Early environment often has profound effects on phenotypic development that last throughout the lifetime. It has been suggested that unpredictable environments may favor cognitive abilities. However, cognitive challenges during development may result in life-history trade-offs, because complex neural reorganization required for coping with these challenges entails stress and energy costs. In this study, we experimentally tested whether early exposure to different cognitive challenges influences cognitive ability, brain size and life-history traits in the three-spined stickleback (Gasterosteus aculeatus). For this, juvenile sticklebacks were challenged over a 2-month period to resolve four different learning tasks. Contrary to our predictions, individuals trained in learning tasks later showed a reduced ability to solve a new maze task, suggesting that these learning tasks during early life may impair the ability to cope with new cognitive challenges. Females from the learning task group showed smaller optic tectum volume than the control females. Fish from the learning task treatment reduced their growth during the experiment, then accelerated growth to catch up until the breeding season. Sticklebacks reared in an environment with learning tasks also suffered a greater mortality than the controls both during and after the experiment. For the first time to our knowledge, we demonstrated direct costs of living in environments with cognitive challenges by tracking long-term performances of sticklebacks exposed to dynamic challenges during early life. Our results show that environmental challenges during ontogeny trigger plastic responses, but contrary to the common belief, do not improve the ability to cope with new cognitive challenges.

中文翻译：

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三刺棘鱼早期学习任务的长期负面影响

早期环境通常对终生的表型发育产生深远的影响。有人提出，不可预测的环境可能有利于认知能力。然而，发展过程中的认知挑战可能会导致生命史的权衡，因为应对这些挑战所需的复杂神经重组会带来压力和能量成本。在这项研究中，我们通过实验测试了早期暴露于不同的认知挑战是否会影响三刺棘鱼 (Gasterosteus aculeatus) 的认知能力、大脑大小和生活史特征。为此，幼鱼在 2 个月的时间内接受了挑战，以解决四种不同的学习任务。与我们的预测相反，接受过学习任务训练的个体后来表现出解决新迷宫任务的能力下降，表明早年的这些学习任务可能会损害应对新认知挑战的能力。学习任务组的女性比对照组女性的视顶体积更小。来自学习任务处理的鱼在实验期间减少了它们的生长，然后加速生长以赶上繁殖季节。在有学习任务的环境中饲养的棘鱼在实验期间和之后的死亡率也高于对照组。据我们所知，我们第一次通过跟踪早期生活中暴露于动态挑战的棘鱼的长期表现，证明了生活在具有认知挑战的环境中的直接成本。我们的结果表明个体发育过程中的环境挑战会引发塑料反应，但与普遍看法相反，