Bushbuck: two species where there was one

Back in the day, the bushbuck was considered a single species, Tragelaphus scriptus, found in various habitats across much of sub-Saharan Africa. Recently however, genetic studies have indicated that T. scriptus is actually a complex of two distinct species, the Kéwel (T. scriptus) and the Imbabala (T. sylvaticus). This evidence shows that these two bushbuck species are more closely related to other tragelaphines than to each other; the Imbabala being closest to the Bongo (T. eurycerus) and Sitatunga (T. spekeii), and the Kéwel to the Nyala (T. angasii) (Moodley et al. 2009).

The Kéwel is found from West Africa, across the Sahel into East Africa, and as far south as Angola and the Democratic Republic of Congo (DRC). Meanwhile, the Imbabala is found from the Cape northwards to Angola, Zambia and East Africa, meaning that the two species’ ranges overlap in parts of Angola, DRC and East Africa.

The Kéwel is the smaller of the two, and shows clear stripes and patterning on a reddish to yellowish background; there is little or no sexual dimorphism in this ground colour. In contrast, the Imbabala shows considerable colour variation with geography and habitat, especially in males (yellow to red-brown, through brown and olive to almost black), and only the most genetically ancient of populations (from Angola, Zambia, southern DRC, Botswana and northern Zimbabwe) have any significant striping. Even in these cases the horizontal stripe, where it exists, is formed of a series of spots rather than the solid striping of the Kéwel. never occurs. Mountain-dwelling forms of the Imbabala (Gregory Rift Highlands, Mt. Elgon, Imatong Mountains and Ethiopian Highlands) appear larger and are dark with little or no pattern. Until recently, most bushbuck studies focused on the Imbabala, hence little was known about the biology of the Kéwel beyond what could be obtained from museum specimens and hunting trophies.

Imbalala bushbuck from Zimbabwe (courtesy of Graeme Guy). For a kewel image from The Gambia see here.

Both species are primarily browsers, but will eat other plant matter too. They can be active at any time of day, although are more likely to be nocturnal near humans; their most active times are however early morning and parts of the night, so may appear nocturnal in any case. Most are solitary, with some living in pairs; all have a ‘home range’ of around 5 hectares in the savannah (larger in forests), although these ranges do overlap.

Although the split into two species is fairly well understood (even if most non-scientific sources still refer to a single ‘bushbuck’), the more detailed taxonomy remains disputed with numerous potential subspecies and ecotypes having been described. For example, analysis of mt-DNA sequences (cytochrome b and control region) by Moodley & Bruford (2007) identified 23 phylogenetically distinct groups (‘ecotypes’) whose distribution correlated well with the pan-African eco-regions described by Olsen et al. (2001). 19 of these ecotypes corresponded with previously suggested subspecies, while six other haplotypes were newly recognized forms in the Volta region, Niger, Angola. and Luangwa and Zambesi Valleys. However, further research is onging to clarify the taxonomic status of bushbuck species, subspecies and ecotypes, so the situation is likely to remain somewhat fluid for a while – however, this does provide an opportunity to link the use of genetics in taxonomy to large-scale conservation in Africa, given the widespread distribution of bushbuck (in the broad sense) and apparent more local/region distribution of subspecies and ecotypes (Wronski 2009).

References

Moodley, Y. & Bruford, M.W. (2007). Molecular Biogeography: Towards an Integrated Framework for Conserving Pan-African Biodiversity. PLoS ONE 2(5): e454. doi:10.1371/journal.pone.0000454

Moodley, Y., Bruford, M., Bleidorn, C., Wronski, T., Apio, A., & Plath, M. (2009). Analysis of mitochondrial DNA data reveals non-monophyly in the bushbuck (Tragelaphus scriptus) complex Mammalian Biology - Zeitschrift fur Saugetierkunde, 74 (5), 418-422 DOI: 10.1016/j.mambio.2008.05.003

Olson, D.M., Dinerstein, E., Wikramanayake, E.D., Burgess, N.D. & Powell, G.V.N. (2001). Terrestrial ecoregions of the world: a new map of life on earth. BioScience 51: 933-937.

Wronski, T. (2009). Bushbuck, harnessed antelope or both? Gnusletter 28(1): 17-19.