- Programme Title:Social organisation of possums
- Programme Title:Social behaviour and pathogen transmission of possums
3.3 Behaviour and Pathogen Transmission
One programme investigated the use of scent marks in affecting possum population and movements
and the other researched what social behaviour in possums led to the transmission of disease organisms
3.3.1
Programme Title: Social organisation of possumsResearch Leader:Professor D Stoddart (K Hynes, PhD student) Institution:University of Tasmania |
Summary
This was the final year for research to examine the presence of the resident possums’ scent marks and foreign scent on habitat fidelity and population processes. This included examining the histology (microscopic studies) of scent glands collected from both road kills and wild possums.
The research enabled description of the sternal scent organ, which was found to be more developed in autumn, winter and summer than in spring and early summer for both sexes. Data suggests that maximal activity of the sebaceous (fatty) component of the organ occurs during winter and early spring for both sexes. The size of the nuclei in the apocrine secretory tissue in both sexes was minimal during that time. Thus it appears as if the pattern of secretion of the two components might be temporally complementary.
Description
To continue to determine the extent to which population stability is maintained by the presence of the residents’ scent marks, and what effect "foreign" scent has on habitat fidelity and population processes including by:
- analysing possum movement data collected in 1994;
- completing histological work on material of scent glands collected from Feb 94 to Jan 95; and
- completing analysis of secretary hormones in blood samples collected between Jun 94 and Jan 95.
Approach & Outcomes
Two methods were used to examine the development and annual cycle of the sternal scent gland. One was to collect road-killed brush-tailed possums from Tasmania roads. Ninety male and 32 female possums were collected. The dermal sternal gland and other materials were collected from these carcases. This sample was used to establish a reference baseline for determination of any widespread trends in glandular development. The other method was to remove a biopsy from each of the resident possums on the study site in the Mt. Morrison state forest, Tasmania, and take a blood sample for hormone analysis by radio-immuno-assay.
Data was obtained for males on body weight, testis size and the concentration of testosterone, and for females, body weight, the presence of a pouch, and progesterone concentration. Data were also obtained for males and females on the mean sternal gland thickness, sebaceous tissue nuclear diameter, apocrine nuclear diameter and apocrine gland lumen diameter respectively. This data enabled description of the sternal scent organ, which was found to be more developed in autumn, winter and summer than in spring and early summer for both sexes. Measurements of the size of the nuclei in the sebaceous secretory tissue suggested that maximal activity of the sebaceous component of the organ occurs during winter and early spring for both sexes. The size of the nuclei in the apocrine secretory tissue in both sexes was minimal during that time. Thus it appears as if the pattern of secretion of the two components might be temporally complementary.
Results from this study have not been fully analysed and written up. This programme is part of a PhD study which is due to be completed soon.
3.3.2
Programme Title: Social behaviour and pathogen transmission of possumsResearch Leader:Dr C O’Connor Institution:Animal Behaviour & Welfare Research Centre (ABWRC) Hamilton |
Summary
This programme aims to identify environmental and social interactions that influence Leptospira interrogans serovar balcanica transmission in possums, in order to facilitate the identification of appropriate vectors and the development of biological control strategies.
Possums were infected with L. interrogans serovar balcanica. The infectious and nonpathogenic characteristics of balcanica suggest that it may be suitable as a biological control vector. Behavioural observations showed that interactions such as food sharing, allogrooming, den sharing and fighting would not necessarily lead to balcanica transmission. Therefore, sexual behaviour appears to be important in the transmission of balcanica at low possum densities and over short time periods. A sexual mode of transmission suggests that balcanica is likely to be possum-specific.
Description
To facilitate the development of biological control strategies associated with the use of pathogens, by identifying environmental and social interactions that influence the pattern and rate of transmission of disease organisms between possums in both captive and wild populations by:
- establishing possum colonies free from L. interrogans serovar balcanica;
- developing appropriate protocols for serum and urine testing to determine if individual possums have the bacteria;
- establishing the principal environmental and behavioural modes of transmission of balcanica between possums; and
- investigating the influence of animal density, age, social and physiological status on the spread of balcanica.
Approach & Outcomes
Possums were readily infected with balcanica (100% conversion) by inoculation with 108 organisms. Infection caused reduced daily food intake and an associated loss in body weight which had fully recovered by 96 days after inoculation. The infectious and nonpathogenic characteristics of balcanica suggest that it may be suitable as a biological control vector.
Environmental balcanica transmission was examined in cages and grass enclosures by exposing uninfected possums to areas recently inhabited by experimentally infected possums. None of the 16 uninfected possums exposed to contaminated environments (shown to contain leptospires) became infected with balcanica, suggesting flat environmental exposure alone was insufficient to allow transmission.
Rates of balcanica transmission in 13 pairs of possums (3 female/female, 6 male/female and 4 male/male pairs; one infected animal in each pair), in grass enclosures were recorded over a 69 day period. Social balcanica transmission occurred in three of the six male/female pairs, but not in any single sex pairs. Behavioural observations showed that interactions such as food sharing, allogrooming, den sharing and fighting would notnecessarily lead to balcanica transmission. Therefore, sexual behaviour appears to be important in the transmission of balcanica at low possum densities and over short time periods. A sexual mode of transmission suggests that balcanica is likely to be possum-specific, an essential characteristic for a prospective biocontrol vector.
Publications
Day, T.D.; Waas, J.R.; Carey, P.W.; O'Connor, C.E.; Matthews, L.R. and Pearson, A.J. (1996): Leptospirosis transmission in the brushtail possum, Trichosurus vulpecula. Is serovar balcanica environmentally transmitted? Journal of Wildlife Diseases, (submitted).
Day, T.D.; Waas, J.R. and O'Connor, C.E. (1996): Effect of an experimental infection with Leptospira interrogans serovar balcanica on the health of brushtail possums, Trichosurus vulpecula. New Zealand Veterinary Journal, (submitted).
Day, T.D. (1996): Leptospira interrogans serovar balcanica transmission in the brushtail possum, Trichosurus vulpecula. Unpublished M. Sc. thesis, University of Waikato, Hamilton.
Contract Reports
Pearson, A.J. and Ashby, M.G., (1995): The incidence and spread of Leptospirosis among possums of the Ruakura Colony 1982-1984. MAF Policy contract report, March.
Conferences
Carey, P.W. and O'Connor, C. E. (1995): Social behaviour and pathogen transmission in possums. NSSC Possum Biocontrol Workshop. Wallaceville, April.
Day, .T.E.; Waas, J.R.; O'Connor, C.E.; Matthews, L.R. and Pearson, A.J. (1996): Leptospirosis transmission in brushtail possums. New Zealand Possum Pathogen Meeting, Wallaceville, July.
Contact for Enquiries
Farm Monitoring Programme Manager
Monitoring and Evaluation
MAF Policy
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0623
Fax: +64 4 894 0741
Contact this person
