Graduate Thesis Or Dissertation
 

Seasonal and altitudinal regulation of embryonic and nymphal development in Allonemobius fasciatus (Orthoptera:Gryllidae)

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  • The physiological adaptations involved in the seasonal and altitudinal regulation of the life cycle in Allonemobius fasciatus were studied. This species maintains a univoltine life cycle with an embryonic diapause over an altitudinal gradient of as large as 1,000 m. A more than 1.5 -month difference exists in hatching time between the highest and lowest altitudes studied. Little or no difference was detected among populations from different altitudes when various developmental traits such as diapause intensity, postdiapause development, and nymphal development, were compared in the laboratory. The photo periodic regulation of nymphal development seems to play an important role in compensating for the shorter growing season at higher elevations. The embryo of A. fasciatus showed seasonal variation in diapause characteristics. Diapause intensity measured as the duration of the egg stage at 20°C was greater in eggs laid early in the season than in those laid later. At 20°C, all embryos entered "winter diapause" at the end of the appendage-formation stage. However, when incubated at higher temperatures, another type of diapause was manifested before that stage. The higher the temperature the earlier was the stage at which this developmental suppression (called "summer diapause") was imposed. The induction of summer diapause depended not only upon the temperature of incubation but also upon the time of ovi-position. The capability of entering summer diapause at a high tem perature was decreased as the time of oviposition was delayed. The effects of temperature and moisture on embryonic development were examined using eggs with or without summer diapause and it is suggested that the role of summer diapause is not to ensure the survival of eggs under dry, warm conditions in summer but to avoid untimely hatching before winter, and to stabilize the univoltine life cycle in this species. Non-diapause development was induced when eggs were transferred from 20 to 27°C in early embryonic stages, although they entered diapause when constantly held at either of these temperatures. Based on this and other results, a model for the possible mechanism underlying the control of induction and intensity of diapause was proposed.
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