Zoology - Theses
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ItemEmbryonic diapause in the field cricket Teleogryllus Commodus(University of Melbourne, 1972)The mechanism of control of embryonic diapause in Teleogryllus commodus was investigated by experiments aimed firstly at studying the parental role in diapause determination and secondly, at analysing some of the biochemical changes associated with diapause initiation and termination in the egg. Implantation procedures were used to investigate the possibility that maternal endocrine effects, of the type demonstrated in the silkworm Bombyx mori, operate in Teleogryllus. Endocrine organs were transferred from diapausing T. commodus adult females to adult females of the non-diapausing T.oceanicus species. The organs implanted included the suboesophageal ganglion, brain, corpus cardiacum and corpora allata. The T. oceanicus females were mated with both T. oceanicus and T. commodus males, and the diapause characteristics of the eggs were assessed. The implants were shown to have no positive effect on diapause in the egg. However the experiments did reveal that the T. oceanicus ? x T. commodus ? hybrid has an embryonic diapause. This was contrary to the results of previous hybridization studies with these two species. It was in fact considered generally that diapause is absent in hybrids between diapausing and non-diapausing crickets. The presence of diapause in the T. oceanicus ? x T. commodus ? hybrid was confirmed in an experiment which compared the respiratory rates and morphological development of the hybrid and parent species. A genetical model proposed to fit this result has suggested that diapause in Teleogryllus is controlled by both a cytoplasmic factor produced by the parent female and by factors determined by the embryonic genome. Biochemical investigations were aimed at elucidating the nature of these factors. It was shown that rises in the level of free amino acids associated with proteolytic activity occur at diapause initiation and during diapause development in T. commodus. The rise at diapause initiation was shown to precede water absorption and is likely to be associated with this activity. The occurrence of proteolysis during diapause development would seem to be of significance to the process of diapause termination. Diapause development was shown to involve changes in the acrylamide patterns of soluble proteins and a 20% reduction in the amount of lipoprotein. It was shown to be accompanied by an increase in the in vitro activity of a phenoloxidase enzyme. The activity was dependent on the pH, molarity and lipoprotein concentration of the homogenate. No role for this enzyme in the process of diapause termination could be suggested. A proposal for a biochemical mechanism of diapause is made. It is suggested that diapause is initiated by the inactivation of an enzyme or enzymes essential for embryonic growth beyond the diapause stage. Diapause development is then considered as a process of activation of this enzyme (enzymes) either by the removal of an inhibitor or the production of an activator.