On the Coyne and Orr-igin of species: effects of intrinsic postzygotic isolation, ecological differentiation, X-chromosome size, and sympatry on Drosophila speciation

Coyne and Orr found that mating discrimination (premating isolation) evolves much faster between sympatric than allopatric Drosophila species pairs. Their meta-analyses established that this pattern, expected under reinforcement, is common and that Haldane's rule is ubiquitous in Drosophila species divergence. We examine three possible contributors to the reinforcement pattern: intrinsic postzygotic isolation, dichotomized as to whether hybrid males show complete inviability/sterility; host-plant divergence, as a surrogate for extrinsic postzygotic isolation; and X chromosome size, whether roughly 20% or 40% of the genome is X-linked. We focus on “young” species pairs with overlapping ranges, contrasted with allopatric pairs. Using alternative criteria for “sympatry” and tests that compare either level of prezygotic isolation in sympatry or frequency of sympatry, we find no statistically significant effects associated with X chromosome size or our coarse quantifications of intrinsic pos...科因（Coyne）与奥尔（Orr）的研究发现，同域分布（sympatric）的果蝇物种种对之间的交配识别（交配前隔离，premating isolation）演化速率远快于异域分布（allopatric）的果蝇物种种对。他们的元分析（meta-analyses）证实，这种符合强化选择（reinforcement）预期的模式十分普遍，且霍尔丹法则（Haldane's rule）在果蝇物种分化过程中无处不在。本研究针对该强化模式的三种潜在驱动因素展开探讨：其一为内在合子后隔离（intrinsic postzygotic isolation），按杂交雄蝇是否完全致死或不育进行二分归类；其二为寄主植物分化（host-plant divergence），作为外在合子后隔离（extrinsic postzygotic isolation）的替代指标；其三为X染色体大小（X chromosome size），即基因组中约20%或40%的序列为X连锁（X-linked）。本研究以分布范围重叠的“年轻”物种种对为核心研究对象，并与异域分布的物种种对形成对照。通过采用不同的“同域分布”判定标准，以及对比同域分布物种的前合子隔离水平或同域分布出现频率的检验方法，我们未发现与X染色体大小或我们对内在...