焦于生物学与社会生态因素，以解析母育行为的种群水平变异，但个体作为变异来源的相关探究仍较为不足。本研究依托15年的行为学观测数据，针对苏门答腊猩猩（Sumatran orangutan）的6种母育行为的平均表达水平与行为可塑性的个体间差异开展了研究。研究结果显示，即便在控制社会生态环境、生理状态特征以及后代对母育行为的影响等混杂变量后，4种母育行为的平均表达水平在个体母猩猩间仍存在显著差异。此外，若未对这些混杂效应进行控制，则会夸大或掩盖个体间的真实变异程度。同时，母猩猩在后代发育过程中对3种母育行为的调节模式也存在显著差异，这意味着母育行为的可塑性同样存在个体间差异。本研究结果表明，苏门答腊猩猩的母育行为平均表达水平及其可塑性响应均存在一定约束，这可能会促使个体母猩猩间形成稳定的差异，即所谓的母性人格（maternal personality）。本研究的发现凸显出：母育行为围绕种群均值的个体变异并非单纯的随机噪声，而是为探究塑造母育行为的全新进化过程提供了重要的研究契机。