The Palaeo-Agulhas Plain (PAP) is a now-submerged ecosystem off the southern coast of South Africa. The plain was exposed during the last ice age (~29,000 to 11,700 years ago) because the sea levels were much lower due to water being trapped in ice at the poles. This meant that the coastline was, in some places, almost 100 km further south than it is today, resulting in almost 85,000 square kilometres (approximately the size of Ireland) of extra habitat for both ancient humans and animals, supporting large populations in an ecosystem very different to what is found in southern South Africa today. As the last ice age ended, the sea levels rose and drowned this ecosystem, with the sea level rising to the same level as today approximately 11,700 years ago. This loss of habitat was accompanied by significant changes in the climatic and environmental conditions, leading to changes in both the abundance and composition of species in this area of South Africa. Notably, grazers (herbivores feeding on grass) became much less abundant than browsers (herbivores feeding on leaves). This is visible in the fossil record and has contributed to the understanding that the climate and habitat became more suitable for browsers than for grazers, resulting in large declines of grazer populations.
While these changes are well understood at the species level, how the genetic diversity within these species changed along with their population sizes has not been investigated. Evolutionary theory predicts that genetic diversity decreases with decreasing population sizes. Genetic diversity is a fundamental part of biodiversity, and it provides the substrate on which evolution by natural selection acts. In other words, genetic diversity within a species allows it to adapt to changing climatic conditions, and if genetic diversity decreases too much, it impairs a species’ ability to adapt to climate change. In this project, our objective was to measure whether and by how much the genetic diversity changed between ~20,000 years ago and today of six species that occur in southern South Africa and lived on the PAP during the last ice age, using ancient DNA techniques. We wanted to compare the changes in genetic diversity of grazers and browsers, to determine whether the changes in abundance of these two broad groups seen in the fossil record were also reflected at the genetic level. This could provide valuable insights into how wildlife responded to climate change and habitat loss in the past, to help us predict how those species might respond to ongoing human-caused climate change and habitat destruction. This could help us better manage and conserve species, resulting in more stable ecosystems, which in turn will help buffer against the effects of climate change. While the project may be focused on southern Africa, the results will be instructive for species conservation in general and the conclusions drawn will be relevant at a global scale.
Due to technical challenges and delays we have not yet been able to answer this important question. However, the project will continue beyond this funding stream. Nonetheless, an important outcome of this project was that we were able to obtain ancient DNA and reconstruct mitochondrial genomes from African fossils up to ~7,000 years ago – an important achievement, given the poor preservation conditions for DNA at palaeontological sites in sub-tropical regions and the few studies that have been done at such sites. This shows that it will be possible for us to at least answer the question related to climate change and genetic diversity of wildlife.
