Social interactions among captive brushtail possums (Trichosurus vulpecula)

A biological control strategy relying on a self-disseminating agent may provide the only affordable long-term technique for reducing brushtail possum (Trichosurus vulpecula) numbers throughout New Zealand. The objective of this study was to determine the frequency and patterns of social interactions in single and mixed-sex groups of possums, in order to identify interactions that may assist in the dissemination of biocontrol agents. Thirty-two sexually mature wild-caught possums (16 female, 16 male) were housed in captive groups (of four) in enclosures during the breeding and non-breeding seasons. Groups consisted of either all females, females and males or all males. Four types of social interactions were defined: threats, fights, affiliative and sexual interactions. Interactions only occurred between two animals at one time and were most frequent in the non-breeding season. Within all female groups, possums readily engaged in interactions that had either an agonistic or affiliative nature. Mixed-sex groups interacted less frequently than females, but also engaged in both agonistic and affiliative interactions. In contrast, possums in all male groups rarely interacted, with only a few fights and no affiliative interactions observed. Some mixed-sex dyads appeared to 'associate' during the breeding period. Young were produced by three females that regularly associated with a male and one female that showed little associative behaviour. Given the different interaction patterns observed in each group type, biological control agents that rely on specific interaction patterns for dissemination, are likely to spread at different rates among different possum groups and in different seasons.     

Den sharing behaviour of captive brushtail possums (Trichosurus vulpecula)

Abstract

Den sharing among wild brushtail possums (Trichosurus vulpecula) has important implications for disease transmission. This study investigated den sharing in captive possums, and measured interactions between possums sharing dens. Thirty‐four sexually mature possums (16 female, 18 male) were housed in single‐sex or mixed‐sex pairs in large enclosures that contained two dens. Daily patterns of den sharing were recorded for each pair over a 69 day period in the breeding or non‐breeding season. Social behaviour within shared dens was sampled using miniature infrared cameras. Male pairs rarely shared dens in the breeding or non‐breeding seasons (4% and 1% of days respectively) and usually engaged in ‘threats’ and ‘fights’ associated with den defence. Pairs of female possums (in both seasons) and mixed‐sex pairs housed together in the breeding season shared dens most frequently (between 84% and 91% of days), and also spent the most time together in dens each night. While sharing dens, affiliative interactions were frequent, including long periods of ‘touching’, and also ‘food sharing’ and ‘allogrooming’. The preference for den sharing and close contact shown by captive possums highlights the importance of den sharing as a potential route for disease transmission.     

Body size, age and paternity in common brushtail possums (Trichosurus vulpecula)

Sexual selection should produce sexual size dimorphism in species where larger members of one sex obtain disproportionately more matings. Recent theory suggests that the degree of sexual size dimorphism depends on physical and temporal constraints involving the operational sex ratio, the potential reproductive rate and the trade-off between current reproductive effort and residual reproductive value. As part of a large-scale experiment on dispersal, we investigated the mating system of common brushtail possums inhabiting old-growth Eucalyptus forest in Australia. Paternity was assigned to 20 of 28 pouch-young (maternity known) genotyped at six microsatellite loci. Male mating success was strongly related to body size and age; male body weight and age being highly correlated. Despite disproportionate mating success favouring larger males, sexual size dimorphism was only apparent among older animals. Trapping and telemetry indicated that the operational sex ratio was effectively 1 : 1 and the potential reproductive rate of males was at most four times that of females. Being larger appeared to entail significant survival costs because males 'died-off' at the age at which sexual size dimorphism became apparent (8-9 years). Male and female home ranges were the same size and males appeared to be as sedentary as females. Moreover, longevity appears to be only slightly less important to male reproductive success than it is to females. It is suggested that a sedentary lifestyle and longevity are the key elements constraining selection for greater sexual size dimorphism in this 'model' medium-sized Australian marsupial herbivore.     

