Comparison of whole mitochondrial genome sequences of northern and southern white rhinoceroses (Ceratotherium simum): the conservation consequences of species definitions

The probable extinction of the last confirmed population of northern white rhinoceros ( Ceratotherium simum cottoni ) in the world has ignited debate regarding its species status compared to the southern white rhinoceros ( Ceratotherium simum simum ). Previous studies, based on partial mitochondrial sequences, have reported conflicting results regarding the species status of the northern white rhinoceros. We use whole mitochondrial genomes obtained using Next Generation Sequencing of four northern white rhinoceros and three southern white rhinoceros using novel primers in three overlapping fragments. Phylogenetic relationships were constructed, using Maximum Likelihood, and recovered monophyletic clades for northern white rhinoceros and southern white rhinoceros. The divergence time between the two mitochondrial DNA lineages was estimated to be between 0.46 and 0.97 million years ago using Bayesian inferences. Since there are currently only three surviving northern white rhinoceros individuals these results put into sharp focus the ongoing debate regarding the methods of species definition, and in particular the consequences of such definitions in conservation management of endangered species and subspecies. We conclude that the designation of sub-species status is more applicable to northern and southern white rhinoceros.