Résumé
Since the emergence of a transmissible cancer, devil facial tumour disease
(DFT1), in the 1980s, wild Tasmanian devil populations have been in
decline. In 2016, a second, independently evolved transmissible cancer
(DFT2) was discovered raising concerns for survival of the host species.
Here, we applied experimental and modelling frameworks to examine
competition dynamics between the two transmissible cancers in vitro. Using
representative cell lines for DFT1 and DFT2, we have found that in
monoculture, DFT2 grows twice as fast as DFT1 but reaches lower maximum
cell densities. Using co-cultures, we demonstrate that DFT2 outcompetes
DFT1: the number of DFT1 cells decreasing over time, never reaching
exponential growth. This phenomenon could not be replicated when cells
were grown separated by a semi-permeable membrane, consistent with
exertion of mechanical stress on DFT1 cells by DFT2. A logistic model and
a Lotka-Volterra competition model were used to interrogate monoculture
and co-culture growth curves respectively, suggesting DFT2 is a better
competitor than DFT1, but also showing that competition outcomes might
depend on the initial number of cells, at least in the laboratory. We
provide theories how the in vitro results could be translated to
observations in the wild and propose that these results may indicate that
although DFT2 is currently in a smaller geographic area than DFT1, it
could have the potential to outcompete DFT1. Further, we provide a
framework for improving the parameterization of epidemiological models
applied to these cancer lineages, which will inform future disease
management.