Spermatozoa and relationships in palaeognath birds

Abstract

In this paper the authors describe the ultrastructure of the mature spermatozoon and the spermatid in Struthio camelus and Dromaius novaehollandiae. The first species is characterized by a rod-like perforatorium within an endonuclear canal in the anterior third of the nucleus, while the second is characterized by an extremely reduced completely extranuclear perforatorium. Other differences are in the sperm dimensions, the number of mitochondria and the length of the axonemal accessory fibers. Considering both the present data and previous findings, Palaeognath birds appear to be a peculiar and monophyletic group, characterized by: 1), a conical acrosome surrounding the nucleus; 2), a fibrous sheath around most of the axoneme; and 3), an elongated distal centriole occupying the entire midpiece. Within this group, Tinamiformes seem to be more primitive than Struthioniformes. In the latter order Dromaius is distinctly different from the reduced Struthio and Rhea which are closely related to one another by the presence of a rod-like endonuclear perforatorium.

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

“…Conventional SEM confirmed the basic morphological features of emu sperm previously observed by light microscopy [16] and SEM [12]. The cells were long and narrow and the various segments, namely, the acrosome, nucleus, midpiece, principal piece and endpiece, could be distinguished although the transition was not always clear (Fig.…”

“…The SEM data of Baccetti et al [12] provides little information on the surface morphology of emu sperm other than to note the length of the various segments of the cell and that the midpiece is not as "deeply marked as in the ostrich". The current study, in addition to clearly revealing the various components of the sperm, demonstrated a distinct difference in cell surface characteristics between the acrosome (smooth) and the rest of the head (nucleus) which appeared mottled.…”

“…This phenomenon would seem to indicate that the surface properties of the plasmalemma overlying the acrosome differ from that part of the cell membrane covering the nucleus. The head of ostrich sperm has also been described as being smooth compared to the rest of the cell [12,14]. Whereas the tip of the emu sperm head appears relatively pointed on LM [16], SEM demonstrated that it was blunt, particularly in comparison to that of the ostrich [14].…”

“…Existing data [12] does not adequately illustrate or describe all the salient ultrastructural features of emu sperm necessary for a meaningful comparison of normal and abnormal sperm in this species. This paper re-evaluates and complements the existing data, provides a fully illustrated description of emu sperm ultrastructure and documents some previously unreported morphological features.…”

“…Whereas the ultrastructural features of normal ostrich sperm have been thoroughly described [11][12][13][14][15], only limited information is currently available on the fine structure of emu sperm.…”