Contrasting evolutionary history, anthropogenic declines and genetic contact in the northern and southern white rhinoceros (Ceratotherium simum).

The white rhinoceros (Ceratotherium simum) has a discontinuous African
distribution, which is limited by the extent of sub-Saharan grasslands.
The southern population (SWR) declined to its lowest number around the
turn of the nineteenth century, but recovered to become the world’s most
numerous rhinoceros. In contrast, the northern population (NWR) was
common during much of the twentieth century, declining rapidly since the
1970s, and now only two post-reproductive individuals remain. Despite
this species’s conservation status, it lacks a genetic assessment of its demographic history. We therefore sampled 232 individuals from extant and
museum sources and analysed ten microsatellite loci and the mtDNA
control region. Both marker types reliably partitioned the species into SWR
and NWR, with moderate nuclear genetic diversity and only three mtDNA
haplotypes for the species, including historical samples. We detected ancient
interglacial demographic declines in both populations. Both populations may
also have been affected by recent declines associated with the colonial expansion for the SWR, and with the much earlier Bantu migrations for the NWR.
Finally, we detected post-divergence secondary contact between NWR and
SWR, possibly occurring as recently as the last glacial maximum. These
results suggest the species was subjected to regular periods of fragmentation
and low genetic diversity, which may have been replenished upon secondary
contact during glacial periods. The species’s current situation thus reflects
prehistoric declines that were exacerbated by anthropogenic pressure associated with the rise of late Holocene technological advancement in Africa.
Importantly, secondary contact suggests a potentially positive outcome for
a hybrid rescue conservation strategy, although further genome-wide data
are desirable to corroborate these results.