Life-history analysis of the relative costs and benefits of parthenogenetic versus sexual reproduction revealed that the transition from sexual to parthenogenetic reproduction is associated with increased mortality, decreased egg viability, and a change in the apportionment of eggs across the life span. There are also important differences among parthenogenetic strains in the extent and the way these factors are affected, although when all changes are considered together in the context of population-level parameters, differences between sexual and parthenogenetic strains are greatly reduced, and differences among parthenogenetic strains largely disappear. Decreased survival and fertility can be largely compensated for by relatively small shifts in fecundity with age under the appropriate ecological conditions. Nevertheless, the supposed ecological benefit of parthenogenesis (a doubling of the intrinsic rate of increase) is not realized.

The extremely high abortion rate of parthenogenetic eggs (as high as 95% of eggs that initiate development) is being investigated as a potential developmental constraint on the evolution of parthenogenesis. Taking just one strain at one maternal age (13 days) for which the most data is available (1373 embryos), 133 (10%) of the eggs were laid unhealthy, 777 (57%) of the eggs were otherwise healthy but failed to develop, 398 (29%) initiated development but aborted before a larva formed, 20 (1.5%) aborted development between larval formation and hatching, 24 (1.7%) hatched but failed to pupate, and 21 (1.5%) eclosed as viable adults. Since all of this variation occurs among embryos of an identical genotype in the same environment, the parthenogenetic system has by definition extreme developmental instability. To understand the cause of the extreme developmental instability that characterizes parthenogenetic strains, embryonic development of the four strains previously characterized for life history traits will be compared to qualify and quantify the specific errors that occur in each under parthenogenetic reproduction. In addition, to investigate whether this abortion rate was due to the particular genome of this strain or to the mechanism of parthenogenesis per se, a sexual analog of this parthenogenetic strain was established. It has a genotype identical to the parthenogenetic strain with the exception of the Y chromosome in males. These strains are being investigated to compare rates of development initiation and abortion. In addition, developmental analyses are being conducted to determine if the nature of developmental errors varies with mode of reproduction.