Occurrence of mitochondrial CO1 pseudogenes in Neocalanus plumchrus (Crustacea: Copepoda): Hybridization indicated by recombined nuclear mitochondrial pseudogenes

A portion of the mitochondrial cytochrome c oxidase I gene was sequenced using both genomic DNA and complement DNA from three planktonic copepod Neocalanus species ( N . cristatus , N . plumchrus , and N . flemingeri ). Small but critical sequence differences in CO1 were observed between gDNA and cDNA from N . plumchrus . Furthermore, careful observation revealed the presence of recombination between sequences in gDNA from N . plumchrus . Moreover, a chimera of the N . cristatus and N . plumchrus sequences was obtained from N . plumchrus gDNA. The observed phenomena can be best explained by the preferential amplification of the nuclear mitochondrial pseudogenes from gDNA of N . plumchrus . Two conclusions can be drawn from the observations. First, nuclear mitochondrial pseudogenes are pervasive in N . plumchrus . Second, a mating between a female N . cristatus and a male N . plumchrus produced viable offspring, which further backcrossed to a N . plumchrus individual. These observations not only demonstrate intriguing mating behavior in these species, but also emphasize the importance of careful interpretation of species marker sequences amplified from gDNA.