Survival and fitness variation in Drosophila pseudoobscura
Lebow, Elizabeth Tyler
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Survival variation is partly a function of quality differences among individuals,variation in reproductive activities, social group exposure, and rearing temperature.Similarly, fitness variation partly reflects differences in survival, the number and quality of mates, and the amount of energy available and devoted to reproduction. In these studies we examined survival variation in Drosophila pseudoobscura related to the length of exposure to a mild heat stress, social group composition, mating status, mate preference, and preference status of potential mates. We also examined fitness variation in D. pseudoobscura associated with mate preference and length of time with mate.In the first experiment we tested survival effects of two mild heat stress conditions (exposed for one-week or lifetime) and three social groups (alone, single sex groups, and mixed sex groups). We found that survival significantly decreased with lifetime exposure to a mild heat stress. Individuals alone had the highest survival,individuals in mixed sex groups had the lowest survival, and females outlived males in both stress treatments and all social groups. We also found that survival differences among groups increased under lifetime exposure to a mild heat stress, making this stress an experimental tool for detecting subtle survival differences among treatment groups,and justifying our use of this heat stress in the subsequent experiments.The next two studies examined fitness and survival variation associated with mate preference and length of time with mate. Male and female choosers chose between two potential mates (discriminatees) in arenas that minimized preference constraints. Female choosers with their preferred male for 21 days had increased fecundity, while preferred females with males for one day had increased net fitness and their offspring had higher egg-to-adult viability. Pairs together for 21 days had increased total offspring and egg-to-adult offspring viability compared to those with their mate for one day. While there were no survival differences for female choosers mated with their preferred or non-preferred male, males had significantly increased survival when with their preferred female for one day. There were no survival differences between mated or unmated preferred and non-preferred discriminatees. Finally, we examined survival cost of reproducing in males and females by comparing the survival of virgins, flies that had a single copulation, and flies that had multiple copulations. We found that females with multiple copulations had significantly decreased survival compared to both virgins and females with a single copulation, while males did not experience any survival cost of reproducing.