The Tasmanian devil is more social than we think, making it difficult to control the spread of the disease that is decimating its numbers, say researchers.Ecologist Rodrigo Hamede of the University of Tasmania and colleagues report their work today in the journal Ecology Letters.
Understanding the social networks of Tasmanian devils will help us understand the likely spread of facial tumour disease, which is passed on through animals biting one another, says Hamede, who did the research for his PhD with his supervisor Dr Hamish McCallum.
He says Tasmanian devils have traditionally been thought of as solitary animals, which have relatively small social networks.
But there has not been any direct evidence about their social life. Investigating the social behaviour of devils, which are nocturnal, forest-dwelling and mate underground is tricky, says Hamede.
Unlike humans, who can be quarantined and interviewed, you can't ask a devil who they've had contact with.
Six degrees of separation
Hamede used radio collars to study how animals were interacting with each other in the wild, how frequently they were in contact, and for how long.
The collars, placed around the animals' necks, were able to record when another collar was within 30 centimetres of it.
This is the approximate distance between devils' necks when they are biting each other - something they do when mating or fighting over food, says Hamede.
Hamede gathered information from a group of sexually mature animals living in a Tasmanian national park, between February and July 2006.
The data showed that devils are quite social animals, and are all part of a single giant network.
"All devils are connected in one way or another to an individual that is also connected to the network," he says.
"This is what six degrees of separation is all about."
Being part of a large social network means that if one individual is infected with disease, the whole population can potentially be infected, says Hamede, who presented his research to an international ecology conference in Brisbane this week.
Dangerous sex
Hamede believes the pattern of devil contact gives the tumour the greatest chance of wiping the species out.
He found that most biting happened between males and females in the mating season.
Hamede says this means the tumour is likely to persist in the population in the same way as a sexually transmitted infection does, and is more likely to drive the species to extinction.
He says this explains the high prevalence of the disease despite a massive decline in the number of individual devils.
The spread of the disease through mating presents a dilemma for devils: They need to breed to keep up their numbers, but if they breed they will most likely become infected by a deadly disease.
In response to this, Hamede says devils are reaching sexual maturity early in response to the disease.
They have to mate earlier so they can reproduce before the disease hits them, he says.
'Super spreaders'
Hamede also checked to see which animals in the network had the highest number of social contacts and were therefore most likely to infect others.
Studies of human infectious diseases show 20% of individuals are responsible for 80% of infections.
The plan was to characterise the devil 'super spreaders' so these could be targeted for removal.
But, to his surprise, he could find no particular pattern in terms of sex or age for the devil super spreaders.
Still, Hamede hopes data gathered on how different sexes interact at different times of the year can be used to help improve disease models and management.
"So there are management implications … but there's no magic solution."
By: Anna Salleh , science journalist at ABC Science.
A news from abc.net.au , 19 August 2009
But there has not been any direct evidence about their social life. Investigating the social behaviour of devils, which are nocturnal, forest-dwelling and mate underground is tricky, says Hamede.
Unlike humans, who can be quarantined and interviewed, you can't ask a devil who they've had contact with.
Six degrees of separation
Hamede used radio collars to study how animals were interacting with each other in the wild, how frequently they were in contact, and for how long.
The collars, placed around the animals' necks, were able to record when another collar was within 30 centimetres of it.
This is the approximate distance between devils' necks when they are biting each other - something they do when mating or fighting over food, says Hamede.
Hamede gathered information from a group of sexually mature animals living in a Tasmanian national park, between February and July 2006.
The data showed that devils are quite social animals, and are all part of a single giant network.
"All devils are connected in one way or another to an individual that is also connected to the network," he says.
"This is what six degrees of separation is all about."
Being part of a large social network means that if one individual is infected with disease, the whole population can potentially be infected, says Hamede, who presented his research to an international ecology conference in Brisbane this week.
Dangerous sex
Hamede believes the pattern of devil contact gives the tumour the greatest chance of wiping the species out.
He found that most biting happened between males and females in the mating season.
Hamede says this means the tumour is likely to persist in the population in the same way as a sexually transmitted infection does, and is more likely to drive the species to extinction.
He says this explains the high prevalence of the disease despite a massive decline in the number of individual devils.
The spread of the disease through mating presents a dilemma for devils: They need to breed to keep up their numbers, but if they breed they will most likely become infected by a deadly disease.
In response to this, Hamede says devils are reaching sexual maturity early in response to the disease.
They have to mate earlier so they can reproduce before the disease hits them, he says.
'Super spreaders'
Hamede also checked to see which animals in the network had the highest number of social contacts and were therefore most likely to infect others.
Studies of human infectious diseases show 20% of individuals are responsible for 80% of infections.
The plan was to characterise the devil 'super spreaders' so these could be targeted for removal.
But, to his surprise, he could find no particular pattern in terms of sex or age for the devil super spreaders.
Still, Hamede hopes data gathered on how different sexes interact at different times of the year can be used to help improve disease models and management.
"So there are management implications … but there's no magic solution."
By: Anna Salleh , science journalist at ABC Science.
A news from abc.net.au , 19 August 2009
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