Maternal influence on philopatry and space use by juvenile brushtail possums (Trichosurus vulpecula)

1. The causes of juvenile sex-biased philopatry and space use in mammals remain poorly understood, and results of previous research have been conflicting. Experimental interventions and manipulations on wild populations are rare, but can play an important role in establishing the factors governing offspring space use. 2. We experimentally removed mothers of independent juvenile brushtail possums from the maternal home range and examined changes in offspring space use with global positioning system collars. We examined the influence of mother absence on philopatric behaviour, and determined whether or not maternal presence affected offspring space use. 3. We fitted a longitudinal linear mixed effects model to demonstrate a change over time in the home range size of juveniles following experimental treatment by the removal of their mothers. When mothers were removed from the natal range, juveniles occupied significantly larger home range areas, with average increases of 175% in 95% kernel density estimates and 289% in minimum convex polygon estimates. This increase occurred within the first month following mother absence and was independent of juvenile sex. Home ranges of control juveniles did not change during the same time period. 4. Changes in the spatial structure of mammalian populations in response to removal of individuals have important implications for pest management. The impacts of management strategies which target particular individuals in a population may counteract conservation benefits through their effect on the space use of survivors. Studies involving experimental removals provide important information on consequences of control and also yield insights into the causes of mammalian space use, philopatric behaviours and ultimately dispersal.     

Understanding home range behaviour and resource selection of invasive common brushtail possums (Trichosurus vulpecula) in urban environments

Because invasive species are often opportunistic and behaviourally flexible, they tend to be successful in urban landscapes, where they may use space differently than in their more traditional habitats. Consequently, control strategies developed for invasive pest species in non-urban areas may not succeed in an urban context. Using GPS tracking, we examined habitat use by an invasive pest, the brushtail possum (Trichosurus vulpecula) in residential New Zealand habitats; these habitats comprise a large proportion of the urban landscape and are currently not targeted for pest control. We predicted that home ranges of possums in residential areas would be larger than those in non-urban habitats due to lower densities of their primary food resource, plant material; that possums would prefer forest fragment habitat; and that they would avoid roads due to the mortality risk. Home range sizes estimated using mechanistic Brownian bridges and 100 % minimum convex polygons were smaller or similar in size to those recorded in rural and forest habitats. Resource utilization functions and the regression of utilization distribution probabilities against environmental variables showed that possums selected forest fragments primarily, followed by residential habitat characterised by large gardens with a degree of vegetative structural complexity. Roads were not avoided. Control operations should expand their scope to include residential areas containing mature, diverse vegetation rather than only focussing on forest fragments, a strategy that ignores biodiversity values in residential habitats, and is likely to be unsuccessful due to reinvasion potential from neighbouring residential areas.     

Presence of males affects the incidence of ovulation after pouch young removal in brushtail possums (Trichosurus vulpecula)

The traditional method for inducing and synchronising oestrus in the brushtail possum (Trichosurus vulpecula) is by removal of their suckling pouch young (RPY). However, our studies have recently shown that, in addition to wide variation between animals in the time of ovulation after RPY, a proportion of animals failed to ovulate. Evidence from several mammalian species indicates that the presence of males can stimulate ovarian activity and synchronise oestrus in females. The aim of this study was to determine the effect of the male on the oestrous cycle of the female brushtail possum after RPY. A total of 67 adult female brushtail possums were treated as three replicates. In order to observe the day of preovulatory follicle emergence and ovulation, animals underwent laparoscopic examination at 1–4 day intervals over a period from 0–21 days after RPY. The first replicate (N=18, May/June 1995) involved only animals kept in isolation from males, whereas the two remaining replicates compared ovarian responses between animals kept with (N=10, July 1995; N=14, June 1996) or in isolation from (N=10, July 1995; N=15, June 1996) males. The incidence of ovulation after RPY was significantly higher in females that were housed with males than in those kept in isolation from males (100%, 92.8% vs. 50.0%, 66.7%, 14.3%; P<0.001). Every animal that ovulated, had previously had a preovulatory follicle present at the site where the corpus luteum formed. Conversely, none of the animals that failed to ovulate, developed a preovulatory follicle during the period of study. The range of mean day of preovulatory follicle emergence (6.00–6.86 days), of ovulation (11.80–12.20 days) and the synchrony of ovulation between animals (range 8–17 days) after RPY, were not significantly affected by the presence of males. This study demonstrates for the first time, that the presence of males significantly increases the incidence of ovulation after RPY in the brushtail possum. However neither the timing of reproductive events nor the synchrony of ovulation were affected by presence of the male.     

