Ambu Johanna, Litvinchuk Spartak N, Caballero-Díaz Carlos, Nicieza Alfredo, Velo-Antón Guillermo, Gonçalves Helena, Martínez-Freiría Fernando, Martínez-Gil Helena, Beltrán Juan Francisco, Donaire-Barroso David, Hernandez Axel, Suchan Tomasz, Crochet Pierre-André, Martínez-Solano Ĺñigo, Dufresnes Christophe
Laboratory for Amphibian Systematics and Evolutionary Research, College of Biology & the Environment, Nanjing Forestry University, Nanjing, China.
Russian Academy of Sciences, Institute of Cytology, St. Petersburg, Russia.
Mol Ecol. 2025 Apr;34(8):e17736. doi: 10.1111/mec.17736. Epub 2025 Mar 25.
Speciation, i.e., the formation of new species, implies that diverging populations evolve genetic, phenotypic or ecological factors that promote reproductive isolation (RI), but the relative contributions of these factors remain elusive. Here we test which of genomic, bioacoustic, morphological, and environmental differences best predicts RI across a continuum of divergence in the midwife toads (genus Alytes), a group of Western Mediterranean amphibians, using a total evidence approach. We found that, without strong geographic barriers to dispersal, the extent of introgression across hybrid zones between phylogeographic lineages, which should reflect the strength of RI, predominantly covaries with genomic divergence. Overall phenotypic differentiation becomes substantial only between well established, fully isolated species. These results suggest that speciation in midwife toads initially involve cryptic lineages, which probably evolve RI through intrinsic (genetic) hybrid incompatibilities. As they continue to diverge, these nascent species eventually differentiate externally, which potentially enforces pre-mating barriers and facilitates sympatry. This speciation scenario has practical implications for species delimitation, notably when using hybrid zones and divergence thresholds as proxies for reproductive isolation.
物种形成，即新物种的形成，意味着分化的种群进化出促进生殖隔离（RI）的遗传、表型或生态因素，但其相对贡献仍不明确。在此，我们采用全证据法，测试基因组、生物声学、形态学和环境差异中哪一种能最好地预测西地中海两栖动物产婆蟾属（Alytes）在不同分化程度连续体上的生殖隔离。我们发现，在没有强大的扩散地理障碍的情况下，谱系地理谱系间杂交带的基因渗入程度（应反映生殖隔离的强度）主要与基因组分化相关。总体表型分化仅在成熟的、完全隔离的物种之间才变得显著。这些结果表明，产婆蟾的物种形成最初涉及隐秘谱系，它们可能通过内在（遗传）杂交不相容性进化出生殖隔离。随着它们继续分化，这些新物种最终在外部表现出差异，这可能会强化交配前的障碍并促进同域共存。这种物种形成模式对物种界定具有实际意义，特别是在使用杂交带和分化阈值作为生殖隔离的代理指标时。
