Breakthrough could save the Tasmanian Devil (10/3/2007)

This information provides a deeper understanding of the nature of the disease and will aid in developing effective disease control strategies

Sydney University researchers have discovered why the Devil Facial Tumour Disease which has wiped out 90 per cent of some native Tasmanian Devil populations has been so devastating.

The Devil Facial Tumour Disease (DFTD) emerged in the devil population 10 years ago and has steadily spread throughout Eastern Tasmania, decimating devil numbers and threatening the existence of the species in the wild.

Published online in the Proceedings of the National Academy of Sciences, a team of researchers led by Dr Katherine Belov from Sydney University's School of Veterinary Science has confirmed that the tumour is a contagious clonal cell line, essentially a tissue graft that originated from a single source and is now passed between individuals.

"The tumour genotypes are genetically identical (clonal) across the disease range. However, tumour genotypes are different to host genes. We propose that this tumour arose in a single individual and has spread through the population by biting during fights for food and mates," said Dr Belov.

"We found that the Devils do not mount an immune response against the tumour," said Dr Belov. "This was due to a loss of genetic diversity in the most important immune gene region of the genome: the Major Histocompatibility Complex (MHC). Matching of MHC genes is the key to successful tissue or organ transplants. In the case of the devil, genetic diversity at MHC genes is so low, and the MHC type of the tumour and host are so alike, that the host does not see the tumour as "non-self," she said.

"What also worries me is that many other wildlife populations are going through similar bottlenecks - koalas on Kangaroo Island, platypuses on King Island. Loss of genetic diversity in these genes just opens the door for emergence and rapid spread of new and old disease," said Dr Belov.

This information provides a deeper understanding of the nature of the disease and will aid in developing effective disease control strategies. "Essentially, there are no natural barriers to the spread of the disease, so affected individuals must be removed from populations to stop disease transmission," said Dr Belov.

The Sydney University team worked in collaboration with researchers at the University of Tasmania, the Tasmanian Department of Primary Industries and Water and the Australian Museum to understand how a tumour can be contagious.

Scientists at the University of Missouri-St. Louis used DNA sequences from feather lice to study how island populations of their host, the Galápagos Hawk might have colonized the Galápagos islands, home to the endangered and declining raptor.

The study focuses on genes from three parasite species restricted to the Galápagos Hawk. The scientists also sequenced the same genes in the hawk to compare levels of genetic variation across these distantly related species. They traced the family tree of each species across the eight-island range, which were each colonized by the hawks and its parasites.

Because the parasite's mitochondrial DNA was more variable than the host's, the parasite's family tree revealed how four of the hawk's eight populations were related to one another -- the stepping-stone manner in which, over time, the hawks colonized first one island, then another and another, carrying their lice as they went. These relationships were previously obscured due to the hawk's low genetic variation.

The scientists also suggested that their results demonstrate how symbionts of larger and more charismatic species, like hawk lice, can tell scientists a great deal about the history of life.

"The parasites are evolutionary heirlooms that were brought to the islands during the colonization of the hawk, but have continued to evolve along with their hawk hosts," said Noah Whiteman, who conducted this study as part of his dissertation at UMSL and is now a postdoctoral fellow at Harvard University in Cambridge, Mass. "We had a great deal of trouble understanding how the island populations of the hawk were related to one another because of low genetic variation in the hawk's DNA. The rapidly evolving lice that live their entire lives on these birds have helped illuminate their host's evolutionary history."

The Galápagos National Park and Charles Darwin Research Station are working to save Darwin's archipelago from the fate of similar island systems. As part of this effort Patricia Parker, the E. Desmond Lee Professor of Zoological Studies at UMSL, forged a close working relationship with the two organizations to better understand the threats facing the island's endangered birds. Parker initiated this collaboration by examining the basic biology and conservation genetics of the Galápagos Hawk and a few other species that she and her collaborators had studied previously.

A permanent resident found only in the Galápagos island, the Galápagos hawk has intrigued biologists for decades because of its unusual mating system, (cooperative polyandry) within some, but not all, island populations.

In this type of mating system, a single female hawk and up to eight male hawks, who are not close relatives, live in a stable territorial group and cooperate to rear chicks. This type of mating system is rare among birds, and understanding the sequence in which islands were colonized may reveal the point at which it first occurred, and thereby help us understand the evolution of cooperative behavior.

This research was recently published online in the journal Molecular Ecology.

Note: This story has been adapted from a news release issued by the University of Sydney

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