Reproductive capability of brushtail possums (Trichosurus vulpecula) transferred from the wilds of Brisbane, Adelaide, and Armidale into captivity in Brisbane

The transfer of animals from the wild into captivity is an important strategy for the conservation of species that are under threat of extinction. To determine the reproductive capability of animals following transfer from the wild, brushtail possums relocated from Brisbane, Adelaide, and Armidale into captivity in Brisbane were monitored. Seventy five percent of the Brisbane possums (N = 80) gave birth during the months from March to May following transfer from the suburbs of Brisbane and 75% of the young born reached weaning. Thirteen adult females and four adult male brushtail possums were relocated from Adelaide into captivity in Brisbane in June 1994. Four young were born in Brisbane, however none survived to weaning and all the relocated possums had died 2 years after their transfer from Adelaide. Seventeen adult females and seven adult male possums were transferred from Armidale to Brisbane in July 1996. In the first year, 1997, four young were born in Brisbane and none survived to weaning. In the second year, three young were born and survived to weaning. Two years after their transfer, one adult male and three adult females from Armidale and three juvenile possums were housed in the Brisbane enclosures. As the Brisbane, Adelaide, and Armidale possums received the same photoperiod and environmental conditions, some factor must have inhibited breeding activity in the Adelaide possums and to a lesser extent in the Armidale possums. The ability of the Armidale possums to give birth and wean their young after 2 years in Brisbane would suggest that relocated possums require up to 2 years in order to adjust sufficiently to their new environment to reproduce. However, the failure of the Adelaide possums to reproduce successfully after a similar period of time in Brisbane suggests that certain environmental differences inhibit the ability of different populations of possums to adjust to a new environment. J. Exp. Zool. 284:783-788, 1999. Copyright 1999 Wiley-Liss, Inc.     

The development of thermoregulation in the marsupial brushtail possum Trichosurus vulpecula

• 1.1. The adult possums showed a circadian rhythm of body temperature with a peak in temperature around midnight and a nadir at noon.
• 2.2. The young possum within the pouch displayed a circadian rhythm with the highest temperatures during the day and the lowest in the early evening.
• 3.3. Although the body temperature of the young possum exceeded that of the mother occasionally, for the major part of the 24 hr the body temperature of the young was lower than that of the mother.
• 4.4. The young possum could maintain a steady body temperature between 140 and 167 days post partum. A circadian rhythm of temperature was observed between 157–190 days post partum.
• 5.5. All adipose tissue examined with the light and electron microscope had the morphology of white adipose tissue.

     

Oral toxicity of p-aminopropiophenone to brushtail possums (Trichosurus vulpecula), dama wallabies (Macropus eugenii), and mallards (Anas platyrhynchos)

Development of p-aminopropiophenone (PAPP) as a toxicant for pest predator management in New Zealand and Australia prompted investigation of its toxicity to potential nontarget species. Acute oral toxicity of PAPP in brushtail possums (Trichosurus vulpecula), dama wallabies (Macropus eugenii), and Mallards (Anas platyrhynchos) was estimated in pen trials, carried out between February 2000 and September 2001. The susceptibility of possums (LD50>or=500 mg kg(-1)) and wallabies (LD50 89 mg kg(-1)) to PAPP was low in comparison to noncarnivorous placental mammal species, but ducks (LD50 38 mg kg(-1)) were more susceptible than other bird species. These results suggest that the nontarget hazard to possums and wallabies from PAPP bait applied for pest predator control would be low. However, future development of PAPP as a vertebrate pest control agent should include rigorous assessments of the hazard posed by bait formulations to bird species and provision for delivery techniques that could mitigate exposure of nontarget birds.     

