James MacGregor

Population age structure is an important parameter for wildlife population modelling. However, for many species it is not possible to accurately assess the age of adult individuals. We present a hypothetical example to illustrate a previously described method of determining population age structure from the survivorship of individuals of unknown ages that to our knowledge is unused in the fields of zoology and ecology. We then apply this method to data collected over 10 years for a population of wild platypuses (Ornithorhynchus anatinus), a species whose adult individuals cannot be accurately aged and for which only limited data on life history characteristics are available. Our results show a lower mortality rate over the first years of life of platypuses than the one previous study available for comparison, and suggested a Type I or Type III survivorship curve.

Introduction
Physiological responses to anaesthesia are described for the first time in eastern barred bandicoot (EBB; Perameles gunnii) and southern brown bandicoot (SBB; Isoodon obesulus).

Method
Two hundred and six field anaesthetics were carried out on free-ranging bandicoots (82 EBB and 66 SBB) in North West Tasmania. Animals were induced and maintained under general anaesthesia using isoflurane administered via a face mask.

Results
On average, animals required 3% isoflurane for anaesthesia maintenance and recovered within 2–3 min of isoflurane being discontinued. SBB had higher respiratory rates than EBB. Otherwise, we found no significant differences in anaesthetic parameters between the bandicoot species, between sexes or for females with pouch young. Hypothermia was the only anaesthetic-associated adverse event during this study, occurring in 26 anaesthetics (12.6%). At the start of anaesthesia, bandicoots had a mean body temperature of 35.0°C (SEM 0.8, SD 1.2), and 95% of animals lost temperature during anaesthesia. Bandicoots with an initial body temperature of less than 34.5°C had 20 times greater risk (odds ratio 20.52, 95% CI 5.58–77.19) of developing hypothermia (defined as Tb < 33°C). Heart rates ranged from 100 to >300 beats per minute, and respiratory rates ranged from 8 to 64 breaths per minute. Data support a heart rate reference interval of 140–285 (mean 208, SD 42.72) and a respiratory rate interval of 10–34 for SBB (mean 21, SD 8.89) and 8–20 for EBB (mean 12, SD 4.72) during maintenance of inhalant anaesthesia.

Conclusions
With hypothermia the only anaesthesia-related adverse event during this study, results support the safety of this form of chemical restraint in the field and provide empirical data that may be used to guide anaesthesia for bandicoots. Results suggest that standard inhalational anaesthetic protocols are suitable for bandicoots irrespective of weight, sex and reproductive status.

The platypus (Ornithorhynchus anatinus) is an amphibious, egg-laying mammal of high conservation value that is found only in Australia. The zoonotic bacterium Leptospira interrogans serovar Hardjo was discovered in platypuses in prior studies, but little is known about its epidemiology. Samples in the Platypus Serum Bank were tested in 2023 and the results were combined with historical records. Antibodies against L. interrogans serovar Hardjo were found in 50% of 464 serum samples from 411 platypuses collected from 14 river basins in southeastern Australia between 1981 and 2012; prevalence remained high over three decades in the Shoalhaven River population. Seroprevalence increased with age, suggesting environmental exposure. Individual platypuses had persistent titres, some for six years. Seropositive females lactated, juveniles were recruited into the population, and there were no reports of clinical leptospirosis. Three necropsied platypuses were seropositive and had mild nephritis with leptospires in the renal tubules. The high seroprevalence, persistent titres, lack of disease, mild renal lesions, and renal colonisation suggest the platypus may be a maintenance host. Sympatric cattle had L. interrogans serovar Hardjo titres, but the spatial association was statistically weak. Other mammalian wildlife species and sheep also have L. interrogans serovar Hardjo titres; therefore, a complex ecological network must be considered. A landscape-wide study is recommended to properly assess transmission pathways and confirm who is infecting whom.

