Meeting Abstract
Temperature underlies physiological and ecological variation among populations. For example, temperature is a key determinant of water oxygen availability, affecting metabolism, life histories, and morphology in fishes. Since gill area (GA) relates to oxygen diffusion and brains are one of the most metabolically costly organs, we hypothesize that populations at higher environmental temperatures will have faster life histories, larger GA relative to body size, and smaller brains relative to body size. Here, we ask whether GA and brain size vary between two populations of blacktip sharks (Carcharhinus limbatus) living in different environmental temperatures. However, because GA and brain size change with body mass throughout sharks’ lives, these traits must be studied in a scaling context. We predicted that the slope values for both GA and brain size would be similar for the two populations, but that the warmer population would have a larger GA and a smaller brain for a given body size. Gill area and brain mass were measured on individuals from the cooler South Atlantic Bight and the warmer Gulf of Mexico. We found that the Gulf population had a smaller relative brain size than the Atlantic population when we compared immature individuals, but also a smaller relative GA. Finally, both brain mass and GA scaled more steeply with body mass in the Gulf population. These results suggest that temperature influences the scaling of GA and brain mass between populations of blacktips. Investigating how GA and brain size scale between populations with different life histories and environments helps provide a better understanding of the evolutionary effects of environments on two key organs, as well as how environment and physiology impact metabolism and life histories.
