Faculty of Arts and Sciences Informatics Group, Harvard University, Cambridge, Massachusetts, USA.
Centre for Tropical Research and Institute of the Environment and Sustainability, University of California, Los Angeles, California, USA.
Mol Ecol. 2023 May;32(9):2287-2300. doi: 10.1111/mec.16867. Epub 2023 Feb 12.
Accelerating climate change and habitat loss make it imperative that plans to conserve biodiversity consider species' ability to adapt to changing environments. However, in biomes where biodiversity is highest, the evolutionary mechanisms responsible for generating adaptative variation and, ultimately, new species are frequently poorly understood. African rainforests represent one such biome, as decadal debates continue concerning the mechanisms generating African rainforest biodiversity. These debates hinge on the relative importance of geographic isolation versus divergent natural selection across environmental gradients. Hindering progress is a lack of robust tests of these competing hypotheses. Because African rainforests are severely at-risk due to climate change and other anthropogenic activities, addressing this long-standing debate is critical for making informed conservation decisions. We use demographic inference and allele frequency-environment relationships to investigate mechanisms of diversification in an African rainforest skink, Trachylepis affinis, a species inhabiting the gradient between rainforest and rainforest-savanna mosaic (ecotone). We provide compelling evidence of ecotone speciation, in which gene flow has all but ceased between rainforest and ecotone populations, at a level consistent with infrequent hybridization between sister species. Parallel patterns of genomic, morphological, and physiological divergence across this environmental gradient and pronounced allele frequency-environment correlation indicate speciation is mostly probably driven by ecological divergence, supporting a central role for divergent natural selection. Our results provide strong evidence for the importance of ecological gradients in African rainforest speciation and inform conservation strategies that preserve the processes that produce and maintain biodiversity.
加速的气候变化和栖息地丧失使得保护生物多样性的计划必须考虑物种适应不断变化的环境的能力。然而，在生物多样性最高的生物群落中，负责产生适应性变异并最终形成新物种的进化机制常常理解得很差。非洲雨林就是这样一个生物群落，因为关于产生非洲雨林生物多样性的机制的十年辩论仍在继续。这些辩论取决于地理隔离与环境梯度上的分歧自然选择的相对重要性。阻碍进展的是缺乏对这些竞争假说的有力检验。由于非洲雨林因气候变化和其他人为活动而面临严重风险，解决这一长期存在的争议对于做出明智的保护决策至关重要。我们使用人口推断和等位基因频率-环境关系来研究栖息在雨林和雨林-稀树草原镶嵌体（生态交错带）之间梯度上的非洲雨林石龙子 Trachylepis affinis 的多样化机制。我们提供了令人信服的证据表明存在生态交错带物种形成，在这种物种形成中，基因流几乎已经在雨林和生态交错带种群之间停止，这与姐妹种之间很少发生杂交的水平一致。在这种环境梯度上的基因组、形态和生理分化的平行模式以及明显的等位基因频率-环境相关性表明，物种形成主要是由生态分歧驱动的，这支持了分歧自然选择的核心作用。我们的研究结果为生态梯度在非洲雨林物种形成中的重要性提供了有力的证据，并为保护那些产生和维持生物多样性的过程的保护策略提供了信息。
