Academic literature on the topic 'Trichosurus vulpecula'

This review outlines the known endoparasites and ectoparasites of the brushtail possums Trichosurus vulpecula and T. caninus in Australia and T. vulpecula in New Zealand. Associated gross and histopathological changes in the host as a result of parasite infection are also described. Protozoan, cestode and nematode endoparasites have been found in both T. vulpecula (4 protozoa, one cestode and 25 nematodes) and T. caninus (2 protozoa, one cestode and 8 nematodes). The trematode Fasciola hepatica has been recorded only from T. vulpecula, in which it is associated with extensive pathological changes in the liver. Numerous species of fleas, ticks and mites occur on T. caninus (one flea, 4 ticks and 9 mites) and T. vulpecula (7 fleas, 11 ticks and 18 mites) in Australia, but only mites (4 species) occur on T. vulpecula in New Zealand. The only parasite with an indirect life cycle that occurs in T. vulpecula in New Zealand is the cestode Bertiella trichosuri. Other parasites that require intermediate hosts to complete their life cycle are absent. Further studies are required to investigate the effects of parasites on the health and fecundity of T. vulpecula and T. caninus in Australia to determine their potential as direct or indirect agents for the biological control of T. vulpecula in New Zealand.

The taxonomic status of distinctive populations of the widespread and morphologically variable possum Trichosurus vulpecula was examined. For the analysis, morphological characters (body size, fur colour and skull dimensions), karyotypes, electrophoretic allozyme, and ecological data were compared for as many Trichosurus populations as possible. There are insufficient differences between populations of T. vulpecula to reject a null hypothesis that they comprise a single species. Tasmanian, northern and south-western Australian populations could be retained as subspecies, but insufficient data exist to resolve the specific status of Atheton Tabeland and north-eastern Australian populations. One enigmatic result is that the skull morphometrics and allozymes of T. caninus were not distinguishable from those of sympatric T. vulpecula. However, other morphological characteristics and ecological data provide adequate evidence the T. caninus is a distinct species.

The diet of the Common Brushtail Possum, Trichosurus vulpecula, in central Australia was investigated by faecal analysis. Trichosaurus vulpecula ate 34 plant species from the herb, shrub and tree strata. Dicotyledonous species comprised 99 % of epidermis in faecal pellets. Preferred species were Amyema maidenii (a mistletoe), Acacia coriacea, A. estrophiolata, Rhagodia spinescens and Solanum centrale. Grass or eucalypts were rarely eaten. Plant reproductive parts (flowers, buds, seed and fruit) contributed 39 % of epidermis in faecal pellets. Many of the species eaten by T. vulpecula are also browsed by cattle, and this may have contributed to the decline of T. vulpecula in central Australia.

The potential for feral Honeybees (Apis mellifera) to competitively exclude Common Brushtail Possums (Trichosurus vulpecula) from tree hollows was examined in the You Yangs Regional Park, Victoria. The characteristics and occupancy of 77 hollow-bearing trees and 250 hollows were recorded in six 2 ha sites and used to compare the extent of overlap in nest site selection between bees and posssums. Colonies of feral A. mellifera occupied 25 % of all hollow-bearing trees and 8 % of useable hollows, yielding a density of 1.66 colonies per ha, the highest recorded so far in Australia. Trichosurus vulpecula utilised 74 % of hollow-bearing trees and 48 % of useable hollows. Nest site characteristics of bees and possums overlapped in several dimensions, especially in the size of tree and height of nest. Relatively few vacant hollows were suitable for T. vulpecula, whereas many were available to Honeybees. Only 35% of bee nests were in hollows unsuitable for possums, indicating a relatively high potential for competition.

The common brushtail possum (Trichosurus vulpecula) is usually a strictly monotocous species, presenting one offspring at a time. Two concurrent offspring is a rare occurrence, but twin pouch young or young spaced one oestrous cycle apart have been reported. We investigated the biology of urban T. vulpecula populations within the Sydney metropolitan area between November 2002 and April 2005. As part of these studies, we trapped one adult female T.�vulpecula with two young. Analysis of morphological data from the young and development of the female?s mammary gland suggest that only one young was her offspring. The results of genetic analysis support this conclusion. Herewith, we describe an apparent case of adoption in T. vulpecula.

