Abstract:
The distributions of the native crab Ovalipes catharus and the invasive species Charybdis japonica within New Zealand shores may be defined by thermal tolerance. Doppler ultrasound showed that with increasing temperature O. catharus and C. japonica raised their heart rates (p ≤ 0.05). However, C. japonica showed greater plasticity in heart beat duration, or contraction rate with increasing temperature, while O. catharus was more inclined to increase heart rate, and already had a shorter more rapid contraction at 19 °C. Saponin permeabilized heart fibres enabled tests of mitochondrial function in situ and showed that Leak-I respirational flux was highest for O. catharus at all temperatures. C. japonica showed a greater inner mitochondrial membrane integrity which suggests tighter coupling of oxidative phosphorylation. Although Complex I lost function on exposure to 30 °C in both species, this occurred more rapidly in O. catharus. Complex II function remains stable at high temperature in both species. O. catharus had higher cytochrome c oxidase (CCO) flux at all temperatures compared to C. japonica indicating elevated concentrations of CCO in O. catharus. The scope to increase CCO flux was greater in the more stenothermal O. catharus than in C. japonica. Overall, this study shows substantial differences in heart function and mitochondria between crab species and provides evidence that mitochondrial integrity may limit species survival and potentially future distributions.
