Tasmanian Devils Flashcards
Devil Facial Tumour Disease
- 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
Severity of the disease
- Tumours grow rapidly without any local immune response
- Fatal within 6 months of first lesions (due to starvation, secondary infections or metastases
DFTD Histology
- All tumours appear microscopically similar
- Originate in the dermis or oral submucosal CT
- Frequently metastasise (65% of cases)
DFTD Pathology
- 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
DFTD Transmission
- “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
Popular hypothesis for why the tumour is not attacked by immune system
No rejection due to lack of genetic diversity in devils
Low genetic diversity in Tassie Devils
- Low diversity across genome, including Major Histocompatability Complex
- MHC a key region involved in immune response - self/non-self recognition
Low genetic diversity in Cheetahs
- Genetic bottleneck –> very low genetic diversity
- Skin grafts between unrelated cheetahs are not rejected
- Very vulnerable to infectious pathogens
Canine Transmissible Venereal Tumour (CTVT)
- 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
Evidence FOR the low genetic diversity hypothesis
- Very low genetic diversity in devils, including MHC
- Cheetahs do not reject skin grafts of unrelated individuals
- DFTD tumours not rejected
Evidence AGAINST the low genetic diversity hypothesis
- 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
Conservation management of devils
- Mainland zoos
- Free ranging populations - offshore islands
- Captive breeding program to maximise MHC diversity
- -> first attempt t increase immunological fitness in captive population
Additional Issues
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
Semelparity
Reproductive strategy in which species is characterised by s single reproductive episode before death
e.g. Pacific salmon