Data from: Species collapse via hybridization in Darwin's tree finches

Species hybridization can lead to fitness costs, species collapse, and novel evolutionary trajectories in changing environments. Hybridization is predicted to be more common when environmental conditions change rapidly. Here, we test patterns of hybridization in three sympatric tree finch species (small tree finch: Camarhynchus parvulus; medium tree finch: C. pauper; large tree finch: C. psittacula) that are currently recognized on Floreana Island, Galápagos Archipelago. Genetic analysis of microsatellite data from contemporary samples showed two genetic populations and one hybrid cluster in both 2005 and 2010; hybrid individuals were derived from Genetic Population 1 (small morph) and Genetic Population 2 (large morph). Females of the large and rare species were more likely to pair with males of the small common species. Finch populations differed in morphology in 1852-1906 compared with 2005/2010. An unsupervised clustering method showed (a) support for three morphological clusters in the historical tree finch sample (1852/1906), which is consistent with current species recognition; (b) support for two or three morphological clusters in 2005 with some (19%) hybridization; and (c) support for just two morphological clusters in 2010 with frequent (41%) hybridization. We discuss these findings in relation to species demarcations of Camarhynchus tree finches on Floreana Island.

物种杂交可引发适合度代价、物种崩溃，并在环境变化下催生全新的演化路径。现有理论预测，当环境条件快速变化时，杂交事件会更为频发。本研究针对加拉帕戈斯群岛弗洛雷亚纳岛上目前被认可的3种同域（sympatric）树雀（小树雀：*Camarhynchus parvulus*；中树雀：*C. pauper*；大树雀：*C. psittacula*）的杂交模式开展检验。我们对当代样本的微卫星（microsatellite）遗传数据进行分析，结果显示，2005年与2010年的样本均呈现2个遗传种群与1个杂交集群；杂交个体均源自遗传种群1（小型形态型）与遗传种群2（大型形态型）。体型较大且较为稀有的物种的雌性个体，更倾向于与体型较小的常见物种的雄性个体配对。1852—1906年的树雀种群形态与2005/2010年存在显著差异。无监督聚类（unsupervised clustering）分析结果显示：(a) 1852/1906年的历史树雀样本支持3个形态类群，这与当前的物种认定结果一致；(b) 2005年的样本支持2或3个形态类群，存在一定比例（19%）的杂交事件；(c) 2010年的样本仅支持2个形态类群，杂交事件频发（占比41%）。我们结合弗洛雷亚纳岛树雀属（Camarhynchus）的物种界定问题，对上述研究结果展开讨论。