Beyond the disease: Is Toxoplasma gondii infection causing population declines in the eastern quoll (Dasyurus viverrinus)?

Recent aspects on epidemiology, clinical disease, and genetic diversity of Toxoplasma gondii infections in Australasian marsupials

Background

Toxoplasma gondii infections are common in humans and animals worldwide. Among all intermediate hosts of T. gondii, captive marsupials from Australia and New Zealand are highly susceptible to clinical toxoplasmosis. However, most free-range marsupials establish chronic T. gondii infection. Infected marsupial meat may serve as a source of T. gondii infection for humans. Differences in mortality patterns in different species of kangaroos and other marsupials are not fully understood. Lifestyle, habitat, and the genotype of T. gondii are predicted to be risk factors. For example, koalas are rarely exposed to T. gondii because they live on treetops whereas wallabies on land are frequently exposed to infection.

Methods

The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii infecting Australasian marsupials in their native habitat and among exported animals over the past decade. The role of genetic types of T. gondii and clinical disease is discussed.

Results

Fatal toxoplasmosis has been diagnosed in captive Australasian marsupials in Argentina, Chile, China, Germany, Hungary, Japan, Spain, Turkey, and the USA. Most deaths occurred because of disseminated toxoplasmosis. Genetic characterization of T. gondii strains isolated from fatal marsupial infections identified Type III as well as atypical, nonclonal genotypes. Fatal toxoplasmosis was also diagnosed in free-ranging wombats (Vombatus ursinus) in Australia. Genetic characterization of DNA amplified directly from host tissues of subclinical culled kangaroos at slaughter identified many mixed-strain infections with both atypical and recombinant genotypes of T. gondii.

Conclusions

Most Australasian marsupials in their native land, Australia and New Zealand, have high prevalence of T. gondii, and kangaroo meat can be a source of infection for humans if consumed uncooked/undercooked. The genotypes prevalent in kangaroos in Australia and New Zealand were genetically distinct from those isolated or genotyped from most macropods in the USA and other countries. Thus, clinical toxoplasmosis in marsupials imported from Australia is most likely to occur from infections acquired after importation.

Graphic abstract

EARLY-ONSET LEUKOENCEPHALOMYELOPATHY AND POLYNEUROPATHY IN EASTERN QUOLLS (DASYURUS VIVERRINUS) IN THE EUROPEAN CAPTIVE POPULATION

Leukoencephalomyelopathy (LEM) is suggested to be an age-related degenerative condition in geriatric Eastern quolls (Dasyurus viverrinus), manifesting in animals greater than 3.5 yr of age. This case series describes four LEM cases from two zoologic collections; three in nongeriatric animals, with one only 1 yr of age, and details advanced diagnostic investigation, including magnetic resonance imaging, cerebrospinal fluid analysis, and electrodiagnostic studies, not previously reported in Eastern quolls. Animals presented clinically with forelimb proprioceptive deficits and hindlimb and lumbar muscle hypotrophy, which were not noted in previous reports, in addition to hindlimb ataxia. Blindness and emaciation, which have been reported previously, were not seen. Disease progression was variable, and time from first clinical signs to euthanasia ranged from 46 days to over 2 yr. Histopathologic findings in the central nervous system were typical of those in previous LEM cases; concomitant polyneuropathy was observed in two quolls. Our findings suggest that age-related degeneration may not be the only cause of LEM in Eastern quolls. Because all quolls were related, a familial component cannot be excluded. LEM should be further investigated for its potential impact on future captive breeding programs, and our findings suggest that daily quality-of-life assessment should guide euthanasia of affected animals.

Conservation of quolls (Dasyurus spp.) in captivity – a review

Quolls are carnivorous marsupials in the family Dasyuridae with characteristic white spots. They are distributed throughout Australia and New Guinea, but uncommonly seen due to their mostly nocturnal solitary nature, and large home ranges. All Australian quolls are listed as ‘near threatened’ or ‘endangered’ at state, national and international levels, largely due to human-induced threats. Threats include introduced predators, habitat loss through clearing and modifications including changed fire regimes, disease, human persecution, vehicle collisions and accidental or targeted poisoning by humans and cane toads (Rhinella marina). Conservation efforts that have focussed on reducing introduced predators, and minimising the impact of cane toads, have aided some translocations, hence species recovery in some local areas of Australia has occurred. Where species conservation has required captive breeding for translocation, successful captive management has been crucial. We summarise research conducted in captivity on aspects of birth and development, health and disease, and blood and nutrition parameters of quolls, and suggest future directions for research. Further research on captive and wild quoll populations will benefit future translocations, reintroductions and conservation through increased knowledge, improved maintenance and husbandry of captive colonies, and monitoring of wild populations.

