Environmental stress and reproduction in Drosophila melanogaster: starvation resistance, ovariole numbers and early age egg production

BACKGROUND: The Y model of resource allocation predicts a tradeoff between reproduction and survival. Environmental stress could affect a tradeoff between reproduction and survival, but the physiological mechanisms underlying environmental mediation of the tradeoff are largely unknown. One example is the tradeoff between starvation resistance and early fecundity. One goal of the present study was to determine if reduced early age fecundity was indeed a robust indirect response to selection for starvation resistance, by investigation of a set of D. melanogaster starvation selected lines which had not previously been characterized for age specific egg production. Another goal of the present study was to investigate a possible relationship between ovariole number and starvation resistance. Ovariole number is correlated with maximum daily fecundity in outbred D. melanogaster. Thus, one might expect that a negative genetic correlation between starvation resistance and early fecundity would be accompanied by a decrease in ovariole number. RESULTS: Selection for early age female starvation resistance favored survival under food deprivation conditions apparently at the expense of early age egg production. The total number of eggs produced by females from selected and control lines was approximately the same for the first 26 days of life, but the timing of egg production differed such that selected females produced fewer eggs early in adult life. Females from lines selected for female starvation resistance exhibited a greater number of ovarioles than did unselected lines. Moreover, maternal starvation resulted in progeny with a greater number of ovarioles in both selected and unselected lines. CONCLUSION: Reduced early age egg production is a robust response to laboratory selection for starvation survival. Ovariole numbers increased in response to selection for female starvation resistance indicating that ovariole number does not account for reduced early age egg production. Further, ovariole number increased in a parallel response to maternal starvation, suggesting an evolutionary association between maternal environment and the reproductive system of female progeny.