Tasmanian devil reproduction adapts to devastating, contagious cancer
Jeremy Hance, mongabay.com
July 14, 2008
Shortened lifespan leads to earlier mating
Tragic circumstances have led to some astounding behavioral changes in Tasmanian devils. A contagious form of face cancer has engulfed the population, causing the species to be listed as endangered in May. The cancer, which is characterized by large facial tumors, often leads to death by starvation. Casualty rates for infected areas are nearly 90 percent. However, a new study shows that the Tasmanian devils are not taking the disease lying down. The devils, which usually wait until two years for sexual maturity, have begun to breed within their first year of life.
Before the disease, zero to 12.5 percent of Tasmanian devils reproduced before the age of one, depending on the region. That behavior is changing: in Mount William in 2004, 13 percent of Tasmanian devils reproduced before one, two years later it was 83 percent. That is a six-fold increase in two years. “To our knowledge, this is the first known case of infectious disease leading to increased early reproduction in a mammal,” the researchers write. They believe the reproductive changes can be explained, at least partially, by less competition for food, resulting in a faster growth rate for young devils and a quicker route to sexual maturity.
Tasmanian devil, the largest extant carnivorous marsupial, is afflicted with a consistently fatal infectious cancer, facial tumour disease, that is predicted to threaten extinction of wild populations and has caused an abrupt transition from iteroparity towards single breeding. Devils have responded to this disease-induced increased adult mortality with a sixteen-fold increase in precocious sexual maturity. Photograph courtesy of Menna Jones.
The facial cancer has changed the devil’s entire life cycle. Tasmanian devils have a natural lifespan of five to six years, which has been essentially whittled down to one year at best: they die within a few months of contracting the disease. The study found that before the disease 70 percent of females produced more than one litter in their lifetime, now the devils shortened lifespan make multiple litters nearly impossible. Furthermore, some mothers will not survive long enough to rear her young. For the few devils who survive, their lives are essentially sped-up.
The Tasmanian devil’s unexpected reaction to the cancer has the researchers slightly more hopeful for the animal’s long-term survival, but they state that devil’s recovery “remains uncertain”.
The tumors—unique to the Tasmanian devil—are thought to be spread through biting and eating the bodies of dead devils. First reported in 2006 the disease has swept through 60 percent of the endemic population in Tasmania (as of May). Conservationists are working on creating two disease-free devil populations in captivity.
The Tasmanian devil is the world’s largest marsupial carnivore. That title used to be held by the Thylacine, or Tasmanian wolf, which went extinct in 1936 probably due to hunting, the introduction of wild dogs, and disease. The extinction of the Thylacine prompted the government to place the Tasmanian devil under protection in 1941.