Metabolic connections to life history in fishes

Metabolic rate is often assumed to set the pace of life histories because organisms depend upon the energy acquired through metabolism for survival, growth, and reproduction. However, key links between metabolic rate, morphology, and ecology remain unexamined. First, I examined the energetics behind brain size in the blacktip shark (Carcharhinus limbatus) using gill surface area as an integrated correlate of metabolic rate. Both brain mass and gill surface area increased with body mass throughout ontogeny and individuals with larger brains for their body mass also had larger gill surface areas. Second, I asked whether life history traits explained variation in resting metabolic rate across fishes and found that only growth performance, which encompasses the trade-off between growth and maximum size, explained variation. Collectively, this work illustrates the importance of energetic trade-offs and emphasizes the need for empirical tests of assumptions and an integrated view of physiology and ecology.