VARIATION IN CYTOCHROME-C-OXIDASE ACTIVITY IS NOT MATERNALLY INHERITED IN THE COPEPOD TIGRIOPUS-CALIFORNICUS

The mitochondrial enzyme cytochrome-c oxidase (COX) is composed of mul tiple subunits encoded within both the nuclear and mitochondrial genom es. Isofemale lines of the intertidal copepod Tigriopus californicus s howed significant variation in COX activity (measured by a standard sp ectrophotometric method) both within and between populations. This int erline variation was expressed under common culture conditions and is evidence of a genetic component to COX enzymatic activity variation. B ecause the catalytic core of COX (subunits I, II and III) is encoded b y mitochondrial DNA, which is inherited maternally in T. californicus, we hypothesized that variation in COX activity may show maternal inhe ritance. This hypothesis was evaluated by determining COX activity amo ng F-1 progeny of reciprocal crosses between isofemale lines. Results failed to support the hypothesis; COX activity did not show a pattern of maternal inheritance. Rather, the data suggest that genetic regulat ion of interline variation in COX activity is complex and involves nuc lear genes. In general, F-1 offspring tended to have higher COX activi ties than either parent, whereas F-2 offspring had enzyme activities s imilar to or lower than the F-1, suggesting that strong nuclear-nuclea r or nuclear-mitochondrial interactions affect COX function.