De-Extinction as a Means of Restoring Biodiversity

Mika Black – Animal Science B.S.

Emma Weir – Animal Science B.S.

E. Alexandra Panagiotou – Wildlife Conservation B.S.

 

Human action is often a culprit in recent animal extinction. One such victim is the Tasmanian tiger (Thylacinus cynocephalis), or thylacine, who used to be an apex predator of mainland Australia and Tasmania (Attard, 2013). Even though the thylacine was a shy and secretive animal (Bulte, Horan & Shogren, 2003), that avoided contact with humans, it was driven to extinction as a result of human introduction of the dingo as well as human intensification (Prowse, Johnson, Bradshaw, & Brook, 2014). Overhunting of the thylacine was also thought to play a role in its extinction (Attard, 2013). The Javan Tiger and the Western Black Rhino are two other animals humans drove to extinction (Ellis, 2005). These species didn’t go extinct due to natural phenomena and so their disappearance caused imbalance in their natural ecosystems. Resurrecting species to these habitats not only could restore ecosystems, but will help protect and preserve other animal and plant species within that ecosystem. Resurrecting extinct species is now becoming a reality as science is advancing and the environment is changing. With developing biological technology, we can own the opportunity to restore ecological diversity worldwide and perhaps reverse the negative impact that humans placed.

There is a significant rabbit population in the Tasmanian tiger’s former home. Rabbits are an invasive species introduced to Australia in the late 1800’s for human hunting sport, and now cover most of the continent (Australian Government, 2011). Feral rabbits caused not only a decline in various plant and animal species, but also the extinction of some small native Australian mammals (Australian Government, 2011). The presence of the rabbit in Australia threatens the greater bilby, yellow-footed rock-wallaby, southern and northern hairy-nose wombats, malleefowl, and plains-wanderer (NSW Government, 2015). Not only do rabbits wreak havoc on Australia’s ecosystem, but they are a huge economic burden (Zenger, Richardson, & Vachot-Griffin, 2003). They cause approximately $115 million in loss in agriculture (NSW Government, 2015).

Another invasive animal species introduced to Australia is the dingo. The dingo currently occupies the top-order predator role in Australia (Letnic, Ritchie, & Dickman, 2012). Although the dingo is an important and necessary part of the ecosystem now, its initial introduction likely contributed to the loss of other important predators, such as the Tasmanian tiger and the Tasmanian devil, in Australia (Prowse et. al, 2014). These actions left Australia with a massive, destructive prey population, and tiny predator population. We must implement an effective and permanent plan to control the rabbit population in order to prevent  further economic loss by the Australian government.

The attempts at controlling the rabbit population thus far yield poor results. Diseases like Myxovirus and calicivirus were introduced to the rabbit population in the past, however these diseases alone did not prove to be very effective (Zenger et. al, 2003). Some rabbits grew resistant to these diseases, and since the population is so huge, the diseases only exhibit a small level of control (Australian Government, 2011). Reintroduction of the Tasmanian tiger into the Australian Ecosystem will reestablish control of the destructive European rabbit population. Three biological researchers from the Centre for Biostructural and Biomedical Research at the University of Western Sydney conducted an experiment to prove to the audience that the rabbit population holds less genetic diversity in the Western region of Australia, therefore, making it a good place to begin a reintroduction of an extinct predator species (Zenger et al, 2003). The current predators that exist in Australia are also not capable of controlling the population alone. Tortosa, Barrio, Carthey, and Banks (2015) found that the rabbits are very good at avoiding predators because they adapted to the predator’s odors and can flee easily. The Australian Government (2011) suggests employing a variety of methods to control the population. Overall, diseases and poisons are the main methods tested, but no attempts at introducing foreign or unknown predators to the rabbits (Australian Government, 2011). This is likely due to the fact that there are clear repercussions to introducing non-native species.

In order to avoid the detrimental outcomes of non-native species introduction, we must look to a predator that is native to Australia. Unfortunately, the only large predators native to Australia are extinct. Through further development of de-extinction technology, we can resurrect necessary predators to Australia to help control the rabbit population. The reintroduction of the Tasmanian tiger through de-extinction will restore balance to the Australian ecosystem by controlling the rampant rabbit population.

