Mammalian Behaviour & Evolution Group, Faculty of Veterinary Science, University of Liverpool, Neston, UK.
J Evol Biol. 2009 Nov;22(11):2215-21. doi: 10.1111/j.1420-9101.2009.01837.x.
The 'expensive tissue hypothesis' predicts a size trade-off between the brain and other energetically costly organs. A specific version of this hypothesis, the 'expensive sexual tissue hypothesis', argues that selection for larger testes under sperm competition constrains brain size evolution. We show here that there is no general evolutionary trade-off between brain and testis mass in mammals. The predicted negative relationship between these traits is not found for rodents, ungulates, primates, carnivores, or across combined mammalian orders, and neither does total brain mass vary according to the level of sperm competition as determined by mating system classifications. Although we are able to confirm previous reports of a negative relationship between brain and testis mass in echolocating bats, our results suggest that mating system may be a better predictor of brain size in this group. We conclude that the expensive sexual tissue hypothesis accounts for little or none of the variance in brain size in mammals, and suggest that a broader framework is required to understand the costs of brain size evolution and how these are met.
“昂贵组织假说”预测了大脑和其他高能耗器官之间存在体型权衡。该假说的一个特定版本，即“昂贵性组织假说”认为，在精子竞争下选择更大的睾丸会限制大脑尺寸的进化。我们在此表明，在哺乳动物中，大脑和睾丸质量之间没有普遍的进化权衡。这种特征之间的预测负相关关系在啮齿动物、有蹄类动物、灵长类动物、食肉动物或整个哺乳动物目之间都没有发现，而且根据交配系统分类确定的精子竞争水平，总脑质量也没有变化。尽管我们能够证实先前关于回声定位蝙蝠大脑和睾丸质量之间存在负相关关系的报告，但我们的结果表明，交配系统可能是该类群大脑大小的更好预测指标。我们得出结论，“昂贵性组织假说”只能解释哺乳动物大脑尺寸变化的一小部分或根本无法解释，因此需要更广泛的框架来理解大脑尺寸进化的成本以及如何满足这些成本。
