Significance of heterochrony in ostracode higher taxonomy

本计画之主要成果可归纳如下：介形类系统发育关系之评估程序有显著之改善。介形虫线粒体DNA分析的成功，为介形虫的研究带来了新的进展，并根据COI区的DNA分析结果，对3科6属11种介形虫的亲缘关系进行了初步探讨。然而，也证明了COI区域对于近缘种的估计是足够好的，但由于碱基替换的快速速率而不适合于更高的分类群。另一个新的估计程序，通过个体发育的孔隙系统的分化过程，已被证明是非常有效的低和高类群。早期和晚期的个体发育阶段可用于较高和较低的系统发育关系，分别。这两种方法首次给出了介形虫与介形虫之间定量的、客观的关系，并对介形虫与介形虫之间的关系进行了重新整理，对介形虫与介形虫之间的关系进行了详细的形态分析。结果表明，铰链结构是高等植物中最稳定的性状之一，但它很容易被异时性所改变。介形虫的异时性在介形虫系统学中起着重要作用，而介形虫的异时性转化本身也有其独特的趋势。在中生代晚期或第三纪早期爆发性地出现了具有特定类型铰合的各种分类群。然后，后代类群与幼态类型的铰链，他们的优势被发现已经在新近纪。这是一个罕见的案例研究，成功地描述了一个明确的进化趋势。

Essence of the results of this project can be summarized as follows.The procedure to estimate the phylogenetic relationship of ostracodes has been drastically improved. The first improvement was brought by the success of the analysis of ostracode mtDNA,and the relatioship between 11 species belonging to 6 genera, 3 families was estimated based on the DNA analysis of COI region. It is, however, also proved that the COI region is good enough for the estimate of close species, but is not appropriate for higher taxa due to the rapid rate of the replacement of the bases. Another new procedure of the estimate, the process of differentiation of pore-systems through ontogeny, has been demonstrated to be very effective for both lower and higher taxa. Early and late ontogenetic stages are available for higher and lower phylogenetic relatioship, respectively. The two procedures give us a quantitative and objective relationship for the first time.After rearrangement of some ostracode relationship belonging to five cytheracean families, their morphology was carefully analyzed. Results showed that the structure of hingement, which was thought to be one of the stable characters in higher taxa, could be easily transformed by heterochrony. The heterochrony plays an important part in ostracode sytematics and the transformation itself has a unique tendency as follows. Various taxa with specific types of hingement explosively appeared during late Mesozoic or early Tertiary. Then, descendant taxa with paedomorphic type of hingement of their ascendants were found to have evolved during Neogene. This is a rare case study that succeeded to describe a clear evolutionary tendency.