Tasmanian devils have a reputation as a fearsome animal – most of the time this is undeserved. When it comes to the mating season, however, it’s a fair judgement. Between February and April, mating can be incredibly aggressive, with male and female devils prone to biting one another both during and after the act.
That could be deadly for the devils, according to new research published online in the journal Behavioral Ecology.
DFTD is highly unusual for a cancer because it can transfer between individual devils and grow in its new host.
The fact that devils regularly bite one another around the mouth means tumour cells can easily transfer from an infected devil to an open wound on a healthy devil. This makes the buildup of wounds in devils extremely important to our understanding of this disease.
In our study, we examined the accumulation of bite wounds in a population of wild devils in northwest Tasmania.
We found males were much more likely than females to pick up high numbers of bite wounds. But these wounds appear to be related to the amount of time males spent in mating season interactions with females, as opposed to fights with other males (as we had previously thought).
In the mating season, after male devils have mated with females, they spend an extended period either confining the female in a den, or closely following her to make sure other males are unable to mate with her.
During our study we found this behaviour could go on for up to two weeks in the wild. The process is known as “mate guarding” and is relatively common in the animal kingdom.
We found the longer males spent engaging in mate guarding behaviour, the more bite wounds they received. This would seem to put successful males, who mate with a high number of females, in the firing line when it comes to acquiring DFTD.
But no pattern of sex bias in DFTD prevalence has ever been observed in the wild.
So how does this fit with our study on the increased vulnerability in males?
A crucial unknown in the DFTD transmission process involves directionality – which way the deadly disease is passed on by a devil. There are two possibilities:
an infected devil bites an uninfected animal, transferring tumour cells (from its teeth or saliva) directly into the wound it causes
an uninfected devil bites into tumours on an infected animal, and cells transfer into an open wound inside the biter’s mouth.
The reality is likely to involve a combination of the two.
Our results indicate that most disease transmission occurs during extended mating season interactions, when females appear to be causing high numbers of wounds to their mates.
If DFTD can transfer in either direction during these encounters, then both the males receiving the wounds and the females causing them would be equally at risk of acquiring the disease.
We have highlighted mating season encounters between the sexes as crucial transmission points for the spread of DFTD. The behaviour of male devils appears to be driving patterns that support transmission of the disease.
This information is important for potential disease management options, as it pinpoints males in good condition – who are likely to be reproductively successful – as targets for management interventions, such as vaccinations.
Most importantly, these results add one more piece to the puzzle of rapid evolution in the Tasmanian devil, in response to the strong evolutionary pressure DFTD is placing on this iconic species. With almost 100% mortality once devils reach breeding age, any advantage an individual devil might have to survive a little longer and reproduce should – over time – spread through the population.
DFTD is spread through biting so we can expect strong evolutionary pressure for devils to become less aggressive towards each other over time.
With these new results, we can now pinpoint for the first time who (healthy, successful males) and when (guarding females after mating) the intense selection pressure on aggressive behaviour in devils will operate.
Ultimately, devils will solve the DFTD problem themselves by evolving resistance, tolerance and changing their behaviour. One of the best things we can do is let evolution take its course, giving a helping hand along the way via well guided management actions.
David Hamilton, PhD Candidate in Zoology, University of Tasmania; Elissa Cameron, Professor of Wildlife Ecology, University of Tasmania; Menna Elizabeth Jones, Associate Professor in Zoology, University of Tasmania, and Rodrigo Hamede, Post Doctoral Research Fellow, Conservation Biology and Wildlife Management, University of Tasmania
Tasmania’s bushfires may have resulted in the release of significant amounts of mercury from burnt trees into the atmosphere. Our research shows that industrial mercury pollution from decades past has been locked up in west Tasmanian trees.
Mercury occurs naturally in Earth’s crust. Over the past 200 years, industrial activities have mobilised mercury from the crust and released it into the atmosphere. As a consequence, atmospheric mercury concentrations are now three to four times higher than in the pre-industrialisation era.
