Individual behavior varies for many reasons, but how early in life are such differences apparent, and are they under selection? We investigated variation in early-life behavior in a wild eastern gray kangaroo (Macropus giganteus) population, and quantified associations of behavior with early survival. Behavior of young was measured while still in the pouch and as subadults, and survival to weaning was monitored. We found consistent variation between offspring of different mothers in levels of activity at the pouch stage, in flight initiation distance (FID) as subadults, and in subadult survival, indicating similarity between siblings. There was no evidence of covariance between the measures of behavior at the pouch young versus subadult stages, nor of covariance of the early-life behavioral traits with subadult survival. However, there was a strong covariance between FIDs of mothers and those of their offspring tested at different times. Further, of the total repeatability of subadult FID (51.5%), more than half could be attributed to differences between offspring of different mothers. Our results indicate that 1) behavioral variation is apparent at a very early stage of development (still in the pouch in the case of this marsupial); 2) between-mother differences can explain much of the repeatability (or "personality") of juvenile behavior; and 3) mothers and offspring exhibit similar behavioral responses to stimuli. However, 4) we found no evidence of selection via covariance between early-life or maternal behavioral traits and juvenile survival in this wild marsupial.

中文翻译：

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野生有袋动物的早期行为、生存和母性人格。

个体行为因多种原因而有所不同，但这种差异在生命的早期多久就会显现出来，它们是否受到选择？我们研究了野生东部灰袋鼠（Macropus giganteus）种群早期生命行为的变化，并量化了行为与早期生存的关联。测量幼仔在育儿袋中和亚成体时的行为，并监测断奶后的存活率。我们发现不同母亲的后代在育儿袋阶段的活动水平、亚成体的飞行起始距离（FID）和亚成体的存活率方面存在一致的差异，这表明兄弟姐妹之间的相似性。没有证据表明育儿袋幼年阶段与亚成体阶段的行为测量之间存在协方差，也没有证据表明早期生命行为特征与亚成体存活率之间存在协方差。然而，不同时间测试的母亲的 FID 与其后代的 FID 之间存在很强的协方差。此外，在亚成体 FID 的总重复性 (51.5%) 中，超过一半可归因于不同母亲的后代之间的差异。我们的结果表明：1）行为变化在发育的早期阶段就很明显（对于这种有袋动物来说，仍然在育儿袋中）；2）母亲之间的差异可以在很大程度上解释青少年行为的重复性（或“个性”）；3）母亲和后代对刺激表现出相似的行为反应。然而，4）我们没有发现这种野生有袋动物的早期生命或母性行为特征与幼年生存之间的协方差选择的证据。