7-Hydroxy-1,8-cineole (3a) and the corresponding carboxylic acid (3b) have been isolated from the urine of brushtail possums ( Trichosurus vulpecula: Marsupialia ) fed a diet enhanced with 1,8-cineole. Chemical syntheses of these two novel metabolites are described.

The common brushtail possum (Trichosurus vulpecula) has readily adapted to the expanding urban settings of its native Australian environment. This has lead to conflict with humans due to T.�vulpecula?s seemingly bold behaviour in suburbia. Current management strategies encourage people to live harmoniously with possums. However, despite the cooperation of many residents, some object to this policy and illegally remove T.�vulpecula from their properties. Wildlife managers are seeking alternative management options that aim to reduce conflict with people. These include fertility control methods which may be used to adjust possum numbers in a publicly acceptable way. Nest boxes are frequently recommended as alternative den sites for T.�vulpecula which reside in man-made structures. The disease status of possums may alter the rationale for their management in urban areas, due to the potential consequences for humans, domestic animals and possum conservation. Understanding the biology and behaviour of T.�vulpecula can greatly enhance the ability to select and successfully utilise adequate methods and solve outstanding issues. As such, this paper aims to review the scientific knowledge on possum populations as well as urban possum management policies and potential management tools.

Thesis by publication -- 8 co-authored articles.
Thesis (PhD)--Macquarie University, Division of Environmental and Life Sciences, Department of Biological Sciences.
Includes bibliographical references.
Preface -- Management issues of urban common brushtail possums (Trichosurus vulpecula): a loved or hated neighbour -- Effects of deslorelin implants on reproduction in the common brushtail possum (Trichosurus vulpecula) -- Brushtail possums (Trichosurus vulpecula) in metropolotan Sydney: population biology and response to contraceptive implants -- Strategic survey for Toxoplasma gondii and Neospora caninum in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia -- Leptospirosis serology in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia -- Conclusions.
The common brushtail possum (Trichosurus vulpecula) is indeed a common inhabitant of many Australian citites, and one of the few marsupials that has adapted well to the urban environment. Their close proximity to people provides a great opportunity to experience native wildlife in the backyard, however, their utilization of house roofs, bold behaviour and appetite for garden plants often leads to conflict with householders. Population numbers are sufficiently high to require ongoing management to minimise negative impacts for humans and brushtail possums alike in a socially acceptable manner. The aim of this thesis was to identify current management issues and address the need for improved and novel management strategies. The potential of slow-release implants, containing the GnRH agonist deslorelin, as a contraceptive agent for brushtail possums was tested on a captive population. Males appeared resistant to treatment, but deslorelin was found to inhibit reproduction in female brushtail possums for at least one breeding season, making it a promising tool to control fertility in some wild populations. A further aim was to trial deslorelin implants on a wild urban population, to collect more information about the urban biology of this species and to point out issues which have previously not been addressed. Close proximity and interaction of urban brushtail possums with humans and their domestic animals can increase the risk of disease exposure and transmission and influence the health of wild populations. Serosurveys showed that animals were readily exposed to Leptospira spp. and Toxoplasma gondii. This thesis also provides the first data on brushtail possum dispersal in urban areas, knowledge which is highly relevant to the development of management strategies such as fertility control. The findings from this research broaden our knowledge about urban brushtail possums and should assist wildlife authorities in developing alternative or improved management procedures.
Mode of access: World Wide Web.
xxv, 287 p. ill., maps

A total of 9 brushtail possums (Trichosurus vulpecula) were trained to perform a two-manipulanda, conditional discrimination task. The possums learned to press a right lever in the presence of a tone (80 dB(A)) during tone-on trials, and a left lever in the absence of the tone on tone-off trials. Overall sessions of 11 conditions contained tone frequency between 100 Hz and 35 kHz were tested. Each condition contained training and then probe sessions. In training sessions, the possums were presented with tone-on and tone-off trials, pseudo-randomly. Once the possums responded with over 90% accuracy for five consecutive sessions, then probe sessions were introduced. Probe sessions were similar to the training sessions, except that the tone intensity for tone-on trials was reduced by 8 dB(A) across blocks of 20 trials until their response accuracy in a block fall below 60% or reached 24 dB(A). Data were analysed using overall percentages correct and log d analysis. Both measures indicated that overall response accuracy decreased for all possum as tone intensity reduced. Based on these data analyses, threshold values were calculated using the criterions at 75% correct and a log d of 0.48. The threshold values for each possum and across all possums were plotted as a function of the tone frequency to produce an audiogram. A curvilinear regression was fitted for each threshold values. The functions of both measures were very similar. Both audiograms showed that the possums could hear the tones between 100 Hz and 35 kHz, and were most sensitive to tones between 15 and 20 kHz. This experiment involved many difficulties with producing and measuring tones especially outside of human hearing range. Due to these difficulties, several problems and concerns were raised during the experiment, these were discussed in this study and also recommendations for future research were then presented.

