Some lineages of the infectious facial tumours that are devastating populations of the Tasmanian devil (Sarcophilus harrisii) can result in worse outcomes for animals.

Rodrigo Hamede at the University of Tasmania in Hobart, Australia, and his colleagues have monitored the outbreak of devil facial tumour disease at a site in northwestern Tasmania since 2006. Animals at this site initially had higher survival rates than other infected populations and a lower proportion of infected animals overall. Their tumours were found to have four sets of chromosomes.

Around 2011–12, this 'tetraploid' tumour lineage was replaced by a 'diploid' type with two sets of chromosomes, which the authors found was associated with an increased disease prevalence in adults (from around 25% of animals infected to 80%) and a significant population decline. Tumour variance can shape both epidemic patterns and outcomes, the authors warn.

Proc. R. Soc. B 282, 20151468 (2015)