Coevolution and the origins of reproductive isolation

自达尔文以来，关于新物种如何产生的主要观点是通过发生在经历不同生态选择压力的孤立种群中的适应。然而，当种群分化时，存在着生殖隔离(RI)的“非生态”机制。其中，有人认为两性间的共同进化(IC)可能是物种形成的一个特别强大的“引擎”。在两性之间的繁殖、合作或冲突中，一种性别对另一种性别特征的相互适应发生了IC。由于IC是由种群内的适应和逆适应的开放循环驱动的，孤立的种群可能仅仅因为偶然地在一个种群中出现的新的有利突变与在另一个种群中出现的新的有利突变不同而产生分歧。通过这种过程产生的RI被称为突变顺序发散(MOD)。MOD假说几乎没有令人信服的测试，因为独立的自然种群不可避免地存在不同程度的生态差异，通常有未知的历史，可能很难进行实验。*我将利用一个强大的长期进化实验，对果蝇进行量化，以量化物种形成早期阶段的机制。对该物种的大量研究表明，IC可以在S世代10‘的时间尺度上测量。我的15个种群的实验已经进行了25年多，有多达2600代的种群从共同祖先中分离出来，在3种不同的处理下进化。每个处理的种群具有明显不同的特征，特别是与身体大小、发育和繁殖年龄有关的特征，构成了生态分歧的来源。同一处理中的种群具有相同的处理历史，但在基因上是孤立的，就像占据了具有相同生态的不同岛屿一样。初步研究表明，根据不同的特征选择的种群之间已经形成了相当大的交配前隔离，比如在配偶选择上更喜欢相似的种群，以及它们之间的一些物理交配不相容。未来的研究将扩大这项关于配偶选择的工作，着眼于交配后受精前精子之间的竞争，受精成功，以及种群之间第一代和第二代杂交的成功。随着在动物物种中进行的可能是最长时间的进化实验，对环境的控制，对物种基因组和所使用的特定种群的了解，以及对驯化以来品系历史的近乎完美的了解，我们有机会以前所未有的细节描述进化的生殖隔离的性质。

Since Darwin, the predominant view of how new species arise is through adaptation occurring in isolated populations experiencing different ecological selection pressures. However there are “non-ecological” mechanisms by which reproductive isolation (RI) can evolve when populations are divided. Among these, it has been suggested that intersexual coevolution (IC) may be a particularly potent “engine of speciation”. IC occurs through reciprocal adaptation of one sex to features of the other sex in reproduction, cooperation or conflict between the sexes. Because IC is driven by open-ended cycles of adaptation and counter-adaptation within populations, isolated populations may diverge simply because, by chance, new favourable mutations arising in one population are different from those arising in another. RI arising through such a process has been called mutation order divergence (MOD). There are few convincing tests of the MOD hypothesis because separated natural populations inevitably have ecological differences to one degree or another, often have unknown histories, and may be difficult to experiment with.******I will take advantage of a powerful long-term evolution experiment with the fruit fly, Drosophila, to quantify mechanisms contributing to the early stages of speciation. Numerous studies with this species have shown that IC is measureable over time scales of 10's of generations. My 15-population experiment has been running for over 25y and has populations isolated from common ancestry for as many as 2,600 generations, evolved under 3 different treatments. Populations from each treatment have markedly different characteristics, especially related to body size, development and age of reproduction, constituting a source of ecological divergence. Populations in the same treatment have identical handling histories but are genetically isolated, as if occupying separate islands with identical ecology. Pilot studies show considerable pre-mating isolation has evolved between populations selected for different characteristics, like preferring like in mate choice, and some physical mating incompatibilities between them. Future research will expand this work on mate choice, look at post-mating pre-fertilization competition between sperm, fertilization success, and the success of first- and second-generation hybrids between populations. With perhaps the longest running evolution experiment undertaken in an animal species, control over the environment, knowledge of the genome of the species and the specific populations being used, and near perfect knowledge of the history of the lines since domestication, we have an opportunity to characterize the nature of evolving reproductive isolation in unprecedented detail.