Triin Tekko, doctoral student of the Department of Physiology at the Institute of Biomedicine and Translational Medicine of the University of Tartu, writes about research carried out in Tasmania in the blog Zooloogid 2.0: (in Estonian)
Up to now, my closest zoological contacts have been with mice, whom I use in my daily research at the Department of Physiology at the Institute of Biomedicine and Translational Medicine of the University of Tartu, but for a long time, one of my dreams has been to study Tasmanian devils. The Tasmanian devils (Sarcophilus harrisii) can only be found in Tasmania, and after Tasmanian tiger became extinct, they are the largest carnivorous marsupials in the world. Unfortunately, their population may be under the threat of extinction as well due to a disease called Devil Facial Tumour Disease (DFTD) – a contagious form of cancer rare in the animal kingdom. DFTD is transmitted through bites, which allow cancer cells to be transmitted from the body of an infected devil in the body of a healthy devil and start to proliferate, as is characteristic for cancer cells, causing tumours to develop in the facial area. The survival time of infected devils is generally up to 6 months and they die as a result of organ failure or starvation.
There are several reasons, why the contagious form of cancer affects namely Tasmanian devils. Over time, their population has overcome numerous genetic bottlenecks, i.e. periods where only a small portion of genetic diversity is passed on to future generations. The reason for such bottlenecks is thought to be sudden cooling and drying of climate, and mass-hunting of the animal after the arrival of white settlers. DFTD itself has created another bottleneck, having reduced the population of Tasmanian devils by more than 90% in some regions. The result of genetic bottlenecks is the insufficient genetic diversity in the genes responsible for the devils’ immune system. To escape the immune system, tumour cells reduce the expression of major histocompatibility complex I (MHCI) proteins on its own cells. MHCI proteins can be found on the surface of almost all body cells, helping the immune system to recognize its own body cells and distinguish them from foreign cells. In case of DFTD, cytotoxic T lymphocytes fail to recognize cancer cells, and therefore no immune response is initiated.
Another reason, why the contagious cancer spreads namely in Tasmanian devils, is their highly aggressive behaviour. Abundant biting is characteristic of contacts between these animals, while mating rituals are especially violent. During mating, males are accustomed to dragging females in their burrows and keeping them captive there on the backdrop of screams and biting, which is probably accountable for their devilish nickname. Most infections occur namely in the mating season that spans between March and May.
DFTD was first discovered in 1996 in the North-Eastern part of Tasmania, and after that the disease has spread almost across the whole island:
Lately, it has been discovered that some genomic regions related to fighting tumours have rapidly evolutionized during 4–6 generations under strong pressure of selection, and immune response against tumour cells has still been initiated in single Tasmanian devils. At the same time, the race between immune system and cancer has led to the continuous mutation of DFTD. A few years ago, another form of contagious facial cancer was discovered in Tasmanian devil, named DFT2. The first cancer form DFT1 originates in a female animal who lived more than 20 years ago, and DFT2, similar in symptoms, was found in a male devil who was alive only recently.
Numerous different research groups from several universities are studying DFTD from different angles. They are trying to develop a vaccine, form healthy isolated populations, and encourage genetically more diverse specimens to mate. Whether and how much such efforts will improve the fate of Tasmanian devils is to be seen in the future.
I volunteered in the research group of Rodrigo Hamede, a researcher with the University of Tasmania, helping his student Samantha James to trap Tasmanian devils. Trapping took place in February in a research site in West Pencil Pine, located in the Cradle Mountain National Park in the Western part of Tasmania, where the devils have been monitored for ten years already. Forty bait traps are set for ten nights in approximately 25 km2 and checked every morning. The caught Tasmanian devils are chipped and measured, and after taking various samples, the animals are released in the same place. Blood, tumour, hair, whisker and stool samples were sent in different laboratories to be studied by scientists. Samantha’s research project entails describing the distribution of DFT1 and DFT2 in regions that have not yet been thoroughly studied.
Everyone can contribute in DFTD research in different ways. Through the Save the Tasmanian Devil project, donations are collected and volunteers sought for field work.
My only word of warning is that the creatures are addictively cute, and didn’t already the olden folk say that if you offer the Devil a finger, it will take the whole arm – I, for example, have signed up for another field-work session in May.
Photos: Triin Tekko’s private collection and http://animals.sandiegozoo.org/animals/tasmanian-devil
The translation of this article was funded by the European Regional Development Fund through Estonian Research Council.