Meeting Abstract
P2.29 Saturday, Jan. 5 The role of oxygen in determining upper temperature tolerance in the fingered limpet under emersed and immersed conditions BJELDE, B.E.**; MILLER, N.A.; TODGHAM, A.E.; San Francisco State University; San Francisco State University; San Francisco State University bbjelde@mail.sfsu.edu
Predicting an organism’s vulnerability to future increases in temperature requires an understanding of the factors that set their upper temperature tolerance. Previous investigations of cardiac performance and thermal tolerance limits in the fingered limpet, Lottia digitalis, have shown that limpets exposed to a thermal ramp under emersed conditions maintained heart function to a higher temperature than limpets exposed to the same heating while immersed. Here we examined whether differences in O2 concentration in air and water could explain reduced cardiac thermal tolerance under immersed conditions. Limpets were heated at a rate of 6°C/h under hyperoxic (35%), normoxic (21%), or hypoxic (5%) O2 conditions in both emersed and immersed conditions. Thermal limits of heart function were calculated as break point temperatures (BPT). Similar to previous work, emersed limpets were significantly more thermally tolerant than immersed limpets under all O2 exposures. BPTs of emersed limpets were roughly 2-3°C higher than immersed limpets under normoxic and hyperoxic conditions and almost 5°C higher under hypoxic conditions. Thermal tolerance was not increased in either immersed or emersed limpets exposed to 35% O2 suggesting that in both air and water the ability to supply O2 to tissues at high temperatures is already maximized under normoxia. However, under hypoxic conditions both groups of limpets exhibited significantly reduced thermal tolerance providing evidence of O2 limited thermal tolerance at low environmental PO2s. Given the consistent differences in thermal tolerance in emersed and immersed limpets across all O2 concentrations, reduced O2 availability in water is not sufficient to explain air/water thermal tolerance differences.
