Fatter or stronger: Resource allocation strategy and the underlying metabolic mechanisms in amphibian tadpoles.

The allocation of resources between storage and somatic growth is an essential physiological phenomenon in animals. Allocation mechanisms have broad theoretical and applied implications. The real-time resource allocation patterns in animals remain to be elucidated, and there is limited understanding of the metabolic mechanisms. We investigated the resource allocation strategy of Rana omeimontis tadpoles. Their ontogenetic fat accumulation began when body weight increased to 30-50 mg, at which time storage had a high priority in resource allocation. Beyond this weight range, somatic growth accelerated but storage investment was maintained, resulting in a positive correlation between body fat index and body weight at the population level. This pattern could be explained by assuming a positive relationship between storage abundance and growth investment, and this was supported by the prioritized increment of body fat to body weight when tadpoles were provided with increased food. At the metabolic level, hepatic fat accumulation was accompanied by upregulated utilization of fat storage, and the tadpoles presented lipid-based energy metabolism. Activating the mobilization of hepatic fat storage promoted somatic growth. In short, the liver is like a reservoir with valves that regulate energy flow for downstream developmental processes. These results provide novel mechanistic insights into resource allocation.