The XVIIIth (New) International Congress of Zoology

Le XVIIIème (Nouveau) Congrès International de Zoologie

In Chondrichthyes, as individual spermatozoa pass through the male genital ducts they align laterally and become associated with matrix produced largely by secretory activity of the accessory Leydig gland, as well as minor contributions from epithelial cells of the epididymis and ductus deferens. The result of association of laterally bundled sperm with matrix produces spermatozeugmata that are stored in the seminal vesicles until copulation. In sharks, at copulation, secretions of the siphon sac gland are transported down the clasper groove to blend with spermatozeugmata. Batoids lack a siphon sac gland but possess a clasper gland. Secretions of the clasper gland blend with alkaline gland secretions and spermatozeugmata. The action of these various components on spermatozeugmata integrity, sperm motility and activation are currently being investigated. The fate of spermatozoa once inside the female reproductive tract, especially as regards the site of sperm storage and fertilization is debated. Chondrichthyes possess a unique oviducal gland that produces egg jelly, the tertiary egg envelope and harbors sperm. Older literature alleges that sperm are stored in the baffle zone of the oviducal gland, however this generalization has recently been questioned (Hamlett et al., J. Experimental Zoology 282: 399-420, 1998), notably in placental sharks. In the smooth dogfish, Mustelus canis, immediately after insemination, sperm are found embedded in the uterine epithelium in areas adjacent to the former attachment site for the yolk sac placenta. Bundled sperm are also encountered in the terminal zone of the oviducal gland. Fertilization is presumed to occur in the anterior oviduct above the oviducal gland. What physiological mechanisms mediate sperm storage and release currently remain unanswered.

In male viviparous Osteichthyes spermatozeugmata are also formed. In the guppy, Poecilia reticulata, spermatozeugmata are ovoid to rounded structures measuring 135-235 µm in diameter. Sperm nuclei are arranged at the periphery with the tails projecting toward the center of the mass (in goodeids it is the reverse). The number of sperm in each spermatozeugmata seems to be species specific. Matrix is secreted by the former cyst epithelium and contains acidic and neutral glycoproteins. Spermatozeugmata are stored in the main testis duct and up to 400 can be removed from a single male by artificial stimulation. Ageing of sperm probably also occurs. In male halfbeaks (Dermogenys, Nomorhamphus, Hemirhamphodon) sperm are also stored in the main testis duct as highly organized structures, as in poeciliids, or as smaller less well organized aggregations (Hemirhamphodon).

In some viviparous Osteichthyes, in particular the poeciliids and halfbeaks, sperm are stored within folds of the inner ovarian epithelium. In P. reticulata once transferred to the female, spermatozeugmata dissolve within 1 minute in the genital sinus and/or lower portion of the oviduct. Spermatozoa migrate to the ovarian cavity within 10-15 minutes. They are stored in the caudal and cranial parts of the ovarian cavity, as well as in small depressions called "delle" in the ovarian epithelium immediately above the oocytes. Large "true" storage occurs in the cranial and caudal part of the ovary as sperm are deeply embedded in epithelial invaginations. Sperm are not deeply embedded in the delle. Sperm may remain viable for at least one year in the guppy. In female halfbeaks sperm are also embedded in invaginations of the ovarian epithelium but the major site of storage has not yet been determined. Sperm also occur in delle above oocytes. Ultrastructural details are not available and duration of storage is unknown. In Nomorhamphus celebensis 8 litters were produced after a single successful insemination and 7 litters were produced in Dermogenys pusillus.