In order to assess dogs’ personality changes during ontogeny, a cohort of 69 Border collies was followed up from six to 18–24 months. When the dogs were 6, 12, and 18–24 months old, their owners repeatedly filled in a dog personality questionnaire (DPQ), which yielded five personality factors divided into fifteen facets. All five DPQ factors were highly correlated between the three age classes, indicating that the dogs’ personality remained consistent relative to other individuals. Nonetheless, at the group level significant changes with age were found for four of the five DPQ factors. Fearfulness, Aggression towards People, Responsiveness to Training and Aggression towards Animals increased with age; only Activity/Excitability did not change significantly over time. These changes in DPQ factor scores occurred mainly between the ages of 6 and 12 months, although some facets changed beyond this age. No sex differences were found for any of the tested factors or facets, suggesting that individual variation in personality was greater than male/female differences. There were significant litter effects for the factors Fearfulness, Aggression towards People and Activity/Excitability, indicating either a strong genetic basis for these traits or a high influence of the shared early environment. To conclude, from the age of six months, consistency in personality relative to other individuals can be observed in Border collies. However, at the group level, increases in fearful and aggressive behaviours occur up to 12 months and for some traits up to two years, highlighting the need for early interventions. Follow-up studies are needed to assess trajectories of personality development prior to six months and after two years, and to include a wider variety of breeds.

中文翻译：

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边境牧羊犬行为发展的个体和群体水平轨迹

为了评估狗在个体发育过程中的性格变化，对一组 69 只边境牧羊犬进行了 6 至 18-24 个月的随访。当狗分别为 6、12 和 18-24 个月大时，它们的主人反复填写狗的性格问卷 (DPQ)，产生了分为 15 个方面的 5 个性格因素。所有五个 DPQ 因素在三个年龄组之间高度相关，表明狗的性格相对于其他个体保持一致。尽管如此，在组水平上，五个 DPQ 因素中的四个发现了随着年龄的显着变化。恐惧、对人的攻击性、对训练的反应和对动物的攻击性随着年龄的增长而增加；只有活动/兴奋性没有随时间显着变化。DPQ 因子评分的这些变化主要发生在 6 到 12 个月之间，尽管在这个年龄之后一些方面发生了变化。没有发现任何测试因素或方面的性别差异，这表明个性的个体差异大于男性/女性差异。恐惧、对人的攻击性和活动/兴奋性等因素有显着的垃圾效应，表明这些特征具有强大的遗传基础或共享早期环境的高度影响。总而言之，从 6 个月大开始，边境牧羊犬就可以观察到相对于其他个体的性格一致性。然而，在群体层面，恐惧和攻击性行为的增加会在长达 12 个月的时间内出现，某些特征会长达两年，这凸显了早期干预的必要性。