Abstract
BackgroundThe 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.ResultsSelection 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.ConclusionReduced 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.
Highlights
The Y model of resource allocation predicts a tradeoff between reproduction and survival
We examined the relationship between starvation resistance, ovariole number and fecundity in lines of D. melanogaster that were artificially selected for resistance to female starvation
One generation removed from the selective regime refers to the case in which the selection was relaxed for one generation in the dams of daughters used for ovariole number determination
Summary
The Y model of resource allocation predicts a tradeoff between reproduction and survival. It is not clear that the fresh fruit resource of these flies is comparable to the rotting fruit habitat of D. melanogaster, but the main point is that there is an association between ovariole number and environmental variation Another line of evidence for the importance of ecological variation is that D. melanogaster ovariole number varies with latitude on three continents: a Europe-Africa transect [8,9]; North America [10]; and Australia [11]. Such replication of clines strongly implies the action of selection in the creation and maintenance of the clines, as argued for an isozyme cline [12] or quantitative traits such as body size [13] These clines in ovariole number might be associated with differences in temperature, duration of reproductive period, the seasonal pattern of food availability and geographic variation in over-wintering conditions. The evidence from both between and within species suggests that there may be a relationship between environmental variation and ovariole number
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