亚洲平胸龟属物种的分类及分子谱系地理学研究

The genus of Platysternon (Testudines: Platysternidae) is an endangered taxon endemic to Asia, with very important scientific and economic value. At present,the big-headed turtle (Platysternon megacephalum) is the sole living representative of a poorly-studied turtle lineage (Platysternidae). It ranges from Myanmar, Thailand, Cambodia, Laos, and Vietnam to southern China where it inhabits rocky mountain streams. It has no close living relatives, and its phylogenetic position within turtles is one of the outstanding controversies in turtle systematics. Platysternon was traditionally considered to be close to snapping turtles (Chelydridae) based on some studies of its morphology and mitochondrial DNA, however, other studies of morphology and nuclear DNA do not support that hypothesis. Untill 2006, the controversies in the phylogenetic position of Platysternon was over with a reconciliation of phylogenetic hypotheses based on mitochondrial and nuclear DNA. Currently, however, there is still an outstanding controversies in subspecies of Platysternon megacephalum, three to five subspecies are recognized based on morphological evidence: P. m. megacephalum Gray, 1831; P. m. peguense Gray, 1870; P. m. vogeli Wermuth, 1969; P. m. tristernalis Schleich & Gruber, 1984; P. m. shiui Ernst & McCord,1987. Some subspecies may be invalidity because they are distinguished by some varying morphological evidences. Without extensive specimen collection, systematic morphological comparative analysis, and evidence from molecular phylogeny and phylogeography, it is hard to address this taxonomic issue.There may be some new cryptic species in the Platysternon. Without scientific data on taxonomy, genetic divergence, phylogeography of this endangered, conservation policies and measures cannot be made or carry out effectively. In recent ten years, we have conducted extensive fieldwork and collected some important specimens of Platysternon.In this study, based on mitochondrial DNA (cyt b,COI) and nuclear DNA (microsatellites, R35-intron) markers, with integrative taxonomy approach, we plan to conduct a study of taxonomy and molecular phylogeography to 1) re-examine the phylogenetic relationships of Platysternon species, distinguish the species and subspecies, 2) to investigate the genetic structure and genetic diversity of different populations, and the genetic relationships among different lineages, 3) to reveal the phylogeographic patters and evolution of different phylogenetic lineages. This study is important to the taxonomic revision of Platysternon,and can promote deep understanding of genetic divergence, phylogeographic history of Platysternon species, as well as provide important scientific base for conservation of this endangered turtle taxon.

平胸龟属是亚洲特有濒危龟类，具有重要的科研和经济价值。然而，长期以来在该属龟类的分类问题上存在较多学术争议，缺乏对属下单元的分子系统学研究，对各基因谱系遗传分化和地理格局认识不清，从而也严重影响了对这一珍稀濒危动物类群的有效保护。因此，本项目拟在近10年来野外种群调查和标本收集的基础上,进一步系统收集标本资料，分析和归纳形态特征变化规律，采用整合分类学方法，基于线粒体DNA和核DNA多种分子标记,对平胸龟属物种的分类和分子谱系地理学进行系统研究。旨在澄清平胸龟属的种（或亚种）的分类问题；探明平胸龟不同地理种群的遗传结构和遗传多样性，以及不同基因谱系之间的亲缘关系；揭示平胸龟不同基因谱系地理格局的形成与演化机理。该项目研究对正确厘定平胸龟属物种分类问题，深入认识不同基因谱系的遗传分化，以及谱系地理格局形成与演化机理具有重要科学意义，并可为该濒危类群的保护实践提供可靠的理论依据。

平胸龟属（Platysternon）是亚洲特有濒危龟类，具有重要的科研和经济价值。然而，长期以来在该属龟类的分类问题（尤其是亚种分类）上存在较多学术争议，缺乏对属下单元的分子系统学研究，对各基因谱系遗传分化和地理格局认识不清，从而也严重影响了对这一珍稀濒危动物类群的有效保护。本项目在近10年来野外种群调查和标本收集的基础上,进一步系统收集标本资料，分析和归纳形态特征变化规律，采用整合分类学方法，基于线粒体DNA和核DNA多种分子标记，对平胸龟属物种的分类和分子谱系地理学进行研究。研究结果表明：1）平胸龟分布广泛，不同地理种群间形态差异多样，主要体现在背腹甲斑纹及色彩、尾长与腹甲长的比例、头部形状等方面；2）平胸龟总体可以分为2个大的基因谱系，包括珠江-长江谱系和怒江-澜沧江-红河谱系，其中珠江-长江谱系至少包括4-5个分支谱系，怒江-澜沧江-红河谱系包括3个分支谱系，分别为怒江、澜沧江、红河谱系；3）平胸龟怒江谱系、澜沧江-红河谱系、珠江-长江谱系可能分化为3个独立种，越南亚种Platysternon megacephalum shiui 与指名亚种Platysternon megacephalum megacephalum无显著遗传分化。本项目研究结果对明确平胸龟属物种分类问题，深入认识不同基因谱系的遗传分化、谱系地理格局及其形成与演化机理具有重要科学意义，并可为该濒危类群的保护实践提供参考依据。