South African National Biodiversity Assessment 2019: Technical Report Volume 7: Genetic Diversity

Abstract

Life on earth relates directly to the diversity of genes in space and time. The genomes of organisms encode the basic biological structures that define them, and allows individuals to survive and persist through time in changing environments. To this end, DNA can best be described as the foundation of all life on earth, it is recognised as an important component of biodiversity (together with species diversity and ecosystem diversity) and the importance of maintaining genetic diversity has been highlighted by the Convention on Biological Diversity. Genetic diversity can be defined as the amount of variation observed in the DNA of distinct individuals, populations or species. The maintenance of this diversity is of the utmost importance as genetic diversity allows species or populations to adapt to an ever-changing environment. Risks to genetic diversity include genetic erosion through e.g. habitat fragmentation and habitat loss, hybridisation and inbreeding, unsustainable use of species, disease via translocations of individuals, and species extinctions. Genetically modified organisms also present a risk through the escape of undesirable genes into native populations. To recognise and minimise genetic erosion, genetic diversity should be monitored over time for a given species or population. The value of long-term monitoring is well recognised; however, globally, there is a lack of temporal genetic datasets, as well as a lack of genetic diversity indicators and thresholds, with which data can be compared (such indicators have been developed, but lack specific genetic input). To date within South Africa, few short-term monitoring studies have been carried out that explicitly monitor temporal shifts in the genetic diversity of South African taxa. These studies serve as a baseline and provide valuable insight into ongoing and potential future monitoring programmes. The indicators to establish the status and to track trends for genetic diversity are not yet established. Using a case study to test indicators, trends at the national level were tracked by interrogating several high level metrics as indicators of genetic erosion. The case study analyses showed that the greatest historical impacts to phylogenetic richness for reptiles are in the northeast, southwest and the coastal margin of KwaZulu-Natal Province. For the case study, there are several hotspots of elevated genetic erosion in the last few decades, in particular northern KwaZulu-Natal Province, south-eastern Mpumalanga Province, northern Gauteng Province and southern and northern Limpopo Province. The case study highlights the types of indicators that could be used, but additional indicators and other case studies should be examined in the future. To promote future genetic monitoring programmes and studies, a national genetic monitoring framework is required that outlines how to prioritise species for monitoring, what genetic markers and metrics to use, how often populations should be monitored. Moreover, such a framework would not only outline how genetic diversity can be monitored at a population or species level, but be extended to include monitoring for genetic erosion at the national level.