Future In Our Hands

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ethanol to preserve DNA

 

Improvements on DNA storage for BAC library

construction

Improvements in the storage of vector preparations and

HMW DNA samples could save time and costs. During storage,

HMW DNA should be prevented from both shearing

and degrading. Freezing HMW DNA without a protectant

results in DNA shearing and should be avoided. We found

that size-selected HMW genomic DNA fragments in agarose

slices could be stored in 70% ethanol at –20°C for long periods

of time without change of qualities. DNA stored in

agarose slices for long periods of time can be eluted and

cloned. Sometimes the quality even improved possibly due

to diffusing-out of salts, trapped small DNA fragments, and

inhibitors during the storage (data not shown). We also extended

this method to store megabase DNA plugs. Sizeselected

HMW DNA fragments in agarose slices and DNA

plugs that have been stored in this manner for many months

are routinely used for BAC library construction in our laboratory.

Ethanol can be used to preserve DNA for long-term

storage (Sambrook et al. 1989) and is a clear solution that

can be easily removed.

Even though the BAC vector is only 7.5 kb in size,

freeze–thaw cycles still need to be avoided. We stored the

prepared vector at –20°C (for frequent use) or –80°C (for

long-term storage) in 40–50% of glycerol in aliquots and effectively

avoided deterioration of the prepared vector during

freeze–thaw cycles.

May 21, 2008 Posted by | Uncategorized | Leave a comment

Tasmanian Tiger

Tasmanian Tiger

Tasmanina Tiger in Captivity
The thylacine (Thylacinus cynocephalus) is one of the most fabled animals in the world. Yet, despite its fame, it is one of the least understood of Tasmania’s native animals. European settlers were puzzled by it, feared it and killed it when they could. After only a century of white settlement the animal had been pushed to the brink of extinction. Full details of the demise of the thylacine can be found at our threatened species site.

The thylacine looked like a large, long dog, with stripes, a heavy stiff tail and a big head. Its scientific name, Thylacinus cynocephalus, means pouched dog with a wolf’s head. Fully grown, it measured about 180 cm (6 ft) from nose to tail tip, stood about 58 cm (2 ft) high at the shoulder and weighed up to 30 kg. The short, soft fur was brown except for 13 – 20 dark brown-black stripes that extended from the base of the tail to almost the shoulders. The stiff tail became thicker towards the base and appeared to merge with the body.

Description

 

Thylacines were usually mute, but when anxious or excited made a series of husky, coughing barks. When hunting, they gave a distinctive terrier-like, double yap, repeated every few seconds. Unfortunately there are no recordings.

The thylacine was shy and secretive and always avoided contact with humans. Despite its common name, ‘tiger’ it had a quiet, nervous temperament compared to its little cousin, the Tasmanian devil. Captured animals generally gave up without a struggle, and many died suddenly, apparently from shock. When hunting, the thylacine relied on a good sense of smell, and stamina. It was said to pursue its prey relentlessly, until the prey was exhausted. The thylacine was rarely seen to move fast, but when it did, it appeared awkward. It trotted stiffly, and when pursued, broke into a kind of shambling canter.

Tasmaninan Tiger FootprintsBreeding is believed to have occurred during winter and spring. A thylacine, like all marsupials, was tiny and hairless when born. It crawled into the mother’s rear-opening pouch, and attached itself to one of four teats. Four young could be carried at a time, but the usual litter size was probably three. As the pouch-young grew, the pouch expanded, and became so big that it reached almost to the ground. Large pouch-young had fur with stripes. When old enough to leave the pouch, the young stayed in a lair such as a deep rocky cave, well-hidden nest or hollow log, whilst the mother hunted.

Breeding

 

Thylacines lived in zoos for up to 9 years, but never bred in captivity. Their life expectancy in the wild was probably 5-7 years.
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The thylacine was a meat-eater – in fact, the world’s largest marsupial carnivore since the extinction of Thylacoleo,the marsupial ‘lion’. Its diet is believed to have consisted largely of wallabies, but included various small animals and birds. Since European settlement, the thylacine also preyed upon sheep and poultry, although the extent of this was much exaggerated. Occasionally, the thylacine scavenged. In captivity, thylacines were fed on dead rabbits and wallabies, which they devoured entirely, as well as beef and mutton.

Diet

 

Fossils and Aboriginal rock paintings show that the thylacine once lived throughout Australia and New Guinea. The most recent thylacine remains have been dated as being about 2,200 years old. Predation and competition from the dingo may have contributed to the thylacine’s disappearance from mainland Australia and New Guinea.

Distribution and Habitat

 

Bass Strait protected a relict population of thylacines in Tasmania. When Europeans arrived in 1803, thylacines were widespread in Tasmania. Their preferred habitat was a mosaic of dry eucalypt forest, wetlands and grasslands. They emerged to hunt on grassy plains and open woodlands during the evening, night and early morning.

Black and white photograph of two men holding up a dead Tasmanian Tiger by its rear legs.The arrival of European settlers marked the start of a tragic period of conflict that led to the thylacine’s extinction. The introduction of sheep in 1824 led to conflict between the settlers and thylacines.

Why are they extinct?

