Life history and disease in Tasmanian devils

The keywords to the article include, “carnivorous marsupial” and “precocious breeding.” What better teaser could you possibly hope for?

Tasmanian devils are dying because of a transmissible cell line infection, or “cancer,” decimating their population. In fact, in some places it’s killing 9 out of 10, which is way beyond decimation.

The new paper by Menna Jones and colleagues claims that the population is evolving toward a radical life history solution to the problem: Tasmanian devils are starting to mate and have large litters after a single year, before they have a chance to succumb to the disease:

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.

It’s a simple response: young breeders used to have lower fitness, because of competition from older adults. Now, the high mortality after the first year has made it a losing strategy to wait to reproduce. When the early breeders are the only ones having many offspring, the population will evolve quickly to early breeding.

References:

Jones ME, Cockburn A, Hamede R, Hawkins C, Hesterman H, Lachish S, Mann D, McCallum H, Pemberton D. 2008. Life-history change in disease-ravaged Tasmanian devil populations. Proc Nat Acad Sci USA (in press) doi:10.1073/pnas.0711236105