Cytochrome C oxidase activity in interpopulation hybrids of a marine copepod: A test for nuclear-nuclear or nuclear-cytoplasmic coadaptation

The respiratory enzyme cytochrome c oxidase (COX) is composed of subunits e ncoded by both nuclear and mitochondrial genes; thus, COX activity reflects , to some extent, the coordinated function of the two genomes. Because exte nsive mtDNA differentiation exists between populations of the copepod Tigri opus californicus, we hypothesized that laboratory hybridizations that disr upt natural combinations of nuclear and mitochondrial genes might negativel y impact COX activity. Although experimental results varied greatly among d ifferent crosses, replicate sets of crosses between two particular populati ons showed consistent evidence for nuclear-cytoplasmic coadaptation.