Aerial control using 1080 (sodium monofluoroacetate) baits is widely used in New Zealand for the control of introduced brushtail possums (Trichosurus vulpecula), with the aim of protecting national conservation and agricultural values from these damaging pests. This thesis integrates research, completed over 25 years, that was motivated by growing recognition in the 1970s of the extent of possum impacts and the need to improve the effectiveness and efficiency of the control operation. Field research assessed the palatability of three types of cereal-based pellet baits and carrot baits in different regions, habitat types and seasons. Palatability was assessed by the consumption of the different bait types presented independently of each other on 15-30 plots, with rotation of bait types at plots on successive nights to provide equal exposure to each bait type. There was regional variation in possums' bait preferences, possibly reflecting genotypic differences, whereas seasonal variation was less evident. Carrot bait was preferred or equally preferred to cereal bait in 14 out of 20 field trials. The proportion of possums eating baits was then investigated by, firstly, developing a technique for tracing bait acceptance using rhodamine B, a UV-fluorescent dye. In four field trials, more than 95% of possums accepted three types of dye-marked bait, eliminating bait refusal as a major reason for low kills in winter control operations. In a fifth trial, conducted in summer, only 68% of possums accepted bait suggesting that seasonal availability of favoured foods may influence bait acceptance. Since possums must encounter baits before deciding whether to eat them, field studies were undertaken to assess the coverage achieved in normal aerial baiting operations. Large gaps, up to 400 m in width, were often found between baiting swaths; these could allow some possums to survive. A controlled field experiment, using acceptance of rhodamine-dyed bait as a measure of effectiveness, showed that bait distribution was least accurate where flight paths were not marked. Where gaps of 100 m between flight paths were deliberately created, bait acceptance was slower and less than where coverage was complete. Sowing baits at 3 kg/ha was as effective as at 10 kg/ha, indicating the potential for substantially reducing operational costs by using machinery capable of faultlessly distributing baits at low rates. Navigational guidance systems were evaluated and found to improve the accuracy of bait distribution. During 1993-1997, when a lower sowing rate of 5 kg/ha was adopted operationally by regional managers, control effectiveness was unchanged but annual savings of around $9 million accrued. Because of the lack of suitable sowing machinery, a bucket was developed to permit faultless distribution of baits at lower rates, demonstrating the possibility of yet further cost-savings. The possibility of seasonal food availability affecting bait acceptance was investigated in three different forest habitats. Dyed baits were aerially distributed on 100 ha at each site in each season over two years. In each trial, fat-based condition indices of possums were calculated and the abundance of possum-preferred plant foods described. Bait acceptance was consistently high (85-100%) in the 24 trials, and was not influenced by either condition or availability of preferred foods. It seems likely that seasonal variation in operational effectiveness is caused by either the availability of sharply seasonal, scarce foods that possums may feed on intensively for brief periods, or by warmer temperatures that render 1080 less effective. The influence of 1080 on acceptance of (rhodamine-dyed) baits was investigated in a field trial. Examination of possums for dye-marking showed that 25% of possums refused to eat either a lethal quantity of bait or any bait at all, compared with 98% of possums eating non-toxic bait. This indicated that 1080 is aversive to possums, which is a potential major reason for their surviving control operations. Pen trials were therefore conducted to further examine the problem and to seek solutions. Toxic carrot baits were rejected by 27.5% of possums, equally by smell and taste aversion, whereas toxic cereal pellets were rejected by 34%, mainly by taste aversion. Orange and cinnamon were shown to be among the most preferred of 42 flavours tested and, when applied to toxic baits, 1080 was effectively masked. Bait refusal was reduced to ≤7%, the same as that recorded for possums presented with flavoured non-toxic baits. For long-term control of possum populations, aerial 1080 baiting can be used sequentially with other poisoning methods. However, the compatibility of these methods is dependent on the likelihood of possums developing bait shyness if sublethally dosed. Studies were therefore conducted to characterise and compare the four main toxicants used (1080, cyanide, cholecalciferol and brodifacoum) for induction and mitigation of bait shyness. Shyness was induced in approximately 80% of possums sublethally dosed with cyanide, 60% with 1080, 20% with cholecalciferol, and 0% with brodifacoum. Cyanide and 1080 shyness were found to persist in many possums for at least 12 and 24 months, respectively. Use of alternative bait types, and of baits containing an alternative slow-acting toxin (brodifacoum) were shown to be effective ways of overcoming shyness. This, and other related research, is reviewed to provide operational specifications that maximise the likelihood that all targeted possums will (i) encounter bait, (ii) eat it, and (iii) die. The likely future use of aerial 1080 baiting is described and the technological, economic, environmental and social constraints on its sustainability are discussed. Finally, the uptake of the research by possum managers is considered, and areas identified in the thesis where information is incomplete are summarised as prioritised topics for further research.

