Current Biology Vol 15 No 21R858

Having survived the arrival of thedingo and European settlement,the Tasmanian devil is now listedas ‘vulnerable’ and under threatfrom a mysterious infectiouscancer that is spreading rapidlyand appears to kill all infectedanimals.

Locals are quite accustomed tothe eerie shrieking, growlingnoises of the Tasmanian devil, butwhen they started noticing uglyulcerated lesions on the faces ofthese carnivorous marsupialsthey became concerned. And withgood reason: this is themanifestation of what is nowreferred to as ‘devil facial tumordisease’ (DFTD) which has led toa drastic decrease in Tasmaniandevils over the past ten years.Devils were once widespread onthe Australian mainland but are

now restricted to the island stateof Tasmania. It is thought that theintroduction of the dingo, not, foronce, European settlement, led totheir extinction on the mainlandaround 400–600 years ago. Thisnew threat, first reported in 1996in the northeast of Tasmania, hasnow spread over at least 65 percent of the island, probably more,and has already reduced devilnumbers by 20 per cent, thoughsome reports put the numbercloser to 50 per cent.

The disease is a malignantcancer that appears to beneuroendocrine in origin. Itbegins on the face and mouthand eventually erodes bone andsoft tissue, making it increasinglydifficult for affected animals tofeed. It can also spread to theliver, kidney and other organs and

kills its victims within six monthsof onset. In high-density areasDFTD kills up to 80 per cent ofanimals, though in lower densityareas it is less devastating.

The apparently infectiousnature of the disease suggestedthat it was viral, but transmissionelectron microscopic analysis oftumor samples has yet to revealany sign of viral particles.Surprisingly, all tumors seem tobe cytogenetically identical,regardless of the geographicalregion from which they werecollected or the sex of the hostanimal. This has led to thehypothesis that it spreads by thetransmission of cells frominfected to uninfected animals asa result of biting. As implausibleas that may seem, there is aprecedent: canine venerealsarcoma is spread by the transferof cells during coitus.

This is not the first time thedevil has been bedevilled:population crashes are recorded

Features

Devilish declineAn iconic Australian marsupial is under threat from a disease, which isproving a major challenge for conservationists wishing to ensure thesurvival of the species, the Tasmanian devil. Hannah Robertson reportson their efforts.

Under pressure: The Tasmanian devil is under threat from a disease that has led to a drastic decrease in numbers over the past tenyears prompting new conservation efforts. (Picture: Photolibrary.com.)

in the mid-1800s and around theturn of the last century. Althoughin both previous cases devilnumbers rapidly recovered, this isthe first population crash sincethe introduction of foxes toTasmania, and the concern is thatthe foxes will occupy the devil’sniche and make a recovery muchharder. This, of course, hasserious implications for othernative species.

Tasmanian devils are mainlyscavengers and they clean up theenvironment by ridding it ofrotting carcasses. This also hasthe happy effect of limiting thefood supply for foxes, whosenumbers are lower in devil-populated areas than elsewhere.The worry is that, if devil numbersdrop significantly, fox numberswill rise leaving other marsupialsvulnerable to predation andmaking it difficult for Tasmaniandevils to make a comeback.

The rapid spread of DFTD, thehigh mortality in affectedpopulations, and a lack of geneticdiversity among devils meanthere is some urgency to developstrategies to save Tasmaniandevils from possible extinction.The management strategy hasthree main focuses: to define thedisease and develop a diagnostictest; to monitor wild populationsto track the spread and impact ofthe disease; and to try to stop thespread of the disease, andestablish disease-freepopulations. This is not as easyas one might think.

There is no way to identifyinfected animals before theyshow symptoms; researchersdon’t even know what the bloodprofile of a healthy devil is, muchless what to look for that mightbe specific for DFTD.

And, although it appears to beinfectious, the truth is themechanism of transmission is stillunknown. No other species showsigns of the disease, not even thedevil’s closest relative the Easternquoll, but they could still bereservoirs for the infectiousagent. Interestingly, only animalsover two years old normally getthe disease (a few one-year-oldanimals have been affected) andthis has been exploited toestablish two ‘insurance

populations’. Young leave theirmothers and disperse inFebruary/March of each year andup to 60 per cent of them will notsurvive. This year, two ‘insurancepopulations’ were establishedfrom young collected during thisdispersal. Because of the lowgenetic diversity, only twenty fiveanimals were required torepresent the population, andthese were collected from the twogenetically distinct populationson the east and west coasts ofTasmania. They are housed awayfrom wild devil populations, undertight quarantine and closeobservation, and when they reachtwo years of age if they are stilldisease free they will probably bemoved to the mainland to be usedin captive breeding programs.This, too, is not straightforward.Devils don’t breed well incaptivity, have small litters, andtypically only breed four times intheir six year lifespan.

In conjunction with this, trialsare underway to determinewhether culling affected animalsis effective in preventing thespread of DFTD and a majoreffort is being made to define anddiagnose the disease prior to theonset of symptoms. The recentdiscovery that the latency periodcan be as long as ten monthsmakes this particularly important.It is hoped that, in combination,these strategies will save theTasmanian devil.

Known to aboriginals astardiba, devils give theappearance of scrappy,aggressive, threatening littleanimals, making loud shriekingnoises and gaping to show offtheir teeth, but this is mostly bluffand they pose no risk to humans.An icon of Tasmania, the symbolof the Tasmanian National Parksand Wildlife Service, and integralto the ecology of Tasmania, theseendearingly unattractivemarsupials will be sorely missedif DFTD is not quickly broughtunder control.

An Australian appreciation ofits unique marsupial fauna haskicked in with the devil and manyhope this will be a success.

Hannah Robertson is at the Universityof Melbourne.

With US neo-conservativesselectively choosing species theybelieve mark the hand of acreator in design, manyresearchers are delighting inspecies that are far more bizarre,and perfect champions of thesheer power of Darwin’s naturalselection.

Such researchers will welcomea new book, Extreme Nature byMark Carwardine, which highlightsthe limits of the bizarre.

Divided into four sections —extreme growth, extremeabilities, extreme movement andextreme families — the bookaims to catalogue some of theplanet’s most extraordinaryorganisms.

One of the largest and least-known organisms to feature isthe colossal squid, a mysteriousand even less well-known, butlarger, relative of the giant squid.There have only ever been ahandful of specimens of thesquid recovered: mostly from thestomachs of sperm whales.

The squid has been knownsince 1925 from these earlyremains but no one has paid verymuch attention to it. But arecently caught specimen fromthe Ross Sea in Antarctica hasrekindled interest.

Carwardine believes theorganism has the largest knowneyes, recorded at 60 cm indiameter. The species is aformidable predator that hunts inthe depths of the coldest oceans,but as so few specimens havebeen examined so far, exactlyhow it uses its large protrudingeyes is not known.

But it can light up itssurroundings by glowing,suggesting that it is able to focusits eyes on fast-moving prey,such as the large Patagoniantoothfish, which the recent intactspecimen, an immature female,was eating when caught by

Magazine R859

Squids in

A new book highlights theextreme lengths to which someanimals have evolved under thepressure of natural selection.Nigel Williams reports.