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Cytological Investigations On the Male Reproductive System and the Sperm Track in the Spider Mite Tetranychus Urticae Koch (Tetranychidae, Acarina)

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image of Netherlands Journal of Zoology
For more content, see Archives Néerlandaises de Zoologie (Vol 1-17) and Animal Biology (Vol 53 and onwards).

The post-embryonic development of the male internal genitalia, the development and production of the male germ cells, and the sperm track in the female of the two-spotted spider mite Tetranychus urticae Koch has been described. The male reproductive system consists of a testis, two vesiculae seminalis, a sperm pump, a ductus ejaculatorius and an aedeagus. The testis is a single structure in the larva, but during the nymphal stages it is generally divided into a right and a left half. The vesiculae seminalis develop from groups of cells which lie, in the larva, against the lateral sides of an epidermal invagination underneath the testis. In adults the vesiculae are provided with vesicular compartments which originate from the sheath cells. The sperm pump differentiates from the distal part of the invagination and some cells surrounding the latter. The remainder of the invagination forms the ductus ejaculatorius and aedeagus. The germ cells multiply by asynchronous spermatogonial mitoses. They are haploid with three chromosomes. Spermatocytes were not observed, which means a complete reduction of the meiosis. Spermatid formation begins at the nymphochrysalis stage and spermatozoa are found already at the deutochrysalis stage. During spermiogenesis the chromosomes lie in a line suggesting a non-random distribution in the sperm nucleus. The ripe spermatozoon is a spherical nucleus surrounded by two layers of plasm. A nuclear membrane and mitochondria were not observed. Germ cell production is continuous during the lifetime of the male, whether the males copulate or not. The numbers of the various germ cells vary dependent on the stage of life. The numbers of spermatozoa in the vesiculae seminalis and the sperm pump vary considerably, even if copulation does not take place. The numbers do not decrease during the first eight days of adulthood. The males produce an excess of spermatozoa. Ejaculations without copulation may take place. During copulation the spermatozoa are transferred behind each other with the aid of the sperm pump and may then become long-drawn because of a narrow ductus ejaculatorius or a narrow penial canal. One normal insemination supplies the female with a sufficient number of spermatozoa. The entrance to the receptaculum seminis is a short narrow tube which runs from an opening in the epidermis behind the genital opening. The receptaculum is situated posterior to the exit ducts of the ovarium and consists of about forty cells surrounding a lumen. Immediately after copulation spermatozoa are in the lumen and the basal parts of the cells. They may thus be transformed, though recovery takes place, and may adhere together forming packets. They migrate through the cells towards the haemolymph, which may take place within one day. Under influence of the growth of the oocytes and the movements of the mature eggs single spermatozoa are transported in the haemolymph towards the oocytes.

Affiliations: 1: (Institute of Genetics, University of Groningen, Haren, The Netherlands


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