 

  • 1830 Van Diemens Land Co. introduced a thylacine bounties.
  • 1888 Tasmanian Parliament placed a price of £1 on thylacine’s head.
  • 1909 Government bounty scheme terminated. 2184 bounties paid.
  • 1910 Thylacines rare — sought by zoos around the world.
  • 1926 London Zoo bought its last thylacine for £150.
  • 1933 Last thylacine captured, Florentine Valley, sold Hobart Zoo.
  • 1936 World’s last captive thylacine died in Hobart Zoo, ( 07/09/1936).
  • 1936 Tasmanian tiger added to the list of protected Wildlife.
  • 1986 Thylacine declared extinct by international standards.

In 1863, John Gould, a famous naturalist, predicted that the Tasmanian tiger was doomed to extinction:

Do they still exist?

 

‘When the comparatively small island of Tasmania becomes more densely populated, and its primitive forests are intersected with roads from the eastern to the western coast, the numbers of this singular animal will speedily diminish, extermination will have its full sway, and it will then, like the Wolf in England and Scotland, be recorded as an animal of the past…’

 

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Every effort was made, by snaring, trapping, poisoning and shooting, to fulfil his prophecy. Bounty records indicate that a sudden decline in thylacine numbers occurred early in the 20th century. Hunting and habitat destruction leading to population fragmentation, are believed to have been the main causes of extinction. The remnant population was further weakened by a distemper-like disease.

The last known thylacine died in Hobart Zoo on 7th September, 1936.
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Black and white photographer of a hunter seated with his dog - a body of a Tasmanian Tiger across the man's lap.Since 1936, no conclusive evidence of a thylacine has been found. However, the incidence of reported thylacine sightings has continued. Most sightings occur at night, in the north of the State, in or near areas where suitable habitat is still available. Although the species is now considered to be ‘probably extinct’, these sightings provide some hope that the thylacine may still exist.

Sightings and Searches

 

There have been hundreds of sightings since 1936, many of which may have been clear cases of mis-identification. However, in a detailed study of sightings between 1934 and 1980, Steven Smith concluded that of a total of 320 sightings, just under half could be considered good sightings. Nonetheless, all sightings have remained inconclusive.

Interestingly, just as many sightings of equally good quality are reported from mainland Australia – perhaps a comment on the poor evidence that sightings alone represent.

There have been a number of searches for the animal. None of these searches have been successful in proving the continued existence of the animal. The results of a few of these searches are given below:

  • 1937 – Sergeant Summers leads a search in the north-west of he state, recording many recent sightings by other persons in a large area between the Arthur and Pieman Rivers, although the party itself did not see any thylacines. He recommends a sanctuary in that area.
  • 1945 – Well-known naturalist David Fleay searches the Jane River to Lake St Clair area, finding possible thylacine footprints.
  • 1959 – Eric Guiler leads a search in the far north-west, an area which produced many bounties and finds what appeared to be thylacine footprints.
  • 1963 – Eric Guiler leads a search in the Sandy Cape area but finds no evidence.
  • 1968 – Jeremy Griffiths, James Malley and Bob Brown embark on a major search. Although they collect reports of sightings, they find no evidence of the thylacine.
  • 1980 – Parks and Wildlife Officers, Steven Smith and Adrian Pyrke, search a wide area of the State using three automatic cameras. No evidence of thylacines is found.
  • 1982-83 – Parks and Wildlife Officer, Nick Mooney, undertakes an extensive but unsuccessful search to confirm the 1982 sighting reported by Hans Naarding near the Arthur River in the State’s north-west.
  • 1984 – A search in Tasmania’s highlands by Tasmanian Wildlife Park owner, Peter Wright, fails to turn up conclusive evidence.
  • 1988-93 – Separate photographic searches by wildlife photographer, Dave Watts and Ned Terry fail to record a thylacine.

The thylacine is the only mammal to have (possibly) become extinct in Tasmania since European settlement. This is in vivid contrast to mainland Australia, which has the worst record of mammalian extinctions of any country on Earth, with nearly 50% of its native mammals becoming extinct in the past 200 years. Tasmania is unique in that our fauna is abundant, and that the State acts as a refuge – a final hope – for many species that have recently become extinct on mainland Australia.

Hope for the Future?

 

Despite our wishes to have a perfect record, the lack of any hard evidence of the thylacine’s continued existence supports the increasingly-held notion that the species is extinct. Nonetheless, the incidence of sightings introduces a reluctance among some authorities to make emphatic statements on the status of the species. Even if there did exist a few remaining individuals, it is unlikely that such a tiny population would be able to maintain a sufficient genetic diversity to allow for the viable perpetuation of the species in the long-term.

Recent attention has been given to the possibility of cloning the species. However, it is very unlikely to be achievable from a single individual preserved in alcohol. Even if cloning were possible, it should be asked whether such effort and expense is justifiable when many other species are currently threatened with extinction, and when we allow the same processes that threaten habitats and wildlife to continue.

Perhaps the lesson to be learned from the loss of the thylacine is to ensure that the rich natural heritage of our island State is no longer jeopardised.

May 21, 2008 Posted by | Uncategorized | Leave a comment