Responses to Alteration of Atmospheric Oxygen and Social Environment Suggest Trade-Offs among Growth Rate, Life Span, and Stress Susceptibility in Giant Mealworms (Zophobas morio).
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Growth rate, development time, and response to environmental stressors vary tremendously across organisms, suggesting trade-offs that are affected by evolutionary or ecological factors, but such trade-offs are poorly understood. Prior studies using artificially selected lines of Manduca sexta suggest that insects with high growth rates, long development time, and large body size are more sensitive to hypoxic or hyperoxic stresses, such as reactive oxygen species (ROS) production, but the mechanisms and specific life-history associations remain unclear. Here, we manipulated the social environment to differentiate the effects of size, growth rate, and development time on oxygen sensitivity of the giant mealworm, Zophobas morio. Crowding reduced growth rates but yielded larger adults as a result of supernumerary molts and longer development times. The juvenile performance (growth rate, development time, adult mass) of crowd-reared mealworms was less sensitive to variation in atmospheric oxygen than it was for individually reared animals, consistent with the hypothesis that high growth rates are associated with increased sensitivity to ROS. Life span in normoxia was extended by crowd rearing, perhaps due to the larger size and/or increased resources of the larger adults. Life spans of crowd-reared animals were more negatively affected by hypoxia or hyperoxia than life spans of individually reared animals, possibly due to the longer total stress exposure of crowd-reared animals. These data suggest that animals with high growth rates experience a negative trade-off of performance with greater sensitivity to stress during the juvenile phase, while animals with long development times or life spans experience a negative trade-off of greater susceptibility of life span to environmental stress.