Interspecific hybridisation in rhinoceroses: Confirmation of a Black × White rhinoceros hybrid by karyotype,fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridisation (FISH) and microsatellite analysis

Black and white rhinoceroses are among the most charismatic megaherbivores and have become flagship species for international conservation. They are often subject to intense management that includes being compressed unnaturally in space and density. We present chromosomal and microsatellite evidence to substantiate the first recorded instance of interspecific hybridisation between them. The data suggest that the genetic integrity of the African rhinoceros species probably depends on differences in behavioural and ecological preferences that offer semipermeable reproductive isolation. We caution against the retention of both species in captive and other population situations where disruption of species-specific behaviour patterns may result if there is an unnatural composition in terms of age and sex, and where access to conspecific mates is restricted or absent.     

Molecular phylogeny and evolution of the Perissodactyla

The evolution of perissodactyls (rhinoceroses, tapirs, and horses) has been well studied primarily because of their extensive fossil record. Nevertheless, controversy persists regarding relationships of some of the extant taxa, reflecting inconsistencies between molecular and morphological studies. Here we examine the phylogenetic relationships of 16 living perissodactyl species by concatenating two mitochondrial and nine nuclear genes, and we estimate their divergence times using a relaxed Bayesian molecular clock approach. Our analyses recovered the monophyly of the suborders Ceratomorpha and Hippomorpha, and the families Rhinoceratidae, Tapiridae, and Equidae. We supported the early divergence of the Indian rhinoceros in the late Oligocene (26 Mya) relative to the Sumatran and African rhinoceroses, and the split of caballine (domestic horse and Przewalski's wild horse) and noncaballine equids (zebras and African and Asiatic asses) in the Pliocene (4 Mya). An important implication of this study is that Equus asinus, the African wild ass was found to be the sister taxon of Asiatic asses and zebras, diverging from the common ancestor with caballine horses 2 Mya. Rates of chromosome rearrangements were also evaluated in perissodactyls, placing a notably high rate of variation amongst equids, particularly within the zebra clade. The robust phylogenetic results presented here are relevant in terms of understanding the evolutionary history of this highly threatened group of mammals. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 1289–1303.     

Absence of hypomethylation and LINE-1 amplification in a white × black rhinoceros hybrid

Genomic stress resulting from the interspecific hybridization of marsupials has been shown to lead to hypomethylation and transposable element over-amplification. Here we investigated both methylation status and transposable element (LINE-1) activity in an F1 hybrid between the black (Diceros bicornis) and white rhinoceros (Ceratotherium simum). Our data show that in this instance the hybrid genome was not characterised by gross hypomethylation and LINE-1 over-amplification thus extending previous investigations on eutherian mammals. These findings underscore observations that wide-scale genomic instability involving hypomethylation and mobile element release may be marsupial specific phenomena within Mammalia. Gauthier Dobigny, Paul D. Waters: These authors equally contributed to this work