Evidence of infection with Toxoplasma gondii and Neospora caninum in South Australia: using wild rabbits as a sentinel species

OBJECTIVE

The aim of this study was to utilise wild rabbits (Oryctolagus cuniculus) as a sentinel species to study levels of environmental contamination with N. caninum and T. gondii in South Australia, and to examine associations with rainfall, climate and land use.

DESIGN

Toxoplasma gondii (T. gondii), an apicomplexan parasite, causes the clinical disease toxoplasmosis, which can affect sheep as well as humans and many other animals. Neosporosis, the clinical disease caused by closely related Neospora caninum (N. caninum), causes abortions in cattle, with large economic impacts to cattle industries.

METHODS

Aliquots of wild rabbit (Oryctolagus cuniculus) serum were obtained from twelve sites across South Australia over a period of eighteen years, with a total of 2114 samples. An in-house Modified Agglutination Test (MAT) was developed, and samples were screened for the specific antibodies against both T.gondii and N. caninum.

RESULTS

Overall, 9.9% of samples screened for T. gondii tested positive and 6.1% of samples screened for N. caninum tested positive. There was no difference observed in seroprevalence of T.gondii specific antibodies between samples collected throughout summer, autumn, winter or spring. By contrast, a significantly higher (p=0.030) seroprevalence of N. caninum specific antibodies was observed in spring than any other season. T. gondii and N. caninum antibodies were discovered at sites across a broad area of South Australia, indicating these environments maybe infected with both parasites.

CONCLUSION

Results provide evidence that suggests N. caninum oocysts may have different survival characteristics, such as varying tolerances to low relative humidity, than T. gondii oocysts.

Oesophageal sarcocystosis observed at slaughter provides a reliable and efficient proximate measure of Toxoplasma gondii seroprevalence in sheep

OBJECTIVE

Successful disease management requires effective surveillance. Slaughterhouse inspections provide opportunities to efficiently collect regular disease data from many animals across large areas. Toxoplasma is a cat-borne parasite that causes reproduction failure in sheep, although it is not visually detectable at slaughterhouses. Macroscopic sarcocystosis is a disease of sheep that is visually detectable at slaughter and is caused by parasites that share a similar biology with Toxoplasma. We investigated if sarcocystosis could act as a proximate measure for Toxoplasma exposure in sheep to facilitate its efficient surveillance at large scales.

DESIGN/METHODS

We compared the presence of macroscopic sarcocystosis to Toxoplasma serostatus at the animal and farm levels.

RESULTS

At the animal level, we found a weak association between Toxoplasma seropositivity and sarcocysts in the oesophagus (OR = 1.76 [95% CI: 1.17, 2.65; _McFadden's R² = 0.01]) but no association between Toxoplasma seropositivity and sarcocysts in skeletal muscles. At the farm level, the seroprevalence of Toxoplasma was strongly associated with oesophageal sarcocystosis prevalence (OR = 28.59 [95% CI: 13.07, 62.57; _McFadden's R² = 0.34]) but less strongly associated with sarcocystosis prevalence in skeletal muscles (OR = 7.91 [95% CI: 1.24, 50.39; _McFadden's R² = 0.02]).

CONCLUSIONS

For Toxoplasma surveillance in sheep at the farm level, routine slaughter inspection and recording of macroscopic oesophageal sarcocystosis could be are liable and efficient proximate measure. The monitoring of oesophageal sarcocystosis may be a useful passive Toxoplasma surveillance tool for guiding the timing and location of other Toxoplasma detection methods to facilitate the management of Toxoplasma impacts within the sheep industry.

