Genetic structure of the wild populations of the Indian Rhinoceros (Rhinoceros unicornis)

The Indian (or Greater One-horned) rhinoceros, Rhinoceros unicornis is one of only five extant rhinoceros species. In the wild it occurs exclusively in India (mainly in Assam) and in Nepal. These two populations have been completely separated for at least a few centuries. In addition, both populations experienced a bottleneck during the 20th century. These observations suggest the questions how genetically distinct and how diverse the two populations are. In the present study I review two molecular genetic studies on these aspects, as well as three studies, mainly based on the worldwide R. unicornis zoo population, assessing the consequences of inbreeding and outbreeding (i.e. Assam x Nepal matings) on juvenile mortality. In addition, I present the results of an analysis of the effects of inbreeding and outbreeding based on the latest studbook data. In this analysis - in contrast to earlier studies - I no longer found a negative effect of outbreeding on offspring mortality, but still a higher mortality in primiparous offspring and still no negative effect of inbreeding on juvenile mortality. These results suggest that outbreeding between the two populations is not as problematic as it was once suggested to be, but it also confirms that inbreeding avoidance may not be as important in the Indian rhinoceros as it is in other species.