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Insular dwarfism in hippos and a model for brain size reduction in Homo floresiensis

机译：河马的岛状矮化和弗洛瑞斯人脑缩小模型

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摘要

Body size reduction in mammals is usually associated with only moderate brain size reduction, because the brain and sensory organs complete their growth before the rest of the body during ontogeny. On this basis, 'phyletic dwarfs' are predicted to have a greater relative brain size than 'phyletic giants. However, this trend has been questioned in the special case of dwarfism of mammals on islands. Here we show that the endocranial capacities of extinct dwarf species of hippopotamus from Madagascar are up to 30% smaller than those of a mainland African ancestor scaled to equivalent body mass. These results show that brain size reduction is much greater than predicted from an intraspecific 'late onto-genetic' model of dwarfism in which brain size scales to body size with an exponent of 0.35. The nature of the proportional change or grade shift observed here indicates that selective pressures on brain size are potentially independent of those on body size. This study demonstrates empirically that it is mechanistically possible for dwarf mammals on islands to evolve significantly smaller brains than would be predicted from a model of dwarfing based on the intraspecific scaling of the mainland ancestor. Our findings challenge current understanding of brain-body allometric relationships in mammals and suggest that the process of dwarfism could in principle explain small brain size, a factor relevant to the interpretation of the small-brained hominin found on the Island of Flores, Indonesia.
机译：哺乳动物的体型缩小通常仅与大脑的中度缩小相关，因为在发生个体发育过程中，大脑和感觉器官会在身体其余部位之前完成其生长。在此基础上，预计“进化矮人”的相对大脑大小要比“进化巨人”大。但是，这种趋势在岛上哺乳动物侏儒症的特殊情况下受到质疑。在这里，我们显示，来自马达加斯加的绝种矮河马物种的颅内容量比按同等体重缩放的非洲大陆祖先的物种小30％。这些结果表明，大脑尺寸的减小远大于在侏儒症的种内“后期遗传”模型中的预测值，在该模型中，大脑的尺寸与体重成比例，为0.35。此处观察到的比例变化或等级变化的性质表明，对大脑大小的选择性压力可能独立于对身体大小的压力。这项研究从经验上证明，与基于大陆祖先的种内缩放的矮化模型所预测的相比，岛上的矮人哺乳动物在机械上可能进化出明显较小的大脑。我们的发现挑战了当前对哺乳动物脑体异形关系的理解，并表明侏儒症的过程原则上可以解释小脑尺寸，这与印度尼西亚弗洛雷斯岛上发现的小脑人豆素有关。

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  • 来源
    《Nature》 |2009年第7243期|85-88|共4页
  • 作者

    Eleanor M. Weston; Adrian M. Lister;

  • 作者单位

    Department of Palaeontology, Natural History Museum, London SW7 5BD, UK;

    Department of Palaeontology, Natural History Museum, London SW7 5BD, UK;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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