Trade-offs, limits to adaptation, and multiple solutions: rules elucidated by selective breeding for high activity levels

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This project focuses on understanding how organisms make trade-offs in energy allocation to different activities and how multiple solutions to enhance locomotor activity may evolve. Biological diversity encompasses not only numbers of species but the functional diversity that they exhibit. Organisms work in a variety of ways, and often exhibit trade-offs and multiple solutions. One example of a trade-off is the negative relationship between the number of offspring produced and the size of individual offspring, as documented in many groups of plants and animals. This trade-off is often attributed to a constraint on the total amount of energy available for reproduction. Multiple solutions are apparent in the various ways that flight has evolved (e.g., birds versus bats). This research project addresses both of these phenomena in the context of a novel experiment that involves selective breeding for high voluntary levels of exercise in house mice. Two hypotheses will be tested: (1) selection for high activity is associated with reductions in lifetime reproductive success, representing a trade-off between locomotor activity and fitness, and (2) the trade-off between average running speed and duration that has evolved among the high-activity mouse lines is reflected in corresponding differences in characteristics of their muscle tissues. The project will help to elucidate the fundamental nature of biodiversity. The results will be disseminated in scientific publications and Wikipedia pages will be created and updated. An online Open Educational Resource version of Ecological and Evolutionary Physiology, an undergraduate course, will be developed. This project will involve training for both graduate students and undergraduates in a collaborative, integrative, and cross-disciplinary research setting. To increase participation and diversity, students from underrepresented groups and educationally or economically disadvantaged backgrounds will be recruited.Trade-offs and multiple solutions are inherent to life and appear to underlie a substantial amount of the variation in biodiversity over time. However, few studies have used experimental evolution to address these topics. The proposed research will use selection for high locomotor activity, in a model organism (laboratory house mice), to elucidate trade-offs and multiple solutions during locomotor evolution. Because locomotor activity is a key component of the life history of animals, results of these studies should provide insight into general principles. The research will take advantage of a unique resource comprising four replicate lines of High Runner mice that have been selectively bred for more than 90 generations for voluntary locomotor activity, and an additional four lines that serve as non-selected Controls. Aim 1 will test for reduced lifetime reproductive success in the selected lines and whether this trade-off manifests in different ways in the replicate lines (e.g., reduced litter size vs. reduced length of reproductive lifespan). Aim 2 will test whether trade-offs in muscle function underlie the trade-off between average running speed and duration that has evolved among the four selected lines, and if multiple solutions at the level of muscle performance are involved. The mouse lines will be made available to other researchers, and the online course materials and Wikipedia content to be developed will be broadly disseminated. Several undergraduate and graduate students, recruited from groups traditionally under-represented in science, will participate in the research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.