BASELINE HEALTH AND DISEASE ASSESSMENT OF FOUNDER EASTERN QUOLLS (DASYURUS VIVERRINUS) DURING A CONSERVATION TRANSLOCATION TO MAINLAND AUSTRALIA

We evaluated the health of 31 (eight males, 23 females) founder eastern quolls (Dasyurus viverrinus), translocated to a fenced reserve in the Australian Capital Territory between February 2016 and July 2017. Quolls were wild caught in Tasmania (16 animals) or captive bred at Mount Rothwell Biodiversity Interpretation Centre, Victoria (15 animals). Quolls were assessed for the presence of selected potential pathogens (Toxoplasma gondii, herpesviruses, Salmonella serovars, hemoprotozoa, and ectoparasites). We assessed the relationships among sex, provenance (captive or free ranging), T. gondii or herpesvirus infection, weight, and hematologic and biochemical variables. Six of 21 quolls (29%) tested were seropositive for antibodies to T. gondii. Seropositive quolls weighed significantly more and had significantly lower potassium levels, anion gaps, and urea and triglyceride levels than seronegative quolls had. Eighteen of 31 (58%) combined conjunctival-pharyngeal-cloacal swabs collected from quolls were PCR positive for a newly identified gammaherpesvirus, tentatively named dasyurid gammaherpesvirus 3. There were no significant differences among hematologic and biochemical variables or body weights from PCR-positive and PCR-negative quolls. Eighteen of 18 (100%) of rectal-swab samples were culture negative for Salmonella serovars. Three species of tick (Ixodes tasmani, Ixodes fecialis, and Ixodes holocyclus), two species of mite (Andreacus radfordi, one unidentified), and four species of flea (Pygiopsylla hoplia, Acanthopsylla rothschildi rothschildi, Uropsylla tasmanica, and Stephanocircus dasyuri), were detected on wild-caught quolls, whereas a fifth species of flea, Echidnophaga myremecobii, was detected only on captive-bred quolls. Five of 15 blood samples (33%) were positive for hemoprotozoan DNA via PCR, a novel Hepatozoon species, a novel Theileria species, Theileria paparinii, and Trypanosoma copemani were detected. Despite the presence of several potential pathogens known to be associated with disease in other marsupials, the quolls were considered to be in good general health, suitable for translocation, and a viable population was subsequently established.

We need to worry about Bella and Charlie: the impacts of pet cats on Australian wildlife

Research and management attention on the impacts of the introduced domestic cat (Felis catus) on Australian fauna have focussed mainly on the feral population. Here, we summarise the evidence for impacts of predation by pet cats on Australian wildlife. We collate examples of local wildlife population decline and extirpation as a result, at least in part, of predation by pet cats. We assemble information across 66 studies of predation by pet cats worldwide (including 24 Australian studies) to estimate the predation toll of pet cats in Australia, plus the predation pressure per unit area in residential areas. We compared these estimates to those published for feral cats in Australia. The per capita kill rate of pet cats is 25% that of feral cats. However, pet cats live at much higher densities, so the predation rate of pets per square kilometre in residential areas is 28–52 times larger than predation rates by feral cats in natural environments, and 1.3–2.3 times greater than predation rates per km2 by feral cats living in urban areas. Pet cats kill introduced species more often than do feral cats living in natural environments, but, nonetheless, the toll of native animals killed per square kilometre by pet cats in residential areas is still much higher than the toll per square kilometre by feral cats. There is no evidence that pet cats exert significant control of introduced species. The high predation toll of pet cats in residential areas, the documented examples of declines and extirpations in populations of native species caused by pet cats, and potential pathways for other, indirect effects (e.g. from disease, landscapes of fear, ecological footprints), and the context of extraordinary impacts from feral cats on Australian fauna, together support a default position that pet cat impacts are serious and should be reduced. From a technical perspective, the pet cat impacts can be reduced more effectively and humanely than those of feral cats, while also enhancing pet cat welfare. We review the management options for reducing predation by pet cats, and discuss the opportunities and challenges for improved pet cat management and welfare.