Mining is the largest source of the global atmospheric mercury, accounting for 37% of mercury emissions. When Europeans first arrived in Australia, there was, of course, no Environmental Protection Act in place to limit emissions from industrial activities. In western Tasmania, where mining has occurred for more than a century, this meant mercury was being released without control into the local atmosphere until changes in technology, market conditions, and later, regulation, conspired to reduce emissions.
Because mercury is also very persistent in the environment, past mining activity has generated a reservoir of mercury that could be released to the atmosphere under certain conditions. This is a concern because even small amounts of mercury may be toxic and may cause serious health problems. In particular, mercury can threaten the normal development of a child in utero and early in its life.
How much mercury has been released into the Australian environment and when has remained largely unknown. However, in a new study we show how mercury levels in Tasmania have dramatically changed over the past 150 years due to mining practices. Long-lived Huon pine, endemic to western Tasmania, is one of the most efficient bioaccumulators of mercury in the world. This makes it a good proxy for tracking mercury emissions in western Tasmania. If concentrations of mercury in the atmosphere are high in a given year, this can be detected in the annual ring of Huon pine for that year.
Mercury pollution from past mining practices in western Tasmania has left a lasting environmental legacy. The sampled trees contained a significant reservoir of mercury that was taken up during the peak mining period in Queenstown. Changes in mercury concentrations in the annual rings of Huon pine are closely aligned with changes in mining practices in the region.
Increased concentrations coincide with the commencement of pyritic copper smelting in Queenstown in 1896. They peak between 1910 and 1920 when smelting was at its height. In 1922, concentrations begin to decline in parallel with the introduction of a new method to separate and concentrate ores. This method required only one small furnace instead of 11 large ones. In 1934, a new dust-collection apparatus was installed in the smelter’s chimney, coinciding with the further decrease in mercury concentrations in nearby Huon pine.
Toxic elements or compounds taken up by vegetation can also be released back into the local environment. Bushfires that burn trees that have accumulated mercury may release this mercury as vapour, dust or fine ash, potentially exposing people and wildlife to the adverse effects of mercury. It is estimated that bushfires release 210,000kg of mercury into the global atmosphere each year. As these fires become more frequent and ferocious in Australia, mercury concentrations in the atmosphere are likely to increase. Mercury released by bushfires can persist in the atmosphere for a year, allowing for long-distance transportation depending on wind strength and direction. This means that mining activity from over a century ago may have regional implications in the near future. The Tasmanian fires in December-February burned almost 200,000 hectares, including areas around Queenstown.
It is not currently possible to know how much mercury has been released by these recent fires. Our results simply highlight the potential risk and the need to better understand the amount of mercury taken up by vegetation that may one day be released back to the atmosphere via bushfires.
Although there is no simple way to remove bio-accumulated mercury from trees, the history of mercury contamination recorded in tree rings provides important lessons. Decreased uptake of mercury after upgrades to the Queenstown copper smelter operations demonstrates the positive impact that good management decisions can have on the amount of mercury released into the environment.
To control mercury emissions globally, the United Nations Environment Programme (UNEP) has developed the Minamata Convention on Mercury. Its primary goal is to protect human health and the environment from the negative effects of mercury. Australia has signed the convention and but has yet to ratify it. Once ratified, Australia would be required to record sources of mercury and quantify emissions, including those from bushfires.
But to do this, the government must first be able to identify environmental reservoirs of mercury. Our study, the first of its kind in the Southern Hemisphere, shows that the long-lived Huon pine can be used to for this purpose. Further work to determine what other tree species record atmospheric emissions of mercury and other toxic elements in other regions of Australia is required.
Larissa Schneider, DECRA fellow, Australian National University; Kathryn Allen, Academic, Ecosystem and Forest Sciences, University of Melbourne, and Simon Haberle, Professor, Australian National University
The Tasmanian devil – despite its name – once roamed the mainland of Australia. Returning the devil to the mainland may not only help its threatened status but could help control invasive predators such as feral cats and foxes.
