Reinforced butterfly speciation.
Reinforced butterfly speciation.
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强化蝴蝶物种形成。
DOI：
10.1038/sj.hdy.6800754
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发表时间：
2006
期刊：
影响因子：
3.8
通讯作者：
Jiggins CD
中科院分区：
文献类型：
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作者：
Jiggins CD
蝴蝶翅膀的图案不仅对艺术家、作家和博物学家有吸引力，对其他蝴蝶也有吸引力。事实上，它们在潜在蝴蝶配偶之间的信号传递中发挥着重要作用，这意味着模式的变化可以导致新物种的进化。一项新的研究表明，与生活在不同地区（异域）相比，生活在一起（同域）的近亲蝴蝶更有可能在模式上有所不同。这提供了新的证据来支持选择可以直接导致孤立增加的想法，这一过程被称为强化。在这种情况下，这种隔离表现为颜色模式的变化。物种形成主要是作为导致种群内进化变化的同一过程的副产品发生的：自然选择或遗传漂变。选择通常不直接支持生殖隔离的原因是显而易见的：降低杂交个体适合度的不育性等性状总是代价高昂的，因此必须是亲本种群进化的副产品。然而，在某些情况下，自然选择有可能直接有利于新生物种之间隔离的增加（Dobzhansky，1937），这一过程被称为强化（Butlin，1987）。如果不同的种群在接触时杂交，而杂交交配的生产力低于种内交配，那么选择可能有利于降低杂交概率的性状。强化之所以有吸引力，是因为它为自然选择在物种形成中提供了直接作用，但其重要性仍不清楚。人们普遍认为，强化在理论上是合理的，在一系列的情况下，和一些令人信服的实证例子支持这一点（马歇尔等人，2002年; Servedio和努尔，2003年）。因此，突出的问题不是强化是否会发生，而是多久发生一次。Coyne和Orr对果蝇生殖隔离的综述（Coyne and Orr，1989; Coyne and Orr，1997）在重振强化的热情方面发挥了关键作用，这表明同域物种对与年龄相近的异域物种相比，交配前隔离明显增加，这种模式被称为生殖特征置换。如果强化发生了，这正是预期的模式，但不幸的是，也有其他解释。首先，物种在异地分布中可能总是会发生分歧，而只有那些在交配前已经有很大程度隔离的物种对才能在机会出现时共存。这种解释意味着同域物种应该类似于异域物种的一个子集，这在科因和奥尔的数据中似乎不是这样，因为最年轻的同域物种比相应年龄的任何异域物种表现出更大的隔离。其次，在同域性中发生的其他过程可能会产生类似的结果。生态特征置换是指同域物种之间因资源竞争而导致生态分化的过程。这种分歧可能导致生殖隔离的增加，这是一个副产品。或者，强化可以启动分歧，将继续主要是由于性选择（刘和价格，1994年）。最后，在物种形成完成后（例如，如果所有的杂交种都是不育的），可以进化出生殖特征置换，以减少昂贵的种间求偶和交配。这些过程都是相当困难的区分从“真正的强化”没有知识的生态，交配系统和程度的杂交发生在特定的情况下。
Butterfly wing patterns are attrac-tive, not just to artists, writers and naturalists, but also to other butterflies. In fact, they play an important role in signalling between potential butterfly mates, which means that a change in pattern can lead to the evolution of a new species. A new study has shown that closely related butterfly species are more likely to differ in pattern if they live together (sympatric) than if they live in different areas (allopatric). This provides new evidence to support the idea that selection can directly lead to increased isolation, a process known as reinforcement. In this case that isolation is manifested as a change in colour pattern. Speciation mostly happens as a byproduct of the same processes that lead to evolutionary change within populations: natural selection or genetic drift. The reason that reproductive isolation is usually not directly favoured by selection is obvious: traits such as sterility that reduce the fitness of hybrid individuals, will always be costly and must therefore be a by-product of evolution in the parental populations. Under certain scenarios, however, it is possible for natural selection to directly favour an increase in isolation between nascent species (Dobzhansky, 1937), a process known as reinforcement (Butlin, 1987). If divergent populations hybridise while in contact and hybrid matings are less productive than within-species matings, then selection may favour traits that reduce the probability of hybridisation. Reinforcement is appealing because it provides a direct role for natural selection in speciation, but its importance remains unclear. It is generally accepted that reinforcement is theoretically plausible over a range of scenarios, and a handful of convincing empirical examples support this (Marshall et al, 2002; Servedio and Noor, 2003). The outstanding question is therefore not whether reinforcement can occur, but rather, how often it does. One data set that played a key role in reviving enthusiasm for reinforcement was Coyne and Orr’s review of reproductive isolation in Drosophila (Coyne and Orr, 1989; Coyne and Orr, 1997).This showed a clear pattern of increased premating isolation in sympatric species pairs compared to allopatric species of a similar age, a pattern known as Reproductive Character Displacement. This is exactly the pattern expected if reinforcement has occurred, but unfortunately there are also alternative explanations. First, it is possible that species always diverge in allopatry while only those species pairs that already have a significant degree of premating isolation can coexist if the opportunity arises. This explanation imples that sympatric species should resemble a subset of the allopatric species, which does not seem to be the case in the Coyne and Orr data, since the youngest sympatric species show greater isolation than any allopatric species of a corresponding age. Secondly, there are other processes that occur in sympatry that might generate similar results. Ecological character displacement is the process whereby competition for resources leads to ecological divergence between sympatric species. Such divergence could lead to increased reproductive isolation as a by-product. Alternatively, reinforcement can initiate divergence that would continue primarily due to sexual selection (Liou and Price, 1994). Finally, reproductive character displacement can evolve after speciation is complete (eg if all hybrids are sterile), to reduce costly interspecific courtship and mating. These processes are all rather difficult to distinguish from ‘true reinforcement’without knowledge of the ecology, mating systems and degree of hybridisation occurring in particular cases.