Demographics of polycystic kidney disease and captive population viability in pygmy hippopotamus (Choeropsis liberiensis)

Abstract

Polycystic kidney disease (PKD) was previously diagnosed at necropsy in several pygmy hippopotami (Choeropsis liberiensis) from the Smithsonian National Zoo and Zoo Basel, suggesting a threat to the long-term viability of the captive population. We determined the incidence and demographics of PKD in the captive population historically; we tested if the condition is linked to pedigree; we investigated mode of inheritance; we examined effects of PKD on longevity; we conducted survival analysis; and we examined long-term population viability. Thirty-seven percent of 149 necropsied adult pygmy hippos were affected by PKD, and it was more common in females, controlling for the overall female-biased sex-ratio. Prevalence increased significantly with age, but most hippos were beyond their reproductive prime before developing clinical signs; thus fecundity was likely unaffected. PKD was linked to pedigree and may exhibit X-linked dominance, but further research is needed to definitively establish the mode of inheritance. PKD did not affect longevity, overall or within any age class. There was no significant correlation between inbreeding coefficient (F) and PKD, and the prevalence in wild-caught and captive-born animals was similar. Longevity for both captive-born and inbred hippos (F > 0) was significantly shorter than longevity for their wild-caught and non-inbred counterparts. Demographic projections indicated the extant population will likely experience a slow increase over time, provided there are no space constraints. We conclude that although PKD is an important cause of morbidity and mortality in pygmy hippos, the condition is not a primary concern for overall viability of the captive population.

What is the role of the studbook in zoo and aquarium research?

“…From the data generated in this study, it is clear that studbooks are being used to understand population mortality (Duque‐Correa et al, 2022; Metz et al, 2017). Studbooks contain information on cause of death, and lifespan, and can be used to rapidly identify the most common reasons why animals in a population are dying (Flacke et al, 2017). With this knowledge, husbandry interventions can be put in place that reduce species‐specific risks.…”

Explorative statistical analysis to identify factors affecting the survival of pygmy hippopotamus (Choeropsis liberiensis) kept in zoological gardens

“…The study of FlaCke et al (2016) evaluating causes of deaths described a number of reasons for mortality, some of which could also be linked to inbreeding levels in the population, as inbred animals are more susceptible to pathogens and have higher rates of recessive disease than do non-inbred ones. For example, analysis of survival in polycystic kidney disease in 149 individuals, showed that non-inbred animals had a higher chance of survival to 1 year of age than did inbred pygmy hippos, even though the inbreeding itself did not have a significant effect on occurrence of the studied disease (FlaCke et al 2017).…”

A new method to determine the diet of pygmy hippopotamus in Taï National Park, Côte d’Ivoire

“…There is little information from the wild, which is mainly due to the species' cryptic behaviour and difficulties accessing their natural habitat. In captivity, individuals suffer from persistent health problems, such as polycystic kidney disease and dental skin and foot problems, which may originate from inadequate diet (Flacke et al, 2017; von Houwald et al, 2007). Pygmy hippos appear to forage mainly at night over a period of about 6 hours (Eltringham, 1999; Mallon et al, 2011; Robinson, 1981).…”