But now we’ve explored the idea from a palaeontological view. We looked at the fossil record of mainland devils, in a paper published online and in print soon in the journal Biological Conservation.
The fossil record helps us better understand how the devils co-existed on mainland Australia with other wildlife. It also helps us see how these iconic animals may possibly interact with small and medium-sized animals if reintroduced to the mainland in the future.
Ecologists have reintroduced several apex predators to environments where they were once driven to localised extinction. This has helped restore past ecosystems by providing a clearer ecological balance.
One of the best-known examples is the reintroduction of wolves to Yellowstone National Park in the United States, to check the overgrazing and destruction of habitat by elk.
By reintroducing Tasmanian devils into mainland Australia, can we possibly help restore ecological systems that support devils along with small to medium-sized native mammals?
But these iconic Australian predators were still able to survive in Tasmania. The island was created 10,000 years ago by rising sea levels, well before the arrival of dingoes on mainland Australia.
Dingoes have now been eradicated across much of mainland Australia, particularly within the seclusion zone of the dingo fence in the southeast of the continent. The 5,400km fence stretches eastwards across South Australia into New South Wales and to southeast Queensland.
Exotic predators such as foxes and cats now thrive across many parts of Australia, and have devastating impacts on small to medium-sized Australian mammals.
But until recently they have not been able to gain a foothold in Tasmania. Many ecologists believe the presence of the devil has prevented these other animals making their destructive mark on the ecology of Tasmania.
Sadly the situation is changing as a result of the deadly devil facial tumour disease, an infectious cancer that has destroyed many populations of Tasmanian devils. Estimates range up to 90% of some population groups now wiped out.
As a result, feral cats are now moving into former devil habitats and hunting native species on Tasmania.
So what does the fossil record tell us about the past life of the Tasmanian devil in mainland Australia?
The Willandra Lakes World Heritage Area, in southeast Australia, provides an extraordinary archaeological and palaeoecological record of Ice Age Australia.
In the past, skeletal remains buried within the landscape were commonly fossilised. Evidence of small animals that dug burrows (such as burrowing bettongs) and the predators that pursued them in their burrows, are exceptionally well preserved.
Our excavations reveal how devils and other small-to-medium sized mammals and reptiles interacted over more than 20,000 years in this area. Even during the peak arid phase, known as the Last Glacial Maximum, it seems that devils and their prey successfully co-existed.
The fossil record shows that the range of habitats occupied by devils in the past was far more diverse than today, with populations being found across environments from the central arid core to the northern tropics.
This suggests that devils today should, theoretically, be able to reoccupy a similarly extensive range of habitats.
Some ecologists suggest dingoes should be reintroduced into Australian habitats in order to reduce the impact of cats and foxes on native mammals.
One problem is that dingoes also prey on livestock. This is the reason the dingo fence was constructed during the 1880s.
But devils are not active predators of cattle and sheep. So reintroducing a predator that has a much longer evolutionary history with other native mammals in this country would likely receive far less opposition from pastoralists.
A reintroduction of devils back to the mainland may be a new approach to consider for controlling the relentless, destructive march of exotic predators and restore crucial elements of Australia’s biodiversity.
It still needs to be demonstrated that devils can suppress the activities of cats and foxes on the mainland, as they seem to have done in Tasmania. Experiments with devils in a range of different settings would help to establish this.
A new research approach involving palaeontologists, conservation biologists and policy makers may help us understand how we can restore biodiversity function in Australia.
Every year Tasmania is hit by thousands of lightning strikes, which harmlessly hit wet ground. But a huge swathe of the state is now burning as a result of “dry lightning” strikes.
Dry lightning occurs when a storm forms from high temperatures or along a weather front (as usual) but, unlike normal thunderstorms, the rain evaporates before it reaches the ground, so lightning strikes dry vegetation and sparks bushfires.
