Brain Size: A Global or Induced Cost of Learning?
Brain Size: A Global or Induced Cost of Learning?
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大脑大小：学习的整体成本或诱发成本？
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
W. Gronenberg
中科院分区：
文献类型：
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作者：
Emilie C. Snell‐Rood;D. Papaj;W. Gronenberg
大脑大小作为学习成本的作用仍然是个谜；这种成本的性质和时间尤其不确定。一方面，比较研究表明，与生俱来的大大脑有助于更好的学习和记忆。在这种情况下，大脑的大小带来了即使没有学习也会产生的整体成本；另一方面，一些发育研究表明，大脑随着经验的增长而增长，这表明学习发生时会产生成本。成本如何产生的问题是一个重要的问题，因为全球成本预计会比引发成本更大地限制学习的发展。我们测试了在菜心白蝴蝶身上，大脑的大小是否代表了学习的整体和/或诱导成本。我们分析了全同胞家庭学习定位绿色宿主或红色宿主的能力，绿色宿主是蝴蝶与生俱来的搜索偏好，红色宿主更难学习定位。幼稚的蝴蝶在羽化时被牺牲，先天性脑体积估计为全球成本的衡量标准；经验丰富的蝴蝶在学习和脑体积变化后被牺牲，大脑体积估计为诱导成本的衡量标准。只有蘑菇体--参与其他昆虫学习和记忆的大脑区域--在出现时的体积与学习或寄主发现有关。在两天的寄主搜索过程中，出现了相对较大蘑菇体的蝴蝶家族表现出更大的倾向，它们发现红色宿主的能力有所提高。大多数脑区的体积随着时间的推移而增加，这表明寄主体验本身是重要的：第一，在寻找寄主的过程中着陆的总次数与蘑菇体花冠体积正相关，第二，与红色寄主的体验与蘑菇体叶体积正相关。在家庭水平上，学习后蘑菇体花冠和触角叶的相对体积与发现红色宿主的总体成功呈正相关。总体而言，我们的结果表明，在物种内部，大脑大小可能是学习的一小部分全球成本，但大脑大小因环境而异的变化可能会减少神经组织在学习进化中的整体成本。
The role of brain size as a cost of learning remains enigmatic; the nature and timing of such costs is particularly uncertain. On one hand, comparative studies suggest that congenitally large brains promote better learning and memory. In that case, brain size exacts a global cost that accrues even if learning does not take place; on the other hand, some developmental studies suggest that brains grow with experience, indicating a cost that is induced when learning occurs. The issue of how costs are incurred is an important one, because global costs are expected to constrain the evolution of learning more than would induced costs. We tested whether brain size represented a global and/or an induced cost of learning in the cabbage white butterfly, Pieris rapae. We assayed the ability of full sibling families to learn to locate either green hosts, for which butterflies have an innate search bias, or red hosts, which are more difficult to learn to locate. Naïve butterflies were sacrificed at emergence and congenital brain volume estimated as a measure of global costs; experienced butterflies were sacrificed after learning and change in brain volume estimated as a measure of induced costs. Only for the mushroom body, a brain region involved in learning and memory in other insects, was volume at emergence related to learning or host-finding. Butterfly families that emerged with relatively larger mushroom bodies showed a greater tendency to improve their ability to find red hosts across the two days of host-search. The volume of most brain regions increased with time in a manner suggesting host experience itself was important: first, total number of landings during host-search was positively related to mushroom body calyx volume, and, second, experience with the red host was positively related to mushroom body lobe volume. At the family level, the relative volume of the mushroom body calyx and antennal lobes following learning was positively related to overall success in finding red hosts. Overall, our results suggest that within species, brain size might act as a small global cost of learning, but that environment-specific changes in brain size might reduce the overall costs of neural tissue in the evolution of learning.