Bruni Giacomo, Chiocchio Andrea, Nascetti Giuseppe, Cimmaruta Roberta
Viale Palmiro Togliatti Sesto Fiorentino Italy.
Department of Ecological and Biological Sciences Tuscia University Viterbo Italy.
Ecol Evol. 2023 Aug 23;13(8):e10437. doi: 10.1002/ece3.10437. eCollection 2023 Aug.
Hybrid zones occur where genetically distinct populations meet, mate and produce offspring with mixed ancestry. In Plethodontid salamanders, introgressive hybridization is a common phenomenon, where hybrids backcross with parental populations leading to the spread of new alleles into the parental genomes. Whereas many hybrid zones have been reported in American Plethodontid salamanders, only a single hybrid zone has been documented in European plethodontids so far, which is located at the Apuan Alps in the Italian Peninsula. Here, we describe a previously unreported hybrid zone in the Northern Apennines involving all the three Plethodontid salamander species inhabiting the Italian Peninsula. We found 21 new sites of occurrence, from a hitherto unexplored area located at the boundaries between three species ranges. Using mitochondrial (Cytb and ND2 genes) and nuclear markers (two diagnostic SNPs at the NCX1 gene), we revealed a three-way contact zone where all the three mainland species hybridize: , and . We observed a strong mitonuclear discordance, with mitochondrial markers showing a conspicuous geographic pattern, while diagnostic nuclear SNPs coexisted in both the same populations and individuals, providing evidence of hybridization in many possible combinations. The introgression is asymmetric, with mitogenome usually associated with and, to a lesser extent, to nuclear alleles. This finding confirms that Plethodontid are a group of choice to investigate hybridization mechanisms and suggests that behavioural, genetic and ecological components may concur in determining the direction and extent of introgression.
杂交带出现在基因不同的种群相遇、交配并产生具有混合血统的后代的地方。在无肺螈科蝾螈中，渐渗杂交是一种常见现象，即杂种与亲本种群回交，导致新等位基因扩散到亲本基因组中。虽然在美国无肺螈科蝾螈中已报道了许多杂交带，但迄今为止在欧洲无肺螈科中仅记录到一个杂交带，位于意大利半岛的亚平宁阿尔卑斯山。在此，我们描述了亚平宁山脉北部一个以前未报道的杂交带，涉及栖息在意大利半岛的所有三种无肺螈科蝾螈。我们从位于三个物种分布范围边界的一个迄今未被探索的区域发现了21个新的出现地点。使用线粒体（Cytb和ND2基因）和核标记（NCX1基因的两个诊断性单核苷酸多态性），我们揭示了一个三方接触带，其中所有三个大陆物种都发生杂交：、和。我们观察到强烈的线粒体-核不一致，线粒体标记显示出明显的地理模式，而诊断性核单核苷酸多态性在相同的种群和个体中同时存在，提供了许多可能组合杂交的证据。渐渗是不对称的，线粒体基因组通常与和，在较小程度上与核等位基因相关。这一发现证实无肺螈科是研究杂交机制的一个理想类群，并表明行为、遗传和生态成分可能共同决定渐渗的方向和程度。
