Admixture and reproductive skew shape the conservation value of ex situ
populations of the Critically Endangered eastern black rhino
Abstract
Small populations of endangered species risk losing already eroded
genetic diversity, important for adaptive potential, through the effects
of genetic drift. The magnitude of drift can be mitigated by maximising
the effective population size, as is the goal of genetic management
strategies. Different mating systems, specifically those leading to
reproductive skew, exacerbate genetic drift by distorting contributions.
In the absence of an active management strategy, reproductive skew will
have long-term effects on the genetic composition of a population,
particularly where admixture is present. Here we examine the contrasting
effects of conservation management strategies in two ex situ populations
of the Critically Endangered eastern black rhino (Diceros bicornis
michaeli), one managed as a semi-wild population in South Africa (SAx),
and one managed under a mean-kinship breeding strategy in European zoos.
We use molecular data to reconstruct pedigrees for both populations and
validate the method using the zoo studbook. Using the reconstructed
pedigree and studbook we show there is male sex-specific skew in both
populations. However, the zoo’s mean-kinship breeding strategy
effectively reduces reproductive skew in comparison to a semi-wild
population with little genetic management. We also show that strong male
reproductive skew in SAx has resulted in extensive admixture, which may
require a re-evaluation of the population’s original intended role in
the black rhino meta-population. With a high potential for admixture in
many ex situ populations of endangered species, molecular and pedigree
data remain vital tools for populations needing to balance drift and
selection.