Why does metabolic rate scale with body size?

Metabolic scaling, the relationship between metabolic rate and body size, plays a crucial role in understanding the ecological and evolutionary dynamics of organisms. In this study, we investigated metabolic scaling in Amphiprion chrysopterus and Ostorhinchus angustatus, across various taxonomic levels. By estimating metabolic rates using respirometry and quantifying specific growth rates, we made significant findings:

1. During the early life stages of the orange-fin anemonefish, we observed a positive correlation between metabolic scaling slopes and growth rates, suggesting the influence of pleiotropic gene control. However, as individuals matured, this correlation weakened, indicating the involvement of additional factors in the metabolic rate-growth relationship.
2. Comparing metabolic scaling across species and within individuals, we found that evolutionary metabolic scaling was steeper than static scaling, reflecting the impact of natural selection favoring faster-growing larvae in the wild. Additionally, static scaling was shallower than the mean of ontogenetic metabolic scaling, likely due to low larval-stage mortality in species benefiting from parental care.

By expanding the scope of our investigation to encompass multiple taxonomic levels, our study breaks new ground in the field of metabolic scaling research and provides valuable insights into the ecological and evolutionary processes of organisms in response to changing environmental conditions.