Significance of heterochrony in ostracode higher taxonomy

点击翻译按钮获取中文摘要

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.