Tissue distribution of cytochrome P450 3A (CYP3A) in brushtail possums (Trichosurus vulpecula) exposed to Eucalyptus terpenes

We evaluated the distribution pattern of a specific xenobiotic metabolizing enzyme, cytochrome P450 3A (CYP3A) in the common brushtail possum (Trichosurus vulpecula). Western blot studies using CYP3A antibodies were used to compare CYP3A levels in the intestine, liver, kidney, brain, testes and adrenal gland in possums fed diets with and without a mixture of terpenes. Possums appear to produce at least 3 different CYP3A-like isoforms that are differentially expressed in various tissues. The liver and duodenum produce all three isoforms (CYP3A P1, P2, P3), the jejunum only produces CYP3A P1, the ileum, kidney, testes and adrenal only produce CYP3A P2 and the brain only produces CYP3A P3. Terpene treatment did not alter relative levels of isoforms present in any tissue type. This study is the first to identify the presence and differential expression of several CYP3A-like isoforms in a variety of tissues of a wild mammalian herbivore. Data suggest that CYP3A-like enzymes are not induced by terpenes. However, the wide distribution of CYP3A-like isoforms in a variety of tissues, suggests that these enzymes are an important mechanism for metabolism in possums and may contribute to the high tolerance possums have to a wide range of xenobiotics.     

Acid loads induced by the detoxification of plant secondary metabolites do not limit feeding by common brushtail possums (Trichosurus vulpecula)

We fed common brushtail possums artificial diets containing a buffer and the plant secondary metabolite (PSM), orcinol, to test the hypothesis that organic acids, common products of PSM metabolism, limit feeding by common brushtail possums (Trichosurus vulpecula). We introduced several diets containing orcinol and a buffer (urinary alkalising agent) over a course of three experiments. A diet containing 2% orcinol (wet matter) caused possums to reduce their food intake immediately, but feeding returned to normal 1–2 days later. Even though possums excreted strongly acidic urine (pH 5.1) and had perturbed nitrogen metabolism, they maintained their food intake and body mass until the experiment terminated 9 days after the introduction of orcinol. Possums ate 52% less when the basal diet contained 4% orcinol. As expected, the acid loads caused a change in the composition of urinary nitrogen with possums excreting more ammonium than urea and a large amount of unidentified nitrogenous material. Supplementing the diet containing orcinol with buffer neutralised the metabolic acid load and partly restored normal nitrogen metabolism, but did not restore feeding. Also, animals eating orcinol excreted normal amounts of 3-methylhistidine, indicating no increase in muscle protein catabolism. This suggests that a limitation to the rate of detoxification or toxicosis, rather than acid loads, limits the ingestion of acid-inducing PSMs.     

Natural immigration of brushtail possums,Trichosurus vulpecula,onto Aroha Island,Kerikeri Inlet,Bay of Islands,New Zealand

Abstract

Aroha is a 5 ha island in Kerikeri Inlet, Bay of Islands, which is joined to the North Island mainland by a 200 m long causeway. Introduced Australian brushtail possums (Trichosurus vulpecula) spread into the general area only in the mid 1970s, and were first trapped on Aroha Island in June 1979. Since then possums have regularly crossed the causeway, and have been systematically trapped to keep the island free of them. Two hundred and sixty two possums have been trapped on Aroha Island to December 1990, and the annual catch has increased steadily since 1981. About equal numbers of males and females have been trapped. Most possums were caught in March-April and fewest in July-August. Captures on the island were clustered, particularly during the breeding seasons. Average body weight was 2.2 kg; 97% were greys and 3% blacks; the young of females trapped on the island had been born in all months except December to February. In colour, body weight, and breeding pattern the possums trapped on Aroha Island were similar to other possum populations from the northern North Island. Most of the possums invading Aroha Island were 1-2 years old: in contrast to findings from previous studies of possum dispersal, Arona Island was invaded year-round by young male and female possums equally. Some older animals may also have been attracted to the island by fruits available in an orchard there. Maintenance of the possum-free state of Aroha Island will require continuous management.     

Leptospirosis serology in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia

The common brushtail possum (Trichosurus vulpecula) is indeed a common marsupial in major cities of Australia. This species is known to be susceptible to leptospirosis and often lives in close contact with humans, raising concerns about the potential for transmission of this disease in urban areas. A total of 192 brushtail possum blood samples were collected from 136 individuals in suburban areas of metropolitan Sydney from November 2002 to November 2004. Sera were screened against a reference panel of 21 Leptospira spp. using the microscopic agglutination test. Leptospiral antibodies were detected in 9.6% (13/136) of tested brushtail possums and represented two serovars; antibodies to Leptospira interrogans serovar Hardjo were most frequently identified (11/136). A representative of the exotic sero-group Ballum, most likely serovar Arborea, was found in two of 136 brushtail possums. Exposure to leptospirosis seemed to be associated with age, as older animals had a higher incidence, but there was no distinction in relation to gender. Antibody prevalence varied between the different sampling sites and seropositive animals were clustered and restricted to a few sites. These data support the possible role of brushtail possums as a maintenance host for Leptospira spp. in urban environments and also identified them as a previously unknown and potential source of serovar Arborea.     

