A re-evaluation of sperm ultrastructure in the emu, Dromaius novaehollandiae

Abstract

Existing reports on sperm structure in the emu do not adequately illustrate or describe all the salient ultrastructural features necessary for a meaningful comparison of normal and abnormal sperm in this species. As sperm morphology forms an important parameter in determining semen quality, and in view of the proposed role of artificial insemination in the farming of ratites, this paper re-evaluates and complements the existing data on the topic, provides a fully illustrated description of emu sperm ultrastructure and documents some unreported morphological features. Conventional transmission (TEM) and scanning (SEM) electron microscopy, as well as high resolution SEM, was used to describe the ultrastructure of sperm harvested from the distal deferent duct of sexually mature birds slaughtered during the breeding season. In addition to broadly confirming the basic ultrastructural characteristics previously described for emu sperm, this study revealed a number of unreported morphological features. These included distinct differences in surface properties between the acrosome and nucleus, the presence of a thread-like appendage near the base of the nucleus, variable positioning of the annulus relative to structures located at the midpiece -principal 1 piece junction and regional differentiation of the principal piece. Although the emu displayed similar basic morphological features to sperm of other ratites and the tinamou, marked structural peculiarities were obvious, notably the lack of an endonuclear canal and a perforatorium as well as the presence of significantly more mitochondria in the midpiece coupled with an absence of inter-mitochondrial cement. Whereas the broad morphological features of emu sperm would appear to add credence to the general view that the ratites, together with the tinamous, form a monophyletic group at the base of the avian phylogenetic tree, it is also clear that emu sperm are distinctly different from those of the ostrich, rhea and tinamou which together share morphological affinities This observation may lend some support to the alternate view that the Australasian ratites represent a separate clade that developed independently from flightless ancestors.

Ultrastructural characteristics of black marsh turtle spermatozoa obtained by electroejaculation

“…There is a little bulging in S. crassicollis , but we found that this was not the case. The acrosomal region was narrower than the head, which differs from those found in other freshwater turtles (Al‐Dokhi et al., 2007; Hess et al., 1991) and in emu (du Plessis & Soley, 2014). The proportion of acrosomal length to head length of S. crassicollis (one‐fifth) was smaller than that found in M. caspica (approximately half of the head length) (Al‐Dokhi et al., 2007) and C. picta (one‐third) (Hess et al., 1991).…”

“…Fresh spermatozoa staining with eosin/methylene blue showed a paler sperm head tip compared to the acrosomal structure under SEM . This structure was similar in avian species such as emu (du Plessis & Soley, 2014). In mammals, the acrosome covers the head.…”

“…The head surface of S. crassicollis was similar to that of emu spermatozoa. At a lower SEM resolution, the acrosomal surface appeared smoother than the rest of the head surface, which is similar to the emu spermatozoon head (du Plessis & Soley, 2014). However, the surface of spermatozoa collected by electroejaculation is usually contaminated and covered in mucous or debris.…”

“…This study revealed the outer surface of the head, acrosome and acrosomal edge. The ultrastructure of the head surface in other reptiles, such as crocodiles, and in avian species, such as emu, has been previously reported (Fitri et al., 2020; du Plessis & Soley, 2014). The head surface of S. crassicollis was similar to that of emu spermatozoa.…”

Histomorphology, ultrastructure and fatty acid composition of the adipose tissue in pansteatitis, the potentials in understanding the underlying mechanism and diagnosis of pansteatitis in the Nile crocodile

“…Samples were cleared with propylene oxide for 20 minutes and embedded in epoxy resin (TAAB 812 resin; TAAB Laboratories, Berkshire, England). Thin sections were cut with Reichert-Jung Ultracut (C. Reichert AG, Vienna, Austria) ultra-microtome using a diamond knife, and stained with lead citrate and uranyl acetate as previously described [ 10 ]. TEM viewing was done on Philips CM10 transmission electron microscope at 80 kV (Philips Electron Optical Division, Eindhoven, Netherlands).…”