In nature we see many similar looking species living in close proximity to one another yet they remain as separate species. Would cross-breeding ever be possible?
Looking around camp one sees Nyala and Bushbuck – two similar looking antelope species – inhabiting the same riverine vegetation but remaining genetically distinct. More specific to the question posed above; Black and White rhino occur in overlapping habitats, but have they ever been known to mate?
The answer, unbelievably, is yes. However before we go into it, it is important to know the major differences between the two species, which is explained in detail in a previous blog by Amy Attenborough. In short though, the major differences are that the white rhino is larger and that the mouth structures differ. The white is a grazer with a wide square lip, whereas the black is a browser with a hooked lip.
In the late ‘80s a female rhino calf was born in a large enclosure that housed two female white rhino (one being the mother), a 4 year old white rhino bull and a mature black rhino bull. At 4 years of age the white rhino bull, in natural conditions, would have been too young to be responsible for impregnating the female.
Male white rhino breeding is dependent on them first acquiring a territory at around the age of 12 years. It was thus assumed at the time that this calf must have been a cross between the white rhino female and black rhino male. This was only proven to be the case much later in a 2004 paper published in the journal Springer by Robinson et al.
The researchers, however, had a slight problem in doing the study in that they did not have tissue samples of either of the potential fathers. A simple genotyping of both bulls (the young white rhino and the adult black rhino) would otherwise have made determining paternity simple. They did however gave a gene sample of the calf, which was unfortunately culled when still quite young. So they used data from a previous study which had tissue samples of 117 black and 6 white rhino. By studying the chromosomes of the two species they were able to compare them to those of the putative hybrid calf.
From a total of 18 alleles, or characteristics at a chromosomal level, detected in the hybrid calf, six were exclusive to black rhino and four to white! This was one of the major findings that showed that this calf was actually a true cross between a black and white rhino. Physically it also exhibited traits of both species.
In the animal kingdom, individuals of different species that are capable of producing offspring tend to be grouped into the same genera. One of the most commonly know is the cross between a horse and a donkey to produce the mule. In this case both the horse and donkey are of the genus Equus. The liger is a hybrid cross between a male lion (Panthera leo) and a female tiger (Panthera tigris). Interestingly, the black rhino (Diceros bicornis) and white rhino (Ceratotherium simum) have been grouped into different genera.
What implications may crossbreeding of rhino have for the future conservation of this species? Artificial insemination and in vitro fertilization are being looked into as possible last resorts for the Northern white rhino, a subspecies of the white rhino found in Central Africa. This subspecies has been reduced to one surviving male. Sperm and egg cells of the northern white rhino have however been saved and are stored in a laboratory in Berlin. A surrogate mother may have to be found in the form of a southern white rhino, but with the species on the brink of extinction, the fact that even a glimmer of hope still remains is fantastic!