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Figure 1: A Tasmanian devil

Tasmanian devils are dog-sized carnivorous marsupials native to Tasmania, south of Australia which are affected by a transmissible type of cancer known as Devil Face Tumor (DFT). There are two types of DFT, the first identified in the 1990s and the second in 2016. Whereas some cancers are known to be caused by virus, it is believed that DFT is transmitted directly when devils bite each other in fights. This is only one of three types of transmissible cancer identified in nature. As this is a direct transfer of cancer cells from an external source, the host immune system should destroy the ‘foreign’ cells, but they grow regardless and this process is not fully understood.

 

Over the past 20 years 80% of the wild population of devils has been lost. The local government has initiated a scheme to help save the devils by studying the disease with the aim of developing a vaccine or cure. It’s not all bad, however. Researchers from Washington State University noticed that models of animal decline predicted that the devils should be extinct, but they aren’t; and so they set out to identify why this may be. They sequenced the genomes of 294 animals across three areas of Tasmania (Figure 2), specifically trying to identify any large genomic changes between devils from areas of pre and post DFT exposure.

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Figure 2: Spread of DFT shown by red boundary lines and corresponding dates. Areas of sample collection marked by red dots.

The researchers found changes in a region of the devil genome that modulates the immune system and is the same region in humans that is also linked to cancer progression. They suggest that there is an evolutionary pressure on this part of the devil’s genome and that it is changing in response to DFT. Typically evolution works by positively selecting for mutations in an organisms’ genome in response to an environmental pressure. In devils it appears a specific region of its genome already contains genes that are helping some individuals to resist the cancer. This is interesting because it demonstrates evolution without the need for mutations to occur.

These findings are interesting for a number of reasons. Firstly, it’s an example of a population that is experiencing an epidemic and responding genetically in only a few generations, which is very fast and has not been identified before. Secondly, there may be implications in the way we treat cancer in humans as the genomic area in devils that is evolving is similar to the one in humans. Finally, identifying an example of ‘rapid’ adaption to a population threat, without the need for new genetic mutations, means that other organisms may be similarly able to adapt to changes such as climate change.

Follow this link to the research paper for more…

Written by Jake Howden