Meeting Abstract
Fundamental to the survival of animals in temperate climates is the ability to acclimate to temperature changes. The metabolic thermal response is relatively well-characterized, and reversible cellular mechanisms of acclimation can be broadly distributed into two categories: changes in mitochondrial density, the size and number of mitochondria in a cell; and changes in mitochondrial efficiency, a variety of factors affecting the ATP production rate of individual mitochondria. Both strategies facilitate thermal acclimation, yet few studies have investigated their timing. How long does the acclimation process take? How do mitochondrial efficiency and density interplay to produce a response over time? These are the questions that we chose to investigate within Nematostella vectensis, a small, salt marsh-dwelling anemone that experiences seasonal variation of ≥35˚C. We transitioned animals from 18˚C to six temperatures between 6 and 33˚C and, weekly, assayed two physiological responses: oxygen consumption of individual animals, indicative of the extent of acclimation; and citrate synthase (CS) activity, a standard proxy for mitochondrial density. We hypothesized that animals would acclimate first by altering their mitochondrial efficiency and later by adjusting mitochondrial density. Over six weeks, we found that respiration rates diverge significantly between temperature groups as early as the second week (p < 0.05). In the same animals, however, CS activity does not significantly change. This suggests that, though Nematostella do acclimate, mitochondrial density does not play a role in their initial acclimation response. Whether they regulate mitochondrial density on longer time scales remains an open question.
