Recently seven lions made a 4,000 kilometer long journey from South Africa to Rwanda. They have been translocated to Akagera National Park, as the foundation of a new population. Lions have been extinct in Rwanda since 1994, a fate of many populations in recent decades.
Local extinctions affect ecosystems and can lead to instability, because certain roles in the ecosystem change as a member of the food chain is lost. In addition to the ecological aspect, there is an evolutionary one. Local extinctions may also lead to the disappearance of evolutionary lineages within species. These evolutionary lineages, visible as differences in the DNA, represent diversity below the species level.
Translocations and reintroductions may be able to bring back previously lost species and functions. This makes them a promising tool for conservation. On the negative side if genetics are not considered when translocating, the evolutionary line of a species can be affected.
Taking the Rwanda lion translocation as an example, researchers and managers spent a lot of time and effort in finding a suitable source population. Many arguments were taken into account. Prevalence of diseases need to be known and selecting individuals for the translocation cannot negatively influence the source population. One of the guidelines for this is that priority should be given to a source population in close geographic proximity to the destination.
Genetics are hugely important
During the evolutionary history of the species, populations in distant regions will have accumulated genetic differences. This leads to genetic diversity. On the species scale, genetic diversity can be seen as different genetic clades, or different branches on the lion-tree. These patterns of genetic diversity are disrupted when two populations from different regions are mixed.
The seven lions used in this translocation came from two parks in South Africa. They have ancestors from several South African regions and Namibia. All African lions are considered to belong to a single subspecies. However, there is a clear genetic difference between populations from Namibia, South Africa and East Africa. For that reason the selected source populations are less than ideal, at least from a genetic perspective.
Disruption of existing patterns of genetic diversity occurs particularly when individuals from different genetic clades start hybridising. This will have a homogenising effect. The loss of genetic diversity that comes from this is a cause for concern for two reasons.
First, genetic differences may translate into local adaptation. Examples of local adaption are resistance against certain diseases or tolerance for harsh climatic conditions. But it is difficult to quantify potential local adaptation. Lions are generally known to be fairly resilient. Studies on other species have found effects on fitness only after gathering long term data over many generations, illustrating the risk of certain interferences.
Second, genetic diversity on the species level can be considered as its evolutionary potential. It contains the blue print on which selective pressures can act. It therefore functions as the insurance for long term survival of a species, which is exceptionally important in a changing environment.
Contrary to popular belief, mixing of genetic lineages does not lead to higher genetic diversity. This would only be the case when dealing with highly inbred populations, where generations of breeding between direct relatives has led to loss of genetic diversity. This is often visible as the loss of heterozygosity, the state in which an individual has two dissimilar copies of any hereditary characteristic.
This loss of heterozygosity may ultimately lead to inbreeding depression, also affecting birth rates and mortality. Due to these effects a small population can be pushed into an extinction vortex, where small populations tend to suffer more strongly from negative genetic effects, resulting in an even smaller population.
In such a case, the introduction of individuals of a distant population may have a beneficial effect, as it can increase the heterozygosity when translocated individuals start breeding with the original population.
But in the context of translocations, scientists refer to another type of genetic diversity. The scale is not the population, where levels of heterozygosity may be reason for concern, but the different genetic clades within the entire species. When distinct genetic clades are lost due to the homogenising effect of hybridisation, levels of diversity are eroded rather than increased.
Of course, species and populations are dynamic entities which may move around and change in time. It is important to recognise this and not try to conserve everything as a strict status quo. On the other hand, when conservationists intervene to manage populations and species, it is advisable to maintain the patterns and processes that were shaped during the animals' evolutionary histories.
Despite a clear role for genetics in translocation operations, I do not want to preach an overly puristic approach. A certain degree of pragmatism is needed to get things done and to move forward. These projects often have to deal with long procedures, including complex local politics, which may eliminate a preferred source population as a candidate.
But genetics should play a role as it can guide management strategies for the future, by giving insights into the evolutionary past. For now, I hope that the seven lions in Rwanda can pave a road for stable lion populations in the region and that this is another step to ensuring the lion’s future in its full diversity.