Exemplar D: Excellence exemplar Project
Possums
Possums, known as Trichosurus vulpecula, are pests that were introduced
into New Zealand in the late 1830's. People thought that they would be
very good supply of furs and skins. Only a few were introduced into the
South Island but when things went well they were introduced into the
North Island and now they are found over 90% of New Zealand. It is
estimated that there are currently 60 to 70 million possums in New
Zealand (MAF web site 2003). The reasons possum numbers are so high
is a result of the fact that there are no natural predators for the possum
in the New Zealand ecosystem as well as a plentiful food supply.
Most people are aware that possums are a pest because they damage the
trees in the forests. They eat the young foliage and flowers of a number
of different types of plants. They have caused so much damage to
pohutakawa trees that there are whole populations of these trees dying.
The extent of the damage is because of two main factors. Firstly, simply
the numbers of possums are so high but also because of New Zealand's
evolutionary history. The native trees in New Zealand have evolved
alongside birds as the dominant animal group. Birds feed on nectar,
seeds and berries so the trees never had to adapt to the type of feeding
carried out by possums — browsing on the foliage. Many people are not
aware that possums also eat native birds eggs and compete with the
birds for food (nectar, seeds and berries). This predation and strong
competition has resulted in decreasing native bird populations as the
possum populations have increased.
I believe that another current issue linked to the possum population is
the possibility of TB (tuberculosis) being transferred from possums to
cattle and people. Having the disease TB in cattle and deer has a huge
financial impact on the milk and export meat industries. Currently there
are a number of procedures in place to eliminate the disease from the NZ
cattle population. For example dairy cows are killed when they test
positive for TB, stock movement control is placed on herds of deer that
test positive for the disease. However these control methods will not win
the battle against TB if the cattle and deer herds are constantly being
reinfected from possums in wild populations that are carrying the
disease. For this reason it is important to control populations of possums
throughout New Zealand.
Explanation of
the issue
Discussion of the
issue and biology
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a implication
There are many ways for controlling possum numbers; biological,
chemical and mechanical.
Hunting
The local community of Waitangi would like individuals to go on possums
hunting trips. As the possum are nocturnal the workers would need to
stay in the bush overnight waiting to carry out nightshooting. Workers
would be paid per possum killed and they could also take the carcasses
to get the fur off them. This method has the advantages that it provides
employment for some and resources that can be made into clothing and
textiles. It will not work to reduce the possum numbers in some places
because many of the possums live in rugged, remote areas of forest that
shooting is difficult and the shooting parties will have to travel long
distances to get to. A difficulty with this idea is that few people are
prepared to follow this demanding lifestyle for the low returns that
possum hunters usually get. An advantage is that no other animals are
killed, usually, except for the odd rabbit who gets in the firing path of the
hunter! The biggest problem is that the number of possums is so great
now that hunting is not an efficient way of reducing their numbers.
Discussion of
a implication
1080 poison drops
Possums love eating cereals and carrots and these are used to carry the
1080 poison for aerial drops over possum country. The cereal pellets and
carrots are usually coloured green and smell of cinnamon so that birds
are less likely to feed on them. In the past the Department of
Conservation have done drops of 1080 poison in our area. While these
were very successful and killed a reasonable number of possums (baiting
reduced possum numbers by 78% in a l km zone beyond the edge of a
forest. (Eson 2000)), people where concerned about poisoning of birds
and other animals, leakage of 1080 into water ways and the
accumulation of the poison in soils. However the bird populations have
been shown to recover quickly (after an aerial drop in the Hinuera Ranges
bird numbers were surveyed each month and after 7 months were found
to be back to pre-drop numbers (Dr Phil Cowan, 2001,DOC, pers. com.).
David Morgan (Landcare) is concerned about the issues surrounding the
use of 1080 poison. His concerns are about "bait shyness, public
perceptions that using toxins in general, and 1080 in particular, is
dangerous to environmental and human health, the huge costs of using
1080 in large-scale control operations, and the possibility that 1080 may
become unavailable for various reasons".
There are a number of reported cases of 1080 poisoning of sheep (one
case involved 570 ewes), cows, deer (1992 70 deer killed, Watts) and
dogs. Dogs are 10 times more susceptible to 1080 poisoning than
possums. They can be killed by eating possum meat from a possum
killed by 1080, by licking some 1080 paste or by eating a single 1080
cereal pellet. Dogs that have been poisoned by 1080 exhibit over
stimulation of the central nervous system. Their pulse rises, they become
incontinent, and they run around frenzied, barking and howling in pain.
