April 19, 2012
Lack Of Genetic Diversity Put The Tasmanian Tiger In Danger
While the Tasmanian tiger was being driven to extinction in the early 20th century by territorial interlopers and government bounties, the population of the bizarre marsupial also suffered from an extreme lack of genetic diversity, according to a study published this week in PLoS ONE.
The Tasmanian tiger, also known as the thylacine, was as large as a medium-sized dog that roamed across both Australia and Tasmania and had no natural predators. It was one of only two marsupials, along with the water opossum, to have a pouch in both sexes.The animal was hunted to extinction due to an Australian government bounty and the introduction of dogs and settlements into their habitat, with the last known thylacine dying in a Tasmanian zoo in 1936.
Using DNA sequencing methods, a team of University of Connecticut researchers led by Brandon Menzies and Andrew Pask compared mitochondrial DNA extracted from 14 museum specimens that were over 100 years old. Their findings demonstrated a limited DNA variability between individual thylacine specimens.
The study said that the thylacine specimens were more than 99.5 percent similar over a portion of DNA that is usually highly variable between individuals.
"If we compare this same section of DNA, the Tasmanian tiger only averages one DNA difference between individuals, whereas the dog, for example has about five to six differences between individuals," Menzies said in a statement to LiveScience.
This lack of diversity could be a warning sign for the tiger´s cousin the Tasmanian devil, whose population also suffers from the dangers of low genetic diversity and geographic isolation.
"We found that the thylacine had even less genetic diversity than the Tasmanian devil," Pask said in a press release on the university's website.
"Due to the similarly poor genetic diversity of the animals, this new data suggests that the genetic health of the Tasmanian tiger and devil may have been affected by the geographic isolation of Tasmania from mainland Australia approximately 10-13 thousand years ago,” Menzies, an Honorary Fellow of the University of Melbourne. said in a press release.
Scientists have a fascination with the marsupial because of its unique evolution and the fact that it resembles a dog so much that most archaeologists can't tell the two skeletons apart. According to Pask, the two animals likely had a common ancestor around 160 million years ago.
“The striking convergent evolution of the dog and the thylacine provides an absolutely unique system in which to examine how evolution occurs at the genome level. Our team is currently sequencing the complete thylacine genome to address this question,” he told Jennifer Viegas of Discovery News.
A large genetic variability is essential for the survival of any species. The low level of variability for the thylacine means the species may have difficulty adapting to existential threats and was more susceptible to genetic disorders. Geographic isolation of any species would cause those animals to start inbreeding, therefore severely cutting the genetic variability of its population.
The Tasmanian devil is currently under threat much like the thylacine because of its population´s low genetic variability, according to Pask. A deadly virus that covers the Tasmanian devil's face with tumors is currently driving the animal to extinction because the population does not have the genetic flexibility to adapt to this threat.
Image Caption: A group of Tasmanian tigers in captivity. (Photo courtesy of the Tasmanian Museum and Art Gallery)