Studies of Oogenesis in Natural Populations of Drosophilidae. II. Significance of Microclimatic Changes on Oogenesis of Drosophila mimica

Abstract

The reproductive mode of D. mimica, a species endemic to the island of Hawaii [USA] was determined by analyzing ovarian development of 3 natural populations during a 9 mo. period. The developmental profile of the ovaries remained qualitatively the same in all populations and for the entire collecting period. Each fly had comparatively few ovarioles (23.8 .+-. 4.21) and each developmental stage was present in only a fraction of the ovarioles. Mature eggs were usually found in half of the ovarioles and some vitellogenic oocytes were always degenerated. Quantitative differences occurred between populations and between collections; these differences were correlated with the environmental conditions. Low relative humidity was the most important factor in disrupting ovarian development by terminating, directly or indirectly, growth of oocytes at the stage of RNA-yolk synthesis. A 7 day period of constant low relative humidity causes degeneration of growing oocytes, while constant high humidity for the same period reinitiates normal development. This mechanism assures the presence of not more than 1 mature egg/ovariole and avoids overpopulation of the natural breeding substrates. Adaptive significance and the theoretical implications of such a reproductive strategy are discussed.