Sexual aggression key to spread of deadly tumours in Tasmanian devils



Both male and female Tasmanian devils can become very violent during sexual interactions.
Shutterstock/PARFENOV

David Hamilton, University of Tasmania; Elissa Cameron, University of Tasmania; Menna Elizabeth Jones, University of Tasmania, and Rodrigo Hamede, University of Tasmania

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.

Unfortunately, biting drives the spread of devil facial tumour disease (DFTD) a transmissible cancer that has been afflicting the species since the mid-1990s.




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Survival of the fittest? Perhaps not if you’re a Tasmanian devil


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.

When devils mate

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 Tasmanian devil with the Devil Facial Tumour Disease.
Menna Jones/PLOS ONE, CC BY

Disease transfer

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:

  1. an infected devil bites an uninfected animal, transferring tumour cells (from its teeth or saliva) directly into the wound it causes

  2. 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.

Future of the devil

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.

The species has already shown remarkably rapid shifts in their life history and genome, while some are able to mount an immune response and recover from the tumours.

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.




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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.The Conversation

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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How Australian wildlife spread and suppress Ross River virus



File 20181230 47292 1isykoi.jpg?ixlib=rb 1.1
Mozzies feed on many native species, including the Nankeen Night Heron.
Janis Otto/flikr

Eloise Stephenson, Griffith University; Cameron Webb, University of Sydney, and Emily Johnston Flies, University of Tasmania

Ross River virus is Australia’s most common mosquito-borne disease. It infects around 4,000 people a year and, despite being named after a river in North Queensland, is found in all states and territories, including Tasmania.

While the disease isn’t fatal, it can cause debilitating joint pain, swelling and fatigue lasting weeks or even months. It can leave sufferers unable to work or look after children, and is estimated to cost the economy A$2.7 to A$5.6 million each year.

There is no treatment or vaccine for Ross River virus; the only way to prevent is to avoid mosquito bites.




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Explainer: what is Ross River virus?


Mosquitoes pick up the disease-causing pathogen by feeding on an infected animal. The typical transmission cycle involves mosquitoes moving the virus between native animals but occasionally, an infected mosquito will bite a person. If this occurs, the mosquito can spread Ross River virus to the person.

Animal hosts

Ross River virus has been found in a range of animals, including rats, dogs, horses, possums, flying foxes, bats and birds. But marsupials – kangaroos and wallabies in particular – are generally better than other animals at amplifying the virus under experimental infection and are therefore thought to be “reservoir hosts”.

The virus circulates in the blood of kangaroos and wallabies for longer than other animals, and at higher concentrations. It’s then much more likely to be picked up by a blood-feeding mosquito.

Kangaroos are a common sight around Australia’s coastal wetlands.
Dr Cameron Webb (NSW Health Pathology), Author provided

Dead-end hosts

When we think of animals and disease we often try to identify which species are good at transmitting the virus to mosquitoes (the reservoir hosts). But more recently, researchers have started to focus on species that get bitten by mosquitoes but don’t transmit the virus.

These species, known as dead-end hosts, may be important for reducing transmission of the virus.

With Ross River virus, research suggests birds that get Ross River virus from a mosquito cannot transmit the virus to another mosquito. If this is true, having an abundance of birds in and around our urban environments may reduce the transmission of Ross River virus to animals, mosquitoes and humans in cities.

Other reservoir hosts?

Even in areas with a high rates of Ross River virus in humans, we don’t always find an abundance of kangaroos and wallabies. So there must be other factors – or animals yet to be identified as reservoirs or dead-end hosts – playing an important role in transmission.

Ross River virus is prevalent in the Pacific Islands, for instance, where there aren’t any kangaroos and wallabies. One study of blood donors in French Polynesia found that 42.4% of people tested had previously been exposed to the virus. The rates are even higher in American Samoa, where 63% of people had been exposed.




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It’s unclear if the virus has recently started circulating in these islands, or if it’s been circulating there longer, and what animals have been acting as hosts.

What about people?

Mosquitoes can transmit some viruses, such as dengue and Zika between people quite easily.

But the chances of a mosquito picking up Ross River virus when biting an infected human is low, though not impossible. The virus circulates in our blood at lower concentrations and for shorter periods of time compared with marsupials.

Stop mozzies biting with insect repellents.
Elizaveta Galitckaia/Shutterstock

If humans are infected with Ross River virus, around 30% will develop symptoms of joint pain and fatigue (and sometimes a rash) three to 11 days after exposure, while some may not experience any symptoms until three weeks after exposure.

To reduce your risk of contracting Ross River virus, take care to cover up when you’re outdoors at sunset and wear repellent when you’re in outdoor environments where mosquitoes and wildlife may be frequently mixing.




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Mozzie repellent clothing might stop some bites but you’ll still need a cream or spray


The Conversation


Eloise Stephenson, PhD Candidate, Griffith University; Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney, and Emily Johnston Flies, Postdoctoral Research Fellow (U.Tasmania), University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How the melting Arctic could spread invasive species far and wide


Grist

After 300 years of fruitless (and sometimes deadly) attempts to find the fabled Northwest Passage, a sea route to connect the Atlantic and Pacific oceans via the Arctic, global warming’s shown up all those hard-man sailors by suddenly making the journey easy. In 2007, higher temperatures had melted enough of that pesky Arctic ice to open the passage up to non-icebreaking vessels for the very first time, and since then the ice has only continued to melt — meaning more and more shippers will be using this efficient trade route.

But what’s good news for shippers is not necessarily good news for the rest of us: More vessels taking the northern course is also projected to spread harmful invasive species.

The Northwest PassageNASAThe Northwest Passage

“What’s happening now is that ships move between oceans by going through the Panama or Suez [canals], but that means ships from higher latitudes have to divert south into…

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Australia: New South Wales – Cane Toad Hunt


March 30 is Toad Busting Day at Brooms Head

The link below is to a media release concerning a joint effort by NSW National Parks and Wildlife Service (NPWS) and the Clarence Valley Conservation in Action Landcare Group (CVCIA) in seeking to stop the spread of Cane Toads at Brooms Head. March 30 is Cane Toad Busting night at Brooms Head.

For more, visit:
http://www.environment.nsw.gov.au/media/OEHmedia12032301.htm

Dharug National Park: Myrtle Rust Brings Closure of the Mill Creek Camping Area


The introduced fungal infection ‘Myrtle Rust’ has spread from gardens and nurseries into the Dharug National Park. The Mill Creek Camping Area has been temporarily closed in consequence of the spread, with National Park and Wildlife Service staff carrying our control measures during the closure in an attempt to prevent any further spread of the disease.

For more information see:

http://www.environment.nsw.gov.au/media/DecMedia10112604.htm