The common brushtail possum (Trichosurus vulpecula) is the most significant vertebrate pest in New Zealand as an ecological threat to the indigenous biodiversity and an economic threat as a vector for bovine tuberculosis. Biological control is considered to be the most accepted management strategy to reduce the population, specifically by impairing fertility. Successful development of a biocontrol agent (most likely a protein or peptide macromolecule) requires identification of a compound that is species-specific and potent. The challenge is also to deliver the bioactive to this free-ranging, widespread, feral animal and ensure sufficient bioavailability. Macromolecules have low oral bioavailability, thus new formulation strategies are required to enhance stability and absorption in the gastrointestinal tract (GIT) of T. vulpecula. Oral administration of the bioactive contained within a non-toxic bait is the most practical delivery strategy. Essential to designing an oral delivery system is to quantify the transit time of different sized delivery systems. The gastrointestinal transit in T. vulpecula was investigated (n = 72) by gamma scintigraphy. Technetium-labelled (99mTc) anion exchange resin particles (75 - 125 (mu)m or 500 - 700 (mu)m) or solution (99mTc-DTPA) was administered orally. After 3, 6, 12, 24 or 32 h, distribution of radioactivity in excised GITs was determined. Transit profiles were similar for each formulation. For delivery to the hindgut, bioactives need protection for 12 h though the upper GIT. Particulate formulations may be retained in the caecum for up to 32 h. Transit time was not different between animals dosed in the evening or the morning. Furthermore, GIT morphology is different between specimens in this study from southern New Zealand and Australian specimens. This may reflect improved diet quality in New Zealand. A model protein (insulin) was incorporated into poly(ethyl 2-cyanoacrylate) (PECA) nanoparticles prepared by interfacial polymerisation of water-in-oil microemulsions. The mean size of nanoparticles was 220 nm with a mean entrapment efficiency of 78%, determined using reverse phase HPLC. In vitro release of insulin from PECA nanoparticles in phosphate buffer (0.067 M, pH 7.4) at 37°C was triphasic and not all entrapped insulin was released. Following in vitro incubation of nanoparticles with enzyme solutions prepared from the GIT of T. vulpecula, lumen enzymes were more aggressive towards insulin compared to mucosal enzymes and the hindgut lumen was the GIT region with the lowest degradation. For the first time in a marsupial species, the in vivo pharmacokinetics of insulin-loaded, PECA nanoparticles were investigated following i.v. and intra-caecal administration and measured by radioimmunoassay. The low cross reactivity of human and endogenous brushtail possum insulin means that T. vulpecula is a suitable non-diabetic model to study pharmacokinetics of insulin. The i.v. pharmacokinetics of insulin solution and insulin-loaded nanoparticles were similar. On intracaecal dosing, co-administration of a permeation enhancer (EDTA) resulted in a small increase in plasma insulin concentration compared to insulin-loaded nanoparticles alone. In conclusion, transit time to the caecum of T. vulpecula following oral delivery was 12 h for fluid and particulate formulations < 1 mm diameter and was independent of the time of day the dose was given. T. vulpecula is a potential non-diabetic model for the study of insulin pharmacokinetics. This thesis demonstrates the potential application of oral peptide and protein delivery technology in the area of wildlife management.

