Sukhum Kimberley V, Freiler Megan K, Wang Robert, Carlson Bruce A
Department of Biology, Washington University in Saint Louis, 1 Brookings Drive, Campus Box 1137, St. Louis, MO 63130-4899, USA.
Department of Biology, Washington University in Saint Louis, 1 Brookings Drive, Campus Box 1137, St. Louis, MO 63130-4899, USA
Proc Biol Sci. 2016 Dec 28;283(1845). doi: 10.1098/rspb.2016.2157.
A large brain can offer several cognitive advantages. However, brain tissue has an especially high metabolic rate. Thus, evolving an enlarged brain requires either a decrease in other energetic requirements, or an increase in overall energy consumption. Previous studies have found conflicting evidence for these hypotheses, leaving the metabolic costs and constraints in the evolution of increased encephalization unclear. Mormyrid electric fishes have extreme encephalization comparable to that of primates. Here, we show that brain size varies widely among mormyrid species, and that there is little evidence for a trade-off with organ size, but instead a correlation between brain size and resting oxygen consumption rate. Additionally, we show that increased brain size correlates with decreased hypoxia tolerance. Our data thus provide a non-mammalian example of extreme encephalization that is accommodated by an increase in overall energy consumption. Previous studies have found energetic trade-offs with variation in brain size in taxa that have not experienced extreme encephalization comparable with that of primates and mormyrids. Therefore, we suggest that energetic trade-offs can only explain the evolution of moderate increases in brain size, and that the energetic requirements of extreme encephalization may necessitate increased overall energy investment.
较大的大脑能带来一些认知优势。然而，脑组织的代谢率特别高。因此，进化出更大的大脑要么需要降低其他能量需求，要么需要增加总体能量消耗。先前的研究为这些假设找到了相互矛盾的证据，使得脑化增强进化过程中的代谢成本和限制尚不清楚。长颌鱼目电鱼的脑化程度极高，与灵长类动物相当。在此，我们表明，长颌鱼目物种的脑大小差异很大，几乎没有证据表明存在与器官大小的权衡取舍，相反，脑大小与静息耗氧率之间存在相关性。此外，我们表明，脑增大与缺氧耐受性降低相关。因此，我们的数据提供了一个非哺乳动物的极端脑化例子，其通过总体能量消耗的增加来实现。先前的研究发现，在未经历过与灵长类动物和长颌鱼目相当的极端脑化的分类群中，脑大小的变化存在能量权衡。因此，我们认为能量权衡只能解释脑大小适度增加的进化，而极端脑化的能量需求可能需要增加总体能量投入。
