Page last updated at 18:13 GMT, Tuesday, 15 July 2008 19:13 UK

Tumours 'alter devils' sex lives'

By Mark Kinver
Science and nature reporter, BBC News

Tasmanian devil (Getty Images)
The mysterious diseases threatens to wipe out the wild population of devils

A disease that threatens to wipe out the wild population of Tasmanian devils has triggered an abrupt change in their breeding habits, a study shows.

Devil facial tumour disease (DFTD) has led to the animals mating at an unusually young age and females having just one litter, say scientists.

The observed changes in the creatures' life cycle could affect the chances of saving the iconic species, they added.

The findings appear in the Proceedings of the National Academy of Sciences.

A team of Australian scientists said they believed it to be the first known case of an infectious disease leading to increased early reproduction in a species of mammal.

The researchers, lead by Dr Menna Jones from the University of Tasmania, analysed data from five sites where devil (Sarcophilus harrisii) populations had been studied before and after the arrival of the disease.

"Devils have shown their capacity to respond to this disease-induced increased adult mortality with a 16-fold increase in the proportion of individuals exhibiting precocious sexual maturity," they reported.

Devil dynamics

At all five sites, DFTD had significantly changed the age structure of the devil populations.

DEVILS IN DETAIL
Tasmanian devils (Getty Images)
Weight: males 11kg; females 7kg
Jaws are more powerful than a tiger's
Opportunistic feeders, not specialised predators
Can smell food up to one kilometre away
Devils have at least 11 distinct vocal calls
Became "devils" in 1803 when sailors reported "unearthly" calls

The team noted that before the arrival of the disease, there was a much higher proportion of adults more than three years old.

They also observed that the disease appeared to influence the number of litters female devils produced.

Before the emergence of DFTD at one of the sites, the Freycinet Peninsula on the east coast of the island, a typical female began breeding aged two, and went on to produce annual litters for three years, before dying in its fifth or sixth year.

"Females now generally have one breeding opportunity and may not survive long enough to rear that litter. Hence they are now largely semelparous [breed only once]."

Symptons of DFTD were first reported in 1996, and by 2007 the disease had spread to more than half of the species' range on Tasmania.

The cause of the disease, which first appears as lumps or lesions around the mouth, is unknown. There are no historical records describing disfigured devils; although cancer was normal in the creatures, it was usually internal.

There are a number of theories explaining the rapid emergence of the disease, including pesticides, population dynamics, and a dormant virus in the animals.

"This consistently fatal disease is an infectious cancer... with tumour cells spread directly between devils biting," the researchers explained.

"Evidence shows that most penetrating biting injuries occur among adult males and females in the mating season."

Populations in areas where the disease has spread have experienced declines of up to 89%, with the tumours primarily affecting adults aged two or more, killing the animal within five months of manifestation.

The team suggested that the disease may be frequency-dependent, meaning that it did not disappear even when the number of hosts fell to very low levels.

As a result, they added, there were concerns that the world's largest carnivorous marsupial could become extinct in the wild within 20-25 years.

"This novel disease could have catastrophic consequences for the Tasmanian devil," they warned.




SEE ALSO
Bites spread fatal 'devil' cancer
02 Feb 06 |  Science/Nature

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