title: Conservation genetics for the management of black rhinoceros (Diceros bicornis michaeli) in Tanzania
Creators: name: Mellya, Ronald Vincent
Publisher: name: University of Glasgow
Year: 2024

description: As anthropogenic impacts continue to rise, many species are confined to small, isolated populations. Conservation efforts aimed at reducing extinction risks often involve strategies like enhancing habitat connectivity, translocating individuals from captive populations, reintroductions, or closely monitoring highly protected closed populations. Despite potential variations in individual fitness resulting from different selection pressures in these scenarios, the genetic consequences of these strategies are frequently overlooked.

Eastern black rhinoceros (Diceros bicornis michaeli) are critically endangered mega herbivores that had suffered 96% decline in in their native range due to poaching and now persist as small and fragmented populations totaling less than 2300 individuals across the globe. Although there have been studies on genetic diversity in some geographic regions, no previous studies have assessed genetic variation of extant populations in Tanzania. The purpose of this study was to use conservation genetic techniques to assist the management of the eastern black rhinoceros in Tanzania.

I used the mitochondrial DNA (mtDNA) control region to investigate the genetic impacts of past management interventions on mitochondrial control region diversity in extant subpopulations in Tanzania. Six maternal haplotypes were identified, with an overall haplotype diversity of h = 0.72, but lower nucleotide diversity within populations (π = 0.017) compared to historical populations (π = 0.021). Translocated populations did not share haplotypes with native populations, although all haplotypes from translocated individuals were found among historic samples from Kenya, indicating successful restoration of previous diversity but restricted female movement between subpopulations due to current management practices. The extant haplotypes were distributed among three East African haplogroups, suggesting preservation of multiple lineages despite the loss of historical haplotypes. A recommendation is made to enhance previous translocations by facilitating natural movements between subpopulations, which could be a more cost-effective and welfare-conscious management strategy compared to targeting specific animals for translocation based on genetic data.

We used whole genome sequencing data to assess the scale of inbreeding that has been induced by the severe bottlenecks and subsequent expansion of native populations as well as what impacts previous attempts at population supplementation have had on the accumulation of potentially deleterious mutations. We found that offspring from individuals dispersing from native populations or translocated from captive ones had lower inbreeding levels compared to a closed native population. However, compared to native individuals, offspring resulting from captive parents or hybridisation between wild and native parents had a larger relative abundance of deleterious mutations, and this load was sheltered by higher heterozygosity. Our work underlines the value of maintenance of habitat corridors between populations and emphasizes the significance of natural dispersal in managing the trade-off between supplementing variation and introducing potentially harmful mutations if populations are allowed to inbreed following targeted translocations.

I assessed the demographic parameters of the eastern black rhino population in Tanzania and explored different management options that minimize the risk of extinction of rhinos using a count-based Population Viability Analysis (PVA). Given the current demographic parameters and the current management efforts, there is a low probability of extinction by 2050 for the indigenous native populations, except for Nyamalumbwa (but this is a transborder population where observational records are less accurate), and for both the reintroduced subpopulations of Ndasiata and Grumeti, which exhibit the highest probability of extinction by 2050 (i.e. they do not exceed the 20 animal benchmark of a viable population size as set out by IUCN). Overall, my analyses suggest that translocated populations have not reduced the risk of extinction for black rhinos in Tanzania. With the current protection efforts and demographic performance, Moru and Ngorongoro could serve as a source population for reintroduction to other areas. This approach would reduce the cost and risks associated with international translocation efforts.

Overall, I demonstrated the value of adding ongoing genetic surveillance to conservation management strategic plans, to allow monitoring of both the short- and long-term impacts of different management strategies used to protect small and threatened populations.