Healy Sue, Guilford Tim
Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, U.K.
Evolution. 1990 Mar;44(2):339-346. doi: 10.1111/j.1558-5646.1990.tb05203.x.
Recent evidence shows that, despite earlier beliefs, many birds have a functional sense of smell. There is also considerable variation in olfactory-bulb size among bird species, yet the evolutionary significance of this variation has remained elusive. We argue that birds living under low-light conditions, where vision is less efficient, should have evolved or maintained an increased olfactory ability and, hence, larger olfactory bulbs. Using a family-level comparative analysis to control at least partially for taxonomic artifacts, we show that none of a series of ecological variables (diet, nest type, development, nest dispersion, and migratory behavior) accounts for variation in olfactory-bulb size once the effects of body size and brain size (measured by cerebral-hemisphere length) have been controlled. Activity timing, however, accounts for significant variation even after the removal of these other variables. We discovered 13 independent cases in which nocturnal or crepuscular lineages have evolved a diurnal habit, or vice versa, and compared relative olfactory-bulb sizes between each branch pair. In all but one case, nocturnal or crepuscular birds have larger olfactory bulbs than their diurnal counterparts. We therefore demonstrate a widespread relationship between ecology and the evolutionary development of a part of the brain.
最近的证据表明，尽管早期观点认为许多鸟类没有功能性嗅觉，但实际上它们具备这种能力。鸟类物种之间嗅球大小也存在相当大的差异，然而这种差异的进化意义仍然难以捉摸。我们认为，在视觉效率较低的弱光条件下生活的鸟类，应该已经进化或保持了增强的嗅觉能力，因此拥有更大的嗅球。通过进行科级比较分析以至少部分控制分类学假象，我们发现，在控制了体型和脑容量（通过大脑半球长度衡量）的影响后，一系列生态变量（饮食、巢类型、发育、巢分布和迁徙行为）均无法解释嗅球大小的差异。然而，即使去除这些其他变量后，活动时间仍能解释显著的差异。我们发现了13个独立案例，其中夜行性或晨昏性谱系进化出了昼行性习性，反之亦然，并比较了每个分支对之间的相对嗅球大小。除了一个案例外，在所有案例中，夜行性或晨昏性鸟类的嗅球都比它们的昼行性同类更大。因此，我们证明了生态与大脑一部分的进化发展之间存在广泛的关系。
