Demography, disease and the devil: life-history changes in a disease-affected population of Tasmanian devils (Sarcophilus harrisii)

Examining the demographic responses of populations to disease epidemics and the nature of compensatory responses to perturbation from epidemics is critical to our understanding of the processes affecting population dynamics and our ability to conserve threatened species. Such knowledge is currently available for few systems. We examined changes to the demography and life-history traits of a population of Tasmanian devils (Sarcophilus harrisii) following the arrival of a debilitating infectious disease, devil facial tumour disease (DFTD), and investigated the population's ability to compensate for the severe population perturbation caused by this epizootic. There was a significant change to the age structure following the arrival of DFTD to the Freycinet Peninsula. This shift to a younger population was caused by the loss of older individuals from the population as a direct consequence of DFTD-driven declines in adult survival rates. Offspring sex ratios of disease mothers were more female biased than those of healthy mothers, indicating that devils may facultatively adjust offspring sex ratios in response to disease-induced changes in maternal condition. We detected evidence of reproductive compensation in response to disease impacts via a reduction in the age of sexual maturity of females (an increase in precocial breeding) over time. The strength of this compensatory response appeared to be limited by factors that constrain the ability of individuals to reach a critical size for sexual maturity in their first year, because of the time limit dictated by the annual breeding season. The ongoing devastating impacts of this disease for adult survival and the apparent reliance of precocial breeding on rapid early growth provide the opportunity for evolution to favour of this new life-history pattern, highlighting the potential for novel infectious diseases to be strong selective forces on life-history evolution.