Early nutrition and phenotypic development: 'catch-up' growth leads to elevated metabolic rate in adulthood.

Resting metabolic rate (RMR) is responsible for up to 50% of total energy expenditure, and so should be under strong selection pressure, yet it shows extensive intraspecific variation and a low heritability. Environmental conditions during growth are thought to have long-term effects through 'metabolic programming'. Here we investigate whether nutritional conditions early in life can alter RMR in adulthood, and whether this is due to growth acceleration or the change in diet quality that prompts it. We manipulated dietary protein levels during the main growth period of zebra finches (Taeniopygia guttata) such that an episode of poor nutrition occurred with and without growth acceleration. This produced different growth trajectories but a similar adult body mass. Only the diet that induced growth acceleration resulted in a significant (19%) elevation of RMR at adulthood, despite all the birds having been on the same diet after the first month. This is the first study to show that dietary-induced differences in growth trajectories can have a long-term effect on adult metabolic rate. It suggests that modification of metabolic efficiency may be one of the mechanisms mediating the observed long-term costs of accelerated growth, and indicates links between early nutrition and the metabolic syndrome.