Incidence, structure and morphological classification of abnormal sperm in the emu (Dromaius novaehollandiae)

Abstract

Little detailed information is currently available on the incidence and morphological characteristics of abnormal sperm in the emu (Dromaius novaehollandiae) and of ratites in general. This situation is further compounded by the lack of a uniform system for the morphological classification of avian sperm defects. Considering the important role that sperm morphology plays in the assessment of semen quality, a detailed description of avian sperm defects is of paramount importance. Based on morphological data provided by light and electron microscopy, a mean of 17.3% abnormal sperm was recorded in semen samples collected from the distal deferent duct of four adult emus during the middle of the breeding season. Four categories of defects were identified. Head defects (57.2% of total defects) consisted of bent heads, macrocephalic heads, round heads and acephalic sperm. Zones of incomplete chromatin condensation and retained cytoplasmic droplets appeared to be implicated in head bending, while giant heads were often associated with multiple tails. Acephalic sperm revealed a complete tail devoid of a head which was replaced by a small spherical structure. Tail defects (22.6% of total defects) were subdivided into neck/midpiece defects and principal piece defects. In the neck/midpiece region disjointed sperm were the exclusive defect noted and were characterized by the complete separation of the head and midpiece in the neck region but within the confines of the plasmalemma. Defects observed in the principal piece were subdivided into short tails, coiled tails and multiple tails. No conclusive evidence was obtained that tail coiling represented the 'Dag' defect. Biflagellate sperm were the most common form of multiple tails, demonstrating two complete tails with all the normal structural elements. Cytoplasmic droplets (13.9% of total defects) were classified as a separate defect. The location and eccentric positioning of retained cytoplasmic droplets was similar to that described in ostrich sperm although the composition of the droplets differed markedly between the two species. A small percentage of sperm (6.3% of total sperm defects) displayed multiple abnormalities. Based on these findings we propose a morphological classification for abnormal ratite sperm identifying head and tail defects, with additional categories for cytoplasmic droplets and multiple defects. Each category is further subdivided to reflect a range of specific defects within the category. It is envisaged that additional defects will be added to each category or that new categories may be added as future studies on the detailed morphology of avian sperm defects are completed.

Head-base bending and disjointed spermatozoa in the emu (Dromaius novaehollandiae): A morphological comparison of two closely related defects

“…Head bending in the emu was, with few exceptions, confined to the base of the head [29] and was associated with incomplete chromatin condensation in the vicinity of the bend. The areas of 11 incomplete condensation were generally positioned towards the outside of the bend and displayed coarse granules and intervening spaces, similar to regions of uncondensed chromatin described in mammalian sperm [33][34][35].…”

“…Semen samples were prepared for electron microscopy as previously described [29]. Tissue samples were routinely prepared for transmission electron microscopy (TEM) using standard techniques.…”

“…In a recent study of abnormal sperm in the emu it was noted that the majority of defects occurred at the base of the head and in the neck region. The head-base defects exclusively involved varying degrees of bending as well as looping and kinking of the nucleus, whereas in the neck region a defect referred to as "disjointed sperm" and which superficially resembled a form of "bending" was displayed [29].…”

Structural peculiarities associated with multiflagellate sperm in the emu, Dromaius novaehollandiae

“…However, considering the primary importance of semen evaluation in establishing AI programmes, relatively little information is currently available on the morphology of sperm defects in this commercially important group of birds, particularly at the ultrastructural level. Whereas various abnormal forms of spermatozoa have been named in the ostrich [5] and emu [6] but not described, and some morphological data provided on cytoplasmic droplets in ostrich sperm [7,8], the only comprehensive accounts of abnormal sperm structure in ratites are those on the emu [9][10][11]. The evaluation of sperm motility, sperm concentration and sperm morphology form the three most important parameters in semen analysis [12][13][14][15][16].…”

“…Most classification systems on avian sperm defects fail to reflect multior biflagellate sperm [32][33][34][35][36]. However, this anomaly has been mentioned [37][38][39], briefly described and/or illustrated in some avian species such as the Houbara bustard [40], goose [41][42][43], duck [44], guinea fowl [45] and, more recently, in the emu [9]. With the exception of a detailed study on the ultrastructure of multiple sperm tails in the drake [44], the morphological features of this defect are poorly understood in birds.…”