Karen Viggers

Wide range of Chlamydiales types detected in native Australian mammals

The Chlamydiales are a unique order of intracellular bacterial pathogens that cause significant disease of birds and animals, including humans. The recent development of a Chlamydiales-specific 16S rDNA polymerase chain reaction (PCR) assay has enabled the identification of Chlamydiales DNA from an increasing range of hosts and environmental sources. Whereas the Australian marsupial, the koala, has previously been shown to harbour several Chlamydiales types, no other Australian marsupials have been analysed. We therefore used a 16S rDNA PCR assay combined with direct sequencing to determine the presence and genotype of Chlamydiales in five wild Australian mammals (gliders, possums, bilbies, bandicoots, potoroos). We detected eight previously observed Chlamydiales genotypes as well as 10 new Chlamydiales sequences from these five Australian mammals. In addition to PCR analysis we used antigen specific staining and in vitro culture in HEp-2 cell monolayers to confirm some of the identifications. A strong association between ocular PCR positivity and the presence of clinical disease (conjunctivitis, proliferation of the eyelid) was observed in two of the species studied, gliders and bandicoots, whereas little clinical disease was observed in the other animals studied. These findings provide further evidence that novel Chlamydiales infections occur in a wide range of hosts and that, in some of these, the chlamydial infections may contribute to clinical disease.

Adult survival and microsatellite diversity in possums: effects of major histocompatibility complex-linked microsatellite diversity but not multilocus inbreeding estimators

Adult survival is perhaps the fitness parameter most important to population growth in long-lived species. Intrinsic and extrinsic covariates of survival are therefore likely to be important drivers of population dynamics. We used long-term mark-recapture data to identify genetic, individual and environmental covariates of local survival in a natural population of mountain brushtail possums (Trichosurus cunninghami). Rainfall and intra-individual diversity at microsatellite DNA markers were associated with increased local survival of adults and juveniles. We contrasted the performance of several microsatellite heterozygosity measures, including internal relatedness (IR), homozygosity by loci (HL) and the mean multilocus estimate of the squared difference in microsatellite allele sizes within an individual (mean d2). However, the strongest effect on survival was not associated with multilocus microsatellite diversity (which would indicate a genome-wide inbreeding effect), but a subset of two loci. This included a major histocompatibility complex (MHC)-linked marker and a putatively neutral microsatellite locus. For both loci, diversity measures incorporating allele size information had stronger associations with survival than measures based on heterozygosity, whether or not allele frequency information was included (such as IR). Increased survival was apparent among heterozygotes at the MHC-linked locus, but the benefits of heterozygosity to survival were reduced in heterozygotes with larger differences in allele size. The effect of heterozygosity on fitness-related traits was supported by data on endoparasites in a subset of the individuals studied in this population. There was no apparent density dependence in survival, nor an effect of sex, age or immigrant status. Our findings suggest that in the apparent absence of inbreeding, variation at specific loci can generate strong associations between fitness and diversity at linked markers.

How effective is spotlighting for detecting the greater glider (Petauroides volans)

The efficacy of spotlighting as a field survey technique for detecting the greater glider (Petauroides volans) was assessed by comparing the precise location of radio-tracked animals with locations determined simultaneously from spotlighting searches. Radio-collars were fitted to 20 greater gliders in three eucalypt patches embedded within an extensive radiata pine (Pinus radiata) plantation near Tumut in south-eastern New South Wales. Our success rate for detecting collared animals was low, even when survey effort was increased. These findings suggest that spotlighting underestimates actual population size. A further, properly designed study, in different forest types is needed to provide precise estimates of the magnitude of the bias in counts of P. volans obtained by spotlighting.

A population study of the Mountain Brushtail possum (Trichosurus caninus) in the Central Highlands of Victoria

Life-history attributes are described for the mountain brushtail possum (Trichosurus caninus) in mountain ash (Eucalyptus regnans) forest at Cambarville in the central highlands of Victoria, south-eastern Australia. The population was trapped on a regular basis between 1992 and 1995. Population density of T. caninus at Cambarville was high (2.3 animals ha–1). The adult sex ratio was female-biased (1.4 : 1) and the age class structure differed between sexes. There were more adult females than males in very old age classes (those animals assigned to Age Classes 7–9 and exceeding an estimated 10 years of age), whereas there were more males in the young adult cohorts (Age Classes 3 and 4). The breeding season was restricted to March–April, when a single young was produced. A second young was not produced if the first was lost. The survival of young from birth to emergence from the pouch showed strong between-year variation (30–80%). Sex ratios at birth were strongly male-biased (average = 2.6 : 1) but female young were far more likely to survive to advanced back-young stage. Breeding success of females at Cambarville was not influenced by the presence of semi-independent young from a previous year remaining in the natal territory. There was some evidence of senescence in breeding success among females in older age cohorts (Age Classes 7–9) and these animals did not successfully rear young. Many animals were trapped repeatedly at the same place, whereas others ranged over a much wider area (up to 3 ha). There was also considerable overlap between individuals in the spatial location of the areas where they were trapped.

The effects of parasites on a wild population of the Mountain Brushtail Possum (Trichosurus caninus) in south-eastern Australia.

The effects of a reduction of parasite burdens were determined in adult female Mountain Brushtail Possums, Trichosurus caninus, on the birth, mortality and growth rates of pouch-dependent young, as well as the haematological and serum biochemical values of the mothers. The efficacy of the anthelmintic drug ivermectin for reducing parasite burdens in this host was assessed using faecal and necropsy examinations of a small number of animals. Ivermectin began to reduce parasite burdens by 48 h after treatment. In the second stage of the experiment, animals were treated or sham injected (control individuals) with ivermectin and praziquantel at 8-10-week intervals throughout the breeding season to the time of emergence of young from the pouch. Treatment with ivermectin and praziquantel had no significant effect on the proportion of females giving birth, or on the survival of young to emergence. An effect of treatment was recorded for absolute eosinophil counts in adult females, which, in spring; were higher among control animals than those that were treated.

Hematological and Plasma Biochemical Values of the Greater Glider in Australia

Reference hematological and plasma biochemical values are presented for the greater glider (Petauroides volans) at Tumut (southeastern New South Wales, Australia). Nineteen animals were sampled during a capture period of 1 wk in August 1999. Values for red cell counts were significantly higher in male animals (x̄ ± SE; males: 5.6 ± 0.1; females: 5.2 ± 0.1). Young animals had higher white cell counts than older ones (x̄ ± SE; young: 4.9 ± 0.4; older: 2.8 ± 0.4). Lymphocytes were the predominant white blood cell type in this species.