Genetic diversity at loci concerned with fitness is an important part of the ability of a wild population to adapt to changes in its environment, including climatic events, disease and pollution. Research into the effects of genetic diversity on the impacts of disease on wildlife populations has focussed on genes of the major histocompatibility complex (MHC). This study investigated the genetic diversity at the MHC class II DZB gene, as well as the distribution of alleles of the same gene, for platypuses Ornithorhynchus anatinus in the Seabrook Creek Catchment in northwest Tasmania. This study detected 10 previously identified alleles and two previously unreported alleles at the MHC Class II DZB locus in 18 platypuses from the Seabrook Creek Catchment. An additional sequence isolated from two individuals was consistent with a pseudogene. Alleles were reasonably well distributed geographically through the catchment, but there was evidence of a degree of isolation at one site. Consistent with evidence that smaller wildlife populations have relatively low genetic diversity, and that there is relatively slow gene flow between river catchments, the observed genetic diversity at the MHC Class II locus was lower than those in larger previously studied river catchments but higher than those in two island populations. Consequently, this population of platypuses may have a limited capacity to respond to new infectious challenges, such as the fungal disease mucormycosis.

Worldwide, Ehrlichia spp. are emerging infectious organisms of domestic animals and people, however, most Ehrlichia spp. naturally infect wildlife reservoirs causing mainly asymptomatic infections. Australian ecosystems have been under-explored for these potentially pathogenic organisms, and recent studies have identified a range of novel Ehrlichia, and their sister genera, Anaplasma and 'Candidatus Neoehrlichia' species, from native Australian ticks. We used bacterial 16S rRNA (16S) next-generation sequencing and genus-specific PCR to profile the bacterial communities in platypus (Ornithorhynchus anatinus) blood samples and platypus ticks (Ixodes ornithorhynchi), and identified a high prevalence of Ehrlichia sequences. We also observed Ehrlichia-like intra-neutrophilic inclusions (morulae) in PCR-positive stained platypus blood films that were consistent in morphology with other Ehrlichia spp. Bayesian phylogenetic analysis of 16S (1343 bp), gltA (1004 bp), and groEL (1074 bp) gene sequences group the platypus Ehrlichia with 'Candidatus Ehrlichia khabarensis' from far-eastern Russia, and demonstrate that the platypus Ehrlichia is clearly distinct from all other Ehrlichia spp. Enough genetic divergence exists to delineate this platypus Ehrlichia as a separate species that we propose to designate 'Candidatus Ehrlichia ornithorhynchi'. There is no evidence that 'Candidatus Ehrlichia ornithorhynchi' causes disease in wild platypuses, however, the organism does seem to be widespread in Australia, being found in both Queensland and Tasmania. 'Candidatus Ehrlichia ornithorhynchi' is the second native Australian Ehrlichia described and adds to the rapidly growing diversity of recently described native Australian tick-borne bacteria.

Changes in the health of individuals within wildlife populations can be a cause or effect of population declines in wildlife species. Aspects of individual platypus (Ornithorhynchus anatinus) health have been reported. However, holistic studies investigating potential synergistic effects of both pathogens and environmental factors are needed to expand understanding of platypus individual health. We collected baseline data on the health of platypuses in two Tasmanian river catchments (including evidence of the potentially fatal fungal disease mucormycosis) and on individual, demographic, and geographic patterns associated with health data results. We examined 130 wild platypuses from the Inglis River Catchment and 24 platypuses from the Seabrook Creek Catchment in northwest Tasmania between 29 August 2011 and 31 August 2013. More than 90% of captured platypuses were infected with ticks, Theileria spp., and trypanosomes. Evidence of exposure to other infections, including Salmonella spp., Leptospira spp., and intestinal parasites, was low (<10%). Three platypuses had single fungal granulomas in the webbing of a forefoot, but no evidence of mucormycosis was found in any of the study animals. Possible subclinical hepatopathies or cholangiohepatopathies were found in six platypuses. Exposure to infectious agents did not cluster geographically, demographically, or in individuals, and there was minimal evidence of morbidity resulting from infection. This study has provided important baseline data for monitoring the effects of threatening processes, including mucormycosis, on the health of infected populations.

