Morphological and cytochemical aspects of spermatozoa in the genus Cochliomyia (Diptera: Calliphoridae)

Abstract

The objective of this study was to characterize, structurally and ultrastructurally, the spermatozoa of the screwworm flies Cochliomyia hominivorax and Cochliomyia macellaria. To visualize the ultrastructure of microtubules and identify basic proteins, techniques such as the tannic acid fixation and the cytochemical method of ethanolic phosphotungstic acid (EPTA) were used. These methods of fixation are important because they reinforce the evidence of the protofilaments present in the microtubular wall and identify basic proteins, respectively. With the tannic acid fixative it was possible to observe a significant number of microtubules in the cell cytoplasm during spermiogenesis. Microtubules were observed in all regions of spermatids (head, 'overlap' zone and tail). The EPTA technique highlighted the presence of basic proteins on the border of the nucleus and nuclear envelope in the two species analyzed, and in the centriolar adjunct and on the border of mitochondrial derivatives in C. macellaria. The axoneme is of a conventional insect type with a 9+9+2 microtubular arrangement and the spermatozoa of C. hominivorax and C. macellaria are similar to those described for other Brachycera. The spermatozoa are long and thin in these two species, ∼190µm in length, of which the head region measures ∼26µm in C. hominivorax and 29µm in C. macellaria. A polymorphism was observed in C. hominivorax and C. macellaria. These features are consistent with the structural diversity of the dipteran spermatozoa, constituting an essential tool for understanding the complex variations found in the Diptera order.