Dissertation Research: Physiological and life-history responses to variation in food availability in a parthenogenetic insect

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Dissertation Research: Physiological and life-history responses to variation in food availability in a parthenogenetic insectKaren A. Bjorndal and Alison M. RoarkUniversity of Florida Life-history theory seeks to explain how natural selection has optimized life cycles to maximize fitness. Central to this body of theory is the prediction that trade-offs occur between traits such as current and future reproduction, longevity and fecundity, growth rate and longevity, egg size and clutch size, and age and size at maturity. The existence of these trade-offs implies that organisms are limited in their capacity to maximize simultaneously the amount of acquired resources allocated to various traits that influence fitness. Although life-history literature is replete with examples of trade-offs exhibited under different but constant levels of food availability, variation in resource acquisition throughout an animal's lifespan is an often overlooked component of life-history experimentation. The purpose of this study is to evaluate how restricted and ad libitum feeding imposed at different stages of an animal's life cycle affect physiological and life-history traits of females and their offspring. The novelty of this study is the use of a parthenogenetic species (the Indian stick insect, Carausius morosus) as the animal model. This approach obviates the need for captive mating and thus avoids potential complicating factors such as mate compatibility, gender-specific differences in growth and development rates, and differential effects of nutrition on egg and sperm production. By avoiding paternal effects, a parthenogenetic species allows direct evaluation of the effects of variable food availability in females on the condition, growth, and survival of their offspring. Because this species feeds on the same diet (English ivy, Hedera helix) throughout its lifetime, nymphs and adults can be maintained on the same food source so that food quantity can be varied at different stages without also varying food quality. Throughout this study, physiological and life-history responses to six patterns of variable food availability imposed throughout each insect's lifetime will be evaluated. With these data, the theoretical predictions of life-history and allocation models (including the occurrence of trade-offs) can be rigorously tested under conditions of changing food availability. Furthermore, this study will yield insights into the effects of differences in food availability at different developmental stages on response variables such as fecundity and offspring condition that have substantial influences on population structure and dynamics. This project promotes integration of science and education through the participation of undergraduate students from diverse backgrounds. These students will have the opportunity to volunteer or to obtain college credits for their involvement in various components of the project. The results of the proposed study will be disseminated to a broad audience via displays, presentations, and publications. This research will yield insights into the effects of intake pattern on fitness and will therefore be of interest to scientists and the general public.