Coevolution and the origins of reproductive isolation

自达尔文以来，关于新物种如何产生的主流观点是，在经历不同生态选择压力的孤立种群中发生的适应。然而，当种群分裂时，生殖隔离（RI）可以通过“非生态”机制进化。其中，有人认为两性间的共同进化（IC）可能是一个特别强大的“物种形成引擎”。交配是通过两性之间在繁殖、合作或冲突中相互适应另一性别的特征而发生的。由于IC是由种群内的适应和反适应的开放式循环驱动的，孤立的种群可能仅仅因为一个种群中出现的新的有利突变与另一个种群中出现的突变偶然不同而发生分化。通过这一过程产生的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，因为分离的自然种群不可避免地会有某种程度的生态差异，往往有未知的历史，而且可能很难进行实验。******我将利用一个强大的长期进化实验，果蝇，量化机制有助于物种形成的早期阶段。对这个物种的大量研究表明，IC可以在10代的时间尺度上测量。我的15个种群实验已经进行了超过25年，并且从共同祖先中分离了多达2600代的种群，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，特别是在体型、发育和繁殖年龄方面，这构成了生态差异的来源。同样的种群有着相同的处理历史，但在基因上是隔离的，就好像居住在不同的岛屿上，有着相同的生态环境。初步研究表明，在选择不同特征的种群之间，如择偶偏好，以及它们之间的一些生理交配不相容，已经形成了相当大的交配前隔离。未来的研究将扩展这方面的工作，研究交配后、受精前精子之间的竞争、受精成功以及种群间第一代和第二代杂交的成功。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，以及对驯化以来的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本质。

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.