15.3 Wednesday, Jan. 4 Warm fish with cold hearts: Cardiac thermal plasticity of Pacific bluefin tuna Thunnus orientalis JAYASUNDARA, N.*; GARDNER, L.D.; TOWLE, D.T.; BLOCK, B.A.; Stanford University; Stanford University; Mount Desert Island Biological Laboratory; Stanford University email@example.com
Bluefin tunas are renowned for their exceptional locomotory capabilities, elevated metabolic rates and unique endothermic physiology. Their hearts, operating at ambient temperature, sustain an enhanced cardiac performance across a thermal gradient to support this high energy demanding life style. However, little is known about the molecular processes underpinning the thermal plasticity of tuna hearts. In this study we investigated the transcriptomic response to temperature acclimation (14oC, 20oC and 25oC) in atrial and ventricular tissues of Pacific bluefin tuna (PBFT) using quantitative PCR and a bluefin tuna specific microarray. qPCR data suggested that genes involved in Ca2+ induced Ca2+ release pathway are altered with cold (14oC) and warm (25oC) acclimation. We compared this data against cardiac gene expression of wild caught PBFT and two spatiotemporally co-occurring closely related tuna species (T. alalunga and T. albacares) with varying degrees of endothermic capacity. Transcriptomic analysis on PBFT acclimated to temperature indicated changes in genes associated with energy metabolism, protein bio synthesis, cellular stress response, apoptosis and oxidative stress. A principal component analysis revealed that thermal response is tissue specific, with gene expression in atrium at 25oC showing the greatest difference. In the ventricle, compact layer appears to be more thermally labile compared to spongy layer. This study demonstrates that tuna heart function is optimized at 14oC, potentially improving aerobic performance in the cold. Conversely the cardiac transcriptome at 25oC is indicative of limitations in cardiac performance at warmer temperatures.