GENOME SIZE, PLOIDY CHARACTERS OF SEVERAL SPECIES OF STURGEONS AND PADDLEFISHES WITH COMMENT ON CELLULAR EVOLUTION OF ACIPENSERIFORMES

Using of DNA of chicken erythrocyte (3. 22pg/2C) as a standard, genome size (somatic nuclear DNA content) of five species of sturgeons and paddlefishes including Chinese paddlefish (Psephurus gladius ), Yangtze sturgeon (Acipenser dabryanus ), Chinese sturgeon (A. sinensis ), Amur sturgeon (A. schrenckii ) and American paddlefish (Polyodon spathula ) were determined by microspectrometry. The DNA contents of each said species were 4. 11, 8. 26, 9. 07, 6. 07 and 3. 96pg, respectively. The genome size of two species including Yangtze sturgeon and Chinese sturgeon, was found two times as big as that of Chinese paddlefish and American paddlefish. Obviously, Chinese paddlefish and American paddlefish belong to the tetraploidy group whereas Yangtze sturgeon and Chinese sturgeon are octoploids. According to the present results and data reported, Amur sturgeon is possibly an octoploid (8n), however, it is more likely that two or more kinds of polyploids (4n, 8n and so on) have existed in the species of Amur sturgeon. Combination of the present results and data reported among Acipenseriformes including two families and six genera, the genus Acipenser possessed 4n. 8n. 12n and 16n while the other five genera possessed only 4n. It is deduced that the polyploidization took place at early time of formation of Acipenseriformes and within the genus Acipenser. Polyloidization has played an important role in the diversity of Acipenser which has more than 65% species in Acipenseriformes.