Dasyuroides Research Articles

Does reducing grazing pressure or predation conserve kowaris? A case study at Diamantina National Park

Livestock contributes to the decline of many species in Australia. However, they may have less impact in arid environments, where annual plant species dominate. Kowaris (Dasyuroides byrnei), a small carnivorous marsupial, living on Diamantina National Park were monitored to assess the success of ecosystem recovery following a reduction in cattle. Kowaris were found at 10 locations within the study area: five where they had been recorded prior to the area becoming a national park and five ‘new’ locations. No kowaris were found at one of the historical sites. The density was estimated to range from 1 to 2.5 kowaris per square kilometre from 2007 to 2009. The results suggest that the population likely increased following a reduction in grazing pressure. However, a boom in rodents and predators occurred during the study with a corresponding decline in kowari detections. Kowaris have not been detected at any of the study sites since 2012. These results suggest that management of top-down factors as well as bottom-up factors are required to conserve kowaris. The work further highlights the need for replicated, long-term studies if the interactions between complex ecological processes, at a landscape scale, are to be understood so that threatened species, like the kowari, can be managed effectively.

A search for the desert rat-kangaroo or ngudlukanta (

The desert rat-kangaroo or ‘ngudlukanta’ (Caloprymnus campestris) was once sparsely distributed in the Lake Eyre Basin of north-eastern South Australia and adjacent parts of Queensland, but has not been collected since the 1930s. However, numerous reported sightings, including some recent, provide some hope that it may still be extant. In 2018 and 2019, we searched for evidence of this species at sites where it had been collected in the 1930s, and at places where people have since reported seeing an animal that fits its description. Our survey, which analysed data from more than 6000 camera trap nights, 536 predator scats and 226 km of spotlight transects, was the most extensive field-based search ever undertaken for this animal; but we found no evidence for its continued existence. However, our work did detect other threatened species including a range extension for the kowari (Dasyuroides byrnei), thereby demonstrating the value of surveys like this one. Because of the vastness and inaccessibility of much of the terrain comprising the supposed distribution of C. campestris, we do not see our null result as definitive for this poorly surveyed animal; we instead hope that it provides a starting point for future surveys aimed at resolving its status.

Introduced cats Felis catus eating a continental fauna: inventory and traits of Australian mammal species killed

Abstract Mammals comprise the bulk of the diet of free‐ranging domestic cats Felis catus (defined as including outdoor pet cats, strays, and feral cats) in most parts of their global range. In Australia, predation by introduced feral cats has been implicated in the extinction of many mammal species, and in the ongoing decline of many extant species. Here, we collate a wide range of records of predation by cats (including feral and pet cats) on Australian mammals and model traits of extant, terrestrial, native mammal species associated with the relative likelihood of cat predation. We explicitly seek to overcome biases in such a continental‐scale compilation by excluding possible carrion records for larger species and accounting for differences in the distribution and abundance of potential prey species, as well as study effort, throughout each species’ range. For non‐volant species, the relative likelihood of predation by cats was greatest for species in an intermediate weight range (peaking at ca. 400 g), in lower rainfall areas and not dwelling in rocky habitats. Previous studies have shown the greatest rates of decline and extinction in Australian mammals to be associated with these traits. As such, we provide the first continental‐scale link between mammal decline and cat predation through quantitative analysis. Our compilation of cat predation records for most extant, terrestrial, native mammal species (151 species, or 52% of the Australian species’ complement) is substantially greater than previously reported (88 species) and includes 50 species listed as threatened by the IUCN or under Australian legislation (57% of Australia's 87 threatened terrestrial mammal species). We identify the Australian mammal species most likely to be threatened by predation by cats (mulgaras Dasycercus spp., kowari Dasyuroides byrnei, many smaller dasyurids and medium‐sized to large rodents, among others) and hence most likely to benefit from enhanced mitigation of cat impacts, such as translocations to predator‐free islands, the establishment of predator‐proof fenced exclosures, and broad‐scale cat poison baiting.

Trophic ecology of marsupial predators in arid Australia following reshaping of predator assemblages

The extirpation of marsupial predators and their replacement by eutherian carnivores are likely to have cascading ecological impacts on the trophic structure of arid Australia. Here, we assessed the diet and characterized the trophic role of the 3 largest remaining carnivorous marsupials (< 200 g body mass) in arid Australia: cresttailed mulgaras (Dasycercus cristicauda), kowaris (Dasyuroides byrnei), and brush-tailed mulgaras (Dasycercusblythi). The species show a high level of trophic connectivity; each is highly interactive, being predator or prey of numerous species across multiple phyla. The prey base of each of the predator species was broad and included vertebrates, invertebrates, and plants. Crest-tailed mulgaras consumed the most vertebrates including prey up to the size of the southern marsupial mole (Notoryctes typhlops). Kowaris consumed prey up to the size of the European rabbit (Oryctolagus cuniculus). Although capable of capturing or scavenging vertebrates, the diet of each species was dominated by arthropods < 2 g in body mass.

