Darren Touchell and Kingsley Dixon at the Kings Park and Botanic Garden in Perth have created large numbers of genetically identical specimens from frozen plant tissue of a rare grevillea. Touchell says the technique could ensure the survival of Grevillea scapigera, of which only a few specimens are thought to remain in the wild.

Already, Touchell and Dixon have potted up hundreds of plantlets which were reproduced by tissue culture of the thawed plant material. ‘They will be reintroduced into the wild next year,’ says Touchell. ‘Cryostorage has been used successfully on about 150 species of agricultural plants, but as far as we know this is its first application to rare and endangered species.’

The tips of shoots are treated for up to 48 hours with a ‘cryoprotectant’, or antifreeze – in this case, 5 per cent dimethylsulfoxide. The researchers then slowly cool the shoots at a rate of about 0.5 degreesC per minute until they reach -40 degreesC. Because the shoots are both treated with antifreeze and cooled, the plant tissue is dehydrated sufficiently to prevent ice crystals forming. Such crystals would tear apart the cells and kill the plant.

After this treatment, Touchell and Dixon plunge the shoots into liquid nitrogen at a temperature of -196 °C. The extreme cold stops all metabolic processes.

This method of storage has two advantages. First, specimens at this temperature are cheap to maintain and will keep virtually indefinitely. Conventional tissue culture must be replaced about every month as the medium in which the plantlets grow deteriorates. Usually, the plantlets are ready for division again after this time.

The second advantage of this method of storage is that at this temperature no genetic mutations occur, which is important for the storage of rare agricultural crop genomes or, in this case, rare and endangered plants. Usually, genetic mutations occur as a plant grows – for instance, when it is exposed to ultraviolet light.

Touchell and Dixon revive the grevillea by placing vials of frozen tissue in a water bath at 40 °C. Once the tissues have thawed, the researchers wash away the antifreeze and culture them on a recovery medium. Shoot tissues may take from three weeks to four months to begin regenerating.

The Western Australian team has also used cryostorage on the seeds of about 70 common native species. Touchell says this was a much simpler process. However, unlike the shoot-tip method of propagation, it did not provide genetically identical material. Propagation of seeds does not guarantee any genetic characteristics because both parent plants contribute genetic material.

‘Cryostorage isn’t intended to replace the preservation of native bushland as the main tool of conservation,’ says Touchell. ‘But it could mean the difference between survival and extinction for species whose numbers are critically low.’

According to Tim Stone, a postgraduate student at the Australian National
University, Canberra, the midden-like structures at Weipa, on the Cape York
Peninsula, were built by generations of scrub fowl (Megapodius reinwardt),
raking soil and shells into heaps to incubate eggs. They are not, he says,
the result of a gradual build-up of camp refuse and material discarded by
Aborigines. Artefacts in the mounds were introduced by the birds, together
with other debris from the surface of the soil.

Critics of Stone’s theory point to cockle shells, which are very common
in the mounds. Cockles are eaten by humans on the Cape York Peninsula. John
Chappel of ANU thinks that both Aborigines and birds may have had a hand
in the structures.

Chappel has examined similar mounds at Princess Charlotte Bay, also
on the Cape York Peninsula. He found that mounds of cockle shells were built
on a beach ridge of shell debris carpeted by a layer of Aboriginal refuse
about 40 centimetres thick. ‘It’s conceivable,’ he says, ‘that the Weipa
mounds were raked up in the same way by the scrub fowl on ridges carpeted
in midden material, but this needs to be confirmed.’

Accounts of Aborigines camping on the mounds, or even burying their
dead in them, do not detract from the theory, according to Stone. He says
that the remains of those activities would leave traces without contributing
greatly to the growth of the mounds.

‘If the mounds were of human origin,’ he says, ‘you would expect to
find complete assemblages of ‘living floors’ beneath the mound surface,
but this hasn’t been the case.’ The Aborigines themselves have described
the mounds as ‘natural’ rather than man-made. According to Stone, European
indifference to the opinions of local Aborigines ensured that prehistorians
and anthropologists continued to believe that the mounds were of human origin.

Stone’s theory has received support from biogeographers and geomorphologists,
but he has encountered hostility from some prehistorians. His most vigorous
critics have been Cambridge-trained researchers, whose influence is widely
felt in Australian archaeological circles. Stone counters their criticisms
with a claim that these academics have been conditioned by European archaeology
and assume that any large unusual feature must be made by humans.

Geoff Bailey, an archaeologist from the University of Cambridge, has
examined more than 300 of the deposits at Weipa. He says that the mounds
of shells, accepted as Aboriginal middens, are easily distinguishable from
the scrub fowl’s conical, steep-sided nest mounds which contain mostly sediment.
His reply to Stone’s paper, published last year in Arachaeology in Oceania,
is due to appear in the forthcoming issue of the journal.

Richard Wright, an anthropologist from the University of Sydney, has
also seen the mounds at Weipa and believes they are of human origin. Scrub
fowl include humus in their mounds because it decomposes, generating heat
that aids the incubation of eggs. The question here is how long does it
take for most of the humus and other sediment to leach out of the mound,
leaving a skeleton of shells.

Wright also argues that the distribution of the mounds does not match
that of the scrub fowl – a point that Stone disputes. ‘There is some discrepancy
between the occurrence of birds and mounds in the southern part of their
distribution, but this could be due to the heavy agricultural use of the
land in this region and the consequent clearing of the scrub fowl’s habitat,’
says Stone.

He also rejects accusations that his theory will harm Aboriginal land
claims by diminishing the archaeological significance of the sites. ‘The
issue is whether a site is of significance to Aboriginals, not to archaeologists.
A sacred site will remain sacred whether or not it has the blessing of white
archaeologists,’ says Stone.