Ultrastructural demonstration of the model of Litopenaeus vannamei (Crustacea, Penaeidae) male sexual maturation and spermatozoal capacitation

Abstract

The present study demonstrates ultrastructurally the model of Litopenaeus vannamei male sexual maturation and spermatozoal capacitation. The results show that phase 1 of the model occurred in the seminiferous tubules and includes spermatogenesis. In this phase, throughout differentiation of spermatogonia into late spermatids the following processes were observed: (1) decondensation of chromatin; (2) rupture of the nuclear envelope; (3) reduction of the cytoplasm and degeneration of organelles; (4) formation of the acrosome via fusion of cytoplasmic vesicles. Phase 2 comprised of spermatozoal maturation, a process that started with the transfer of late spermatids into the seminiferous ducts and ended with the formation of the acrosomal spike in the terminal ampoules. During this phase, development of the subacrosomal region and lateral electron-dense particles occurred in the seminiferous ducts, which is a novel finding of this species. Phase 3 was observed after spermatophore placement on the female thelycum and was mainly characterized by ultrastructural changes in the nucleus and the subacrosomal region. These results are in agreement with the model of male sexual maturation and spermatozoal capacitation proposed for L. vannamei.