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 Post subject: Interbreeding
Unread postPosted: Tue Aug 01, 2006 12:12 pm 
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The rangers apparently call it the Roable. These photos were taken in the rare antelope enclosure near Pretoriuskop in September 2001.

My friend and I were driven around the camp by a very friendly ranger who told us about it. He warned that it is (was) very skittish and seldom seen.

The only article that I could find on the web is this one

Quote:
I decided to join ranger Andrew Stainthorpe on a walk through the Hlangwini breeding and quarantine boma, situated just south of the camp. Although such a walk doesn't offer the same experience as the popular wilderness trails conducted by qualified guides, it does offer visitors to Pretoriuskop the experience of walking through the African bush, albeit in the safe sanctuary of a predator-proof holding camp.

According to Andrew, the 300-hectare enclosure hosts Lichtenstein's hartebeest, tsessebe, steenbok, kudu, mountain reedbuck and, much to my surprise, a 'roable'. The latter is a bizarre creature resulting from the natural hybridisation between a roan and a sable and the one at Hlangwini is the only known example.

On our three-hour ramble we had distant sightings of Lichtenstein's hartebeest, tsessebe and kudu and spent much of the walk identifying trees. The highlight was a brief sighting of the roable: I clearly noticed a flash of a roan's characteristic masked face curiously blended with a sable's elegantly curved horns.


I have sent KNPSM a PM, so hopefully he can shed some more light on this interesting animal, like when it was born, if it is still alive, if the father was the sable or the roan etc.

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 Post subject:
Unread postPosted: Tue Aug 08, 2006 4:18 pm 
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The story of a roble (Africa Geographic, March 2006 issue, page 14).

Dr. Richard Estes found one known hybrid of the two Hippotragus species. In the Kruger NP.

Some quotes from the article (comments made by Dr. Ian Whyte, Sanparks research's manager for large herbivores ):

"This hybrid resulted from a situation where a roan bull joined a sable herd in the area north of Satara in Kruger. Where the roan bull came from, we do not know, as there where no roan in this area."

"The outcome, he says, was the appearance of a hybrid calf, a female, in the sable herd. It was recommended that it be captured and removed to prevent it from breeding and contaminating Kruger's pure sable stock, even though the park authorities were fairly sure it was sterile, as are most hybrids. This roble - as this possible unique roan x sable had been dubbed - was placed in a large enclosure located in the Pretoriuskop area of the park, a section free of other sable or roan. Last year it was suggested that as the hybrid was now 19 years old, it should be euthanased for the benefit of science."

"Before this could happen, however, it died of natural causes and so ended the life of the roble."


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Unread postPosted: Tue Aug 08, 2006 4:28 pm 
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Thanks Impisi08!
So it happened in the park and not in the enclosure- thats interesting!

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Unread postPosted: Tue Aug 08, 2006 9:31 pm 
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Bigmouth wrote:
Then most probably a crossing between Roan and Sable. I have read somewhere that this does occur and that is one of the reasons why both are on the danger list.


To elaborate a bit on this. It is difficult for me to see how hybridization between the two species could be a reason for both being on the "danger list".
Having heard about this crossbreeding for the first time here, I don´t think (but I might be poorly informed) it is a major problem.

However, this interaction between the species might raise concern if the hybrid is of higher fitness than the "pure" species, and if the distribution of the species is at its highest concentration in the hybridization area.

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 Post subject:
Unread postPosted: Tue Aug 08, 2006 10:13 pm 
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In closely related animals such as black and blue wildebeest or blesbok and bontebok, hybridisation is a big problem. This is also the reason why you are not supposed to keep the two species together nor move the one species in to the distribution area of the other.

I do however not think that it is a real problem between roan and sable, nor a substantial reason for them being scarce. That has more to do with factors such as habitat preference and the influence of man.
:wink:

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 Post subject:
Unread postPosted: Tue Aug 08, 2006 10:48 pm 
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Imberbe wrote:
In closely related animals such as black and blue wildebeest or blesbok and bontebok, hybridisation is a big problem. This is also the reason why you are not supposed to keep the two species together nor move the one species in to the distribution area of the other.

I do however not think that it is a real problem between roan and sable, nor a substantial reason for them being scarce. That has more to do with factors such as habitat preference and the influence of man.
:wink:


One should definitely try to avoid moving two closely related species together. In most cases they have become separated species due to geographic isolation, but they still can interbreed and produce fertile offspring (the speciation process is not completed). And if this offspring have higher fitness than the "pure" species, one can expect it will outcompete the other individuals. If than one (or both) of the "pure" species have most of their distribution range where there are hybrids, it will have face a severe extinction risk.

It is not impossible that the roan and sable will interbreed more in the coming future, due to a mechanism called Fisher´s run-away. But that is a somewhat different story.

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 Post subject:
Unread postPosted: Wed Aug 09, 2006 11:34 am 
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So are the males off these offspring fertile? While Roan and Sable are similar they are not as closely related to one another as Bontebock are to Blesbuck. Just wondering if maybe they throw a "mule" effect?


