Structural comparison between eupyrene and apyrene spermiogenesis in Calpodes ethlius (Hesperiidae, Lepidoptera)

Calpodes ethlius, like other Lepidoptera, produce two kinds of sperm, nucleated eupyrene and anucleated apyrene. The latter lack not only a nucleus but also reticular lacinate appendages at maturity in the testis. It is, however, possible to distinguish between them much earlier as secondary spermatocytes. The larger eupyrene spermatocytes have larger, spherical nuclei with dispersed chromatin, while the smaller apyrene spermatocytes have smaller more oval nuclei with clumped chromatin. A more extensive perinuclear reticular system surrounds the eupyrene nucleus. The nucleus of the eupyrene spermatid is small with condensed chromatin; however, the apyrene spermatid contains many micronuclei which are later cytolysed and eliminated. An acrosome forms in the eupyrene spermatid and differentiates into a tubular structure which extends along the elongating nucleus, in which the chromatin simultaneously undergoes characteristic changes in distribution and condensation. The reticular appendage first appears extracellularly where the acrosome makes contact with the plasma membrane, and later extends the full length of the sperm. The lacinate appendages appear much later, after elongation of head and of the tail are completed. The mature testicular sperm are distinguishable on the basis of detailed differences in mitochondrial derivatives, and axonemal structure. The free apyrene sperm undergo fewer changes than do the still encysted eupyrene sperm as they pass from the testis into the reproductive tract and finally into the bursa copulatrix of the female.