Developmental Programming, Life-History Trade-Offs, and the Mechanisms that Drive them: Insights from Australian Skinks

Abstract

The conditions experienced during development can have lasting, "programmatic", consequences for phenotypes and fitness. Developmental programming may be initiated through direct effects of the environment acting on the individual, or via indirect effects of the maternal environment through maternal phenotypes. The individual effects of developmental environments and maternal effects have long been appreciated, but how they interact to program phenotypes is poorly understood. Likewise, developmental effects are highly dependent on the context in which these traits are expressed, potentially differing among species with alternative life-history strategies. Consequently, recent work has aimed to characterise the mechanisms underlying developmental programming and how conserved these mechanisms are among species. Additionally, while developmental effects in early life are well-characterized, relatively few studies have followed individuals throughout the lifespan, thereby limiting our understanding of their long-term fitness consequences. The paucity of longitudinal, multi-species studies which measure life-history traits alongside physiological mechanisms is often attributed to logistical constraints - particularly the limitations of current methods for quantifying physiological biomarkers. Therefore, in my thesis, I aimed to characterize how the developmental environment and maternal effects interact to shape key life-history traits throughout the lifespan of two species with differing life-history strategies, and developed and utilized novel methods to quantify multiple physiological biomarkers of fitness. Specifically, I tested the effects of incubation temperature and maternal stress hormones (corticosterone) on the growth and survival of delicate skinks (Lampropholis delicata) and garden skinks (Lampropholis guichenoti) throughout their lifespan in naturalistic conditions. I developed a novel function assay panel utilizing flow cytometry techniques to quantify mitochondrial function and oxidative stress - which are associated with performance and survival - both early and late in life. In doing so, I aimed to address the questions: 1) Do the developmental environment and maternal effects interact to shape early-life fitness and phenotypes?; 2) Do developmental effects have programmatic effects on life-history trajectories?; 3) Are developmental effects mediated by species' life-history strategies?; and 4) Are developmental effects driven by programmatic changes in mitochondrial or oxidative physiology? My findings generally suggest that developmental conditions have important consequences for early-life fitness, but a limited role in programming long-term patterns of phenotypic variation, that life-history strategy variation among species may play a role in buffering species from developmental effects, and that mitochondrial and oxidative physiology were not the mechanisms responsible for the patterns observed. Yet, there remain alternative mechanistic pathways and ecological contexts that may reveal a more complex relationship between developmental environments and life-history trajectories, which warrants further investigation. The comprehensive design of this thesis establishes a powerful foundation for more targeted investigations of these alternative mechanisms and pathways, while the novel flow cytometry methods presented herein provide a powerful tool for mechanistic life-history studies both in the context of developmental programming and more broadly. Thus, my thesis provides important data, experimental designs, and methodological tools for additional studies of developmental programming, life-history trade-offs, and the mechanisms that drive them. Show more