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Unread postPosted: Wed Aug 09, 2006 12:35 pm 
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bwana wrote:
So are the males off these offspring fertile? While Roan and Sable are similar they are not as closely related to one another as Bontebock are to Blesbuck. Just wondering if maybe they throw a "mule" effect?


Due to varaitions, one can always find fertile hyrbrids. In some cases (with very closely related "species") it is quite common, while in others, such as the mule, it ought to be very rare.

Don't know how the case is with the roan/sable. Any litterature or other references anyone?

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 Post subject:
Unread postPosted: Sun Aug 13, 2006 9:08 pm 
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lepus wrote:
Due to varaitions, one can always find fertile hyrbrids. In some cases (with very closely related "species") it is quite common, while in others, such as the mule, it ought to be very rare.

Don't know how the case is with the roan/sable. Any litterature or other references anyone?

Fertile hybrids seem to be more common among bird species than mammals?? (and no!, I'm not bringing up the Mallard subject again! :twisted: :lol: )

I found one other rather technical reference. The term "anecdotal" in the article clearly emphasises the isolated character of this particular "roable"'s occurrence, but obviously it is possible.
Quote:
Absence of geographic chromosomal variation in the roan and sable antelope and the cytogenetics of a naturally occurring hybrid.

Robinson TJ, Harley EH.

Department of Zoology and Entomology, University of Pretoria, South Africa.

The determination of geographic chromosomal variation in rare or endangered species, or those of special management concern, is important, since geographically defined cytotypes can negatively influence breeding programs involving founders drawn from widely divergent localities. We cytogenetically analyzed specimens of the roan (Hippotragus equinus) and sable antelope (H. niger) collected from widely divergent localities throughout their respective ranges. Each species was characterized by a diploid number of 60 and an invariant karyotype. In contrast to the absence of intraspecific variation, however, the two species differ with respect to centromeric constitutive heterochromatin and numbers of nucleolar organizer regions. These cytogenetic landmarks were subsequently used to verify an anecdotal account of a naturally occurring roan x sable hybrid. The data show that, despite their markedly distinct phenotypes, the roan and sable antelope are nonetheless sufficiently similar genetically to produce viable offspring. Hybridization, although a rare event between these species, is probably partly promoted by behavioral differences which are not always sufficient to prevent mating between them.



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Unread postPosted: Sun Aug 13, 2006 10:57 pm 
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Jose wrote:
Fertile hybrids seem to be more common among bird species than mammals?? (and no!, I'm not bringing up the Mallard subject again! :twisted: :lol: )



I've never thought of this before. But you might be right. The explanation that first comes to my mind is that birds are less likely to become spatial isolated compared to mammals. However, I'll need some thinking (and looking through some books) on this one.

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 Post subject:
Unread postPosted: Mon Aug 14, 2006 7:13 am 
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Thanks guys- this is really interesting!
Quote:
...and the one at Hlangwini is the only known example...


By looking at the study Jose added, it would seem that other "naturally occuring roables" could have been recorded- interesting!
I was always under the impression that this x came about because of, and inside the enclosure.

Any word from KNP spokesman?

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Unread postPosted: Tue Aug 15, 2006 8:58 pm 
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matthew wrote:
<...>By looking at the study Jose added, it would seem that other "naturally occuring roables" could have been recorded- interesting!<...>

Or... maybe the "anecdotal account" mentioned in the study is in fact referring to the Hlangwini specimen? I'm still trying to find the rest of the publication.


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Unread postPosted: Wed Aug 16, 2006 8:56 am 
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Impisi08 wrote:
The story of a roble (Africa Geographic, March 2006 issue, page 14).

Dr. Richard Estes found one known hybrid of the two Hippotragus species. In the Kruger NP.

Some quotes from the article (comments made by Dr. Ian Whyte, Sanparks research's manager for large herbivores ):

"This hybrid resulted from a situation where a roan bull joined a sable herd in the area north of Satara in Kruger. ...This roble - as this possible unique roan x sable had been dubbed - was placed in a large enclosure located in the Pretoriuskop area of the park, a section free of other sable or roan. Last year it was suggested that as the hybrid was now 19 years old, it should be euthanased for the benefit of science."

"Before this could happen, however, it died of natural causes and so ended the life of the roble."


Ok, maybe some of you guys didn't read Impisi's post properly.

It happened north of Satara. No enclosure involved.
Lone animal was then moved to enclosure where it stayed alone and died alone.
No other roble sighted before, during or since. (that they're telling us about)

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Unread postPosted: Wed Aug 16, 2006 9:11 am 
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I'm sorry Johan. Please excuse my typing- I can see how it can be read. As I replied to Impisi08's post at the time:
Quote:
Thanks Impisi08!
So it happened in the park and not in the enclosure- that's interesting!


I was stating that I had always thought the x to be forced by the confines of the camp, and was therefore doubly surprised by the fact that it occurred in the park, and by the fact that it could have happened elsewhere!
Apologies for the confusion!

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 Post subject:
Unread postPosted: Wed Sep 13, 2006 5:15 pm 
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Their was a genuine case of roan sable inbreeding recorded in the park - in this case a roan male ventured too far south out of its natural habitat - it then joined up with some sable females - the result a roable!

The unfortunate animal was seperated by rangers and placed in an enclosure where it died recently


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