Effects of the early environment on juvenile and adult phenotype in sexually sized dimorphic species

The environment that an organism faces during development (from embryogenesis to independence) can profoundly shape adult condition, phenotype and fitness. However, it is only recently that the long-term effects of early environmental conditions have been explored. Maternal effects, developmental stress and resource availability can all influence the environment during development. Using two sexually-sized dimorphic species, the ring-billed gull ( Larus delawarensis) and the Japanese quail (Coturnix japonica ), I characterized the sex-specific effects of early environment on juvenile and adult phenotype and condition. In ring-billed gulls, mothers allocated more albumen in ovo to male embryos and more yolk to female embryos, but external egg morphology remained constant between the sexes. Ring-billed gulls hatched with a developed stress response, detectable levels of natural antibodies, complement-mediated lysis activity and immunoglobulins. Levels of complement activity and immunoglobulins increased with age. Acute stress affected natural antibody and complement-mediated lysis activity, but not immunoglobulin levels. However, no sex differences were detected. Using Japanese quail, I explored the effects of food restriction on juvenile and adult phenotype. Japanese quail that underwent food restriction during development demonstrated catch-up growth, but metabolic rate was not elevated. Birds undergoing food restriction throughout development had not caught up to the same size as birds in other treatment groups at adulthood. Furthermore, metabolic rate was not elevated at adulthood in birds that had experienced food restriction, whereas previous studies demonstrated elevated adult metabolic rate in zebra finches. No sex differences in growth rate or metabolic rate were detected. Plasma corticosterone levels were elevated in Japanese quail chicks during food restriction regardless of timing or duration of food restriction. Levels of plasma corticosterone dropped after re-feeding, but were still high 2 days after re-feeding in birds that had been restricted throughout development. At no time were there sex differences in plasma corticosterone levels. The results of this thesis suggest that the early environment has effects on an organism's physiology during development, but it remains unclear whether there are effects on adult fitness. Moreover, there may be sex-specific effects of early environment, but it is dependent on life stage. Future studies should focus on how fluctuating conditions in early environment can affect physiology across multiple life-history stages, and investigate any possible effects on adult fitness.;Key words: early environment, developmental stress, sexual-size dimorphism, corticosterone, resource availability, catch-up growth, resource allocation, maternal effects...