gene flow

Can we help endangered species help themselves?

Humans are having an immense impact upon the natural world. Australia has lost 30 mammal, 24 bird and 78 frog species since European settlement, and with many more listed as endangered or critically endangered, these numbers are set to climb.

Conservationists are (of course) very keen to stop this from happening. But many of the threats impacting our native species - diseases, habitat loss and invasive species - are almost impossible to reverse or eradicate. Mitigating these threats can often be costly, time-consuming, and ultimately futile.

I won’t deny it - the situation is pretty dire. But there is still hope. It’s a hope that comes not from humans, but from the threatened species themselves.

It’s something we don’t hear about very often, but endangered species are not always completely helpless. In some circumstances, we are seeing a small number of individuals surviving despite the widespread decline of the majority of their species.

Unconfirmed reports suggest a small number of Tasmanian devils on the north-western tip of Tasmania appear to show some resistance to Devil Facial Tumour Disease, which has wiped out around 95% of wild devils. At the other end of our continent, populations of northern quolls, which have experienced massive declines thanks to their habit of eating the poisonous cane toad, have since recovered in Queensland and now live alongside toads.

These pockets of resistance possibly occur because a small number of individuals possess a trait that makes them resistant to the threat. Genetic variation is something that occurs in every species on the planet. This is when slight differences in each individual’s genetic makeup leads to an assortment of traits in a single population.

As a threat spreads through a landscape, some individuals may be more genetically equipped to deal with it. Any individual that survives the threat because they possess a certain gene or set of genes (e.g. they are genetically resistant to a disease) goes on to reproduce and pass that superior set of genes on to their offspring. As they hurtle towards extinction, endangered species are under intense selection, so any gene that promotes survival would spread quickly through a population.

So if selection is such a driving force, and there are animals out there that can survive certain threats, why are we seeing such widespread declines and extinctions?

Well firstly, there is a lot of complexity in all of these systems: species are often subjected to multiple threatening processes at once, and the interactions between these lead to complex outcomes that are difficult to predict.

Another issue is that these resistant traits often do not occur frequently enough to spread through a population, or only occur in isolated sections of the landscape. For instance, although Queensland populations of the northern quoll may have evolved to live alongside toads, this is not a trait shared by Northern Territory populations on the toad invasion front, making the quolls who are about to encounter toads for the first time extremely vulnerable to local extinction.

In a recent paper published in Conservation Biology, my research team has suggested a management technique that could capitalise on this natural adaptation to promote the resistance of an entire population to a threatening process, and hopefully help species avoid extinction.

This technique, called targeted gene flow, involves moving pre-adapted genes to areas in the landscape where they would be the most beneficial. The small number of resistant genes would be artificially promoted through captive breeding and translocations to improve the resilience of the population to a certain threat.

This idea is already being applied to improve species’ adaption to climate change. By translocating individuals adapted to relatively warmer environments to cold-adapted populations, conservationists can increase the proportion of genes that match the future climate of the warming site. Already, it has been used to conserve conifers in the USA, with drought resistant strains being moved to areas that are being affected by global warming.

Yet, targeted gene flow could have much broader applications. Variation in adaption is not something that occurs only in response to climate change; there are a broad range of populations and threatening processes to which it could be applied. Adaptive genes may already be present in the population or may rapidly evolve in response to a threat.

The idea is similar to that of genetic rescue, which involves bringing animals into a small, inbred population to bolster the variety and number of genes in the gene pool. Genetic rescue has recently helped strengthen the isolated population of mountain pygmy possums on Mount Buller. Males from neighbouring Mount Hotham were introduced to the Mount Buller population and successfully bred with females to produce hybrid offspring, which were not only heavier (so more likely to survive winter) than their purebred counterparts, but also carried much needed genetic variation to help the population endure. With targeted gene flow, conservationists would be looking to encourage a certain trait that helps a species deal with a threat, rather than just promoting general genetic variation.

Of course, translocating individuals across habitats is a tricky business and is not something we suggest entering into lightly. However, in certain instances and with very careful planning and execution, targeted gene flow could allow us to help endangered species help themselves. By promoting adaption to many of the unavoidable and unstoppable threats in Australia, we could hopefully reduce the number of native species on Australia’s list of extinctions.

For my PhD, I am looking at the feasibility of using targeted gene flow to conserve northern quoll populations. If there are individuals that have evolved to be “toad-smart” - a trait that is heritable - we could introduce these individuals ahead of the invasion front and reduce the chance of extinction in populations of quolls in the Northern Territory and Western Australia. But first, I need to examine the toad-smart behaviour to work out how it is passed between individuals – is it genetic or learnt?  So far, it seems that this behaviour may be more complex than I originally imagined, but if I can understand how it is sustained in a population, it will be the first step towards harnessing it for conservation. Watch this space!

Ella Kelly

Ella is a PhD Candidate at the University of Melbourne, where she spends a lot of time thinking about why some quolls don’t eat cane toads (if only she could ask them!). She also enjoys talking and writing about science, and would ultimately love to have an actual impact on the conservation of Australia’s biodiversity.

