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

Abstract

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.

A young age of subspecific divergence in the desert locust inferred by ABC random forest

“…In this study, we used an advanced ABC‐RF methodological framework, including prior knowledge on genetic markers and check for prediction accuracy, to investigate the evolutionary history of the desert locust, Schistocerca gregaria . Altogether our results refute the hypothesis that the species colonized Africa with the expansion of its desert habitat during ancient Quaternary glacial climatic episodes, in contrast with some other African arid‐adapted species (Atickem et al., 2018; Moodley et al., 2018). As a matter of fact, our work dates this event to about 2,600 years ago, in the present interglacial period when tropical forests were abundant in Central Africa, and thus rather suggests a recent long‐distance migration event by which a small number of locusts would have crossed the thousands of kilometers separating the deserts of northern and southern Africa (Figure 5).…”

“…One can therefore reasonably assume that, at the inferred divergence time between the two locust subspecies, the connectivity between the two African hemispheres was still limited by the moist equator, in particular at the west, and by the savannahs and woodlands of the eastern coast. Consequently, contrary to most phylogeographic studies on other African arid‐adapted species (Atickem et al., 2018; Moodley et al., 2018), it is unlikely that the rather ancient Quaternary climatic history explained the Southern range extension of the desert locust.…”

“…with the expansion of its desert habitat during ancient Quaternary glacial climatic episodes, in contrast with some other African aridadapted species (Atickem et al, 2018;Moodley et al, 2018). As a matter of fact, our work dates this event to about 2,600 years ago, in the present interglacial period when tropical forests were abundant in Central Africa, and thus rather suggests a recent long-distance migration event by which a small number of locusts would have crossed the thousands of kilometers separating the deserts of northern and southern Africa ( Figure 5).…”

“…(2011) on the ostrich; Atickem et al., 2018 on the black‐backed jackal; and Moodley et al. (2018) on the white rhinoceros.…”

“…Similarities in extant distributions of African arid-adapted species across divergent taxonomic groups point to a common climatic history and an important role of environmental factors. Yet, to our knowledge, studies relating evolutionary history and climatic history have rarely been carried out in this continent; but see mitochondrial studies by Miller et al (2011) on the ostrich; Atickem et al, 2018 on the black-backed jackal; and Moodley et al (2018) on the white rhinoceros.…”