In the past decade, there has been a drastic decline in the number of Eastern Black rhinoceros (black rhinoceros) (Diceros bicornis michaeli), primarily because of poaching across their natural habitats, leaving few individuals in small, isolated populations that are vulnerable to demographic extinction, disease epidemics, genetic drift and inbreeding. However, genetic consequences of the demographic decline on the remaining populations have not been investigated. Using the mitochondrial control region, this study investigated how current levels of genetic diversity relate to historical patterns, quantified genetic differentiation between extant populations and assessed the impacts of previous translocations on genetic diversity across populations. A total of 74 individual eastern black rhinoceroses were sampled from five extant populations in Tanzania and one neighbouring cross-border population in the Maasai Mara in Kenya. Six maternal haplotypes were identified, with an overall haplotype diversity of h=0.7 but low overall nucleotide diversity within populations (pi = 0.017) compared to historical populations from Tanzania (pi = 0.021). There was extensive variation in haplotype distribution between populations, with more variation exists within (65.5 %) than among the populations (35.5%), which may indicate lack of migration between populations. Specifically, some geographically close populations with different histories of introductions didnt share any haplotypes, suggesting that gene flow is currently restricted. The haplotypes were distributed among three east African haplogroups (CV, CE and EA) that have been described in previous studies, suggesting that multiple lineages have been preserved despite loss of haplotypes. One of the haplotypes was highly divergent and matched sequences previously classified as a subspecies that has not been recognised in recent years (D. b. ladoensis). We recommend that current levels of diversity be maintained by allowing natural movements of rhinoceroses between the populations, with the possibility of introducing additional variations by translocation of individuals between sites.
In the past decade, there has been a drastic decline in the number of Eastern Black rhinoceros (Diceros bicornis michaeli), due to poaching, leaving few individuals in small, isolated populations that are vulnerable to extinction. However, the genetic consequences of the demographic decline on the remaining populations have not been investigated. Using the mitochondrial control region, this study investigated how current levels of genetic diversity relate to historical patterns, quantified genetic differentiation between extant populations, and the impacts of previous translocations on genetic diversity across populations. A total of 74 eastern black rhinoceroses were sampled from five extant populations in Tanzania and one neighboring cross-border population in the Maasai Mara in Kenya. Six maternal haplotypes were identified, with an overall haplotype diversity of h = 0.7 but low overall nucleotide diversity within populations (π = 0.017) compared to historical populations from Tanzania (π = 0.021). There was extensive variation in haplotype distribution between populations, some geographically close populations didn’t share haplotypes, suggesting limited maternal dispersal. The haplotypes were distributed among three east African haplogroups (Shari-Victoria(CV), Central-East(CE), and East-Africa(EA) as described in previous studies, suggesting that multiple lineages have been preserved despite the loss of haplotypes. One of the haplotypes was highly divergent and matched sequences previously classified as a subspecies that has not been recognized in recent years (Diceros bicornis ladoensis). We recommend that current levels of diversity be maintained by allowing natural movements of rhinoceroses between the populations, with the possibility of introducing additional variations by translocation of individuals between sites.
There has been a drastic decline in the number of eastern black rhinoceros (Diceros bicornis michaeli) across Africa, leaving individuals restricted to small, isolated populations that are vulnerable to extinction. Focusing on highly threatened populations in Tanzania, this study investigated the genetic impacts of past management interventions on mitochondrial control region diversity in extant subpopulations, assessed whether there has been evidence of dispersal of females between populations based on haplotype sharing, and related current haplotype diversity to historical patterns. Across extant subpopulations in Tanzania, six maternal haplotypes were identified, with an overall haplotype diversity of h = 0.72 but lower overall nucleotide diversity within populations (π = 0.017) compared to historical populations (π = 0.021). Translocated populations did not share haplotypes with native populations, even though all haplotypes from translocated individuals had been found among historic samples from Kenya. This suggests that translocations have been successful at restoring previous diversity to the region but that the current Intensive Protection Zone (IPZ) management practices have restricted the movement of females between subpopulations. Extant haplotypes were distributed among three East African haplogroups described in previous studies, suggesting that multiple lineages have been preserved despite the loss of historical haplotypes. Our recommendation is to enhance the utilisation of previous translocations by enabling the natural movements of individuals between subpopulations. Such a change in management strategy could be less costly both economically and in terms of animal welfare than the alternative of using genetic data to target specific animals for translocation in order to supplement diversity.
Due to ever increasing anthropogenic impacts, many species survive only in small and isolated populations. Active conservation management to reduce extinction risk includes: increasing habitat connectivity; translocations from captive populations; or intense surveillance of highly protected closed populations. The fitness of individuals born under these scenarios may vary due to differences in selection pressures. However, the genetic impacts of such strategies are rarely assessed. Using whole genome sequences from cohorts of the critically endangered eastern black rhinoceros as a model, we compare the consequences of past conservation efforts. We find that offspring of individuals that had either dispersed from native populations (FROH>100Kb = 0.13) or translocated from captive populations (FROH>100Kb = 0.08) showed lower inbreeding compared to closed populations (FROH>100Kb = 0.17). However, the frequency of highly deleterious mutations was higher for offspring resulting from translocation compared to the other groups and this load was sheltered by higher heterozygosity. This could increase risks of inbreeding depression if captive founders subsequently inbreed after translocation. In contrast, native dispersers reduced the negative effects of inbreeding without compromising the benefits of past purging of deleterious mutations. Our study highlights the importance of natural dispersal and reiterates the importance of maintaining habitat corridors between populations.
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