Early‐life adversity modulates growth trajectories and red blood cell mitochondrial metabolism in king penguin chicks

In many avian species, variation in breeding phenology is known to affect repro-ductive success. In king penguins, the breeding cycle lasts more than a year, and thestart of egg-laying extends over three months, with early-breeders laying eggs aroundDecember and late-breeders around February. Consequently, late-born chicks have lesstime to grow and build-up their energy reserves before the austral winter. Variation inmetabolic rate is one important pathway affecting differences in growth patterns, asit is directly involved both in energy allocation processes and fitness. The conversionof resources into energy occurs in mitochondria, and the efficiency of this conversionis likely to play a fundamental role in explaining individual variation in growth andsurvival. The purposes of this study were to investigate the differences in red bloodcell mitochondrial metabolism between early- and late-born king penguin chicks andto assess whether growth patterns could be explained by differences in mitochondrialmetabolism. Late chicks expressed higher mitochondrial metabolism than early chicksat 100 days post-hatching, probably linked to the stress related to winter environ-mental conditions and a decrease in parental feeding rates. We did not find a clearassociation between chick mitochondrial metabolism and growth patterns, suggest-ing that environmental conditions mostly contributed in explaining different meta-bolic phenotypes. As king penguin populations in Crozet may face changing breedingconditions (changes in feeding area and foraging trips duration) in relation to globalchanges, studying the physiological traits and adaptations underlying the chick growthand survival may help in understanding the response of king penguins facing challeng-ing conditions.