Dangerous, large fires occur when dry lightning strikes in very dry environments that are full of fuel ready to burn. Cold fronts in Tasmania, which often carry fire-extinguishing rain, have recently been dry, making these fires worse. The fronts draw in strong hot, dry northerly winds, fanning the flames.
Research has found that as climate change creates a drier Tasmania landscape, dry lightning – and therefore these kinds of fires – are likely to increase.
Lightning has always started fires across Tasmania. Fire scars and other paleo evidence across Tasmania show large fires are a natural process in some places. However, frequent large, intense fires were rare. Now such fires are being fought almost every year.
Contrary to anecdotal belief, our recent preliminary work suggests that lightning activity has not increased over recent decades. So why do fires started by lightning appear to be increasing?
As temperatures rise, evaporation rates are increasing, but current rainfall rates are about the same. In combination this means the Tasmanian landscape is drying. The landscape is more often primed, waiting for an ignition source such as a dry-lightning strike. In such conditions, it only takes one.
Lightning struck just such a landscape in late December 2018, starting the Gell River bushfire in southwest Tasmania. This uncontrollable fire burnt about 20,000 hectares in the first half of January and is still burning. These large fires deplete the state’s resources, fatigue our volunteer and professional fire fighters and can have disastrous effects on natural systems.
With no significant rain falling over Tasmania since mid-December, the island is breaking dry spell records and thousands of dry lightning events have occurred. On January 15 alone over 2,000 lightning strikes sparked more than 60 bushfires.
Most of these were controlled rapidly, a credit to Tasmania’s emergency responders. One of the worst-hit areas was the Tasmanian Wilderness World Heritage Area, where many bushfires continue to burn in inaccessible locations.
This is putting some of Tasmania’s most pristine and valuable places in danger of being lost. The state stands to lose its most remarkable old-growth forests, like Mount Anne, which is home to some of the world’s largest King Billy Pines, a species endemic to Tasmania.
Ongoing climate change is making dry spells longer and more frequent, increasing the fire-prone area of Tasmania. Almost the whole state is becoming vulnerable to dry lightning.
Some regions of the west coast of Tasmania used to have very little to no risk of bushfires as they were always damp. However, this is no longer the case, resulting in species coming under threat.
Unlike most of Australia’s vegetation, many of Tasmania’s alpine and subalpine species evolved in the absence of fire and therefore do not recover after being burnt. Endemic species like Pencil Pine, Huon Pine and Deciduous Beech may be wiped out by one fire.
So what does the future hold? Using data from Climate Futures for Tasmania, we can peek into the future. Our models indicate that climate change is highly likely to result in profound changes to the fire climate of Tasmania, especially in the west.
With a warming climate, the rain-producing low-pressure systems are moving south and many storms that used to hit Tasmania are drifting south, leaving the island drier. This, combined with increasing evaporation rates, result in rapid drying of some areas. Areas that historically rarely experienced fire will become increasingly prone to burn. The drying trend is projected to be particularly profound throughout western Tasmania.
By the end of the century, summer conditions are projected to last eight weeks longer. This drying means that lightning events (and therefore dry lightning) will become an ever-increasing threat and the impact of these events will become more significant.
Higher levels of dryness will mean when bushfires occur the potential for these to burn into the rainforest, peat soils and alpine areas will be significantly increased.
How far away was that lightning?
These changes are already happening and will get progressively worse throughout the 21st century. Climate change is no longer a threat of the future: we are experiencing it now.
Nick Earl, Postdoctoral associate, School of Earth Sciences, University of Melbourne; Peter Love, Atmospheric Physicist, University of Tasmania; Rebecca Harris, Climate Research Fellow, University of Tasmania, and Tomas Remenyi, Climate Research Fellow, Climate Futures Group, Antarctic Climate and Ecosystems CRC, University of Tasmania