Retrospective pathology review of captive black rhinoceros Diceros bicornis in the EAZA Ex-situ Programme (1995-2022)

The husbandry of black rhinoceros Diceros bicornis is challenging due to a number of peculiar diseases affecting this species. Causes of mortality and morbidity were evaluated from 67 necropsy reports of black rhinos deceased in the EAZA Ex-situ Programme (EEP) in 1995–2022, and the prevalence of specific diseases were compared with previous surveys in the literature. Whereas some problems described as typical, such as haemolytic anaemia, aspergillosis or specific skin diseases presented at low prevalence, signs of iron overload disorder (IOD) were close to ubiquitous across animals, and skin disease, excessive tooth wear (often linked to impaction) and gastric ulceration were particularly prevalent. While this evaluation cannot add to understanding of the aetiology of these conditions, it emphasises the need to further investigate IOD and other diseases (which will require access to routine blood samples of both healthy and diseased animals facilitated by medical training). The findings also recommend further investigation of measures to rdce stress, possibly including that triggered by conspecifics as well as humans. Species-adequate nutrition still requires proactive approaches in providing dicot-based forages without resorting to monocot (grass) products

Ancient and modern genomes unravel the evolutionary history of the rhinoceros family

Only five species of the once-diverse Rhinocerotidae remain, making the reconstruction of their evolutionary history a challenge to biologists since Darwin. We sequenced genomes from five rhinoceros species (three extinct and two living), which we compared to existing data from the remaining three living species and a range of outgroups. We identify an early divergence between extant African and Eurasian lineages, resolving a key debate regarding the phylogeny of extant rhinoceroses. This early Miocene (∼16 million years ago [mya]) split post-dates the land bridge formation between the Afro-Arabian and Eurasian landmasses. Our analyses also show that while rhinoceros genomes in general exhibit low levels of genome-wide diversity, heterozygosity is lowest and inbreeding is highest in the modern species. These results suggest that while low genetic diversity is a long-term feature of the family, it has been particularly exacerbated recently, likely reflecting recent anthropogenic-driven population declines