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THE WESTERN ZAMBIAN SABLE: A NEW SUBSPECIES OR EXTENSION OF ITS ANGOLA COUSIN?

A recent paper by C·I·B core team member Bettine Jansen van Vuuren has shed light on the need for renewed and intensified conservation efforts to ensure the survival of the giant sable in Angola.

Over recent years many studies have looked at the effects that translocations have on the conservation of evolutionary patterns within game species. One of the most valuable game ranch species in South Africa is the sable antelope (Hippotragus niger). Four subspecies of this species are recognised based on morphological characteristics; these include the Roosevelt (Hippotragus niger roosevelti, and Kirk's sable (Hippotragus niger kirkii) in East Africa, the southern sable (Hippotragus niger niger) found from south-western Tanzania southwards including in South Africa, and the giant sable (Hippotragus niger variani) which occurs in Angola.

One subspecies whose survival is of great concern is giant sable. Years of civil unrest in Angola, and being limited to a small area and interbreeding with its congener the roan antelope, has lead to the giant sable being listed as critically endangered by the IUCN. Originally known to occur only in the central part of Angola, sightings of antelopes that superficially resemble the giant sable antelope have been reported in the eastern areas of Western Zambia. The antelopes sighted resembled the giant sable antelope in phenotype, most notably the distinct facial markings and coat colour. These reports prompted speculation in the popular media that the distribution area of the giant sable may be larger than is reflected in the scientific literature, a view that could have a serious impact on current conservation efforts to protect the giant sable antelope.

The recent study by Jansen van Vuuren and colleagues compared the genetic profiles from representative specimens from all four subspecies (including animals from western Zambia) to determine the evolutionary placement of western Zambian sable within Hippotragus niger niger or Hippotragus niger variani based on genetic characters rather than just morphological characteristics.

Their results confirmed previous reports that indicate significant separation of genetic variation (differences at genetic level) in sable antelope subspecies across their pan-African distribution. In addition, although the western Zambian and giant sable antelope resemble one another in morphology, particularly with respect to facial markings, significant genetic differences underpin these two evolutionary lineages with the western Zambian sable falling within the southern sable subspecies (Hippotragus niger niger).

These results indicate substantial phenotypic plasticity (the ability of an organism to change its phenotype in response to changes in the environment) in the characters that are conventionally used to distinguish the giant sable antelope from other sable subspecies. Consequently, neither horn length nor facial markings of the giant sable antelope should be driving conservation concerns, but rather its unique evolutionary history. The findings from this study underscore the need for rethinking decision making in conservation efforts to ensure the survival of the giant sable in Angola.

Further details: Prof. B. Jansen van Vuuren

Jansen van Vuuren, B., Robinson, T.J., VazPinto, P., Estes, R., Matthee, C.A. (2010) Western Zambian sable: Are they a geographic extension of the giant sable antelope? South African Journal of Wildlife Research, 40 (1): 35-42.

(A) The majestic giant sable antelope with its characteristic horns which curve backwards and the largely black face. Photo: Richard Estes and Kobus du Toit

(B) The western Zambian sable showing close phenotypic resemblance to the giant sable of Angola (Hippotragus niger variani). Note the browning of the rump in the western Zambian sable specimen. Photo: Richard Estes and Kobus du Toit