Structure and ultrastructure of spermatozoa in Meliponini (stingless bees) (Hymenoptera: Apidae).

In spite of their importance in the reproduction of phanerograms, few bees have received an adequate description of their sperm ultrastructure. In this study, we concluded that it was possible to define a characteristic pattern for Meliponini spermatozoa. However, we have also found species-specific differences that could be used, for example, in a taxonomic or phylogenetic evaluation. Meliponini spermatozoa are made up of a head and a flagellar region. The head includes an acrosome containing the perforatorium, covered by the acrosomal vesicle and a nucleus. In transverse sections, the acrosome is circular at the tip but becomes triangular as it nears the nucleus. The perforatorium base penetrates into a small cavity in the nuclear tip. The flagellum consists of an axoneme, a pair of mitochondrial derivatives, a centriolar adjunct and a pair of accessory bodies. The axoneme has a typical 9+9+2 microtubule pattern. In the final portion, the axoneme becomes gradually disorganized with the accessory microtubules terminating last. The mitochondrial derivatives are asymmetric in length and diameter. In cross-section, they are ellipsoidal and the larger one has a paracrystalline region. The centriolar adjunct begins at the nuclear base and extends parallel to the axoneme up to the anterior end of the smaller mitochondrial derivative.