This study investigates the ecology of one of the best known Australian marsupials, the Common Brushtail Possum Trichosurus vulpecula, in central Australia. Trichosurus vulpecula is one of few medium-sized mammal species that persist in arid Australia today. Its distribution within the arid zone has declined markedly since European settlement. Two populations, one within the East MacDonnell Ranges along the Hale River and the other on Irving Creek, a River Red Gum creek in the Petermann Ranges, were studied in the southern Northern Territory. Others locations in the region were visited opportunistically. Trie central Australian Trichosurus is not distinct genetically from populations elsewhere in Australia. The diet of T. vulpecula consisted of a range of leaves, flowers and fruits of perennial dicotyledonous species as well as some ephemeral herbs. Grasses were absent from the diet. Variation in the diet reflected seasonal availability in flowers and fruits. The species preferentially consumed at each site had significantly higher moisture content and dry matter digestibility than species not consumed. Preferred species included Amyema maidenii leaves (a mistletoe), Acacia spp. flowers and fruits, Santalum lanceolatum leaves (a shrub), Marsdenia australis leaves (a vine), Solarium quadriloculatum fruit (shrub) and Euphorbia spp. leaves (herb). Small amounts of invertebrate material were consumed throughout the year. Other non-plant material consumed included honeycomb and unfledged birds eg. Budgerigars. There were no significant differences in the diet between the sexes. Trichosurus vulpecula were found in six main habitats: Acacia aneura/Callitris glaucophylla on rocky hills; E. camaldulensis sandy creek-lines; mixed Acacia rocky hills, Rocky Eucalyptus creek-lines; Degraded drainage lines; and Wet gullies. Logistic regression modelling revealed a significant correlation between mistletoe species richness, higher levels of soil nitrogen and the presence of T. vulpecula. In habitats occupied by T. vulpecula species richness of mistletoes was associated with the absence of fire and the presence of reliable ground water supplies. Trichosurus vulpecula were highly mobile with mean home ranges at Hale River of 44.21 � 22.76 ha and considerably higher than those recorded in previous studies in Australia. Mean home ranges at Irving Creek were much smaller, at 4.99 � 1.46 ha and VII similar to that recorded in other studies in Australia. At both sites, males had larger home ranges and there was a high degree of overlap with other males and females. At the Hale River study site, T. vulpecula predominantly denned in caves or cavities in rocks, whereas at Irving Creek all den sites were in large Eucalyptus camaldulensis on the drainage line. Adult and pouch young sex ratios were at parity. During this study, T. vulpecula was found to breed continuously, with births recorded in almost all months. Growth of the young were more rapid than previously recorded for Trichosurus in Australia. This is interpreted as an adaptation for living in an arid environment, enabling the young to achieve independence before quality food supplies diminish. No single exotic predator or competitor was solely responsible for the decline of T. vulpecula in arid Australia, implying an interactive impact. Prey switching by dingoes from rabbits to T. vulpecula, macropods and echidnas followed the crash of rabbit populations at Hale River. Predation by dingoes on T. vulpecula was only recorded once, at the Irving Creek study site, where numbers of rabbits remained stable throughout the study. The impact of exotic herbivores occurred through habitat degradation rather than competition. Evaluation of the ecological data collected during this study generally supports current models of decline and extinction in medium-sized mammals in arid Australia, integrating the effects of predators, competitors, drought and fire. However, the importance of each factor on populations of T. vulpecula was found to vary depending on their location in the landscape. This study suggests two separate models to explain the decline of T. vulpecula in arid Australia after the arrival of Europeans. The first operates in the riparian lowlands and the second on the rocky ranges. In both models, prior to European settlement, T. vulpecula occupied refuge habitats characterised by readily available moisture for plant growth (run on areas and/or shallow water tables) and soils with higher soil nutrient concentrations. The impact of fires on these refugia was minimal, as Aboriginal burning practices protected them with mosaic burning generally preventing large-scale fires from developing. Following European settlement, the forces impacting on populations were different in the riparian lowlands from those affecting rocky ranges. In the riparian lowlands, the effects of rabbits and livestock together with predation were found to have the major impact on T. vulpecula populations. Fire was not a significant factor in these areas. In the rocky ranges, fire was the most significant factor affecting T. vulpecula populations. Introduced herbivores did not degrade these habitats as they did in the riparian lowlands because the rugged and steep nature of the ranges acted as a physical barrier. Similarly, predator numbers were lower because of the relative difficulty in moving over rough ground and the generally lower relative abundance of preferred prey such as rabbits. An adaptive management strategy needs to be implemented to determine the effects of different management regimes on T. vulpecula population viability. The key elements of a management strategy in the riparian lowlands involves the manipulation and monitoring of predators, rabbits and livestock numbers. In the rocky ranges, the key management strategy involves the implementation of a patch burning to prevent fires entering habitats occupied by T. vulpecula. Importantly, any management strategies should involve Aboriginal people. Trichosurus vulpecula is an important part of Aboriginal culture. Its decline is of great concern to many people and several of the remaining populations and potential reintroduction locations are on Aboriginal land. Because of their relationship with the land and the animals, people have both the knowledge of the animal and the skills (such as patch burning) to provide information to managers which will assist with management. To achieve these management directions a coordinated national education programme is required to inform and convince the Australian community that conservation of T. vulpecula is deserving of attention in arid and semi-arid Australia. This is particularly important given the perception that T. vulpecula is a common species throughout Australia, despite its massive decline in arid Australia since European settlement.