They suffer convulsions and die of heart failure. This is one reason that
biological control of possums is favoured over 1080 poisoning. The
biological controls are being researched to check that they are specific to
possums and not random, affecting dogs, birds and maybe people, like
1080 can.
Everyone wants to get rid of the possum but generally people do not like
the idea of these (cute and fluffy) creatures to be hunted or to die a slow
death. Some people work as possum trappers and sell the possum meat,
skins and fur. The meat is used to make cat and dog food. Although some
people see this as meaning that possums are useful because they are
providing jobs for the unemployed people, others think that the damage
that possums do far outweighs the benefits. The use of possum control
methods such as traps, 1080 or cyanide baits also cause problems
because animals such as kiwis and cats get caught in the traps and other
animals can get poisoned.
Biological control
As a consequence of the controversy over the use of these methods
scientists have been investigating a range of biological control options. If
the scientists are going to use some of the methods being investigated
they have to also find ways to deliver the biocontrol method to lots of
possums. Some possible ways include: baits, sprays, use of a natural
vector such as possum viruses and use of transgenic plants. Because
the environmental conditions are so favourable for them in New
Zealand, possums breed very quickly and have two breeding seasons
per year. While this is one of the main problems with possums it is also
has the potential to be used in very clever biocontrol methods being
researched at present. This method will use possum reproduction to
control possum numbers!!!
These
methods
are
called
immunocontraception
and
immunosterilisation. In these methods the possum is immunised
against some of the proteins that are involved in their reproduction
process. The proteins used only occur in possums and are located on
the surface of possum sperm. After it has been immunised the
possum's body will make antibodies against these proteins. The
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possum's body will then attack the sperm as if it is a foreign invader
because of the protein on its surface. This will make the male infertile. .
In the female the immunisation reaction to the sperm will stop
fertilisation from occurring. This interferes with the reproductive cycle
and prevent possums from reproducing.
The research into immunocontraception and immunosterilisation
included feeding trials where Landcare Research and Marsupial
Cooperative Research Centre scientists tested genetically modified
potatoes as a way of introducing the proteins into the possum. The
potatoes were grown by the Boyce Thompson Institute for Plant Research
in the United States. This Institute is a world leader in developing plantbased vaccines for humans. The next trial, due to start during the
possum breeding season, will involve feeding possums carrots or potatoes
that contain a protein called possum ZP3. ZP3 comes from the coating of
the female possum's eggs. Scientists believe that feeding possums these
plants will cause the possums' immune system to make antibodies
against the eggs and prevent successful breeding ie the possums will be
immunised against conceiving. "The feeding trial will be carried out in
containment under strict controls required by ERMA and MAF. Possums
will be fed three small doses of the carrots or potatoes over a 21 day
period. Their immune responses will be measured by analysis of blood
samples and effects on fertility will be assessed by a breeding trial in
captivity under containment conditions."
(Landcare Research new release). Results are expected to be positive,
however computer modelling suggests that more than 60% of the females
would need to be made infertile (Landcare Research web site) for this to
have a real impact on possum numbers. The Landcare Research and
Marsupial CRC research team aims to have a prototype potato bait for
limited experimental testing in the field by 2005, and a product for more
general use by 2011.
Another potential method of biological control was outlined in a paper
written by a Landcare Research scientist named Dr Phil Cowan, which he
presented to the biotechnology conference. He states that possums have
few parasites and so it is not easy to get a parasite to infect and kill
possums. They do though have a worm which lives in their gut and at
times kills them — perhaps this could be used. However Dr Cowan
believes the best way to control possum numbers is through the use of
viruses. One potential virus is called wobbly possum virus. Special videos
taken in the dark showed possums with this disease wandering as if
intoxicated amongst cattle hence the name "wobbly possum". This virus
is thought to have been in NZ since the time of the possum release and
infected possums, just like people with the flu, recover from the disease.
Mr Cowen thinks that it is worth finding out if this virus can be altered
so that it killed the infected possums because then it may be able to be
used to kill possums in larger numbers. (Mr Cowen is a consultant and
has no direct benefit in using the virus so I take his opinion at face value
and do not believe it is biased).
Other methods
Doug Eckery is involved with the Wallaceville programme investigating
potential physiological ways to harm possum growth and development.
They are looking at the potential for using a wide range of different
biological chemicals such as growth factors and hormones, special
proteins such as riboflavin carrier protein, and reproductive hormones. If
a toxin was attached to the hormone that causes gonadotrophin to be
released it would effect the release of sex hormones from pituitary gland
which would cause possum sterility.
Research is under investigate ways to limit the ability of the mother
possum to produce milk for lactation. If this could be achieved it is hoped
that it would retard the growth of the immature possums or even cause
their death.
