白头鹎两广亚种和指名亚种表型分化的遗传基础及其演化机制

The microevolution, studies of speciation and adaptation is one of the frontiers in molecular ecology and evolutionary biology. Conspecific subspecies of birds usually show distinct phenotypes and unique geographical distribution patterns, which suggests that they are good examples to understanding speciation process and its associated local adaptation to geographical ranges. The two subspecies of Light-vented Bulbul (Pyconotus sinensis), P. s. hainanus and P. s. sinensis, mainly distribute in southern China, showing distinct phenotypic differentiation, especially the color pattern in head. However, our preliminary studies showed little genetic differentiation at several genetic markers, e.g. mitochondrial DNA, neutral nuclear loci and the pigmentation gene, melanocortin-1-receptor. To resolve the dis-concordance between phenotypic and genotypic differentiations, it requires us to identify candidate genes associated adaptive population divergence at the genomic level and annotate their functions. Here, we will screen many markers randomly scattered across the genome of P. s. hainanus and P. s. sinensis using AFLP-based genome scans and distinguish between the neutral genetic background and outlier loci displaying an atypical behavior (e.g., a higher differentiation between subspecies). Then the outliers will be sequenced by 454 pyrosequencing, and determined location and annotated function by comparative genomic approaches. Thus, we can discuss the genetic and evolutionary context of phenotypic variation between P. s. hainanus and P. s. sinensis. The result will uncover the molecular and genetic underpins of adaptive divergence of the two subspecies, and enrich studies about speciation and its evolutionary mechanism. Moreover, the project will also be a preliminary to further genetic analysis about adaptive phenotypic variations of P. sinensis based on gene regulation system, and be implicated in fast-detection of candidate genes and determination of their functions in wild avian species.

与物种形成和适应相关的微进化过程是近年来分子生态与进化研究的热点问题之一。鸟类种下亚种往往表现为独特的表型和地理分布，是探讨适应趋异的代表类群。白头鹎两广亚种与指名亚种形态差异显著，但基于线粒体基因、中性核位点及羽色主控基因(MC1R)等分子标记没能解决其亚种分化问题，推测该表型分化可能主要是由自然选择驱动的快速适应引起的，需采用与适应相关的分子标记才能检测到。本研究拟通过AFLP法从基因组水平上筛选与白头鹎两广亚种与指名亚种表型适应分化相关的基因，并通过454焦磷酸测序将其转化为序列数据，由比较基因组学的方法，寻找其可能的基因注释，从而鉴定两个亚种的遗传分化，探讨其适应机制。研究结果不仅可以揭示与白头鹎亚种表型分化相关的微进化过程的分子和遗传基础，也将为白头鹎表型适应变异后续的多基因调控机制的研究提供研究基础，同时还可以为其他鸟类自然种群中表型变异的微进化过程的研究提供参考依据。

白头鹎指名亚种P. s. sinensis（白头型）与两广亚种P. s. hainanus（黑头型）形态差异显著，同时白头鹎台湾亚种P. s. formosae（白头型）与台湾鹎P. taivanus（黑头型）形态上也存在类似的差异变化，由于其较短的分化时间，前期基于线粒体、微卫星及羽色主控基因（MC1R）的研究未能将它们鉴定区分开来。本研究通过性状分析法（population aggregation analysis）和溯祖分析法（Bayesian Phylogenetics and Phylogeography），结合羽色、线粒体基因和核基因内含子等不同性状进行分析，研究结果表明：羽色数据支持3个种，线粒体支持2个种，而核基因支持1个种。整合所有这些独立数据的一致性特征我们认为该复合种存在3个种的分化，即白头鹎指名亚种P. s. sinensis、台湾亚种P. s. formosae (包括琉球亚种P. s. orii) 和台湾鹎 P. taivanus，同时数据相对弱的支持第4个种--白头鹎两广亚种 P. s. hainanus 的分化；本研究还证实在近期分化的物种鉴定中，基于溯祖法未必像公认的那样，优于传统的性状法。相关研究结果将对物种界定尤其是近期分化的物种界定具有重要的参考价值。而关于白头鹎和台湾鹎这一鸟类复合种具体的分化细节将在对新一代测序法获得的基因组数据分析的基础上进行进一步讨论。