Electrolyte transport in the intestine of the common brushtail possum (Trichosurus vulpecula) differs from that observed in eutherian mammals. This study has used molecular physiology to identify and characterise the expression and distribution of membrane transporters potentially responsible for these differences in electrolyte transport in the possum intestine. In the possum ileum, secretagogues stimulate an electrogenic Cl⁻-independent HCO₃⁻ secretory response but secretagogue-stimulated Cl⁻ secretion does not occur in this tissue. Based on the ion dependence and pharmacology of the stimulated secretory response, the expression of the cystic fibrosis transmembrane conductance regulator (CFTR), pancreatic Na⁺ HCO₃⁻ cotransporter (pNBC) and Na⁺ K⁺ 2Cl⁻ cotransporter (NKCC1) were investigated in the ileum. Reverse transcription PCR experiments showed that CFTR, pNBC and NKCC1 mRNA transcripts were expressed in the ileal epithelium. It was then demonstrated by in situ hybridisation that both CFTR and pNBC were localised predominantly in the crypts and the levels of expression decreased along the crypt-villous axis towards the lumen. Significantly, the in situ hybridisation results showed that there were low levels of NKCC1 transcript in the ileal epithelium. Western blot studies confirmed that mature CFTR and pNBC proteins were expressed in the ileum, while NKCC1 protein was not detected. The findings of the present study suggest that the absence of Cl⁻ secretion in the ileum is because NKCC1 expression is not elevated in the epithelium. The expression of mature CFTR and pNBC protein suggest that these membrane transporters are involved in the stimulated electrogenic HCO₃⁻ secretory response. The evidence also suggests that CFTR may mediate HCO₃⁻ efflux in the ileum. In contrast, secretagogues do not stimulate an electrogenic secretory response in the proximal and distal colon. This study has shown that CFTR, NKCC1 and pNBC proteins are expressed in the proximal and distal colon. Both NKCC1 and pNBC transcripts were localised to the crypt base in the proximal colon. However, it was shown that CFTR has a punctate distribution and the transcript was predominantly observed in the upper crypt and surface cell region. This study indicated that NKCC1 and pNBC were distributed in a different region of the epithelium compared to CFTR. It was concluded that the distribution of these membrane transporters in different regions of the epithelium accounts for the absence of a stimulated electrogenic secretory response in the possum colon. Given that no stimulated electrogenic secretory response is observed in the colon, it is suggested that HCO₃⁻ secretion by the ileum may have an important physiological role in maintaining an appropriate fluid and pH composition for fermentation in the colonic lumen.

