Mitochondrial and Nuclear DNA Survey of Zootoca vivipara across the Eastern Italian Alps: Evolutionary Relationships, Historical Demography and Conservation Implications

The European common lizard Zootoca vivipara exhibits reproductive bimodality, with populations being either viviparous or oviparous. In the central-eastern Italian Alps oviparous populations (Z. v. carniolica) and viviparous populations (Z. v. vivipara) partly overlap geographically. Studying the evolutionary relationship between these taxa presents an interesting opportunity to gain insight into the evolution of this trait. We aim to: i) test whether Z. v. carniolica, which is endangered, constitutes an ESU (Evolutionary Significant Unity); ii) infer mtDNA divergence time between the Z. v. carniolica clade and all the other Z. vivipara subspecies with the aid of an external calibration point; and iii) describe the phylogeographical and demographic scenarios in the area. To do so we sequenced about 200 individuals for mitochondrial variation; 64 of them were also analysed for three nuclear genes. Furthermore, we analysed the same nuclear markers in 17 individuals from the other oviparous subspecies Z. v. louislantzi and 11 individuals of Z. v. vivipara from widespread geographical origins. The mtDNA and nDNA loci that we examined supported the monophyly of Z. v. carniolica. The mtDNA-based estimate of divergence time between Z. v. carniolica and all the other subspecies indicated a separation at 4.5 Mya (95% CI 6.1–2.6), with about 5% of sequence divergence. Considering that Z. v. carniolica harbours higher genetic diversity, while Z. v. vivipara from central-eastern Alps shows a signature of recent population and spatial expansion, we argue that Z. v. carniolica represents a distinct evolutionary unit, with a presumably long-term evolutionary history of separation. Z. v. carniolica populations, occurring at higher latitudes and altitudes than insofar supposed, live in peat bogs, a seriously threatened habitat: taking into account also its evolutionary distinctness, specific conservation measures should be considered.欧洲胎生蜥蜴（Zootoca vivipara）呈现生殖二态性，种群可划分为胎生种群与卵生种群两类。在意大利中东部阿尔卑斯山区，卵生种群（Z. v. carniolica）与胎生种群（Z. v. vivipara）存在部分地理重叠。对这些类群间的演化关系开展研究，可为解析该生殖性状的演化历程提供极具价值的契机。本研究旨在达成以下三项目标：其一，检验处于濒危状态的Z. v. carniolica是否属于进化显著单元（Evolutionary Significant Unity）；其二，借助外部校准点，推断Z. v. carniolica支系与其他所有Z. vivipara亚种之间的线粒体DNA（mitochondrial DNA，mtDNA）分化时间；其三，阐明该区域的系统地理学与种群历史情景。为实现上述研究目标，我们对约200个个体的线粒体变异进行了测序；其中64个个体还额外开展了3个核基因位点的分析。此外，我们还对来自另一卵生子亚种Z. v. louislantzi的17个个体，以及采集自广泛地理分布区域的11个Z. v. vivipara个体的相同核标记进行了分析。本研究检测的线粒体DNA与核DNA（nuclear DNA，nDNA）位点均支持Z. v. carniolica的单系性。基于线粒体DNA估算的Z. v. carniolica与其他所有亚种的分化时间显示，二者的分化发生在4.5百万年前（95%置信区间：6.1–2.6百万年前），序列分化度约为5%。考虑到Z. v. carniolica拥有更高的遗传多样性，而采自中东部阿尔卑斯山区的Z. v. vivipara种群呈现出近期种群扩张与空间扩张的遗传信号，我们认为Z. v. carniolica是一个独特的演化单元，具备长期的演化分化历史。Z. v. carniolica种群的分布纬度与海拔均高于此前的认知，它们栖息在泥炭沼泽这一受严重威胁的生境中；结合其演化独特性，应考虑制定针对性的保护措施。