Corresponding Mitochondrial DNA and Niche Divergence for Crested Newt Candidate Species

Genetic divergence of mitochondrial DNA does not necessarily correspond to reproductive isolation. However, if mitochondrial DNA lineages occupy separate segments of environmental space, this supports the notion of their evolutionary independence. We explore niche differentiation among three candidate species of crested newt (characterized by distinct mitochondrial DNA lineages) and interpret the results in the light of differences observed for recognized crested newt species. We quantify niche differences among all crested newt (candidate) species and test hypotheses regarding niche evolution, employing two ordination techniques (PCA-env and ENFA). Niche equivalency is rejected: all (candidate) species are found to occupy significantly different segments of environmental space. Furthermore, niche overlap values for the three candidate species are not significantly higher than those for the recognized species. As the three candidate crested newt species are, not only in terms of mitochondrial DNA genetic divergence, but also ecologically speaking, as diverged as the recognized crested newt species, our findings are in line with the hypothesis that they represent cryptic species. We address potential pitfalls of our methodology.线粒体DNA（mitochondrial DNA）的遗传分化并不必然与生殖隔离相对应。但若线粒体DNA谱系占据互不重叠的生态位空间，则可佐证其演化独立性的论断。本研究针对三类以独特线粒体DNA谱系为特征的冠螈候选物种开展生态位分化分析，并结合已正式认定的冠螈物种所呈现的生态位差异对研究结果进行解读。我们量化了所有冠螈（候选）物种间的生态位差异，并采用两种排序分析技术——环境主成分分析（PCA-env）与生态位因子分析（ENFA）——检验生态位演化相关假说。生态位等价性假说被否决：所有（候选）物种均被证实占据显著分化的生态位空间。此外，三类候选物种的生态位重叠值并未显著高于已确认物种的生态位重叠值。鉴于这三类冠螈候选物种不仅在线粒体DNA遗传分化层面，在生态学维度上也与已确认的冠螈物种达到了同等分化水平，本研究结果契合‘它们属于隐存物种（cryptic species）’这一假说。我们还探讨了本研究方法可能存在的局限性。