By Matthew Cobb
Okapis (Okapia johnstoni) are the closest living relative of the giraffe (their lineages separated about 16 million years ago). They live in the rainforest of the Democratic Republic of Congo (DRC) in central Africa. Although their bodies are brown, their legs are striped like a zebra’s. They first became known to science at the end of the 19th century.
These animals browse on plants growing in gaps in the forest caused by tree fall – this means that their food is relatively sparsely and randomly distributed around the forest. The precise number of okapis in the wild is unknown (figures vary between 10-50,000), but the overall trend is downwards (an estimated 50% decline in the last three generations). They are already extinct in neighbouring Uganda. As a result, the IUCN to have put the animal on its Red List of Endangered Animals.
The major problems for the okapi are, predictably, associated with humans – logging is destroying its habitat, and contact with humans is leading to hunting for bushmeat. Furthermore, illegal armed groups involved in elephant poaching, bushmeat hunting, illegal mining (gold, coltan and diamonds), illegal logging, charcoal production and agricultural encroachment, all make it difficult for conservationists to operate in the area.
Little is known about the ecology of the okapi because it lives in such difficult terrain. In the 1980s radiotracking of eight individuals suggested that they were solitary, with home ranges that were about 10.5 km2 for males, and 5.1 km2 for females. However, there is little solid evidence for how they live their lives, and how the sexes interact.
That has recently changed, with a new study by researchers in the UK and in DRC that looked at DNA extracted from 208 faecal samples collected in an okapi reserve (see map below). (In passing, hats off to the team for succeeding in this – a while back a student of mine tried extracting DNA from fresh howler monkey turds; we failed dismally.) Once the DNA had been extracted, they then looked at a short parts of the genome that they knew would show variability (these are known as ‘microsatellites’ in the trade). A total of 105 samples provided valid DNA.
The team then did some fancy population genetics to draw a number of conclusions about the social system, the mating system and the dispersal of the okapis they were studying. (Another note in passing: many zoology students dislike both DNA extraction and population genetics – this study shows why both these techniques are important if you want to understand animals.)
Social system: the lack of overlap in genotypes found at the different dung sites suggests that okapi do not form social units, apart from mother-offspring and adult male-female pairings. There was no evidence of large social groups. This was expected, both from previous research, and from the behaviour of other animals that can be heavily predated (in the case of the okapi, by leopards). Because there was no indication of what is called ‘genetic structure’ to the population they sampled – that is, certain genotypes were not found more often in one area than another – the authors conclude that there are no physical obstacles to okapi moving around the region (see also below).
Mating system: The frequency with which the study picked up full and half siblings sugstes that okapi are genetically polygamous (each male will mate with more than one female) and promiscuous (this situation is typical of most mammalian species). However, varying population densities in different regions may mean that it is possible that in some areas males may defend a territory containing several females, although the team found no direct evidence of this.
Dispersal: evidence of dispersal/movement was hard to estimate because they found so few genotypes more than once (in other words, they did not sample the same animal very often – only 13 individuals provided two data points). One male was recorded twice, 25.5 km apart, but the average distance between samples, if this individual was excluded, was 0.337 km.
The conclusion is that the okapi is indeed a solitary beast. They are isolated for most of their lives, having social interactions only while a calf, or during mating. These beautiful animals, which always appear timid and slightly sad in zoos, are solitary and secretive. If we are not careful, the only place they may be safe is in a zoo.