Endogenous type D retrovirus in a marsupial, the common brushtail possum (Trichosurus vulpecula)

We have sequenced and characterized an endogenous type D retrovirus, which we have named TvERV(D), from the genome of an Australian marsupial, the common brushtail possum (Trichosurus vulpecula). Intact TvERV(D) gag, pro, pol, and env open reading frames were detected in the possum genome. TvERV(D) was classified as a type D retrovirus, most closely related to those of Old World monkeys, New World monkeys, and mice, based on phylogenetic analyses and genetic organization. Approximately 30 TvERV(D) proviruses are present in the genomes of possums, as detected by Southern hybridization. However, variability in fragment patterns between possums was observed and suggests recent (or ongoing) retrotranspositional activity.     

Chemical characterization of milk oligosaccharides of the common brushtail possum (Trichosurus vulpecula)

Structural characterizations of marsupial milk oligosaccharides have been performed in only three species: the tammar wallaby, the red kangaroo and the koala. To clarify the homology and heterogeneity of milk oligosaccharides among marsupials, 21 oligosaccharides of the milk carbohydrate fraction of the common brushtail possum were characterized in this study. Neutral and acidic oligosaccharides were separated from the carbohydrate fraction of mid-lactation milk and characterized by ¹H-nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The structures of the 7 neutral oligosaccharides were Gal(β1-3)Gal(β1-4)Glc (3’-galactosyllactose), Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc (3”, 3’-digalactosyllactose), Gal(β1-3)Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc, Gal(β1-3)Gal(β1-3)Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc, Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (lacto-N-novopentaose I), Gal(β1-3)Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (galactosyl lacto-N-novopentaose I), Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-3)Gal(β1-4)Glc (galactosyl lacto-N-novopentaose II). The structures of the 14 acidic oligosaccharides detected were Neu5Ac(α2-3)Gal(β1-3)Gal(β1-4)Glc (sialyl 3’-galactosyllactose), Gal(β1-3)(O-3-sulfate)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (lacto-N-novopentaose I sulfate a) Gal(β1-3)[Gal(β1-4)(O-3-sulfate)GlcNAc(β1-6)]Gal(β1-4)Glc (lacto-N-novopentaose I sulfate b), Neu5Ac(α2-3)Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc, Neu5Ac(α2-3)Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (sialyl lacto-N-novopentaose a), Gal(β1-3)(?3-O-sulfate)Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc, Gal(β1-3)Gal(β1-3)[Gal(β1-4)(?3-O-sulfate)GlcNAc(β1-6)]Gal(β1-4)Glc, Gal(β1-3)[Neu5Ac(α2-6)Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (sialyl lacto-N-novopentaose b), Neu5Ac(α2-3)Gal(β1-3)Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc, Gal(β1-3)(?3-O-sulphate)Gal(β1-3)Gal(β1-3)Gal(β1-3)Gal(β1-4)Glc, Neu5Ac(α2-3)Gal(β1-3)Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc, Gal(β1-3)(?3-O-sulphate)Gal(β1-3)Gal(β1-3)[Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc, Gal(β1-3)Gal(β1-3)Gal(β1-3)[Gal(β1-4)(?3-O-sulphate)GlcNAc(β1-6)]Gal(β1-4)Glc and Gal(β1-3)Gal(β1-3)[Neu5Ac(α2-6)Gal(β1-4)GlcNAc(β1-6)]Gal(β1-4)Glc (galactosyl sialyl lacto-N-novopentaose b). No fucosyl oligosaccharides were detected. Galactosyl lacto-N-novopentaose II, lacto-N-novopentaose I sulfate a, lacto-N-novopentaose I sulfate b and galactosyl sialyl lacto-N-novopentaose b are novel oligosaccharides. The results are compared with those of previous studies on marsupial milk oligosaccharides.