SPECIES-SPECIFIC CHARACTERISTICS OF SPERMATOGENESIS IN DROSOPHILA-MOJAVENSIS (PATTERSON) (DIPTERA, DROSOPHILIDAE)

Spermatogenesis in Drosophila mojavensis (Diptera : Drosophilidae) begins with the proliferation of a primary gonial cell, leading to the formation of a cyst with 16 primary spermatocytes that subsequently enter a growth phase towards the end of meiosis. As their development proceeds, primary spermatocytes assume a characteristic species-specific appearance regarding the morphology of their nucleus. Meiosis produces a syncytium of 64 spermatids, each one of which bears one nucleus and one compact mass (nebenkern), composed of mitochondria. During spermiogenesis, the newly formed spermatids undergo a structural transformation that leads to the formation of the mature sperm: the spherical nucleus is reduced to a 0.1 x 75 mum cylinder and the nebenkern separates into 2 mitochondrial derivatives, which elongate to 2400 mum, while associated with the axoneme. Both mitochondrial derivatives of the mature sperm, although disparate in size, are relatively large and have paracrystalline bodies that occupy a great part of their mass.