You can find her on Twitter at: @elkelly1210

Evolving in a Changing World

Climate change is causing temperatures to rise, but what does this actually mean for the various species and populations of the world? Organisms have always had to respond to naturally occurring climate change. However, anthropogenic greenhouse emissions are prompting changes in environmental factors - not just temperature, but also factors such as rainfall and ocean acidity  - at a rate and scale of change far above what would have occurred naturally. Consequently, there is a considerable amount of concern regarding whether natural populations can respond fast enough to ‘keep up’ with this increased rate of change.

Encouragingly, we’re seeing some species respond to climate change through migration. Natural populations, including species of insects, birds, mammals, plants, fish and marine invertebrates, have shifted their range poleward towards cooler areas of higher latitude.  

Australian species of sea urchins are among those shifting their distribution poleward in recent years. Photo: Peter Southwood (Wiki Commons)

Australian species of sea urchins are among those shifting their distribution poleward in recent years. Photo: Peter Southwood (Wiki Commons)

Unfortunately, migration is more challenging for some species than others. Many have poor dispersal abilities and others lack any suitable alternative habitat to disperse to. The latter is especially an issue for those that are specialised to small or sporadically distributed habitats, such as high altitude alpine areas. The ability of natural populations to migrate has also been severely hampered by habitat fragmentation and the construction of human-made structures, including cities and roads, which may act as barriers to migration. 

Natural populations in which migration is not a sufficient solution to adapting to the effects of climate change must either adapt or face extinction. While factors such as temperature are expected to shift beyond what many natural populations can currently tolerate, groups of animals may have the capacity to respond to these changes by undergoing adaptive evolution.

Evolution involves changes in a population’s genetic make-up from one generation to the next. In the case of adaptive evolution to climate change, these genetic changes over multiple generations may facilitate changes in traits, such as thermo-tolerance, that can allow populations to mitigate the effects of climate change. 

Although evolution is frequently perceived as a laboriously slow process, this is often not the case. Evolution can be rapid, especially for species with short lifetimes. For instance, an ecologically important species of phytoplankton was shown in an experimental study to significantly improve its performance under increased levels of ocean acidity in less than a year of adaptive evolution. We are also seeing evidence of populations being able to adaptively evolve to the effects of climate change through studies on natural populations. One example of this is the Canadian Red Squirrel, that has adapted to seasonal changes in food availability by giving birth to offspring earlier in Spring when more food is available.

Some species, such as the Canadian red squirrel, have shown an evolutionary response to the effects of climate change. Photo: Gilles Gonthier (Wiki Commons)

Some species, such as the Canadian red squirrel, have shown an evolutionary response to the effects of climate change. Photo: Gilles Gonthier (Wiki Commons)

However, it is far from all good news. Some populations have been found to possess worryingly limited potential to adapt to climate change. In tropical Queensland, populations of fruit flies have very little ability to improve their resistance to lower levels of environmental humidity, which are predicted to occur with future climate change. While I can certainly see how the possible extinction of a fly species might sound like fantastic news to some, such results in any natural population are troubling. Furthermore, even if a population has the capacity to adapt to current rates of climate change, this does not guarantee that they will be able to continue to evolve fast enough to keep up with changes in the future. 

Continued research is crucially important. Photo: Evatt Chirgwin

Continued research is crucially important. Photo: Evatt Chirgwin

Evolution is likely to have an enormous role in determining which species and populations can adapt to long-term climate change, and as such needs to be considered by natural resource managers. Through incorporating evolutionary processes into their management strategies to counter climate change, these managers can create more efficient methods of protecting biodiversity. For instance, identifying species of low evolutionary potential can assist them in identifying which species are of high vulnerability to extinction from climate change. 

Importantly, natural resource managers need to employ strategies to safeguard against loosing the existing evolutionary capacity held by natural populations. Though this is often easier said than done, the best way to protect a population’s ability to adapt is by maintaining a large population size. The larger a population, the more likely it is to to maintain high levels of genetic diversity, and the less likely it is to loose beneficial genes that could confer a greater ability for adaptation to climate change.

Additionally, management can protect the evolutionary capacity of species by sustaining connectivity between populations through habitat preservation or establishment of artificial wildlife corridors. Connectivity can allow genes that are beneficial for adaption to spread more easily through multiple populations. Alternately, if natural links are not possible, it may be appropriate in some circumstances for individuals to be artificially moved between populations of the same species to aid the spread of beneficial genetic information.

Increasing population connectivity can aid the movement of beneficial genes between populations. Photo: Krd (Wiki Commons)

Increasing population connectivity can aid the movement of beneficial genes between populations. Photo: Krd (Wiki Commons)

Despite the potential of these and several other possible strategies to reduce the effects of climate change on biodiversity, most simply treat the symptoms of the problem and not the problem itself. The most effective strategy in protecting biodiversity is to reduce anthropogenic greenhouse emissions as greatly and as quickly as possible, so that our planet’s range of amazingly diverse species have a better chance to survive.

Cover photo taken by Allison Chirgwin.