Pulling together or pulling apart: hybridization in theory and practice
Pulling together or pulling apart: hybridization in theory and practice
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DOI：
10.1111/jeb.12080
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发表时间：
2013-02-01
影响因子：
2.1
通讯作者：
Ritchie, M. G.
中科院分区：
文献类型：
--
作者：
Butlin, R. K.;Ritchie, M. G.
Abbott等人（2013）声称，“如果杂交被定义为基因不同的群体成员之间的繁殖（Barton & Hewitt, 1985），产生混合祖先的后代，那么它几乎发生在所有提出的物种形成过程中”。一位匿名评论者在回应这一说法时指出，“这句话本身就是一个重要的贡献，这一点也不夸张……因此，作者的结论表明了进化生物学的一个主要范式转变，远离了新达尔文综合理论的类型学背景。”这里汇集的评论表明，任何承认动物和植物物种形成中几乎普遍存在的杂交现象的新范式都被广泛接受。然而，关于它在物种形成过程中的影响和潜在作用，意见分歧更大。这些评论中出现的问题包括杂交（当然还有物种）本质的定义，以及强化选择及其后果的可能性。然而，主要的争论涉及自然杂交的更广泛意义及其在生物多样性中的潜在作用。理论生物学家与经验生物学家的主要对比观点尤其引人注目，发人深省。在关于这一点的讨论中，Jim Mallet说：“理论家对杂交数据的立场让我想起了Arthur Eddington的著名俏皮话，‘在没有被理论证实之前，任何实验都不应该被相信。“很难想象两种形式在接触时可能保持遗传差异或发生分歧，因为Sewall Wright提出的两态规则，其中FST为1/(1+ 4 Nm)。如果Nm<< 1散度可以发生。如果Nm b> >，它就不会。尼克·巴顿（Nick Barton）曾在上世纪80年代告诉我们，昆虫的宿主种族不应该存在，它们以合理的速度交换基因，但在生态适应方面存在分歧。现在很清楚，它们确实如此，尽管它们为什么这样做仍然是个谜。杂交起源的物种，无论是多倍体还是同倍体，似乎在植物中很常见，无论理论如何（见Servedio et al., 2013）。也许爱丁顿的名言还有另一个同样有效的版本：“没有足够的数据证实，任何好的理论都不应该被相信。”Abbott等人（2013）采用的杂交定义将注意力集中在混合交配产生的后代上。当不同种群接触时，有许多因素可能影响杂交合子形成的概率（Hochkirch, 2013; Rosenthal, 2013; Svensson, 2013），包括物候、交配信号和偏好、配子竞争、配子识别等。不管是否产生了可存活的受精卵，这些相互作用都是昂贵的，因此对潜在性状施加了选择。由于这是直接选择，它可能比混合适应度降低导致的间接选择更强大（Shaw & Mendelson, 2013）。与性选择的类比是一个重要的类比：配偶偏好的直接成本和收益可能比由于后代适应性而产生的间接收益具有更强的影响（Svensson, 2013）。由于这些原因，区分两种选择来源是很重要的（如Shaw和Mendelson， 2013年所述），因此，有助于从后代生产的角度定义杂交。后代的产生是基因流动的必要条件，尽管它不能保证。因此，区分杂交后代的产生和交配的相互作用是很重要的。然而，交配互动，包括那些生殖隔离的物种之间不会产生杂交后代的交配互动，是一种……
Abbott et al.(2013) claimed that,‘If hybridization is defined as reproduction between members of genetically distinct populations (Barton & Hewitt, 1985), producing offspring of mixed ancestry, then it occurs in almost all proposed processes of speciation’. An anonymous reviewer noted in response to this claim,‘It really is not hyperbole to state that this statement alone makes this an important contribution… The conclusions of the authors are thus indicative of a major paradigm shift in evolutionary biology, away from the typological setting of the Neo-Darwinian synthesis’. The Commentaries assembled here suggest that any new paradigm recognising the near ubiquitous occurrence of hybridisation in animal and plant speciation is widely accepted. However, opinions vary much more widely as to its impact and potential role in the process of speciation. Issues emerging from these commentaries include definitions of the nature of hybridisation (and, of course, species) and the likelihood of reinforcing selection and its consequences. However, the main debate concerns the broader significance of natural hybridisation and its potential role in biodiversity. The mainly contrasting views of theoreticians versus empirical biologists are particularly striking, and thought-provoking. In a discussion on this point, Jim Mallet said,‘The stance of theoreticians to the data on hybridization reminds me of Arthur Eddington’s famous quip,“No experiment should be believed until it has been confirmed by theory.”’It is hard to imagine that two forms may maintain genetic differences or undergo divergence while in contact because of the two-state rule suggested by Sewall Wright, where FST 1/(1+ 4 Nm). If Nm<< 1 divergence can take place. If Nm>> 1 it will not. Nick Barton used to tell us in the 1980s that host races in insects, forms that exchange genes at a reasonable rate yet nevertheless diverge in ecological adaptations, should not exist. It is now clear that they do, although why they do is still a bit of a puzzle. Species of hybrid origin, both polyploid and homoploid, appear to be common in plants whatever the theory might say (see Servedio et al., 2013). Perhaps there is another, equally valid, version of Eddington’s dictum:‘No good theory should be believed until confirmed by adequate data’. The definition of hybridization adopted by Abbott et al.(2013) focuses attention onto the offspring resulting from mixed matings. When divergent populations are in contact, there are many factors that potentially influence the probability of the formation of hybrid zygotes (Hochkirch, 2013; Rosenthal, 2013; Svensson, 2013) including phenology, mating signals and preferences, gamete competition, gamete recognition and so on. Regardless of whether viable zygotes are produced, these interactions can be costly and so impose selection on the underlying traits. Since this is direct selection, it may be more powerful than indirect selection resulting from reduced hybrid fitness (Shaw & Mendelson, 2013). The analogy with sexual selection is an important one: direct costs and benefits of mate preferences can have much stronger effects than indirect benefits due to offspring fitness (Svensson, 2013). For these very reasons, it is important to distinguish between the two sources of selection (as argued by Shaw & Mendelson, 2013) and, therefore, helpful to define hybridization in terms of offspring production. Offspring production is necessary for gene flow, although it does not guarantee it. So, it is important to distinguish production of hybrid offspring from mating interactions. Nevertheless, mating interactions, including those between reproductively isolated species that do not result in hybrid offspring, are a …