Colour under investigation

Research on springbok in the Free State focuses on the implications of selecting game animals for their colour. Roelof Bezuidenhout reports.

Colour  under  investigation
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There is more to the colour of a springbok than meets the eye – the human eye, and the eye of a female springbok choosing a mate. This is just one observation scientists studying the behaviour of colour variants in springbok have made. The research attempts to gauge the effects of artificially selecting for colour in game populations and how this growing trend could affect the future of African antelope and the game industry.

Ranching for colour
According to Hennie Butler of the Department of Zoology and Entomology at the University of the Free State, the lack of scientific data available on selective breeding for colour variants complicates the debate. Butler believes that industry players should work together to map the way forward.

“Game ranchers may feel that colour variants are a natural part of evolution and increase biodiversity,” he explains. “They often say that every farmer has the right to create wealth from breeding whatever animal gives the best economic returns.
“Ranchers feel it is up to national or provincial conservation authorities to ensure the viability of genetically fit animal populations.”

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Much in demand, the colours of the springbok rainbow. Photo by Francois Deacon

Others argue that while breeding scarce or threatened species and conserving habitat can be seen to be within the scope of private wildlife ranchers, certain practices are in conflict with conservation principles. These practices, notes Butler, include intentional cross-breeding or hybridisation of different species or subspecies, selective breeding for trophy hunting, the introduction of alien species and the deliberate breeding of recessive colour variants.

“Although colour variation is a natural phenomenon, the large-scale breeding of such animals could threaten the long-term conservation of the species,” he says. “The problem associated with breeding colour variations, specifically, is that it weakens the population’s genetic base as the genes for those colours are usually recessive and can have negative effects.” It is generally accepted that such animals are more disease-prone and are easy targets for predators.

In addition, Butler points out, pressured selective breeding can lead to inbreeding and abnormalities. For example, deformed or under-developed horns which occur in springbok populations seem to appear more often in white springbok, probably because the animals are genetically closer to one another. He warns that the argument against colour variations stretches further, especially in springbok, which are showing a worrying population decline.

“In the Kalahari, springbok numbers have been falling for the last 20 years while in some Free State nature reserves, a population decline of up to 60% has been recorded. In Botswana, national population estimates of springbok plunged from 128 468 in the 1989-1991 period to only 13 200 in 2007,” he says. Butler is concerned that if springbok numbers continue to drop, private game ranchers may once again be called upon to save a species as they did in the past with bontebok, black wildebeest and Cape mountain zebra. This will not be possible with herds of doubtful ancestry.

“Clearly, private landowners could in future play an even more significant role in the conservation of species and habitats. But long-term conservation of a species can only be achieved by effective management of populations – not easy now that natural, free-ranging populations are a thing of the past,” says Butler. He suggests that to benefit future generations, ranching should be based on sound ecological principles.

“The management of a game ranch or nature reserve should ensure adequate genetic integrity and diversity. That is why any form of ranching must take place within the ecological and economical limits of the area. If not, it is doomed to failure,” he says.

Population genetics
In the case of springbok, a pristine environment subjected to natural processes such as migration no longer exists. Migration routes have been cut off by fences, populations have been divided and the natural exchange of genetic material has stopped. There are already many small, isolated and inbred springbok herds throughout the country. The crash in springbok numbers is so widespread that it cannot simply be ascribed to a single factor such as predation or management.

The normal springbok are in the foreground while the white springbok are further back. This demonstrates the clustering behaviour of the colour variants. Photo by Phillip Olivier

Butler explains that if the decline in springbok numbers is genetically linked, selective breeding on game farms may mean that game reserve populations cannot be genetically invigorated by privately farmed game animals. The problem is aggravated by the fact that conventionally coloured individuals may carry the gene for the recessive colour. These are referred to by game farmers as ‘split’ animals (see box).

“As there is no visual method of determining whether an animal is a split or a true normal coloured individual, DNA testing may eventually be essential before new animals can be introduced into a population,” he says. “Currently, natural selection is being trumped by artificial selection to allow males of a specific colour to become dominant.” One method of selecting for colour is apparently to cull all males that do not display the desired colouration.

A matter of choice
According to Butler, constant artificial selection could influence future sexual selection in various ways. “In male-to-male competition physical characteristics, such as size, are generally important in determining which individual will win mating rights. Springbok males must defend a territory before they can mate – those defending territories with better resources (food and water) will mate with more females.”

When white rams happen to be more dominant than their normal counterparts, individuals expressing the recessive white gene would out-compete other males for the best territories and mate with the most females, transferring the trait to the next generation. Mate selection, which usually depends on the female, has an even greater influence. Females choose the strongest male because he offers the best direct benefits.

Her choice can be influenced by the following factors:

  • Secondary sexual traits such as ornaments, displays and colour: It has been found that coat colour in Stone’s sheep influences sexual selection. Possibly, colour may also influence sexual selection in springbok.
  • Sexual imprinting: This occurs when offspring reference the physical characteristics of their parents, choosing a mate that resembles those parents. 
  • Mate choice copying: Here, young females observe and choose rams that have successfully mated with other females. Young ewes base their choice on the experience of older ewes.

Runaway selection
Butler cautions ranchers to be aware of the possibility of ‘runaway’ sexual selection – a process that occurs when a female preference for a specific male trait, in this case colour, becomes stronger and more frequent with every generation.
For example, if a percentage of springbok ewes in a population develop a preference for white rams and consequently mate with them, their offspring will probably be white, and their daughters will have the same sexual preference.

“With passing generations, this trend could continue until white becomes the population’s dominant colour,” he says. Butler admits that colour variation is a natural phenomenon, but points out that it occurs at a low frequency in the wild. “Colour variants do not contribute to conservation or the long-term survival of a species, since they usually do not survive in nature,” he says. “Ranchers cannot claim a contribution to conservation if they are breeding animals with little chance of surviving under natural conditions.”

Master’s student Phillip Olivier, investigating colour variations in antelope would be grateful for relevant information from game ranchers.

Contact him at [email protected]. Contact Hennie Butler at [email protected]