Dr Jennifer Pierson, Senior Ecologist
What do you think of when you hear the word biodiversity? For most of us, we see biological communities full of different plants and animals, areas teeming with life. But we often forget about the building blocks of that vision of biodiversity – the genes behind the scenes of life.
Genetic diversity is the foundation of all biodiversity. Evolution has led to the incredible diversity of species and communities we have here in Australia, so many of which can be found nowhere else on the planet. Evolution is a genetic process, whereby four main mechanisms drive patterns of diversity:
1) Mutation – random mistakes that lead to new genes;
2) Drift – random changes in gene frequencies due to chance;
3) Migration – the movement of genes through dispersal followed by mating;
4) Selection – the differential survival and reproductive output of individuals based on heritable traits (i.e., genotypes or gene complexes).
AWC’s mission to reverse the biodiversity decline in Australia includes actions to conserve and manage the precious genetic diversity that remains. Many of Australia’s threatened species, such as the Bilby, Woylie and Mala once occupied vast areas of the continent in considerable numbers. Large populations are reservoirs for genetic variation and species whose ranges extend across varied environments have different frequencies of genes. These differences are of benefit under varied conditions and increase the capacity of a species to adapt to environmental change.
The massive declines in population numbers, combined with the fragmentation of remaining habitats has disrupted evolutionary processes such as migration and has resulted in dramatic declines in the genetic diversity in many species.
Small populations continue to lose diversity much more quickly than large populations, due to the influence of genetic drift, where random changes in gene frequencies occur due to chance. Small populations are also more at risk from what is called inbreeding depression, or lower survival and reproductive rates due to the expression of rare deleterious alleles (genes). If genetic diversity is not managed in these small populations, even as they grow larger due to restoration efforts, the adaptive capacity, or ability for selection to drive genetic variation, is limited as selective forces can only act on the genetic variation present.
AWC is managing the genetic diversity of reintroduced populations closely. There are a number of actions AWC scientists undertake to give reintroduced species the best chance at recovery. Firstly, when new populations are founded, we ensure the number of individuals used to start the population is large enough to avoid negative outcomes such as inbreeding depression. The tricky part of genetic management is that not all founders are lucky enough to reproduce and without mating genes are not shared and passed on. So, we need to make sure we have more founders than simply the minimum needed to avoid inbreeding. The other aspect is making sure individuals are not too genetically similar, as even large numbers of individuals that are genetically very similar can lead to negative fitness consequences.
Secondly, we aim to create a ‘genetic mix’ of remaining genetic diversity and maximise the genetic variation of these newly established populations. This provides insurance for conserving the valuable diversity left in a species and provides the basis for populations to adapt to varying environmental conditions. Australia’s ecosystems are known for their extremes and climate change will likely exacerbate conditions. As such, having the maximum diversity possible gives species a fighting chance to adapt to the uncertain future conditions they may face.
In order to achieve the best outcomes, AWC has partnered with the Australasian Wildlife Genomics Group (AWGG) at the University of Sydney to obtain high quality genetic data using the newest sequencing technologies. For example, AWC scientists established a Red-tailed Phascogale captive breeding program to support our recent reintroduction to Newhaven and planned reintroduction for Mallee Cliffs. AWC worked closely with AWGG, along with Alice Springs Desert Park and Zoos South Australia to optimise the genetic mix of the founder populations. Wild populations were targeted to source the founder individuals and the field team were able to get genetic data quickly to determine whether the captive population genetic mixing worked and identify where to target in the second round of sampling for more wild founders.
Woylies provide another great example of the benefits of working in close collaboration with AWGG to achieve the best genetic outcomes. When Woylies were reintroduced to Mt Gibson, three different source populations were used to try to attain a good genetic mix representing diversity from different areas. Recent genetic analysis has shown that Mt Gibson has no genetic inbreeding, and good levels of diversity. This meant we could test how well a genetically mixed population could serve as a single source population. Woylies from Mt Gibson were translocated to Newhaven in early August 2021 and small tissue samples were sent directly to AWC’s university partners for genetic analysis. The results will dictate whether the new Newhaven population will need to be supplemented or if our ‘lucky dip’ of Woylies from Mt Gibson provided a sufficient amount of initial diversity. In truth, it is not quite a lucky dip, as field teams set traps in a spatial manner to minimise the chance of catching related individuals.
These are just a few of the examples of AWC’s commitment to conserving and managing the genetic diversity of Australia’s threatened wildlife. In the end, it is all connected. Wherever an animal goes, it takes it genes with it…
Read and download the full issue of Wildlife Matters here.