Tasmanian Devil at the Zoo Duisburg, in 2017. The only zoo in Germany that keeps them. (Credit: Mathias Appel / CC0)

With the seemingly endless stream of bad news relating to the environment we’re often faced with these days, hearing ecosystem restoration or conservation success stories are always a welcome relief. With the number of species that have been displaced from their native habitats, the news of an endangered species being successfully introduced to a new area should be shouted out. So you cannot blame a conservation geneticist like me for jumping happily when I heard news of the release of the European bison and Tasmanian devil back to their native habitat. 

The word that the media has been using is “release”, which is one of the most important steps in “species reintroduction”. Species reintroduction is the process whereby a species re-establishes a population where they have previously been driven out of. It starts with choosing the individual, making sure it is healthy, and then choosing where to release it.

Maintaining an insurance population is not an easy task. I was watching the plenary talk of Carolyn Hogg at the Biodiversity Genomics 2020 Conference when she explained how she has been assisting captive breeding effort of Tasmanian devils using genetics and genomics approaches. She even co-edited a book titled “Saving the Tasmanian Devil: Recovery through Science-Based Management” to document the whole journey. 

After hearing her talk, I felt how amazing it would have been to be able to reintroduce a previously endangered species back to where they belong. While enviously hearing about how the Australian government seem to highly appreciate evidence-based policy *cough*, I noted her step-by-step journey in using genetic data to save the devils.

1. Maintain an Insurance Population

If the species’ population has become so low in the wild that the only way to save them is to intervene with their breeding process, captive breeding kicks in. Before we start that process though, we need to answer a few key questions so that we know we’re taking the right approach:

• Which population/habitat should we start with as the target of reintroduction?
• Where to source the species to establish an insurance population?
• What is the survival rate upon release?
• Do they breed when released?

This information is used to identify an ‘insurance population’, used as the population from which the individuals to be released into the new habitat will be picked. In the case of Tasmanian devils, the insurance population has been established since 2006 and sourcing more ‘founders’ (species to interbreed with the insurance population) from the wild has been done at least until 2015. The health of this population has been monitored annually to evaluate their breeding attempts. They are monitoring how the individuals survive after release, whether inbreeding is decreasing their fitness, and much more (enough material for a book of 300 pages, of course). The captive insurance population are the source of the reintroduction, so they need to be healthy and genetically diverse.

2. Know Where to Release Them

You cannot just find a mysterious forest and release your insurance population into the unknown (Frozen II pun intended). Often you will be reintroducing a species into an area where there is already an established population of that species, in order to boost local numbers. But if the already-established population has adapted specifically to that environment, extra genotypes that are not adapted as such will probably not cope as well, and breeding with the local population may even weaken that local population’s adaptation. Geneticists call this phenomenon ‘outbreeding depression’, one of the risks of species introduction.

Ideally, individuals should have a degree of similarity, whether physical or genetic, to minimize any risk of incompatibility in breeding. The population you’re releasing the new individuals to should be well-studied, as is the case with Florida panthers. That way you know what kind of individuals will suit best. To minimize risk, practitioners usually do a simulation study to check how certain genetic makeup will prevail in the target location (also what was done for the Tasmanian devils). 

Other than how the new individual introduced will affect its own species, you need to know whether it benefits the ecosystem as a whole. The loss of Tasmanian Devils causes what has been dubbed ‘trophic downgrading’. Carnivores lower the level of competition among their prey species, allowing more of those species to thrive. If you remove carnivores, one or two species are more likely to outcompete the others.

Simulation studies have shown that the devil’s existence in mainland Australia will suppress foxes and cats, potentially benefiting many mainland species. As with any reintroduction project, however, these predictions need long-term evaluation.

3. Evaluate

After releasing individuals into the well-known population, you sit back and watch how they survive and breed. If they do not survive, you begin again, evaluating the entire population. If they survive, you note what is working and what is not. Species-wise, the evaluation goal is usually around whether the species survive and breed, and how genetic diversity has changed after reintroduction in this target population. 

Unfortunately, this species-based approach to conservation cannot answer concerns about what effect they will have one other species. They were captive-bred under the assumption that the ecosystem has been needing them! Why would the ecosystem suddenly not need them?

When you release species to an area where they have never been present before for very long time, things might’ve changed there. The case with the devils and bison, for example, is that they were and about to be re-introduced to where they have previously lived, albeit thousands of years ago. The bisons that will be introduced to UK’s woodland will be coming from free-ranging European bison, whereas the devils that have been released by Chris Hemsworth were coming from an insurance population from the island of Tasmania. Will the environment still be suitable for them now?

This is why genetics and ecology should go together in harmony. Cases of species conservation that focus too much on genetics and neglect the issue on habitat suitability, can make the situation even worse. We have grown more careful as many of the next generation of conservation scientists embrace interdisciplinary and collaborative work, keeping an eye on both ecosystem dynamics and population genetics. We hope this will keep our ecosystems healthy, and keep those important success stories rolling in.

Sabhrina Gita Aninta is a conservation geneticist currently pursuing her PhD at Queen Mary University of London to understand how genome-wide variation of the endemic pigs and buffalos from Southeast Asia could assist their conservation. Follow her Twitter here for an update of her work, along with a mix of conservation, biodiversity, evolution, but mostly various rants and random stuffs in Indonesian and English. You can find more of her work at Ecology for the Masses at her profile.

Title Image Credit: Mathias Appel, CC0 1.0