Tasmanian Devils

Question 1

Devil Facial Tumour Disease

Answer 1

• Emerged in NE TAS in 1996
• Currently recorded over 59% of TAS
• Local declines of up to 90%
• Restricted to devils
• Devils likely to be extinct in 5-25 years

Question 2

Severity of the disease

Answer 2

• Tumours grow rapidly without any local immune response

- Fatal within 6 months of first lesions (due to starvation, secondary infections or metastases

Question 3

DFTD Histology

Answer 3

• All tumours appear microscopically similar
• Originate in the dermis or oral submucosal CT
• Frequently metastasise (65% of cases)

Question 4

DFTD Pathology

Answer 4

• Clonally derived from neural crest lineage cells at least 15 years ago, probably Schwann cells
• Cell implantation during biting
• DFTD cells from diff devils are identical at microsatellite markers and MHC genes
• 4 closely related by karyotypically distinct strains

Question 5

DFTD Transmission

Answer 5

• “Infectious” - direct contact required (cell implantation during biting)
• Incubation period not known
• Nearly all between 2 & 3 yr - fighting at sexual maturity
• No sex predilection

Question 6

Popular hypothesis for why the tumour is not attacked by immune system

Answer 6

No rejection due to lack of genetic diversity in devils

Question 7

Low genetic diversity in Tassie Devils

Answer 7

• Low diversity across genome, including Major Histocompatability Complex
• MHC a key region involved in immune response - self/non-self recognition

Question 8

Low genetic diversity in Cheetahs

Answer 8

• Genetic bottleneck –> very low genetic diversity
• Skin grafts between unrelated cheetahs are not rejected
• Very vulnerable to infectious pathogens

Question 9

Canine Transmissible Venereal Tumour (CTVT)

Answer 9

• Thought to have developed in inbred wolves lacking MHC diversity
• Spread onto mucous membranes by direct contact or implanted subcutaneously in bite wounds
• Not prevalent in wolf populations –> does not seem to be a relationship between low genetic diversity and prevalence of CTVT

Question 10

Evidence FOR the low genetic diversity hypothesis

Answer 10

• Very low genetic diversity in devils, including MHC
• Cheetahs do not reject skin grafts of unrelated individuals
• DFTD tumours not rejected

Question 11

Evidence AGAINST the low genetic diversity hypothesis

Answer 11

• CTVT not associated with low genetic diversity in dogs
• CTVT not a major problem in inbred pops of wolves
• Devils rejected skin grafts from MHC-similar devils

Question 12

Conservation management of devils

Answer 12

• Mainland zoos
• Free ranging populations - offshore islands
• Captive breeding program to maximise MHC diversity
• -> first attempt t increase immunological fitness in captive population

Question 13

Additional Issues

Answer 13

Devils changing behaviour

• Very young age- structure populations in which females are reduced to single breeding (previously 3)
• Compensation - 3 fold increase in females breeding in first year
• Lead to semelparity in devils?

High phenotypic plasticity and evolutionary potential of DFTD
- allows to change its genetics and possibly behaviour

Question 14

Semelparity

Answer 14

Reproductive strategy in which species is characterised by s single reproductive episode before death

e.g. Pacific salmon