The principal use of sodium monofluoroacetate (1080) in New Zealand is to control brushtail possums (Trichosurus vulpecula). Aerial application of baits containing 1080 is the most common method used for large-scale control of possums. The use of 1080 attracts a great deal of controversy, in particular the effects on the environmental, non-target species, and the potential chronic effects in humans associated with environmental exposures. Although the nature of the acute toxicity of 1080 has been known for more than fifty years, little is known of its effects on humans, in particular its chronic effects to environmental exposures. A benchmark dose (BMD) as an alternative to a no-observed-adverse-effect-level (NOAEL) approach was investigated as a means to improve current health risk assessment values of 1080. Both approaches were investigated for three critical toxicological end points, namely cardiomyopathy, testicular toxicity and teratogenic effects identified from the few available critical studies. The calculated BMDs and lower-bound confidence limits (BMDLs) for the three end points were estimated using the Weibull, probit and quanntal linear models. A benchmark response (BMR) of 10% (extra risk) was chosen and the Akaike�s information criterion (AIC) was used in selecting the appropriate model. The BMDL estimates derived were generally slightly higher but comparable to the corresponding NOAEL for those same endpoints. The computed BMD₁₀ and BMDL₁₀ for cardiomyopathy and testicular effects were 0.21 mg kg⁻�bw⁻� and 0.10 mg kg⁻�bw⁻�, respectively. Tolerable Daily Intakes (TDIs) were derived using the NOAEL approach and the BMD methodology and applying an uncertainty factor of 3000. The resulting TDI using the BMDL were generally consistently slightly higher than those derived using the NOAEL approach. Based on the best fit of modelled dose-response data, a TDI of 0.03 [mu]g kg⁻�bw⁻�day⁻� is proposed for human health risk assessment. Two sets of Provisional Maximum Acceptable Values (PMAV) were derived using the highest concentration of 4.0 [mu]g L⁻� 1080 found in water (N=1450), and using the maximum allowable concentration of 2.0 [mu]g L⁻� of 1080 in water for adults (0.58 [mu]g L⁻� and 0.94 [mu]g L⁻�, respectively) and children (0.23 [mu]g L⁻� and 0.4 [mu]g L⁻�, respectively). Parameters used in the derivation of PMAVs were average weight, average quantity of water consumed, and proportion of total intake allocated to drinking water. The derived adult PMAV of 0.60 [mu]g L⁻� is proposed in revising the PMAV for 1080 in the Drinking Water Standards New Zealand. This value is 6-fold lower than the current PMAV of 3.5 [mu]g L⁻�. Additional toxicology studies are recommended to meet the definition of a "complete database" and therefore estimating a more defensible TDI, and consequently a PMAV for 1080. Risk management approaches are consistent with the Ministry of Health�s current precautionary approach. A PMAV of 0.60 [mu]gL⁻� in drinking water is recommended to consider it suitable for human consumption and that continuous monitoring be carried if the level of 1080 exceeds 50% of the proposed PMAV as a requirement for Priority 2 determinands in the Drinking Water Standards. Precautionary approach appears to be warranted and this was supported by information provided by the Public Health Units (PHU) where 1080 was permitted to be dropped onto drinking water catchments. The PHUs exercised precautionary measures by imposing appropriate conditions to suit local circumstances. As 1080 may likely remain an essential tool to contain tuberculosis spread by possums and to reduce possum damage to forests and crops until better methods of control are developed, a number of recommendations were proposed to protect public health.

In Experiment one 7 Brushtail possums were trained, using food, to perform a Delayed-Matching-To-Sample procedure using still and flickering light stimuli, over a 0, 1 and 2 second delay. A criterion of 80 percent correct for 5 consecutive days was set for the requirement to probe test. Probe session delays were 0, 0.5, 1, 2, 4, and 8 seconds. Performance was analysed using the measure of discrimination log d. Log d = 1 at the possums training delay and dropped back to log d = 0 at the longer inexperienced delays. The possums performance at this task was only adequate, so in case the stimuli were causing discrimination difficulties they were changed for the following experiment to horizontal and vertical light stimuli. Experiment two used the horizontal and vertical light stimuli to further test DMTS in possums. The possum's responding stayed at 50 percent correct, or chance, so the task was changed to a Simultaneous-Choice procedure. However, this did not have any effect on improving their results with responding accuracy remaining at 50 percent correct. Experiment three involved a conditional discrimination procedure, which was implemented to find out whether the possums could in fact discriminate between a horizontal and vertical light. All the possums in this experiment reached 80 percent correct overall and at responding to either a horizontal or vertical light. These results are enough to conclude that it was not the stimuli used in the previous two experiments which that had been causing the difficulties but the task itself. It is not known exactly why the possums were so unsuccessful in performing a DMTS or MTS task. More research into DMTS in possums in greatly needed and would offer a better understanding of the results of this study.