Environmental stressors are ubiquitous. Animals will face a variety of natural and anthropogenic stressors throughout their life cycle. The physiological mechanisms that mediate stressful stimuli can have pleiotropic effects on life history traits, such as reproduction and development. Furthermore, these phenotypic changes can affect larger-scale ecosystem dynamics, like nutrient cycling and disease epizootics. Animals are not equally susceptible to stressors across all stages of their life cycles. Critical windows of development, common in young and developing animals, are time periods when stressors have an outsized effect and can permanently alter phenotype. Larval amphibians use a critical window in late larval development wherein activation of the hypothalamic-pituitary-adrenal/interrenal (HPA/I) axis speeds their development, allowing them to metamorphose and escape suboptimal aquatic habitat. Accelerated development comes at a cost, the glucocorticoid (GC) hormones secreted by the HPA/I axis affect other systems such as growth, immune function, metabolism, and nutrient use. In chapter two, I investigated the effects of GC hormones on metabolism, energetics, and nutrient oxidation in larval wood frogs. The results show that GC hormones increase metabolism, reduce lipid stores, and increase protein oxidation during metamorphic climax. Chapter three focuses on the effects of GC hormones on immune function and r susceptibility. I found that chronic exposure to GC hormones increased ranavirus replication in infected wood frog larvae, but did not affect survival time. This could contribute to ranavirus epizootics. Acute GC hormone exposure increased survival, possibly by activing the inflammatory response. Finally, chapter four investigates the effects of GC hormones on nutrient stoichiometry. I found that larvae treated with GC hormones had lower nitrogen to phosphorus ratios, possibly because disrupted skeletal ossification. They also had reduced phosphorus excretion, which could affect ecosystem-level processes like nutrient cycling and decomposition.

Seed reproduction is a key part of the life cycle of the most plant species. It allows for the dispersal of species in space and time and, thus, significantly affects dynamics of plant populations and communities. Seed formation, germination and seedling establishment are subjected to selection pressures from the environment and lead to optimization of maternal investments (maternal care), manifested by the number of seeds and amount and composition of nutrients stored in individual seeds. The thesis aims to answer two questions: (i) whether maternal investments in terms of seed mass and seed nutrient stoichiometry is optimized according to the environmental conditions in which seedling development is expected and (ii) how nutrient availability, considering nutrients both stored in the seed by the mother plant and those available in the substrate, affects seedling growth and development. To answer the first question, we focused on interspecific comparisons of seed nutrient stoichiometry linking it with data on seed mass and species niche along gradients of nu- trient availability. We used a phylogenetically informed comparative approach to explore the ratio between phosphorus, nitrogen and nonstructural carbon in seeds from 510 wild herbaceous species. We analyzed seed nutrient stoichiometry with...

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