Seasonal changes in hematology and serum biochemistry results, described by separate reference intervals for different seasons, have been reported in many animals. We developed a novel method to investigate seasonal variation in values and a reference tool (the reference curve) based on sine wave functions that, for suitable variables, represents data more appropriately than a fixed reference interval. We applied these techniques to values observed in blood samples from 126 adult wild platypuses (Ornithorhynchus anatinus; 58 females and 68 males). Samples were collected under isoflurane anesthesia from animals captured in the Inglis Catchment in northwest Tasmania. In general, packed cell volume (PCV), red cell count (RCC), and hemoglobin (Hb) values appeared to be lower than those in two studies that previously reported platypus hematology reference intervals. This likely resulted from reduced stress-related splenic contraction or isoflurane-associated splenic sequestration of red blood cells in our study. Reference curves were described for five variables (PCV, RCC, Hb, albumin, and magnesium). We found evidence that this seasonal variation may result from metabolic changes associated with seasonal variations in environmental temperature. These observations suggest that it is important for researchers reporting platypus hematology and serum biochemistry to look for seasonal changes in their data to ensure it is appropriately interpreted.

Body condition is an important aspect of the health of any animal. The current standard method of body condition assessment in the platypus is the tail volume index (TVI). Although the tail is the largest repository of fat in the platypus, the reliability of TVI has not been adequately demonstrated. The aims of this study were, first to assess performance of the TVI, and second, to develop and evaluate performance of new techniques for routine field assessment of platypus body condition. Morphometric data were collected under anaesthesia from 137 adult wild platypuses (74 males, 63 females) captured in north-west Tasmania; ultrasound images of tail fat were also collected from 100 of these individuals (54 males, 46 females). Three new indices for platypus body condition were identified. An objective tail fat index (Relative Tail Fat Volume: RTFVTBL) was developed, based on cross-sectional area measurements taken from detailed ultrasound images compared with total body length (TBL). Two body condition indices intended for routine field use were developed - one based on body mass (mb) and bill width (BW) (Body Condition Index; BCIBW), and the other based on a single linear ultrasonographic measurement of tail fat depth and BW (Relative Fat Depth; RFDBW). Results indicated that RFDBW outperforms TVI as an index of platypus tail fat. Further work, however, is needed to determine the relationship between tail fat and total body fat in the platypus before conclusions can be drawn about the effectiveness of BCIBW as a body condition index.

A wide range of factors, including individual animal health, genetic diversity and demographics, are associated with wildlife population declines and investigation of these factors may be more sensitive in detecting early impacts on wildlife populations, than estimates of population size alone. Defining wildlife population health as the ability of a wildlife population to remain viable in the long term, this project developed and implemented a holistic health assessment framework for platypuses to gather baseline data, to investigate environmental, temporal and individual patterns within this data, and to provide insights into potential threatening processes. Platypus distribution and population density in two river catchments in northwest Tasmania were investigated in a live capture/release field study during which 154 individuals were captured. The effect on capture numbers of broad habitat characteristics was investigated. A survey of public sightings provided additional information on platypus distribution and population density. The novel use of in-stream microchip readers to monitor platypus movements/survivorship was developed. Data was collected on the timing and frequency of platypus movements, as well as continued use of monitoring sites by individuals captured in this study and in a study three to six years earlier. The timing of the breeding season in Tasmania was investigated using hormonal, ultrasonographic and remote monitoring observations. Genetic diversity and geographical distribution of alleles at the Major Histocompatibility Complex Class II DZB locus was also investigated. The reliability of existing and novel body condition indices was studied. The prevalence of exposure to a range of parasitic, fungal and bacterial agents was determined. Haematology and biochemistry reference intervals were produced. Little evidence was found that the two study populations were in poor health. Baseline population health data, that for many species has been absent when population declines have occurred, was collected for platypuses; and the project’s general approach will serve as a template for similar research in other species.