Ultraviolet irradiation alters the density of inner mitochondrial membrane and proportion of inter-mitochondrial junctions in copepod myocytes.

The efficient production of energy via oxidative phosphorylation is essential to the growth, survival, and reproduction of eukaryotes. The behavior (position of, and communication between, mitochondria) and morphology of mitochondria play key roles in efficient energy production and are influenced by oxidative stressors such as ultraviolet (UV) radiation. We tested the hypothesis that mitochondria change their behavior and morphology to meet energetic demands of responding to changes in oxidative stress. Specifically, we predicted that UV irradiation would increase the density of inner mitochondrial membrane and proportion of inter-mitochondrial junctions to influence whole-animal metabolic rate. Using transmission electron microscopy, we found that both three and six hours of UV-A/B irradiation (0.5 W/m) increased the proportion of inter-mitochondrial junctions (with increasing mitochondrial aspect ratio) and the density of inner mitochondrial membrane in myocytes of Tigriopus californicus copepods. Mitochondrial density increased following both irradiation treatments, but mitochondrial size decreased under the six hour treatment. Metabolic rate was maintained under three hours of irradiation but decreased following six hours of exposure. These observations demonstrate that the density of inner mitochondrial membrane and proportion of inter-mitochondrial junctions can play formative roles in maintaining whole-animal metabolic rate, and ultimately organismal performance, under exposure to an oxidative stressor.