Tasmanian devils, native to the island of Tasmania, are the world's largest carnivorous marsupial. These nocturnal animals are voracious eaters and have gained a reputation for their aggressive nature. This has been the downfall of this species: devil facial tumor disease (DFTD) is a transmissible cancer that is spread between devils via biting. Consequently, DFTD has caused disastrous local population losses of over .
DFTD tumors develop around the head and face and are mostly fatal within a year. As the tumor grows, the solitary animal has difficulty catching prey and feeding. How DFTD affects devil social interactions over the course of the disease, however, has never been studied before. A research team has now tracked affected individuals over time to learn more about the social aspects of DFTD.
Over a six-month period, including the mating and non-mating season, the team monitored the social interactions of 22 Tasmanian devils and their disease progression. The group fitted 12 female and 10 male devils with tracking collars, which emitted different signals when in close proximity to other collared devils. The animals were recaptured each month to monitor their disease status and identify any newly infected individuals.
At the beginning of the study, three devils presented with DFTD tumors, and over the course of the six months, seven more developed symptoms. The researchers discovered that Tasmanian devils afflicted with the transmissible cancer were less likely to interact with others, particularly during the mating season. As their tumor sizes and infection loads increased, their probability of interaction dramatically declined.
This antisocial behavior may be a mechanism adopted by diseased devils to promote the survival of their species — an act of altruism that could prevent their extinction.