Data from: Molecular patterns of introgression in a classic hybrid zone between the Australian tree frogs, Litoria ewingii and L. paraewingi: Evidence of a tension zone

Hybrid zones provide a rare opportunity to explore the processes involved in reproductive isolation and speciation. The southern hybrid zone between the southeastern Australian tree frogs Litoria ewingii and L. paraewingi has been comprehensively studied over the last 40 years, primarily using reproductive compatibility experiments and male advertisement calls. We used mitochondrial DNA (mtDNA) and eight nuclear microsatellite markers to characterize this hybrid zone along a historically studied transect and to test various dispersal-dependent and dispersal-independent hybrid zone models. The species are genetically distinct and the level of hybridization within the contact zone is low, with the majority of admixed individuals representing later-generation hybrids. Based on previous experimental genetic compatibility studies, we predicted that hybrids with L. paraewingi mtDNA would be more frequent than hybrids with L. ewingii mtDNA. Surprisingly, a greater proportion of the identified hybrids had L. ewingii mtDNA. Geographical cline analyses showed a sharp transition in allele frequencies across the transect, and both the mtDNA and microsatellite data showed concordant cline centres, but were best supported by a model that allowed width to vary. Overall, the L. ewingii–L. paraewingi hybrid zone is best characterized as a tension zone, due to the narrow cline width, concordant genetic clines and low levels of hybridization.杂交带为探究生殖隔离与物种形成的相关过程提供了难得的研究契机。过去40年间，学界针对澳大利亚东南部雨滨蛙（Litoria ewingii）与副雨滨蛙（Litoria paraewingi）之间的南部杂交带开展了全面研究，主要采用生殖兼容性实验与雄性广告鸣声作为研究方法。本研究借助线粒体DNA（mitochondrial DNA，mtDNA）与8个核微卫星标记，对该杂交带沿历史研究样带的特征进行了刻画，并检验了多种依赖扩散与不依赖扩散的杂交带模型。两个物种种群在遗传上存在显著分化，接触带内的杂交水平较低，且多数杂种个体为晚代杂种。基于此前的生殖兼容性实验研究，我们曾预测携带副雨滨蛙线粒体DNA的杂种个体比例会高于携带雨滨蛙线粒体DNA的杂种个体。但令人意外的是，经鉴定的杂种个体中，携带雨滨蛙线粒体DNA的比例更高。地理梯度分析结果显示，样带沿线的等位基因频率存在急剧转变；线粒体DNA与微卫星数据均呈现出一致的梯度中心，但允许梯度宽度变化的模型对数据的拟合效果最优。综合来看，雨滨蛙-副雨滨蛙杂交带的最优分类为张力杂交带，这一结论基于其狭窄的梯度宽度、一致的遗传梯度以及较低的杂交水平。