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the biology and
implications
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the biology
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an opinion
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source
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method
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method
Weighing up the positive and negatives of each of the control
methods is an important task for the Department of Conservation.
Important factors to look at are the effect on endemic and introduced
species, the health risk to people, whether or not the soil biota will be
affected, the sustainability and the economic viability need to be
weighed. For this reason a group of local people have been set up to
discuss the issue. This group is comprised of scientists, local Iwi,
farmers, and members of Parliament.
Validity and reliability
Depending on who you talk to you get a different opinion. Organisations
such as DOC and Landcare Research have to consider all factors before
they make a decision. There is information on the internet from Dr
Cowan suggesting that we need to obtain higher quality baseline data
on effects such as possum predation on birds so that we are able to
better determine the effectiveness of the different control methods (first
website). From what I have read I would say there is a lot of biased
information out there and some organisations find it is easy to use data
and statistics to support their way of thinking.
One of my sources was the Landcare research website and papers
written by Dr Cowan. I believe that this material is valid and reliable
because this is from a respected scientific source that will have quality
control procedures in place and the papers will have undergone peer
review before being delivered at conferences. Another source I looked at
was a book called “The Poisoning of New Zealand”. This book is written
by Merial Watts. Merial Watts is well qualilfi4ed to speak on the subject
of 1080 use and its negative effect on the environment. She has a
Bachelor of agricultural science and is currently a researcher ad writer
for Soil and health Association , a highly respected journal of nonchemical agriculture. She is also a representative of Environment and
conservation organizations to the Pesticides Board. The evidence which
has been presented in this book has been taken from many sources,
scientific and moral. To back up her statements and allegations, she
has used specific case studies, scientific data and experimental
research results. Her book is biased because she is only focusing
specifically on the negative side of poisons instead of looking at in a
broad, equal manner.
Another source was an article from the 'Forest & Bird' magazine.
This magazine is very reliable and respected journal which deals with
both sides of the story. The article was named "1080- Forest saviour or
wildlife poison". It was written by Alan Clark who is actually an
environmental lawyer from the United States. He is obviously qualified
and valid as he has majored in environmental law. His statements were
backed up with research data and case studies. He is not biased
towards a particular side of the controversy but has instead opted to
examine both sides of the debate and evenly supported it with evidence.
He has not made accusations or put the blame on any particular group,
neither has he criticised anyone persons view.
My opinion
I am concerned about the possum problem but I am also not happy
about the use of genetically modified potato plants to produce the bait for
the
Own
opinion
justified
andimmunocontraception
and
immunosterilisation research. I am not supported alone in this concern.
Roger Lindsay Wilkinson (RSNZ website) noted that the general public
understands the need for possum control but they want to debate other
control options before they are prepared to consider the use of GM
technology. Results of a survey of people's view on GM technology
showed: "
· People discriminate on the purpose of the technology. GM in respect to
food was seen as less appropriate than medical applications;
Description of
implications
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opinions
Evaluation
source
of
Evaluation
source
of
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source
of
Own opinion justified
and supported
· Most people were happy for research to continue to increase
·
·
·
·
·
knowledge but that this must be contained;
In respect to gene transfer, the more separate the species the less
acceptable the method;
High number of people were unable to rate the risk of GMOs;
In respect to biocontrol the method must be safe, specific and
humane;
People wanted 100% guarantees which science cannot supply;
Burden of proof was a major issue. People did not want to hear that
there was no evidence of adverse effects, they wanted research which
showed that the technology was not harmful." (RSNZ website).
I would sum up my opinion, saying that currently the use of 1080 poison
seems to be best alternative control because as our experience in using
this poison increases we have reduced the kill of other organisms (native
birds, farm animals and pet dogs) and research has shown that 1080 in
the environment is broken down by widely distributed soil microorganism (bacteria and fungi). In good climatic conditions this occurs
within six months. They use the 1080 as a food source and break it down
into harmless carbon dioxide, water and fluoride. (State of Victoria
Department of Natural Resources and Environment).