The Tasmanian tiger went extinct less than one hundred years ago, in 1936 (Attard, 2013). This means that there are preserved tissues left. These tissues were used to reproduce part of the Tasmanian tiger genome (Pask, Behringer, & Renfree, 2008). DNA from four different thylacine samples was used to produce an enhancer for a protein coding sequence from the Tasmanian tiger genome (Pask et. al, 2008). Pask et. al (2008) then injected this sequence into mice and demonstrated that the sequence could be used in living organisms. The rest of the thylacine genome will need to be sequenced in order to produce a living organism through cloning, but due to the availability of tissue this should not be too difficult. Cloning of an extinct species, however, is a bit more difficult than cloning a living species because researchers must find a suitable egg of a contemporary animal to host the extinct DNA (Dankosky & Archer, 2013). The Lazarus Project, however, demonstrates that this is possible, as seen in the gastric brooding frog (Dankosky & Archer, 2013).

The University of New South Wales continues research on the Lazarus Project (Dankosky & Archer, 2013). This project successfully reproduced the genetic living structure of the gastric brooding frog, which inhabited the state of Queensland, Australia until its official extinction in 1983 (Dankosky & Archer, 2013). One of the researchers on the project, Mike Archer, isolated with his team a sample of preserved tissue and replanted it into an egg of a closely related species (Dankosky & Archer, 2013). Although, the resurrected frogs did not survive more than a few days, it supports successive arguments that de-extinction is a “Jurassic Park” reality (Dankosky & Archer, 2013).

The Lazarus project now progresses towards the resurrection of the Tasmanian tiger (Dankosky & Archer, 2013). Archer (2013) argues that reintroduction of the thylacine would help bring stability and balance back to Australia and may even help eradicate a disease currently threatening Tasmanian devils (Dankosky & Archer, 2013). He supports his claims of the importance of the thylacine, adding “you need new species to originate at about the same rate to offset the ones that are going extinct so that you maintain a balance of the amount of biological diversity in the world” (Dankosky & Archer, 2013). Unfortunately, ecosystems across the world, and as argued in Australia, are not maintaining this structured demand. Upon successful resurrection of the thylacine, this animal could relatively easily return to Australia and resume its natural role as an apex predator.

Although significant details on the diet of Tasmanian tigers do not exist, evidence suggests that rabbits could be likely prey targets. The structure of the Tasmanian tiger’s jaw and teeth suggest that it targeted small prey (Attard, 2013). This also means that the Tasmanian tigers would be unlikely to target large prey, such as livestock and thus would not be a major threat to humans. The home range of the Tasmanian tiger could also provide evidence that its re-introduction would not affect humans negatively and would lead to the decline in the rabbit population. Image 1a shows the historic home range of the Tasmanian tiger (Channell & Lomolino, 2000).  Image 1b is the areas in Australia occupied by human population (Newton, 2001) and Image 1c is the rabbit’s home range in mainland Australia (Invasive Animals CRC, 2010).

 

As seen in Image 1a the Tasmanian tiger’s historic home range is spread throughout all of mainland Australia as well as Tasmania. This make the thylacine’s reintroduction into mainland Australia less complicated and potentially more successful, as reintroduction is possible at several sites. The Tasmanian tiger could be reintroduced into areas that overlap with the catastrophic rabbit populations, mostly Central Australia, and avoid the areas that humans inhabit (Image 1b). These include mostly the coasts of Queensland, New South Wales, Victoria, some of South Australia and the North tip of Western Australia (Image 1b).  Furthermore, since Bulte et. al (2003) suggest the Tasmanian tiger avoided humans, the thylacine would stay away from main residential areas and locations occupied by humans.

The Tasmanian tiger was one of Australia’s only mainland predators until the animal’s extinction. During the Holocene era, Australia lost its marsupial predators due to human activity (Prowse et. al, 2014). This left Australia with only the dingo as an apex predator. Apex predators play crucial roles in ecosystems and having only one on the entire continent of Australia is not ideal. The dingo is shown to be incredibly important in maintaining biodiversity in Australia. The loss of the dingo in specific communities negatively affected the animals and flora within those areas (Letnic et. al, 2012). Specifically, lethal control of dingo populations decreased small mammal and understory vegetation populations (Letnic et. al, 2012). Dingoes are prevalent now, but there is always a possibility of losing populations to disease through human intervention as viewed through the Tasmanian tiger. Relying on this current predator only, then, is risky. However, there are successful cases of reintroducing predator species back into the wild to help maintain biological structure and avoid negative impact.

