title: Abaxial tail implantation in the emu, Dromaius novaehollandiae: morphological characteristics and origin of a rare avian sperm defect.
abstract: Abaxial tail implantation is a defect occurring in the neck region of spermatozoa and is characterized by misalignment of the centriolar complex relative to the head base. This defect has been described in a number of mammalian species, but is rarely reported in birds. In this study, a detailed description of the defect in emu sperm is presented as well as morphological evidence of its origin in the testis. Despite their low incidence defective sperm could readily be identified using light (LM) and transmission electron microscopy (TEM). Affected sperm displayed obvious misalignment of the head and flagellum with many cells additionally showing unilateral swelling and caudal extension of the nuclear base. This material overlapped the anterior aspect of the centriolar complex. More subtle forms of the defect which were not resolved by LM were revealed by TEM. Abaxial sperm development could be identified in the testis during the early elongated spermatid stage of spermiogenesis. At this stage the centriolar complex was clearly misaligned with respect to the longitudinal axis of the condensing and elongating nucleus. The rare occurrence and low incidence of this defect in the emu would suggest that it has little effect on fertility.
authors.affiliation: Electron Microscope Unit, Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Onderstepoort 0110, South Africa. lizette.duplessis@up.ac.za
authors.forename: Lizette
authors.initials: L
authors.lastname: du Plessis
authors.forename: John T
authors.initials: JT
authors.lastname: Soley
mesh_terms: D000818:Animals; D020312:Dromaiidae; D015994:Incidence; D008297:Male; D046529:Microscopy, Electron, Transmission / Q000662:veterinary; D055101:Semen Analysis / Q000662:veterinary; D013082:Sperm Tail / Q000648:ultrastructure; D013094:Spermatozoa / Q000002:abnormalities* / Q000648:ultrastructure