Reference list
Watts, M, (1994). The Poisoning of New Zealand, New Zealand:
Auckland Institute of Technology Press
National Possums Control Agencies, ( 1995). 1080- A Review of the
Science, NPCA Publications
Department of Conservation, (1994). Possum Control in Native Forests,
New Zealand, DOC
Department of Conservation, (1994). Possum Control and the Use of
1080 in New Zealand, New Zealand, DOC
Swan, K, (1995). Goodbye Possums, New Zealand, Halcyon Press
McLauchlan, M, (1996). "Rising to the Bait— Tension Over 1080," North
& South, March 1996, Volume 120,94-101
Clark, J.A, (1993), "!080 Forest Saviour or Wildlife Poison", Forest &
Bird, Volume 270,30-35
Department of Conservation, (1995). Possums and Possum ControlEffects on the Lowland Forest Ecosystem, New Zealand, DOC
Settzer, S, (1992). "Possum- An Ecological Nightmare", New Zealand
Geographic, January-March 1992, p49-70
http://www.landcareresearch.co.nz/research/biosecurity/
http://www.landcareresearch.co.nz/research/biosecurity/biocontrolpossums/
http://www.frst.govt.nz/about/possum/newsletter8.cfm
http://www.marsupialcrc.com.au/webhome/FACTS/FertilityControl.htm
http://www.maf.govt.nz/mafnetJrural-nz/research-and-development/researchresults/2000- 2001/2000-01-research-results-06.htm
www.nre.vic.gov.au
http://www.scoop.co.nz/mason/stories/SC0103/S00027.htm
http://www.frst.govt.nzJabout/possum.cfm
58
Own opinion justified
and supported
Exemplar B: Merit exemplar
Essay done in class time, using research notes
Techniques Used to Provide Desirable Qualities in Crop Plants
There are a number of different techniques that are used to produce
plants with the characteristics that people want. Some of these
techniques involve transfer of genetic material from one type of organism
to a plant. People are often against the use of genetic modification
because they think that these techniques are made up by scientists but
genetic transfer occurs in nature when the soil bacterium, Agrobacterium
tumefaciens infects a plant by entering through a wound. The
Agrobacterium transfers a piece of it's own DNA into the chromosomes of
the plant cells at the wound site (MAP website).
The T-DNA (piece of transferred DNA) contains two genes, characteristics
which switch on when inside the plant cell. The first gene makes the
plant cell produce hormones which cause the cell to grow and divide out
of control, similar to the way a cancer cell does. The cells produced are
loosely packed and form a tumour. The tumour provides an environment
in the cells that is suitable for the bacterium to live in.
The other gene on the T-DNA forces the plant to produce opines which
are sugars linked to amino acids. When the cells divide to produce the
tumour the new cells also contain the genes to produce opines. The plant
can't use the opines produced but are being forced to make them for the
bacterium which needs them for growth and reproduction.
The Agrobacterium lives between the cells in the tumour. It survives by
getting nitrogen and opines from the plant cells. This is a very clever form
of parasitism because through natural genetic engineering the
Agrobacterium causes the plant to provide suitable environment and to
make food for it.
Scientists worked out that the genes controlling the transfer of the
bacterial DNA into the plant weren't part of the T-DNA. They are part of
the rest of the genetic material. This means that the genes for the
production of hormone and opines could be deleted from the section of
T-DNA and replaced with other genes Therefore it would be possible for
Agrobacterium to be used by people to transfer desirable genes to plants
and other organisms
Therefore two new genes could be put on the T-DNA. For example one
of the gens that could be for resistance to a particular pest or disease.
The other gene that scientists would have to use is a market gene that
would allow them to identify which ells have had the desired gene
successfully transferred into them. An example of a gene suitable as a
market is one that gives the organism resistance to Kanamycin
antibiotic.
To genetically modify plants using the method used by Agrobacterium
scientists remove the natural T-DNA from the Agrobacterium and
replace it with a modified T-DNA. Plant tissue from the plant to be
genetically modified eg a leaf disc or segment is then dipped into the
Agrobacterium (Hanson, 1999). The plant tissue is then transferred onto
a culture medium designed to allow the plant cells to divide. The recipe
for the media changes for different plants.
After two days the plant tissue is transferred to the same medium
containing two supplements. The first is an antibiotic to prevent the
Agrobacterium from growing further. The second is used for selecting the
engineered cells which are linked to the marker gene eg. Kanamycin,
which normally kills plant cells. This means only the cells with the
marker genes for Kanamycin resistance are capable of growing (MAF
website).
Description of an
opinion
Description of the
biology (referenced)
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the biology
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the biology
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the biology
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the biology
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the biology
Description of the
steps in a process
(referenced)
After about one month the Kanamycin resistance cell colonies are
removed from the growing medium so that they can be used to produce
plants with the desired characteristics, which in this example is pest or
disease resistance. First the cells are transferred to a culture medium
that will cause the growth of shoots. Once formed the shoots are
transferred to another medium that will cause root formation. The plants
can then be carefully transferred to a greenhouse. The DNA in the plants
can be checked to see if the new genes are present and analysed to see if
the new characteristic gives the desired resistance to a pest or disease.