Successful predator reintroductions occurred in other areas, so the Tasmanian tiger reintroduction would likely be similar. Dobson and Lyles (2000) analyze the successful outcome of the captive breeding program of the black footed ferret, an animal once thought to be extinct and now considered endangered. This captive breeding program held “240 ferrets (90 males and 150 females) of prime breeding age (1 to 3 years old) and were [housed in separate locations] to maintain 80% of the genetic variability” (Dobson & Lyles, 2000, p.985). The population of black-footed ferrets released into the Great Plains continues to thrive and grow, both by natural and facilitated means (Jachowski & Lockhart, 2009). Researchers also successfully reintroduced the African wild dog in certain metapopulations in South Africa (Gusset et. al, 2007). The decrease of human interference with these populations through fencing contributed to this success (Gusset et. al, 2007). These successes indicate that the Tasmanian tiger could realistically return to its role as an apex predator in Australia.

Reintroduction of predators into their former habitats does impact the ecosystem as a whole. Ripple, Beschta & Painter (2015) found that the reintroduction of the grey wolf (Canis lupus) into the Yellowstone National Park caused Rocky Mountain elk to change their grazing patterns, which affected thinleaf alder populations. This is an example of a trophic cascade; the increase in grey wolf population caused an increase in thinleaf alder population (Ripple, Beschta, & Painter, 2015). The Tasmanian tiger would likely cause a similar trophic cascade. Through decreasing the rabbit population, it could counteract the decline in plant populations seen since the introduction of the rabbit to Australia (Australian Government, 2011). These results suggest successful predator reintroduction is feasible and it could play an important role in conservation management and ecological restoration.

Alien predators can cause catastrophic effects on ecosystems and are thought to be much more harmful to biodiversity than their native counterparts. Introduction of non-native species can cause catastrophic effects, as seen with the Indian mongoose in Hawaii. The mongoose was introduced to help decrease rat populations but it did not target rats and instead targeted native bird species (Nuwer, 2012). Now Hawaii is faced with the need to get rid of this invasive species (Nuwer, 2012). Australia could face the same problem if a non-native predator were introduced there. The Tasmanian tiger would be a preferable predator candidate, as it existed on the Australian mainland and Tasmania and was adapted to the ecosystems there.

There are several different issues to look at surrounding this attempt at reintroduction. One such concern: what would prevent the Tasmanian tiger from going extinct again? Human action is believed to be the main factor in the extinction of the Tasmanian tiger (Prowse, et. al, 2014). This is an easy issue to solve, as protective laws could be passed to prevent detrimental human interactions with this animal. Prowse et. al (2014) also cite the dingo as playing a role in the extinction. Although the thylacine would likely still compete with the dingo for resources, this would not occur in combination with the other factors that led to the thylacine’s demise.

Another issue surrounding the attempt at de-extinction is the cost. Since research is still being done in these methods, it will likely turn out to be a costly procedure. Currently it costs approximately $10,000 to acquire a 3-month-old cloned heifer (Dematawewa & Berger, 1998). However, the cost of cloning an animal is far less than the $115 million lost in agriculture due to rabbits (NSW Government, 2015).

The Tasmanian tiger could also hunt animals other than rabbits. Australia contains many endangered and at risk small animals (Australian Government, 2015). The Tasmanian tiger could potentially prey on these animals, thus adding to their threatened status. However, research conducted by Colman, Gordon, Crowther, & Letnic (2014) shows that removing apex predators actually decreases small mammal populations. Thus, reintroducing an apex predator may actually help properly control these small mammal populations. Included in this list of at risk animals are the plains-wanderer, northern hairy-nosed wombat, malleefowl, yellow-footed rock-wallaby, and greater bilby (Australian Government, 2015). All of these are animals whose threatened status is partly attributed to the rabbit (NSW Government, 2015). By decreasing the rabbit population, the Tasmanian tiger would most likely benefit these populations, rather than decrease them.

Although extinct species have not yet been revived, de-extinction appears to be a feasible way of restoring balance to struggling ecological communities across the world. By reintroducing predators into particular habitats, we can stop trophic cascades and restore balance to ecological communities. The uncontrolled rabbit population can be reduced through reintroduction of an unfamiliar predator species and save the Australian economy. Resurrecting species can make an impact on specific ecosystems throughout the world and we could avoid further tragedies. Each study and experiment conducted contributes to advancement of stronger methods and therefore, healthier animals. The loss of the Tasmanian tiger shows us we often do not realize the significance of something until it is lost.

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