Variation in Toxoplasma gondii seroprevalence: effects of site, sex, species and behaviour between insular and mainland macropods

Context Feral cats threaten wildlife conservation through a range of direct and indirect effects. However, most studies that have evaluated the impacts of feral cats on species of conservation significance have focussed on direct impacts such as predation; few studies have considered the indirect impacts of cat-borne disease. Toxoplasma gondii, a cat-borne parasite, causes both acute and latent disease in a range of wildlife species, and macropods are particularly susceptible. Kangaroo Island is Australia’s third largest island and supports a high density of feral cats and high seroprevalence of T. gondii in multiple species, relative to the mainland. This suggests that Kangaroo Island has a high environmental contamination with the parasite and a high risk of infection for other species. Aims We aimed to describe T. gondii seroprevalence in culled and road-killed macropods, so as to assess the effects of island versus mainland location, sex, species and behaviour. Methods Macropod sera were tested for T. gondii IgG antibodies using a commercially available modified agglutination test. Key results The seroprevalence of T. gondii in culled western grey kangaroos (Macropus fuliginosus) was significantly higher on the island (20%, 11/54 positive) than on the mainland (0%, 0/61 positive). There was no difference in T. gondii seroprevalence between culled and road-killed (21%, 21/102 positive) kangaroos from the island. The seroprevalence of T. gondii was significantly higher in female (32%, 12/38 positive) than in male (13%, 8/60 positive) kangaroos, but we observed no sex effect in tammar wallabies (Macropus eugenii), and no effect of species. Conclusions The higher T. gondii seroprevalence in insular macropods supports previous reports of higher T. gondii exposure in other Kangaroo Island fauna. The lack of difference in T. gondii seroprevalence between culled and road-killed kangaroos suggests that T. gondii-positive animals are not more vulnerable to road mortality, in contrast to that suggested previously. Implications Our findings suggest greater potential adverse conservation impacts owing to toxoplasmosis on the island than on the mainland. In light of a recent study demonstrating higher cat abundance on the island than on the mainland, the higher observed T. gondii seroprevalence in insular macropods is likely to be a consequence of higher cat density.

Hematologic and serum biochemical reference intervals for wild eastern quolls (Dasyurus viverrinus): Variation by age, sex, and season

BACKGROUND

The eastern quoll (Dasyurus viverrinus) is an endangered carnivorous marsupial that has recently suffered significant population declines. Several small captive breeding populations have been established, with plans to translocate wild and captive individuals to areas of their former distribution. Accordingly, hematologic and serum biochemical reference intervals (RIs) established from wild eastern quoll populations are essential for monitoring the health and disease status of both captive and wild populations, and to evaluate the health of individuals before, during, and after translocation.

OBJECTIVES

We aimed to establish hematologic and serum biochemical RIs for wild eastern quolls, and examine the effects of age, sex, and season.

METHODS

We collected a total of 202 hematologic samples, 309 packed cell volume samples, and 335 serum biochemical samples from 168 individual quolls between May 2011 and November 2013. Species-level RIs were established, as well as RIs of groups separated by age (juvenile, adult) and sex (adult male, adult female) using nonparametric, robust, and parametric methods. Seasonal variation in age- and sex-specific reference values was also assessed.

RESULTS

Strong age and seasonal variation were evident in many hematologic and serum biochemical analytes, with significant variation observed in serum biochemical analytes between the sexes.

CONCLUSIONS

The observed age, sex, and seasonal variation reflect differences in the timing of growth and reproductive stressors, which interact with seasonal energetic demands. Our findings highlight the importance of using age-, sex-, and season-specific RIs for clinical evaluation of eastern quolls, as species-level RIs will inadvertently smooth and mask important seasonal fluctuations that reflect reproductive status at different times.

Degrees of population-level susceptibility of Australian terrestrial non-volant mammal species to predation by the introduced red fox (Vulpes vulpes) and feral cat (Felis catus)

