Aix-Marseille Université, CNRS, IRD, IMBE - UMR 7263, Equipe Evolution Génome Environnement, Centre Saint-Charles, Case 36, 3 place Victor Hugo, Marseille Cedex 3 13331, France.
Front Zool. 2013 May 1;10(1):22. doi: 10.1186/1742-9994-10-22.
Hybridization is a common phenomenon in fish and is considered to be a major source of diversification. Deciphering the remoulding of genomic regions and phenotypes in zones where hybrid specimens occur is of particular interest to elucidate the emergence of evolutionary novelties. This approach is particularly challenging because the first step of hybridization seems to be the most important stage in the emergence of hybrid lineages. However, the signal can be significantly altered after only a few generations.
We studied 41 microsatellites and partial cytochrome b gene sequences in 970 specimens belonging to two fish species (Chondrostoma nasus and Parachondrostoma toxostoma) in allopatric/parapatric zones, hybrids between them in a natural sympatric zone: the Ardèche basin. We showed that the genomic architecture in hybrids presented pattern heterogeneity of selection for the different loci. Indeed, the upstream part of the river (Rosières and Labeaume) presented an overdominant fitness of heterozygotes (12.20%) corresponding to a genomic compatibility, and underselection was observed for 4.88%-7.32% of the loci tested indicating a genomic incompatibility. Moreover the upstream station (Rosières) presented a positive selection of invasive C. nasus homozygotes (17.07% to 21.95%) indicating that hybridization may increase the fitness of admixed individuals.We showed that hybrid morphology (body shape based on 21 landmarks) correlated with genomic dilution indicating a species fingerprint. However, we demonstrated that the hybrid morphology was not a linear modification between the two parental species but a trade-off between several correlated traits.
Hybrid specimens present a mosaic of genomic combination, showing regions with genomic compatibility and others with genomic incompatibility between the two species. Positive selection (invasive advantage ranging from 9.76% to 21.95% of the loci) was evidenced in the upstream part of the Ardèche indicating that environmental selection makes a substantial contribution. Although the presence of a dam is known to impose heterogeneous hybrid zones between these two species, we demonstrated in this study that a natural environment can also generate a hybrid zone with a large number (and diversity) of hybrids. The combination of the two genomes in the hybrids results in complex ontogenetic trajectories (with different morphological traits evolving at different rates) that correspond to novel developmental pathways.
杂交是鱼类中的一种常见现象，被认为是物种多样化的主要来源。解析杂种出现区域的基因组区域和表型的重塑，对于阐明进化新特性特别重要。这种方法特别具有挑战性，因为杂交的第一步似乎是杂种谱系出现的最重要阶段。然而，这种信号在仅仅几代之后就会发生显著改变。
我们在异质/邻域区的 970 个样本中研究了两种鱼类（黄河雅罗鱼和北方铜鱼）的 41 个微卫星和部分细胞色素 b 基因序列，以及它们在自然同域区的杂种。我们表明，杂种中的基因组结构表现出不同基因座选择的模式异质性。实际上，上游河流部分（罗塞雷斯和拉博梅）的杂合子具有超显性适合度（12.20%），这对应于基因组相容性，而在测试的 4.88%-7.32%的基因座中观察到选择不足，表明基因组不相容。此外，上游站（罗塞雷斯）对入侵的黄河雅罗鱼纯合子进行了正选择（17.07%至 21.95%），表明杂交可能会增加混合个体的适应性。我们表明，杂种形态（基于 21 个标志的身体形状）与基因组稀释相关，表明存在物种特征。然而，我们证明杂种形态不是两个亲物种之间的线性修饰，而是几个相关特征之间的权衡。
杂种标本呈现出基因组组合的镶嵌图案，显示出两个物种之间存在基因组相容性的区域和其他基因组不相容的区域。在阿尔代什河的上游部分，证据表明存在正选择（入侵优势范围在 9.76%至 21.95%的基因座之间），这表明环境选择做出了实质性贡献。尽管已知大坝的存在会在这两个物种之间造成异质杂种区，但我们在本研究中证明，自然环境也可以产生具有大量（和多样性）杂种的杂种区。杂种中两个基因组的组合导致了复杂的个体发生轨迹（不同的形态特征以不同的速度进化），这对应于新的发育途径。
