Karyotype of North American shortnose sturgeon Acipenser brevirostrum with the highest chromosome number in the Acipenseriformes

摘要

The shortnose sturgeon Acipenser brevirostrum was revealed to have a larger number of chromosomes than previously reported for other sturgeon species. Its chromosome number ranged from 362 to 372 ( of ten specimens examined), showing intraindividual variation. The karyotype of metaphase with the highest chromosome number ( 372) consisted of 89 pairs of macrochromosomes and 97 pairs of microchromosomes ( fundamental number; NF = 550). Although the microchromosomes were relatively shorter than the macrochromosomes, most of them had discernible arms and centromeres. Silver-stained nucleolar organizer regions ( Ag- NORs) were localized on the telomeric regions of 5 pairs of chromosomes ( Ag- NORs = 10): 4 were made up of small meta/submetacentrics and 1 of acrocentrics. Polyploidy of A. brevirostrum should be hexaploid based on the karyotype, numerous chromosomes, Ag- NORs, and previously reported large genome size ( ca. 13pg DNA/ cell).