Context Over the last 230 years, the Australian terrestrial mammal fauna has suffered a very high rate of decline and extinction relative to other continents. Predation by the introduced red fox (Vulpes vulpes) and feral cat (Felis catus) is implicated in many of these extinctions, and in the ongoing decline of many extant species. Aims To assess the degree to which Australian terrestrial non-volant mammal species are susceptible at the population level to predation by the red fox and feral cat, and to allocate each species to a category of predator susceptibility. Methods We collated the available evidence and complemented this with expert opinion to categorise each Australian terrestrial non-volant mammal species (extinct and extant) into one of four classes of population-level susceptibility to introduced predators (i.e. ‘extreme’, ‘high’, ‘low’ or ‘not susceptible’). We then compared predator susceptibility with conservation status, body size and extent of arboreality; and assessed changes in the occurrence of species in different predator-susceptibility categories between 1788 and 2017. Key results Of 246 Australian terrestrial non-volant mammal species (including extinct species), we conclude that 37 species are (or were) extremely predator-susceptible; 52 species are highly predator-susceptible; 112 species are of low susceptibility; and 42 species are not susceptible to predators. Confidence in assigning species to predator-susceptibility categories was strongest for extant threatened mammal species and for extremely predator-susceptible species. Extinct and threatened mammal species are more likely to be predator-susceptible than Least Concern species; arboreal species are less predator-susceptible than ground-dwelling species; and medium-sized species (35 g–3.5kg) are more predator-susceptible than smaller or larger species. Conclusions The effective control of foxes and cats over large areas is likely to assist the population-level recovery of ~63 species – the number of extant species with extreme or high predator susceptibility – which represents ~29% of the extant Australian terrestrial non-volant mammal fauna. Implications Categorisation of predator susceptibility is an important tool for conservation management, because the persistence of species with extreme susceptibility will require intensive management (e.g. predator-proof exclosures or predator-free islands), whereas species of lower predator susceptibility can be managed through effective landscape-level suppression of introduced predators.

Wildlife parasitology in Australia: past, present and future

Wildlife parasitology is a highly diverse area of research encompassing many fields including taxonomy, ecology, pathology and epidemiology, and with participants from extremely disparate scientific fields. In addition, the organisms studied are highly dissimilar, ranging from platyhelminths, nematodes and acanthocephalans to insects, arachnids, crustaceans and protists. This review of the parasites of wildlife in Australia highlights the advances made to date, focussing on the work, interests and major findings of researchers over the years and identifies current significant gaps that exist in our understanding. The review is divided into three sections covering protist, helminth and arthropod parasites. The challenge to document the diversity of parasites in Australia continues at a traditional level but the advent of molecular methods has heightened the significance of this issue. Modern methods are providing an avenue for major advances in documenting and restructuring the phylogeny of protistan parasites in particular, while facilitating the recognition of species complexes in helminth taxa previously defined by traditional morphological methods. The life cycles, ecology and general biology of most parasites of wildlife in Australia are extremely poorly understood. While the phylogenetic origins of the Australian vertebrate fauna are complex, so too are the likely origins of their parasites, which do not necessarily mirror those of their hosts. This aspect of parasite evolution is a continuing area for research in the case of helminths, but remains to be addressed for many other parasitic groups.

Mechanisms of climate-change-induced species decline: spatial, temporal and long-term variation in the diet of an endangered marsupial carnivore, the eastern quoll

Context Climate change is having significant impacts on species worldwide. The endangered eastern quoll (Dasyurus viverrinus) has recently undergone rapid and severe population decline, with no sign of recovery. Spatially and temporally-explicit weather modelling suggests a prolonged period of unfavourable weather conditions during 2001–03 as the proximate cause of decline. However, the mechanisms of this weather-induced decline are not currently understood. Aims The aim of this study was to investigate the hypothesis that changing weather conditions have altered the availability of key prey species, potentially contributing to the species’ decline. Methods We analysed 229 scats collected from 125 individual wild quolls across four sites between July 2011 and May 2012. Variation in dietary composition and niche breadth was compared across sites and seasons. We also compared contemporary dietary composition and niche breadth to historic dietary studies performed before the species’ decline, to identify any key changes in dietary composition over time. Key results Dietary composition and niche breadth were similar across sites but differed between seasons. Dietary niche contracted during winter (July) and early spring (September) when insect larvae formed the bulk of quoll diet, rendering the species vulnerable to weather-related fluctuations in food availability at that time. Large differences were also evident between current and historic dietary composition, with a marked shift from insect larvae to mammals, predominantly due to a reduction in corbie (Oncopera intricata) and southern armyworm (Persectania ewingii) moth larvae. Quoll abundance appears positively related to corbie larva abundance during winter, and both quoll and corbie larva abundance appear negatively related to winter rainfall. Conclusions The lower contribution of insects at sites with low quoll densities suggests that insects represent an important food item for eastern quolls during winter, when dietary niche is narrowest and energy demands are highest. Our findings suggest that weather-induced fluctuations in quoll abundance, including the significant statewide decline during 2001–03, are potentially driven by weather-induced fluctuations in corbie larva abundance. Implications Continued deterioration in climatic suitability with recent and predicted climate change could further threaten eastern quolls through reductions in the availability and stability of reliable food sources at critical life-history stages when dietary options are already limited.

