Admixture and reproductive skew shape the conservation value of ex situ populations of the Critically Endangered eastern black rhino - microsatellite and mitochondrial genotype data

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.