Tasmanian devil (nothing like the cartoon, am I right?) Image credit: KeresH
You may have heard about how DFTD or devil facial tumor disease (how’s that for a straightforward disease name?) has decimated the Tasmanian devil population in recent years and is putting the species at risk of extinction. A paper published yesterday in the Journal of Animal Ecology provides surprising insights into how this disease is spread.
Scientists had already discovered that DFTD is spread through direct contact–often through fighting (devils can be jealous bastards when it comes to their mates). But in this study, the researchers focused on the relationship between the number of bites a devil had received and the likelihood that that individual would get DFTD. While one might predict that individuals who were bitten multiple times would be more likely to develop the disease since presumably they have been the victims of attacks from multiple other devils who may be DFTD carriers, the researchers actually discovered evidence that supports an alternative hypothesis: the more aggressive animals (the ones giving the bites) were more likely to get struck down by DFTD than were the peaceful little buggers getting the bites. This could be because the more aggressive devils were actually biting the submissive devils’ tumors (eew–bad idea guys).
What’s most interesting about this finding is that it predicts evolutionary pressure on the Tasmanian devil population that could start to favor submissive animals. This is because submissive animals are less likely to contract the disease and die (and thus likely to raise more genetic offspring). And because these animals are submissive they are less likely to pass on the disease. Could this eventually bring an end to DFTD and save the devils? Or, as the authors of the study offer as a possible future direction, could humans step in and remove aggressive ‘super spreaders’ from the population to try to rein in this terrible disease? On the other hand, could this natural or unnatural selection further decrease the genetic diversity that made the devils so susceptible to the disease to begin with?
Interesting aside: A pregnant Tasmanian devil gives birth to 20-30 offspring, but because she only has four nipples in her pouch (devils are marsupials) very few survive. It’s a rough life from the start for these guys.