Assisted colonisation trial of the eastern barred bandicoot (Perameles gunnii) to a fox-free island

Context Assisted colonisation has the potential to protect species from intractable threats within their historical ranges. The Australian mainland subspecies of the eastern barred bandicoot (Perameles gunnii) is extinct in the wild, with surviving populations restricted to small sites protected by predator–barrier fences. PVA modelling shows that a self-sustaining bandicoot population would require an area free of the introduced red fox (Vulpes vulpes) of at least 2500ha. French Island is outside the historic range of the species, but is fox-free and contains around 9000ha of potentially suitable habitat. Aims This study will assess the suitability of French Island as a potential site for a self-sustaining eastern barred bandicoot population by conducting a 1-year assisted colonisation trial to assess habitat use, body condition and survival. Methods Between July and September 2012, 18 adult bandicoots were released. We radio-tracked bandicoots using intraperitoneal radio-transmitters for up to 122 days and trapped fortnightly. Key results The release group met the three measures of success: (1) appropriate habitat use; (2) recovery of post-release bodyweight; and (3) founder survival exceeding 100 days. Habitat use and body condition throughout the trial reflected that of mainland populations, and seven bandicoots survived longer than 100 days. Mortality was greatest in the first month, with veterinary investigations confirming two deaths due to cat predation, two deaths from toxoplasmosis and one unknown cause of death. Bandicoots that survived longer than 100 days occupied higher, drier ground than those that did not. Toxoplasmosis cases were associated with lower topographic position on the site. Conclusions Our results suggest that French Island provides suitable habitat for the establishment of a population of eastern barred bandicoots. On French Island, toxoplasmosis was identified as an important source of mortality in addition to cat predation, and warrants further investigation. Implications Given the costs and challenges of predator control and the maintenance of predator exclusion fences, assisted colonisation to one or more fox-free islands remains the most viable option to establish self-sustaining bandicoot populations. Our results highlight the value in conducting trial releases ahead of major translocations.

Is Toxoplasma gondii a threat to the conservation of free-ranging Australian marsupial populations?

It has often been asserted that Australian marsupial species are particularly susceptible to Toxoplasma gondii infection and to clinical toxoplasmosis following infection. This implicates T. gondii as a potential threat to marsupial population viability, and contrasts to what is known of T. gondii in populations of several other host species. We reviewed the literature, and found a lack of scientifically robust evidence addressing the occurrence of T. gondii infection in free-ranging populations of Australian marsupial species, and the impacts of the infection on population health. Key limitations included a lack of studies in free-ranging marsupial populations, study findings susceptible to substantial chance influences, and selection, misclassification and confounding biases. The lack of scientifically robust data available on this topic indicates that assertions that free-ranging populations of Australian marsupials are particularly susceptible to T. gondii infection and to toxoplasmosis are premature. The threat of T. gondii to the viability of free-ranging marsupial populations should therefore be regarded, at this stage, as a hypothesis.

Diagnosing species decline: a contextual review of threats,causes and future directions for management and conservation of the eastern quoll

Diagnosing the cause of a species’ decline is one of the most challenging tasks faced by conservation practitioners. For a species approaching extinction, it is not possible to go back in time to measure the agents that operated at various stages of the decline. Accordingly, managers are often restricted to measuring factors currently affecting residual populations, which may not be related to factors that operated earlier in the decline, and inferring other mechanisms from different lines of evidence. In this review, I adopt a methodical diagnostic framework to comprehensively evaluate the potential causal factors for the decline of the eastern quoll (Dasyurus viverrinus) in Tasmania, and propose a hypothesis as to the cause of decline. Potential causal agents were gleaned from two key sources: factors implicated in the eastern quoll’s historical demise on the Australian mainland, and factors that changed during the recent period of quoll decline in Tasmania. The three most likely candidate causal agents were investigated over 4 years to evaluate their likely contribution to the decline. Here, I synthesise the findings from this recent research to advance a hypothesis as to the cause of the eastern quoll decline in Tasmania. I suggest that a period of unsuitable weather reduced quoll populations to an unprecedented low abundance, and that populations are now too small to overcome established threat intensities to which they were robust when at higher densities. Residual small populations are inherently more susceptible to demographic, environmental and genetic stochasticity and are unlikely to recover without management intervention. I propose a study design to experimentally test this hypothesis, and outline priority areas for future research and actions to guide in the future management and conservation of the species. This case study illustrates an approach by which practical species conservation problems might be solved and recovery strategies may be better informed, thereby ensuring positive conservation outcomes for threatened species.

