Testing recurrent ecological speciation processes in microendemic Madagascan reptiles and amphibians of the isolated Amber Mountain

新物种产生的过程长期以来一直是一个活跃的辩论领域，目前对物种形成的研究集中在驱动分化的机制上。生态物种形成（ES）是指自然选择强烈地倾向于不同的生态类型，而生殖隔离则是由于不同生态的适应性差异而进化的结果。然而，合适的设置来研究ES是罕见的。我们对马达加斯加脊椎动物区系演化的长期研究计划初步表明，马达加斯加北方孤立的琥珀山地块拥有各种两栖动物和爬行动物的独特的地方性姐妹分支，其中一些似乎仅限于不同的海拔范围。这表明，这些血统可能起源于地块的ES，并指出琥珀山作为一个合适的模型系统，研究多样化的生态（海拔）梯度。本研究计划将联合收割机结合元编码和群体遗传学的前沿方法，探索该地区小型特有两栖类动物的ES过程。它采用了严格的假设检验框架，以评估是否生态梯度是过去和正在进行的ES的主要驱动力。我们的方法将使用琥珀山整个两栖动物群落的元条形码数据，以及对三个目标类群（可能包括Brookesia，Stumpffia，Escherumsuma或Uroplatus属中的一个或几个）的种群遗传学深入研究。将沿预先确定的、具有生态特征的断面进行沿着密集采样，此外，将采用网格方法进行快速调查，以确定整个两栖类动物区系的分布和生态地理特征。将使用Illumina测序对合并样本进行高通量扩增子元条形码编码，对现场工作期间收集的大量样本进行分析。对于目标分类群，微卫星和RADseq衍生的SNP将用于表征小规模群体分化。如果ES触发了琥珀山两栖动物和爬行动物的多样化，那么我们预测：（i）琥珀山上分化的特有姐妹谱系将分布在不同的海拔范围内，（ii）它们的接触区与生态交错区和整个两栖动物群落的更替相一致，（iii）分布在这些生态交错区的目标谱系将显示与生态梯度有关的基因流动减少，而不是与距离或物理障碍有关。鉴于在马达加斯加测试ES的研究很少，将琥珀山作为此类研究的研究区域的努力将是开创性的，并刺激在这一独特的生物群中进行基于过程的物种形成研究。

The processes by which new species arise have long been an active field of debate Current research on speciation focuses the mechanisms driving the divergence. Ecological Speciation (ES) occurs if natural selection strongly favours different ecotypes, and reproductive isolation evolves as a consequence of adaptive divergence due to differing ecology. However, suitable settings to study ES are rare. Our long-term research program on the evolution of the vertebrate fauna of Madagascar has yielded preliminary indicated that the isolated Amber Mountain Massif in northern Madagascar harbours distinct locally endemic sister clades of various amphibians and reptiles, and some of these appear to be restricted to distinct elevational ranges. This suggests that these lineages might have originated in the Massif by ES, and points to Amber Mountain as a suitable model system for studying diversification across ecological (elevational) gradients. The research project proposed here will combine cutting-edge methods in metabarcoding and population genetics, to explore ES processes in the microendemic herpetofauna of this massif. It applies a strict hypothesis-testing framework to assess whether an ecological gradient is the predominant driver of past and ongoing ES. Our approach will use metabarcoding data for the entire herpetofaunal community of Amber Mountain, and population genetic in-depth study of three target taxa (likely including one or several of the genera Brookesia, Stumpffia, Phelsuma, or Uroplatus). Dense sampling will be carried out along pre-defined transects that will be characterized ecologically, and furthermore, rapid surveys will be done using a grid approach in order to characterize the distribution and phylogeography of the entire herpetofauna in the massif. The large number of samples collected during fieldwork will be analyzed using high-throughput amplicon metabarcoding of pooled samples with Illumina sequencing. For the target taxa, microsatellites and RADseq-derived SNPs will be used to characterize small-scale population differentiation. If ES triggered the diversification of amphibians and reptiles of Amber Mountain, then we predict that (i) endemic sister lineages that differentiated on Amber Mountain will be distributed at distinct elevational ranges, (ii) their contact zones coincide with ecotones and with turnover of the entire herpetofaunal community, (iii) target lineages distributed across these ecotones will show reduction of gene flow related to the ecological gradient rather than to distance or physical barriers. Given the scarcity of research that tests ES in Madagascar, the endeavour to establish the Amber Mountain as study region for such research would be ground-breaking, and stimulate process-based speciation research in this unique biota.