Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands.
BMC Evol Biol. 2012 Aug 30;12:161. doi: 10.1186/1471-2148-12-161.
If the geographical displacement of one species by another is accompanied by hybridization, mitochondrial DNA can introgress asymmetrically, from the outcompeted species into the invading species, over a large area. We explore this phenomenon using the two parapatric crested newt species, Triturus macedonicus and T. karelinii, distributed on the Balkan Peninsula in south-eastern Europe, as a model.
We first delimit a ca. 54,000 km(2) area in which T. macedonicus contains T. karelinii mitochondrial DNA. This introgression zone bisects the range of T. karelinii, cutting off a T. karelinii enclave. The high similarity of introgressed mitochondrial DNA haplotypes with those found in T. karelinii suggests a recent transfer across the species boundary. We then use ecological niche modeling to explore habitat suitability of the location of the present day introgression zone under current, mid-Holocene and Last Glacial Maximum conditions. This area was inhospitable during the Last Glacial Maximum for both species, but would have been habitable at the mid-Holocene. Since the mid-Holocene, habitat suitability generally increased for T. macedonicus, whereas it decreased for T. karelinii.
The presence of a T. karelinii enclave suggests that T. karelinii was the first to colonize the area where the present day introgression zone is positioned after the Last Glacial Maximum. Subsequently, we propose T. karelinii was outcompeted by T. macedonicus, which captured T. karelinii mitochondrial DNA via introgressive hybridization in the process. Ecological niche modeling suggests that this replacement was likely facilitated by a shift in climate since the mid-Holocene. We suggest that the northwestern part of the current introgression zone was probably never inhabited by T. karelinii itself, and that T. karelinii mitochondrial DNA spread there through T. macedonicus exclusively. Considering the spatial distribution of the introgressed mitochondrial DNA and the signal derived from ecological niche modeling, we do not favor the hypothesis that foreign mitochondrial DNA was pulled into the T. macedonicus range by natural selection.
如果一个物种被另一个物种取代，并且伴随着杂交，那么线粒体 DNA 可以从被竞争淘汰的物种不对称地传入入侵物种中，并在很大的区域内传播。我们使用分布在东南欧巴尔干半岛上的两个邻域性的有角蝾螈物种，即马氏真螈（Triturus macedonicus）和喀尔巴阡蝾螈（T. karelinii）作为模型来探索这种现象。
我们首先确定了一个大约 54000 平方公里的区域，其中马氏真螈含有喀尔巴阡蝾螈的线粒体 DNA。这个基因渗入区将喀尔巴阡蝾螈的分布范围一分为二，切断了喀尔巴阡蝾螈的一个领地。渗入的线粒体 DNA 单倍型与在喀尔巴阡蝾螈中发现的单倍型高度相似，表明这是最近跨越物种边界的转移。然后，我们使用生态位模型来探索现代基因渗入区在当前、中全新世和末次冰期最大值条件下的栖息地适宜性。在末次冰期最大值期间，这个区域对两个物种都不适宜居住，但在中全新世时可能是适宜居住的。从中全新世开始，马氏真螈的栖息地适宜性普遍增加，而喀尔巴阡蝾螈的栖息地适宜性则下降。
喀尔巴阡蝾螈领地的存在表明，在末次冰期最大值之后，喀尔巴阡蝾螈首先殖民到现在基因渗入区的位置。随后，我们提出喀尔巴阡蝾螈被马氏真螈所取代，马氏真螈在这个过程中通过杂交基因渗入捕获了喀尔巴阡蝾螈的线粒体 DNA。生态位模型表明，这种替代可能是由于从中全新世开始气候的变化而促成的。我们认为，当前基因渗入区的西北部可能从未被喀尔巴阡蝾螈自身占据，喀尔巴阡蝾螈的线粒体 DNA 仅通过马氏真螈传播到那里。考虑到渗入的线粒体 DNA 的空间分布和生态位模型得出的信号，我们不支持外来线粒体 DNA 是通过自然选择被拉进马氏真螈分布区的假说。
