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 habitat at Londolozi is far more preferable to white rhinos (pictured here) but we do have the occasional sighting of a black rhino.
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.
A black rhino on the move. Notice the rounded outer ear lobes and the pointed upper lip.
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.
The photograph (a) shows a rounded back lobe where the arrow points, typical of a black rhino. In photograph (b) one can see the lip is quite wide typical of a white rhino. However, where the arrow points there is a slight protrusion keeping with that of the hooked lip of the black rhino. Photograph (c) was taken to show that the head length, which is longer in the white rhino, was intermediate in the hybrid calf (Robinson et al 2005).
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!
Interesting blog Rob. Genetics are fascinating. If the two rhino species were not both present at the time in a confined area would the white rhino female have mated with the black rhino?
At least there is hope for Sudan and to ensure the continuation of the northren white rhino.
Fascinating blog! I’ve always wondered about the seemingly non cross-breeding between many of the animals in the wild, especially within the deer families. Within the animal species, it appears they only mate with another of their same kind. Can it be a genetic trait? Thank you for the thought provoking article.
Good post, should have had more responses. Saw Black Rhino in South Africa at Tembe, have also seen Black Rhino on a run. Something between Linford Christie and a Tiger Tank. The key point is will they mate in the wild? I suspect as numbers decrease they will. Not all wild life performs to norms if stressed. I saw lions performing very differently in Ruaha which abuts hunting reserves. i.e. Two males reacted very differently than if they had been in the Kruger.
Great article. I think another key point would be: are the hybrids fertile?
Very Good question Lachlan!
With tiger-lion hybrids, the females are fertile but the males are sterile. It would be interesting if the same were the case here.
Ian, any thoughts?
This gives me hope that there will be a continuation….was unaware that the numbers were so diminutive! Very interesting blog.
So it is possible! Wonder if the same holds true for the three Asian rhino species?