Meeting Abstract
Whole-animal thermal limits are thought to be constrained by processes acting at the level of the mitochondria. In this study we tested the effects of thermal acclimation and local adaptation on mitochondrial performance in the Atlantic killifish, Fundulus heteroclitus. We assessed heart and brain mitochondrial performance, as temperature effects on these organs are thought to place constraints on whole-animal performance. We used a Substrate Uncoupler Inhibitor Titration (SUIT) protocol to assess mitochondrial performance following thermal acclimation (5, 15, 33°C) in Northern (Nova Scotia) and Southern (Georgia) killifish. We hypothesized that low-temperature acclimation would be associated with modest compensation of mitochondrial performance, with Northern cold-adapted killifish exhibiting a greater increase than their Southern counterparts. High-temperature acclimation was predicted to cause a decline in performance that was greater in Northern killifish compared to Southern killifish; an effect we have previously demonstrated in liver mitochondria. Following acclimation to both 5 and 33°C, killifish heart and brain mitochondria exhibited a suppression of respiration (compared to 15°C). These suppression effects were largely associated with flux through ETS complex I. In addition, there was no clear differentiation between populations in these mitochondrial processes. This work demonstrates that thermal acclimation responses in the brain and heart differ from that of the liver, although the primary site of modification (ETS complex I) is the same. The absence of subspecies-specific responses indicates that mitochondrial performance does not account for subspecies differences in whole-animal thermal limits. These effects may, however, be a mechanism underlying the broad thermal tolerance of the species as a whole.
