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争论领域，目前关于物种形成的研究集中在驱动分化的机制上。如果自然选择强烈倾向于不同的生态类型，则会发生生态物种形成（ES），而生殖隔离则是由于不同生态导致的适应性分化而演变的结果。然而，适合研究ES的环境很少。我们对马达加斯加脊椎动物动物群进化的长期研究项目已经初步表明，马达加斯加北部孤立的琥珀山山脉拥有各种两栖动物和爬行动物的独特当地特有的姐妹分支，其中一些似乎仅限于不同的海拔范围。这表明这些谱系可能起源于ES的地块，并指出琥珀山是研究跨生态（海拔）梯度多样化的合适模型系统。本研究项目将结合元条形码和群体遗传学的前沿方法，探索该地块微型特有爬行动物的ES过程。它采用严格的假设检验框架来评估生态梯度是否是过去和正在进行的ES的主要驱动因素。该方法将利用琥珀山整个爬虫动物群落的元编码数据，对三个目标分类群（可能包括Brookesia、Stumpffia、Phelsuma或Uroplatus属中的一个或几个属）进行种群遗传学深入研究。将沿着预先确定的样带进行密集采样，这些样带将具有生态特征，此外，将使用网格方法进行快速调查，以便描述地块中整个爬虫动物群的分布和系统地理特征。在野外工作中收集的大量样品将使用Illumina测序的高通量扩增子元条形码对汇集的样品进行分析。对于目标类群，微卫星和radseq衍生的snp将用于表征小规模种群分化。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：(1)在琥珀山上分化的地方性姊妹谱系将分布在不同的海拔范围内；(2)它们的接触带与过渡带和整个爬行动物群落的更替一致；(3)分布在这些过渡带上的目标谱系将显示与生态梯度相关的基因流减少，而不是与距离或物理障碍有关。鉴于在马达加斯加测试ES的研究缺乏，将琥珀山建立为此类研究的研究区域的努力将具有开创性，并将刺激对这一独特生物群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.