Metabolic costs of altered growth trajectories across life transitions in amphibians.

Climate change is causing increases in temperature and in the frequency of extreme weather events. Under this scenario, organisms should maintain or develop strategies to cope with environmental fluctuations, such as the capacity to modify growth trajectories. However, altering growth can have negative consequences for organisms' fitness. Here, we investigated the metabolic alterations induced by compensatory growth during the larval development of the common frog (Rana temporaria), quantifying changes in oxidative stress, corticosterone levels and telomere length. We induced compensatory growth responses by exposing frog embryos to cold conditions (i.e. a 'false spring' scenario), which cause a delay in hatching. Once hatched, we reared larvae at two different photoperiods (24:0, representing the natural photoperiod of larvae, and 18:6) to test also for the interactive effects of light on growth responses. Larvae experiencing delayed hatching showed fast compensatory responses and reached larger size at metamorphosis. Larvae shortened their developmental period in response to delayed hatching. Non-permanent light conditions resulted in relaxed growth compared with larvae reared under permanent light conditions, which grew at their natural photoperiod and closer to their maximal rates. Growth responses altered the redox status and corticosterone levels of larvae. These physiological changes were developmental stage-dependent and mainly affected by photoperiod conditions. At catch-up, larvae reared at 18:6 light:dark cycles showed higher antioxidant activities and glucocorticoid secretion. On the contrary, larvae reared at 24:0 developed at higher rates without altering their oxidative status, likely an adaptation to grow under very restricting seasonal conditions at early life. At metamorphosis, compensatory responses induced higher cellular antioxidant activities probably caused by enhanced metabolism. Telomere length remained unaltered by experimental treatments but apparently tended to elongate across larval ontogeny, which would be a first evidence of telomere lengthening across metamorphosis. Under the forecasted increase in extreme climatic events, adjusting growth and developmental rates to the dynamics of environmental fluctuations may be essential for survival, but it can carry metabolic costs and affect later performance. Understanding the implications of such costs will be essential to properly estimate the impact of climate change on wild animals.