Other techniques can also be used to insert desirable characteristics into
crop plants. These include: conventional cross breeding, genetic
engineering using Protoplast Fusion, Gene Gun Method and by using
Bacterial Plasmids.
One of the techniques used in conventional plant breeding involves the
prevention of natural cross pollination of the flowers. Instead pollen is
deliberately transferred a plant with the desired characteristics onto the
flower. Unlike the genetic engineering method described above, this method
has the disadvantage that it is unable to produce a large numbers of plants
with exactly the same genetic make-up or even guaranteed to contain the
desired characteristic. However this method is acceptable to all members of
the public as it is not seen as genetic modification because it does not
involved the adding of genes from other organisms (own survey).
In the method called protoplast fusion the cell walls of plant cells are
digested by enzymes. These cells are then treated with polyethylene glycol
which causes the cells containing the desired DNA to fuse.
The Gene Gun Method is when microscopic particles of tungsten or gold
that have a DNA coating are shot through the cell wall by a burst of
helium. DNA can also enter a cell when incorporated into a bacterial
plasmid.
These genetic modification technologies allow scientists to transfer any
source of DNA into crop pants. DNA can come from the same plant, other
plants, fungi, bacteria, viruses, animals or, most commonly, artificial
genes that are made in the lab. Scientists think this offers great potential
for creating many crops with resistance to pests and diseases or being
able to cope with drought, salt, temperature extremes or soil toxicities
(MAF website). Colour, shape and texture, longer shelf life and improved
composition, eg adding nutrient and anti oxidants, can be altered in
plants. Crop plants can also be used for making medicines and
biodegradable plastic.
The first commercial genetically engineered crop plant was the `Flavour
Saver Tomato', which was modified so the genes responsible for the fruit
softening were turned off. This means the fruit can be left on the plant to
fully ripen rather than being picked early. Because of this the tomatoes
develop all natural flavours while on the plant. It also means when picked
they stay firmer longer.
Explanation of
the process
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the process
Identification of
other methods
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the biology
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an opinion
Description of
other methods
described
Explanation of
an opinion
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other examples
Other products about to be commercialised include sugarbeet which has
herbicide resistance and Canola which contains modified fatty acids to
make it healthier. Papaya with virus resistance has been produced along
with potatoes, cotton, corn and tomatoes which all have insect
resistance.
One of the main concerns is that people fear the unknown. Fagan (1999)
says that we are being used as "unknowing guinea pigs" by companies
making genetically engineered food. We won't know for sure what will
happen until we try something. The public does not tend to believe
scientists when they assure us that the food is safe. This may be because
in the past the public gave been assured that scientifically based
procedures were safe when in fact they weren't. For example, DDT was
Explanation of
an opinion
used widely as an insecticide for many years before the long term
accumulative effects were realised. Although this isn't directly related to
genetic engineering it illustrates that the public have a reason for
mistrust of new scientific applications.
Some people are concerned about genetically modified food because they
believe these new genes will make compounds that cause allergies (IBAC,
2000) or toxic responses. However scientists maintain that because they
know a great deal of information about the genes and that such
possibilities can be predicted ahead of commercial release. Scientists also
say that such events are just as likely from traditional breeding methods
that have been used for about the last 50 years because not much is
known about the genes being transferred by these methods or the results
once in the new plant. Other genes may also be passed on from the wild
plant. These can go undetected (Lean, Angres & Jury, 2000).
I think it is very important that people understand the science behind the
processes used. Without this knowledge people are basing their views on
emotions and hearsay. The basic ideas are relatively easy to grasp. After
knowing how specific the techniques are, people should be more informed
to make decisions about whether to eat genetically modified food.
Recently legislation has been passed to make genetically modified food
labelled. How strict these regulations will be, is yet to be decided, but it is
considered that labelling will help inform the public and allow them
choice.
Reference list
Conner, A.J. (1997) Genetically Engineered Crops48 Environmental
and Food Safety Issues. The Royal Society of New Zealand.
Fagan, J.B. (1999) The Health Risks of Genetically Engineered Foods. Published
in Canterbury's Digest, Autumn 1999. Christchurch: ASG.
Hanson, M. (1999) University Bursary Biology. Auckland: ESA Publications (NZ)
ltd.
IBAC, (2000). Biotechnology in NZ Consultation Report. Wellington: Independent
Biotechnology Advisory Council.
Leon, G., Angres, V., and Jury, L. (2000). GM genes can spread to people and
animals. Independent. 28 May, 2000.
MAF website http://www.maf.govt.nz/MAFnet/schools/activities/gmfbio.htm
Methods of gene transfer. Accessed 29/8/2001.
Explanation of
an implication
Description of an
opinion
Explanation of
own opinion
Description of an
implication