Culling is Influencing Evolution of Deadly Tasmanian Devil Facial Cancer

A large-scale culling of Tasmanian devils infected with a kind of face cancer has presented researchers an opportunity to study how human selection alters, and in some cases enhances, the evolution of cancerous cells.

Tasmanian devil facial tumor disease (DFTD) has ravaged populations of the marsupial, particularly in the eastern half of the Australian state, with some estimations that it has resulted in a 90 percent population decline since the first "official case" appeared in 1996.

The disease begins manifesting as lesions and lumps around the mouth that go on to develop into cancerous tumors that spread across the face and the animal's body. The cancer has passed through more than 100,000 hosts, evolving and mutating along the way.

A 2012 report on DFTD said that because it was a stable, transmissible cancer, it "provides unique insights into cancer development, progression, and immune evasion and is likely to help increase our understanding of human cancer."

DFTD reproduces asexually, and across the last 16 years the disease has been exposed to negative effects as Tasmanian devils are being culled. Between 2006 and 2010, nearly one-third of the Tasmanian devil population has been removed from one site, the Forestier Peninsula.

The latest research is focused on the disease's ability to "survive and counteract the effect of deleterious mutation, genomic instability as well as being able to infect more than 100,000 devils."

"In this study, we focus on the evolutionary response of DFTD to a disease suppression trial," said Beata Ujvari, from the University of Sydney. "Tumors collected from devils subjected to the removal program showed accelerated temporal evolution of tetraploidy compared with tumors from other populations where no increase of tetraploid tumors were observed."

Tetraploidy refers to a cell containing four homologous sets of chromosomes.

Because the human-induced culling may provide a unique opportunity to study the effects of human-selection on DFTD, the research team spent four years collecting tissue samples across 11 sites in Tasmania.

"Our study clearly demonstrates that DFTD tumors are able to rapidly respond to increased selection and adapt to a selective regime," Ujvari said. "The results suggest that ploidization may offer yet another pathway to which DFTD is able to adapt to the ever-changing evolutionary landscape sculptured by the devils' immune system. Our study is the first to show that anthropogenic selection may enhance cancer evolution in the wild, and it therefore cautions about what measures we employ to try to halt the spread of this devastating disease."

The study appears in the journal Evolutionary Applications.