Abstract:
The fate of the proximal centriole in passeridan birds is an area of controversy and relative lack of knowledge
in avian spermatogenesis and spermatology. This study examines, for the first time, spatiotemporal
changes in the centriolar complex in various phases of spermiogenesis in a passerine bird, the Masked
weaver (Ploceus velatus). It also describes the configuration of the centriolar complex and the relationship
between it and the granular body in both intra- and extra-testicular spermatozoa. It is shown that the
proximal centriole is retained and attaches, at its free end, to the granular body of spermatids in every
step of spermiogenesis, as well as in mature intra-testicular and post-testicular spermatozoa, including
those in the lumen of the seminal glomus. As the centriolar complex, along with its attached granular
body, approaches the nucleus in the early spermatid, the proximal centriole articulates with the distal
centriole at an acute angle of about 45◦, and thereafter, both centrioles, still maintaining this conformation,
implant, by means of their articulating proximal ends, at the implantation fossa of the nucleus. In the
mature spermatid and spermatozoon, the granular body winds itself helically around the centriolar complex
in the neck/midpiece region of the cell, and, thus, becomes the granular helix. The significance of this
observation must await future studies, including possible phylogenetic re-evaluation and classification
of birds.
