Ultrastructural observations on the Sperm of two Apodemus species,Apodemus agrarius coreae and Apodemus speciosus peninsulae,in Korea

Sperm morphology of Apodemus agrarius coreae, Apodemus speciosus peninsulae, Iaboratory mouse and rat were studied. The total length of the sperm ofA. a. coreae, A. s. peninsulae, the mouse and rat was about 133lhm, 124lhm, 13l~em and 192;hm, respectively. Two Apodemus spenu heads had a fish hook shape, while the mouse sperm head had a hook shape; thus, the sperm heads of genus Apodemus were somewhat like those of the mouse. The rat sperm head was unlike the other species in that it had a falciform shape. In addition, two Apodemus spermatozoa had two well-developed ventral spurs (Vs), and the mouse sperm head also had two sirnilar small Vs, but rat sperm head had low ridge line-like Vs. All species had a separated head-cap segment in the ventral side of the anterior acrosomal portion of sperm. In the neck region, the vault formerly occupied by the proxirnal centriole was retained in a niche in the dense substance of the connecting piece in the spermatozoa of two Apodemus species, the mouse and the rat. The neck region of two Apodemus spermatozoa was surrounded by the scroll of a redundant nuclear envelope and a few large mitochondoria. In contrast, in the mouse and rat spermatozoa, the neck region was devoid of mitochondoria, except a fold of the redundant nuclear envelope. Since a very similar sperm head morphology occurs in the two Apodemus species and the mouse, it suggests that these genera are sister groups, to the exclusion of the rat.