Before species go extinct, their populations often shrink and become isolated . Healthy populations tend to have a large gene pool with many genetic variants circulating. But the path to extinction erodes genetic diversity, because a species' gene pool shrinks as the population declines. Losing genetic diversity limits the ability of populations to adapt to threats such as disease and climate change.
Authors
- Robyn Shaw
Research Fellow in Conservation Genomics, University of Canberra
- Catherine Grueber
Associate Professor in Life and Environmental Sciences, University of Sydney
- Katherine Farquharson
Postdoctoral Research Fellow in Bioinformatics, University of Sydney
So, what is the state of genetic diversity in animals, plants, fungi and algae worldwide? And how could focusing on this crucial level of biodiversity help build resilience in the face of global change? We explore these questions in our new study , published today in Nature.
Our team of 57 scientists from 20 countries trawled through more than 80,000 scientific articles across three decades to summarise evidence of genetic change in populations in 141 countries.
Alarmingly, we found genetic diversity is being lost globally across many species, especially birds and mammals. This loss was most severe in studies reporting changes in habitat, new diseases, natural disasters, and human activities such as hunting or logging.
But there's hope. Our study suggests conservation strategies can help maintain or even increase genetic diversity.
What is genetic diversity and why does it matter?
At the core of every cell lies a copy of the instruction manual for living things. This is the genetic code, made up of DNA molecules. But its sequence varies enormously , separating a moth from a tree from a bacterium. Even within a species, we see distinct genetic differences between individuals. These genetic differences contribute to differences in their traits, which is why we get individuals who are taller or shorter, faster or slower, bolder or more cautious.
This genetic diversity stems from mutations. Often, these mutations are not helpful. But at times, they can enable populations to adapt to change.
For example, golden kelp (Ecklonia radiata) likes colder water. But in a population, some individuals will have mutations suited for warm water. When a devastating marine heatwave hit the West Australian coast in 2011, individuals with warm-water mutations were more likely to survive and reproduce. This genetic diversity enabled the kelp population to adapt to the warmer conditions.
This is why genetic diversity is so important - it gives species more resilience in a rapidly changing world. This priority has been recognised in Australia's Strategy for Nature , and in goals and targets discussed at the United Nations biodiversity summit COP16 .
How can we safeguard or restore genetic diversity for threatened species?
To answer this question, we used a technique called meta-analysis to look for patterns. From more than 80,000 published articles, we identified 882 studies which measured changes in genetic diversity over time. These studies came from right around the globe and across the entire "tree of life".
They show there are many ways to conserve genetic diversity. Here are five promising strategies to help keep species resilient.
Action 1: Adding individuals
Adding individuals to an existing population is known as supplementation. Our research found supplementation was the only action linked to a significant increase in genetic diversity, especially in birds.
Supplementation can help reduce the harmful effects of inbreeding, which is common in small, isolated populations. For example, conservationists working to safeguard New Zealand's South Island robins (Petroica australis) moved female birds between isolated islands. The offspring of parents from different islands had stronger immune systems, higher survival rates, and improved reproductive health compared to their inbred counterparts.
Supplementation is key for boosting genetic diversity, improving population health and building resilience.
Action 2: Population control
Doing the opposite - removing individuals - can actually improve outcomes for the population as a whole in some circumstances, by, for instance, reducing competition.
But genetic diversity results varied a lot in studies using population control. So how can this strategy be used effectively?
In one case, conservationists in the United States used population control of coaster brook trout (Salvelinus fontinalis) in a hatchery to prevent any single family from breeding too much. This meant multiple genetic lineages were maintained, increasing genetic diversity.
Action 3: Restoration
Ecosystem restoration can include planting trees, rehabilitating wetlands or restoring natural patterns of fire and water. We found genetic diversity was often maintained over time when ecological restoration was used.
Restoration efforts, alongside supplementation, are important to the survival of the greater prairie-chicken (Tympanuchus cupido), which had lost much habitat. Researchers report restoring and expanding suitable habitat is proving crucial to sustain genetic diversity and achieving long-term recovery.
Action 4: Control of other species
Feral, pest or overabundant species can outcompete, eat, or graze on species under threat. Controlling these species was linked to maintenance of genetic diversity in the studies we analysed overall.
For example, control of red fox numbers helped the Arctic fox (Vulpes lagopu) recover in Sweden. The technique reduced competition over resources such as food while new foxes from Norway were added to the wild population. Inbreeding was reduced, and survival improved.
Action 5: Conservation introductions and reintroductions
Establishing new populations at new sites is known as a conservation introduction, while a reintroduction means restoring populations where they previously existed.
We found mixed results for genetic diversity when these actions were reported. So, what factors contribute to success?
In Western Australia, a large number of golden bandicoots (Isoodon auratus) from a robust island population were reintroduced to three sites. After six generations, genetic diversity at these sites remained similar to the original source population. Success came from careful planning to ensure the new populations had a large gene pool to start from.
Overall, our study revealed many cases of genetic diversity loss. But we also found evidence that conservation action - especially supplementation - can improve the genetic health of a species.
What can you do?
Supporting genetic diversity can be done at home.
If you have a garden, you can plant native species to support habitat connectivity.
Growing heirloom vegetables and rare fruit trees, or breeding heritage chooks can maintain genetic diversity in our food system.
Join community or botanic garden groups, or work with conservation groups to improve habitat or bolster numbers of threatened species.
While enjoying nature, avoid accidentally moving plants, seeds, or soil to new areas to reduce the spread of pests and diseases.
These small actions add up, helping to safeguard biodiversity at all levels - including genetic diversity.
Robyn Shaw was supported during the study by funding from the Australian Research Council. The project workshop was sponsored by the European Cooperation in Science and Technology Action 'Genomic Biodiversity Knowledge for Resilient Ecosystems'. She is a member of the Coalition for Conservation Genetics and the IUCN Conservation Genetics Specialist Group.
Catherine Grueber's research into the conservation genetics of threatened species receives funding from the Australian Research Council and the University of Sydney (Robinson Fellowship). She is a member of the Coalition for Conservation Genetics, and the IUCN Conservation Genetics Specialist Group.
Katherine Farquharson was supported during the study by funding from the Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science. She is affiliated with Koala Conservation Australia.
