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Adaptive Radiation of Darwin's Finches

机译：达尔文雀的适应性辐射

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A powerful metaphor for evolutionary diversification is a tree. A typical spreading tree has a single trunk, two or more major branches, several minor branches and many twigs. Its foundations―its roots and the remnants of the original seed―remain hidden from sight. The metaphor applies to the full set of living things on Earth―"the tree of life"―as well as to small groups of species, whether they are marsupial mammals or Hawaiian Drosophila. We can think of the typical crown of a tree as resembling the shape of an umbrella, with twig-bearing branches radiating in all directions (Figure 2, top). The ends of the twigs represent organisms adapted to separate microenvironments; the tree overall represents an adaptive radiation. Darwin's finches are a prime example of an adaptive radiation. Fourteen or perhaps 15 species, all derived from a common ancestor, occupy individual ecological niches to which they are adapted, principally because of the size and shape of their beaks in relation to the food they eat. Yet on close inspection, we now know that their evolu- tionary relationships depart radically from the orthodox view of an adaptive radiation with one trunk, a few branches and many terminal twigs. The most striking difference from the idealized model is that near the base of the tree, where the main trunk―representing the ancestral species―splits, only one of the resulting trunks leads to several branches and many twigs (Figure 2, bottom). The other trunk gives rise to little more than thin twigs, although they have persisted in growing to the crown. The next division is also asymmetrical. The third division is more orthodox, producing two branches that radiate approximately equally, one yielding the ground finches and the other yielding tree finches. Neverthe-less, the tree as a whole is lopsided.
机译：一棵树是进化多样化的一个强有力的隐喻。典型的传播树具有单个树干，两个或多个主要分支，几个​​次要分支和许多树枝。它的根基-它的根和原始种子的残余-仍然看不见。这个比喻适用于地球上的所有生物，即“生命之树”，也适用于少数物种，无论它们是有袋类哺乳动物还是夏威夷果蝇。我们可以认为树的典型树冠类似于伞的形状，带有树枝的树枝向各个方向辐射（图2，顶部）。树枝的末端代表了适合于分离微环境的生物。该树总体上表示自适应辐射。达尔文的雀科是适应性辐射的一个典型例子。十四种或也许十五种都起源于同一祖先的物种占据着适合它们的单个生态位，这主要是由于它们喙的大小和形状与所食用的食物有关。然而，经过仔细检查，我们现在知道，它们的进化关系与具有一根主干，几个分支和许多末端细枝的自适应辐射的正统观点完全不同。与理想化模型最显着的区别是，在树的根部附近，代表主要物种的主要树干裂开了，只有其中一个树干导致了多个分支和许多树枝（图2，底部）。尽管它们一直长到树冠，但另一根树干只产生细细的树枝。下一个划分也是不对称的。第三部分是更正统的，产生两个分支，它们的辐射近似相等，一个分支产生地面雀，另一个产生树雀。但是，整个树是偏斜的。

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