Fine structural traits of Crocidura shantungensis caudal epididymal spermatozoa

Abstract

The structural and morphometric traits of spermatozoa reflect species-specific evolutionary and functional characters. The shrew, Crocidura shantungensis, which is an indigenous species of Ulleung-do, is dominant on this island and is suspected to have unique traits different from other shrews. Based on a previous sperm ultrastructural analysis, the structural and morphometric traits of caudal epididymal spermatozoa were evaluated by light, scanning, and transmission electron microscopy. Total length was 110.0 μm. The head was paddle shaped with a globular nucleus and was 16.0 μm in length. The acrosomal cap covered four-fifths of the nucleus, and the subacrosomal space had sawtooth-shaped edges. The number of mitochondrial gyres was 84–86. Nine segmented columns in the neck consisted of 12 knobs, and each column was fused with outer dense fiber. The outer dense fibers 1, 5, and 6 were thicker than the others. Outer fiber 1 was shaped like a horseshoe, whereas 5 and 6 were fused with each other. Numerous satellite fibers were scattered on the mid-piece between outer fibers 4 and 5, and 6 and 7. Two specific strong electron-dense fibers were found uniquely near the satellite fibers. In conclusion, our results demonstrate that the caudal sperm of Ulleung-do C. shantungensis has unique ultrastructural and morphometric traits based on common sperm characters of the subfamilies, suggesting unique physiological roles in reproduction.