Effects of microclimatic changes on oogenesis of Drosophila mimica

Abstract

The reproductive mode of Drosophila mimica, a species endemic to the island of Hawaii, was determined by analyzing the ovarian development of three natural populations during a nine month period. Qualitatively the developmental profile of the ovaries remained the same in all the populations and for the entire collecting period. Each developmental stage was represented only in a fraction of the ovarioles, and mature eggs were usually found in half of the ovarioles. Quantitative differences were found between populations and between collections and these differences were correlated with the environmental conditions. The relative humidity was found to be the most important factor in regulating ovarian development by interrupting the growth of oocytes at the stage of RNA-yolk synthesis. A seven day period of constant low relative humidity causes the degeneration of grown oocytes, while a constant high humidity for the same period of time reinitiates normal development. This mechanism serves as a device to assure the presence of not more than one mature egg per ovariole, and thus prevents the overpopulation of the natural breeding substrates after environmental stresses. The adaptive significance and the theoretical implications of such behavior were discussed.