A diseased and emaciated Tasmanian devil (Sarcophilus harrisii) was found last week on a golf course in the town of Zeehan on Tasmania's west coast. Like many of its kind, the animal suffered from the deadly, transmittable cancer known as Devil Facial Tumor Disease (DFTD), which has wiped out at least 70 percent and possibly as many as 90 percent of the world's Tasmanian devils since it was first observed in 1996. This is the first time that DFTD has been seen in western Tasmania, a serious blow to scientists' hopes to maintain disease-free populations of this endangered species.
DFTD manifests as tumors that destroy an infected animal's mouth, making it impossible for a devil to eat. Starvation and death follow within three to six months. Transmission is easy, because devils frequently bite one another on the mouth during mating or while fighting over carcasses.
So far, scientists have not been able to come up with a vaccine or treatment for DFTD, but that's not the only path researchers are taking as they try to save the Tasmanian devil. Justine O'Brien, scientific director at SeaWorld & Busch Gardens Reproductive Research Center in San Diego, Calif., and reproductive biologist Tamara Keeley of the Taronga Conservation Society Australia (TCSA) have been leading the efforts to understand Tasmanian devil reproductive biology to gain a better grasp of male sperm biology and female estrus cycles. They have also created a genome bank or "frozen zoo" located at the society's Taronga Western Plains Zoo in Dubbo, New South Wales, to preserve Tasmanian devil genetic material as the wild population and genetic diversity continue to decline.
The most recent research in this area—supervised by O'Brien and Paul McGreevy, a professor of veterinary science at the University of Sydney—has been conducted by Keeley as her doctoral research. The first of several papers detailing their studies was published in the September 2011 issue of Theriogenology. Four additional articles are pending publication in that journal, along with Reproduction Fertility and Development and General and Comparative Endocrinology.
"In view of the dire forecast for wild devils, where extinction of the species is estimated to occur within 25 to 30 years, a functional genome bank comprised of genetic material from both wild and captive animals is of particular importance," Keeley says. "A genome bank is especially beneficial for species such as the devil which have a short reproductive lifespan—three to four years—since genetically valuable individuals may die before they have reproduced or before they have reached their full reproductive potential." Earlier research has shown that Tasmanian devils do not have broad genetic diversity, so preserving as many genetic lines as possible is important.
One aspect of the latest research has been to come up with a cryodiluent—a solution with components critical for success in freezing sperm—tailored specifically for the reproductive cells of male Tasmanian devils. One of the challenges in creating this solution has been the very low sperm count produced by the male devils (testicular sperm in the thousands compared with millions or billions in other wildlife). O'Brien says her team also discovered that "devil sperm membranes are highly susceptible to damage occurring during the freezing and thawing process." After four years of systematic improvements, their cryopreservation technique now has up to a 48 percent sperm survival rate after thawing.
Luckily, DFTD itself does not appear to have much of an effect on Tasmanian devil sperm. "Our examination of devils with varying severity of DFTD clinical signs suggests that the effect of DFTD on the male reproductive tract and sperm quality is limited," Keeley says. "Even devils with large tumors and metastases continued to produce motile sperm of similar quality to disease-free animals and to those with early-stage tumors." This means they don't need to concentrate on collecting genetic material from disease-free animals and can preserve a wider range of genetic samples. (So far, all of their egg and sperm samples have come from diseased devils that were so sick they needed to be euthanized.)
The next challenge the researchers hope to tackle involves artificial insemination. "The success of artificial insemination procedures remains dependent on the quality of sperm and an extensive knowledge of the female estrous cycle, especially the timing of ovulation in relation to temporal changes in hormone concentrations," Keeley says. "Our recent studies have helped to characterize hormone profiles of devil cycles, but the timing of ovulation is still poorly understood and further research is needed to enable sperm placement in the female at the appropriate time. As female devils have a long period of estrus and are believed to store sperm in their reproductive tract for several days, it is possible that they have a considerable window of opportunity in which artificial insemination can be performed, but this remains to be confirmed."
Once artificial insemination or in vitro fertilization techniques are developed, "genome bank samples may be selectively infused into captive or wild populations to maintain or increase biodiversity," she says.
The research was made possible through collaborative efforts the University of Sydney; Tasmania's Department of Primary Industries, Parks, Water and the Environment; TCSA; and SeaWorld & Busch Gardens. It was funded by the Morris Animal Foundation and the SeaWorld & Busch Gardens Conservation Fund.
Photo by David Boon via Flickr. Used under Creative Commons license