How will warming affect the growth and body size of the largest extant amphibian? More than the temperature-size rule

Abstract

Declining body size is a universal ecological response to global warming in ectotherms. Ectotherms grow faster but mature at a smaller size at higher temperatures. This phenomenon is known as the temperature-size rule (TSR). However, we know little about the details of the relationship between temperature and size. Here, this issue was studied in the Chinese giant salamander (Andrias davidianus), one of the largest extant amphibians and a flagship species of conservation in China. Warm-acclimated A. davidianus larvae (25 °C) had accelerated development but little superiority in body growth when compared to their 15 °C counterparts when fed with red worm. This predicts a drastic decrease in adult body size with warming. However, a fish diet (more abundant lipid and protein) improved the growth performance at 25 °C. The underlying mechanism was studied. Warm-acclimated larvae had enlarged livers but shortened tails (fat depot). Their livers suffered from energy deficiencies and decreased protein levels, even when protein synthesis and energy metabolism were transcriptionally upregulated. This could be a direct explanation for their poor growth performance. Further analyses revealed a metabolic disorder resembling mammal glycogen storage disease in warm-acclimated larvae, indicating deficiency in glycogen catabolism. This speculation is consistent with their increased lipid and amino acid catabolism and explained the poor energy conditions of the warm-acclimated larvae. Additionally, a deficiency in glycogen metabolism explains the different efficiency of worm and fish diets in supporting the growth of warm-acclimated larvae, even when both diets were provided sufficiently. In conclusion, our results suggest that the relationship between temperature and body size can be flexible, which is a significant finding in terms of the TSR. The underlying metabolic and nutrient mechanisms were revealed. This knowledge can help deepen our understanding of the consequences of warming and can contribute to the conservation of A. davidianus.

Keywords: Biological conservation; Chinese giant salamander; Metabolic switch; Organ heterogeneity; Transcriptomics; Warming.