Data from: Hybridization could be a common phenomenon within the highly diverse lizard genus Liolaemus

Hybridization is likely to occur more often between closely related taxa that have had insufficient time to diverge to the point of reproductive incompatibility; hybridization between deeply divergent lineages is rare. In squamate reptiles, hybridization has been proposed as a possible explanation for the extensive paraphyly observed in mitochondrial gene trees in several species complexes of the South American lizard genus Liolaemus. One of the best-documented cases is within the L. boulengeri and L. rothi complexes, which diverged ~5.5 million years ago. Here we describe a comprehensive study for approaching the hybridization hypothesis between these lizard species complexes. We explored the level of gene tree discordance using the novel "extra lineage contribution" statistics (XLC, presented in this study), that quantifies the level of gene tree discordance contribution per individual within a species. We included molecular data (12 nuclear and 2 mitochondrial genes) from 127 individuals, and results of a coalescent model-based analysis show that the most likely explanation for the gene tree-species tree discordance is interspecific hybridization. Our best-supported hypothesis suggests current and past hybridization between L. rothi (rothi complex) and L. tehuelche (boulengeri complex), and independently between L. rothi and L. boulengeri and L. telsen (boulengeri complex). The hybrid descendants are characterized by intermediate phenotypes between the parental species, but are more similar to L. rothi in body size. We discuss the possible role of hybridization in Liolaemus evolution.

杂交更易发生在物种分化尚未达到生殖隔离程度的近缘类群之间；而深度分化支系间的杂交事件则较为罕见。在有鳞目爬行动物中，南美平鳞蜥属（Liolaemus）多个物种复合体的线粒体基因树中存在广泛的并系现象，此前已有研究提出杂交或可解释该现象。其中记录最为详实的案例之一来自布氏平鳞蜥（L. boulengeri）复合体与罗氏平鳞蜥（L. rothi）复合体，二者的分化时间约为550万年前。本研究针对上述两类蜥蜴物种复合体间的杂交假说展开了全面探究：我们采用本研究首次提出的新型‘支系额外贡献（extra lineage contribution）’统计量（XLC）分析基因树冲突水平，该统计量可量化单个物种种内各个体的基因树冲突贡献程度。本研究纳入了127个个体的分子数据（包含12个核基因与2个线粒体基因），基于溯祖模型的分析结果显示，基因树-物种树冲突最合理的解释为种间杂交。本研究支持度最高的假说表明，罗氏平鳞蜥（罗氏复合体）与特乌莱赫平鳞蜥（布氏复合体）之间，以及罗氏平鳞蜥与布氏平鳞蜥、特尔森平鳞蜥（二者均属于布氏复合体）之间，均存在当前与历史上的杂交事件。杂交后代的表型介于亲本物种之间，但在体型上更接近罗氏平鳞蜥。本研究最后探讨了杂交在平鳞蜥属演化过程中可能发挥的作用。