Chemical communication plays an important role in the social and reproductive behaviours and physiology of many eutherian species. Unfortunately, chemical communication is not as well understood in metatherians. Antechinus subtropicus is a small dasyurid marsupial displaying an extreme life history, where a short synchronised breeding period is followed by complete male mortality, resulting from a persistent state of stress. Chemical commimication may be involved with both the synchronicity of breeding and the initiation and exacerbation of the stress response. This thesis explores some aspects of olfaction during the life history of A. subtropicus.
The anatomy of the nasal cavity in A. subtropicus is described. Cutaneous and skeletal features of the nasal cavity are noted. The location and extent of the sensory epithelia associated with both main olfactory and vomeronasal (accessory olfactory) systems and the distribution of glandular tissue are described. A. subtropicus is a macro-osmatic animal and possesses a complex nasal cavity with distinct regions subserving different functions. The vomeronasal complex is well-developed. A possible mechanism for the movement of material into the lumen of the vomeronasal organ is proposed.
The histology and ultrastructure of the tissues of the nasal cavity, main olfactory organ and vomeronasal complex in A. subtropicus are described. A large amount of transitional epithelium is present in the rostral nasal cavity and is suggested to function in the metabolism of inhaled xenobiotics and reclamation of moisture from the expired air. The respiratory epithelium displays regional variations presumably related to differences in function. The olfactory epithelium is well developed. A thickened basement membrane is peculiar to the olfactory sensory epithelium and present in both males and females. The ultrastructure of the vomeronasal sensory epithelium suggests that it is functional. The microvillar vomeronasal receptor cells contain abundant ciliary precursor bodies within their cytoplasm although mature cilia are not observed.
The morphometry of the vomeronasal organ was studied in male and female A. subtropicus to investigate possible functions in the life history. The overall length of the VNO is positively correlated with the size of the animal. The amount of sensory epithelium exhibits a negative correlation, decreasing with increasing size of animal. The effects of sex and breeding condition are not clear-cut, although they did suggest that larger amounts of sensory vomeronasal epithelium in pre-breeding animals appear to decline in the breeding period. It is suggested that the vomeronasal system may be more important to A. subtropicus during the pre-breeding season, when it may participate, via the detection of chemosignals, in synchronising reproduction and in the development of the male stress response.
Some of the central connections of the main olfactory system are identified using carbocyanine neural tracers. The presumptive olfactory regions of the brain are well-developed. In general, the connections linked the main olfactory bulbs primarily with paleocortical areas. In particular, the hippocampal formation is connected with olfactory regions of cortex.
Alterations and pathology of the nasal cavity and vomeronasal organs associated with aging and with the breeding period are described. All animals carry parasites within their nasal cavities. Numbers of parasites markedly increase in breeding males and excite extensive inflammatory reactions. Metaplastic change in response to parasitic infection or inhaled particulate matter is common, although dysplasia and neoplasia are rare. Degeneration of sensory olfactory and vomeronasal epithelia and other nasal structures is observed in breeding males. It is proposed that the changes in the nasal cavity and vomeronasal complex result from the stress state of the males, and also contribute to it. It is also suggested that, due to these changes, and the apparent decrease in vomeronasal sensory epithelium, olfactory acuity in male A. subtropicus may decline during the breeding period.
These results indicate that olfaction is an important sensory modality for A. subtropicus and that there are variations in the structure of the olfactory organs throughout its life that may influence olfactory function.