While parrots are often recognised as iconic species, popular for aviculture and serving as flagship species for conservation, some parrots are paradoxically present in very large numbers and are perceived as pest species. Irrespective of their endangered status or overabundance, there is currently a dearth of information on their reproductive anatomy, endocrinology and dynamics of sperm production; this is the case even in the most popular and domesticated species. This study used the cockatiel (Nymphicus hollandicus) as a model to examine male parrot reproduction. The cockatiel is an endemic species to Australia and is the smallest member of the Cacatuidae family. Opportunistically, a range of other species including the galah (Eolophus roseicapilla), sulphur-crested cockatoo (Cacatua galerita), long-billed corella (Cacatua tenuirostris), pale-headed rosella (Platycercus adscitus) and rainbow lorikeet (Trichoglossus haematodus) were also investigated. Male parrot reproductive anatomy is often thought to be similar to non-passerine species; however, no comprehensive study has been undertaken on reproductive anatomy within the order Psittaciformes. To address this lack of basic reproductive information and to examine whether male parrot reproductive morphology varied between closely related species, this thesis documented for the first time, the gross and micro-anatomy of the male cockatiel reproductive tract and to a lesser extent, the sulphur-crested cockatoo, galah, long-billed corella, pale-headed rosella and rainbow lorikeet.
Testicular assessment in the cockatiel provided baseline data on measurements and relative proportion (%) of cell types found in the testis during the 3 main phases of reproductive development/activity. Testicular asymmetry was pronounced, though differences in testicular proportions and measurements were not of statistical significance. Examination of the excurrent ducts in the cockatiel, illustrated that the epididymal region comprised of the rete testis unit (intratunical and extratesticular portions), the efferent duct unit (proximal and distal segments) and the connecting duct and epididymal duct of the epididymal duct unit. The convoluted deferent duct ran distally from the caudal border of the epididymal region towards the cloaca opening into the urodeum through the ejaculatory duct. Novel aspects of cockatiel male reproductive anatomy that set them apart from non-passerines and other parrots included the location of the epididymis at the dorso-caudal pole of the testis, the ciliated epithelium of the epididymal duct unit and the absence of a seminal glomus. Preliminary observations of the other parrot species that were examined in this thesis were essentially similar to that of the cockatiel, although several exceptions were noted such as; (1) pigment cells (melanocytes) were present within the testicular capsule, interstitial tissue of the testis and periductal tissue of the excurrent ducts in 4 of the other 5 parrot species, (2) testis asymmetry was not as pronounced as in the cockatiel, (3) the epididymal region was not discerned at the dorso-caudal pole of the testis and (4) the epithelium of the deferent duct in the sulphur-crested cockatoo was not ciliated.
The ultrastructure of spermiogenesis was documented and it was found that development of the cockatiel spermatid was similar to those described in other avian species. However, it was observed that some chromatin granules were typically hollow in nature, no fibrous sheath existed around the axoneme of the principal piece and there was no annulus. Additionally, an abnormal formation of the axoneme during spermiogenesis in the cockatiel was observed, axonemes were identified coiling beneath the spermatid cell membrane rather than extending into the seminiferous tubule as typically described. The presence of internalized axonemes was also observed in other parrot species examined in this study including the sulphur-crested cockatoo, long-billed corella and rainbow lorikeet. Other observations from these parrots were essentially similar to that of the cockatiel, although the early acrosomal vesicles of parrots belonging to the Psittacidae family (rainbow lorikeet & pale-headed rosella) did not contain homogeneous, moderately electron-dense material; rather they appeared as electron-lucent vesicles/vacuoles.
To examine the reproductive physiology of the male cockatiel and techniques for the assessment of testosterone secretion, a GnRH stimulation test was developed on 16 male cockatiels. IM injection of 8μg of buserelin (a GnRH agonist) resulted in maximal plasma androgen secretion 60 to 90 minutes after injection. Additionally, the test was conducted on 3 sulphur-crested cockatoos, which resulted in an increase in testosterone secretion with maximal concentrations obtained after 90 minutes. These findings indicated that buserelin can be used to obtain a reliable index of the prevailing testosterone secretion capacity of the cockatoo testis and could, therefore, be incorporated as part of any assessment of reproductive status. Testosterone concentrations in sexually mature/active birds and sexually mature/inactive birds following the GnRH stimulation test were then integrated along with anatomical findings. Observations from individual birds are also discussed.
There is, at present, very little data published on male parrot reproductive biology and the primary objective of this research was to provide an enhanced understanding of the fundamental reproductive anatomy and endocrinology of the male parrot. It is clear that such information is needed both for conservation of parrots but also into the management of problematic species. It is not claimed that this thesis is representative of all parrot reproduction, but it is hoped that this thesis will provide extensive coverage of reproduction in Australian Psittaciformes, highlighting the importance of parrot reproductive biology and its practical implications.