Devil declines and catastrophic cascades: is mesopredator release of feral cats inhibiting recovery of the eastern quoll?

The eastern quoll (Dasyurus viverrinus) is a medium-sized Australian marsupial carnivore that has recently undergone a rapid and severe population decline over the 10 years to 2009, with no sign of recovery. This decline has been linked to a period of unfavourable weather, but subsequent improved weather conditions have not been matched by quoll recovery. A recent study suggested another mechanism: that declines in Tasmanian devil (Sarcophilus harrisii) populations, due to the spread of the fatal Devil Facial Tumour Disease, have released feral cats (Felis catus) from competitive suppression, with eastern quoll declines linked to a subsequent increase in cat sightings. Yet current evidence of intraguild suppression among devils, cats and quolls is scant and equivocal. We therefore assessed the influences of top-down effects on abundance and activity patterns among devils, feral cats and eastern quolls. Between 2011 and 2013, we monitored four carnivore populations using longitudinal trapping and camera surveys, and performed camera surveys at 12 additional sites throughout the eastern quoll's range. We did not find evidence of a negative relationship between devil and cat abundance, nor of higher cat abundance in areas where devil populations had declined the longest. Cats did not appear to avoid devils spatially; however, there was evidence of temporal separation of cat and devil activity, with reduced separation and increasing nocturnal activity observed in areas where devils had declined the longest. Cats and quolls used the same areas, and there was no evidence that cat and quoll abundances were negatively related. Temporal overlap in observed cat and quoll activity was higher in summer than in winter, but this seasonal difference was unrelated to devil declines. We suggest that cats did not cause the recent quoll decline, but that predation of juvenile quolls by cats could be inhibiting low density quoll populations from recovering their former abundance through a 'predator pit' effect following weather-induced decline. Predation intensity could increase further should cats become increasingly nocturnal in response to devil declines.

When the ‘native cat’ would ‘plague’: historical hyperabundance in the quoll (Marsupialia : Dasyuridae) and an assessment of the role of disease, cats and foxes in its curtailment

Since the European settlement of Australia in 1788, 25 mainland terrestrial mammal species have become extinct, more than on any other continent during this period. To determine if the causal factors are still active, it is necessary to better understand the species and their status preceding these regional extirpations or extinctions, and examine the historical record for clues to the cause(s) of these declines. From an extensive review of historical material, primarily newspaper accounts, we collated >2700 accounts of quolls. We discovered 36 accounts that demonstrate the propensity for quolls to become hyperabundant. The geographical distribution of accounts implies that most refer to Dasyurus viverrinus, but an account from Normanton district (Queensland) likely applies to D. hallucatus. More than 110 accounts demonstrate that disease/parasite epizootics occurred in south-eastern Australia, commencing on mainland Australia possibly in the goldfields region of Victoria in the 1850s, or in south-eastern South Australia and south-western Victoria in the mid to late 1860s, and implicate these as the initial primary factor in the regional extirpation of Australia’s quolls. The loss of D. viverrinus populations in south-eastern Australia was reportedly from population abundances and densities that were sporadically extraordinarily high, hence their loss appears more pronounced than previously suspected. Accounts describing the widespread, rapid and major loss of quolls suggest the possible involvement of several pathogens. Ectoparasites such as Uropsylla tasmanica and ticks appear to be described in detail in some accounts. A few others state comortality of Felis catus and Canis lupus familiaris, suggestive of a disease of either or both of these species, such as Canine Distemper Virus, a morbillivirus with a propensity to be non-host specific, that may have caused the decline of the quolls, perhaps vectored by the reported ectoparasites. We also collated 23 presumed independent accounts of cats negatively impacting quolls, two of which describe significant mortality, and three presumed independent accounts of fox predation. These highlight the capacity of both of these introduced predators to have reduced quoll distribution and abundance.