Life-history change in disease-ravaged Tasmanian devil populations

Abstract

Changes in life history are expected when new sources of extrinsic mortality impact on natural populations. We report a new disease, devil facial tumor disease, causing an abrupt transition from iteroparity toward single breeding in the largest extant carnivorous marsupial, the Tasmanian devil (Sarcophilus harrisii), in which males can weigh as much as 14 kg and females 9 kg. This change in life history is associated with almost complete mortality of individuals from this infectious cancer past their first year of adult life. 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. These patterns are documented in five populations where there are data from before and after disease arrival and subsequent population impacts. To our knowledge, this is the first known case of infectious disease leading to increased early reproduction in a mammal. The persistence of both this disease and the associated life-history changes pose questions about longer-term evolutionary responses and conservation prospects for this iconic species.

Fig. 1.

Tasmanian devil facial tumor disease, a recently emerged infectious cancer, has caused virtual semelparity and a dramatic increase in the proportion of juvenile females breeding.

Fig. 2.

Study sites in relation to current distribution of DFTD. A year in brackets is the year in which the disease was first detected at each site. Stars represent the known westernmost distribution of the disease in 2007.

Fig. 3.

Changes in life-history traits of Tasmanian devils (Sarcophilus harrisii) in response to invasion by DFTD at five sites across eastern Tasmania. Filled bars, before disease; open bars, after disease emergence. Sample sizes are provided in Methods. (a) Proportions of all males and all females 3 years or older before and after the appearance of the disease. (b) Proportion of 1-year-old females breeding in populations before and after arrival of the disease.

Fig. 4.

Change in the proportion of all known adult females producing more than one litter in their lifetime before and after invasion of DFTD at Freycinet in eastern Tasmania.