Data from: Rise and fall of a hybrid zone: implications for the roles of aggression, mate choice, and secondary succession

Hybridization can be an important evolutionary force by generating new species and influencing evolution of parental species in multiple ways, including introgression and the consequences of hybrid vigor. Determining the ecological processes underlying evolution in hybrid zones is difficult however because it requires examining changes in both genotypic frequencies over time and corresponding ecological information, data that are rarely collected together. Here, we describe genetic and ecological aspects of a hybrid zone between the Eastern Fence Lizard, Sceloporus undulatus, and the Florida Scrub Lizard, Sceloporus woodi, occurring over at least 23 generations. The hybrid zone, discovered greater than 35 years ago using morphological characters, originally consisted of nearly even proportions of parental species and hybrids. Now, using genetic markers (species-diagnostic mtDNA sites and 6 nDNA microsatellite loci across a total of n = 117 individuals), we confirm not only that hybridization occurred but also that subsequent backcrossing has resulted in highly introgressed hybrids, with many hybrids containing mitochondrial DNA from one species on a nuclear DNA background of the other. Ecological aspects explaining these shifts in genetic composition include female mate choice, changes in habitat associated with secondary succession, and, most strongly, a hierarchy of male territorial advantage—ecological mechanisms likely to be involved in the emergence and disappearance of many animal hybrid zones. Our results suggest that genetic assimilation is not a significant threat to either species and that rather transient hybrid zones such as this may serve to increase genetic diversity and are candidates for causing genetic discordance in phylogeographic analyses.

杂交作用（hybridization）可通过产生新物种，并以多种方式影响亲本物种的演化——包括基因渐渗（introgression）与杂种优势（hybrid vigor）所带来的后果，从而成为一类重要的演化驱动力。然而，解析杂交带（hybrid zone）内演化背后的生态过程颇具难度，因为这需要同时考察基因型频率（genotypic frequencies）随时间的变化，以及对应的生态信息，而这类同时涵盖两类数据的研究样本极少被收集。在此，我们针对一处至少已存续23个世代的杂交带，描述其遗传与生态特征——该杂交带分布于东部栅栏蜥（Sceloporus undulatus）与佛罗里达灌丛蜥（Sceloporus woodi）之间。该杂交带早在35年前便通过形态学特征（morphological characters）被发现，最初亲本物种与杂交个体的比例近乎均等。如今，我们借助遗传标记（genetic markers）——包括物种特异性线粒体DNA（mitochondrial DNA, mtDNA）位点，以及总计117个个体的6个核DNA（nuclear DNA, nDNA）微卫星位点（microsatellite loci）——不仅证实了杂交事件的发生，还发现后续的回交（backcrossing）已产生了高度基因渐渗的杂交个体：诸多杂交个体的核DNA背景来自其中一个物种，而线粒体DNA却来自另一物种。解释这类遗传组成变化的生态机制包括：雌性配偶选择（female mate choice）、与次生演替（secondary succession）相关的生境变迁，以及最为关键的雄性领地优势（male territorial advantage）的层级结构——这类生态机制极有可能参与了诸多动物杂交带的形成与消失过程。我们的研究结果表明，遗传同化（genetic assimilation）对任一物种均未构成显著威胁；且此类短暂型杂交带（transient hybrid zones）非但不会威胁物种存续，反而可能提升遗传多样性（genetic diversity），同时也可能成为系统地理学分析（phylogeographic analyses）中出现遗传不一致性（genetic discordance）的潜在诱因。