Dynamics, habitat use and extinction risk of a carnivorous desert marsupial

AbstractAnimals in hot desert environments often show marked fluctuations in population size, persisting in low numbers in refuge habitats during dry periods and expanding after rain when resources increase. Understanding drought‐wet cycle dynamics is important for managing arid ecosystems, particularly if populations of threatened species are present. Such species may face increased risks of extinction if all populations decrease synchronously toward zero during low‐resource periods, and if key refuge habitats needed during these periods are disturbed or unavailable. Here, we describe the dynamics and habitat requirements of two sub‐populations of the kowari, Dasyuroides byrnei (Marsupialia: Dasyuridae), during long‐term sampling (2000–2015) that encompassed multiple drought‐wet cycles. This species is listed currently as Vulnerable on the IUCN Red List. We found that the study region contains favourable habitat, with kowari occurring on hard stony (gibber) pavements in association with coverage of sand that may facilitate construction of burrows. Both sub‐populations of kowari declined over the study period irrespective of climatic conditions, despite some evidence that both body condition and reproductive output increased after rain. We suggest that the studied sub‐populations are under stress from extrinsic rather than intrinsic factors, with livestock grazing and introduced predators perhaps having the most negative effects. If similar demographic trends are apparent elsewhere in the species’ small geographical range, the species would be eligible for listing on the IUCN Red List as Endangered, with a 20% chance of extinction within the next 20 years. Urgent research is required to quantify and mitigate the extrinsic threats to kowari populations. Proactive measures such as captive breeding to act as insurance populations would be prudent.

Oral Squamous Cell Carcinoma in Three Related Kowari (Dasyuroides byrnei)

We report three kowari (Dasyuroides byrnei) with squamous cell carcinoma affecting the gingiva. These cases occurred in rapid succession in a related group of individuals of similar age, suggesting a familial tendency to this condition and a typical age of presentation. Other conditions affecting the oral cavity can mimic the appearance of oral squamous cell carcinoma in this species, and so knowledge of this condition can assist the veterinarian in making rapid decisions regarding prognosis and improving the welfare of these animals.

Using climate variables to predict small mammal occurrence in hot, dry environments

Many species are considered to be threatened by the direct and synergistic effects of increased temperatures and less reliable rainfall caused by anthropogenic climate change. The climate of arid Australia is naturally defined by high temperatures and highly variable rainfall. In these environments the survival of small mammals is facilitated by a range of physiological, morphological and behavioural adaptive traits (e.g. insectivorous diets, torpor, nocturnal activity and sheltering in burrows). Features within the landscape associated with these traits may have a proximal influence on species occurrence and be critical for predicting the distribution of arid species. Here we explored the contribution of coarse- and fine-scale environmental variables, sampled from 150 to 10,000 m from known species records, to the development of more robust species distribution models. The inclusion of environmental variables representing topography, soil and vegetation better modelled occurrence for all five small mammal species (up to 55.2 % DE increase over climate-only models) and increased discrimination of species occurrence in an out-of-sample cross-validation for Antechinomys laniger, Dasyuroides byrnei and Notomys cervinus (e.g. increase in area-under-the curve by 0.4). For these species, model performance (% DE) increased with the resolution of environmental data used, reflecting a coarse-scale relationship with distance to watercourse (e.g. at 1,000 m), but masking a fine-scale relationship with rainfall during winter (at 150 m). The inclusion of a fine-scale variable shrub cover under 0.5 m (SD) improved the representation of S. macroura occurrence. These results show improved representation of habitats and resources using course- and fine-scale variables, which may be vital to model the occurrence of some species and their refuge habitats, but as static variables may limit accurate predictions of the effect of climate change on species range dynamics.

Activity and torpor in two sympatric Australian desert marsupials

Many biological variables related to energy turnover including torpor, the most efficient energy-saving mechanism available to mammals, scale with body size, but the implications for animals living in their natural environment remain largely unknown. We used radio-telemetry to obtain the first data on the activity patterns and torpor use of two sympatric, free-ranging dasyurid marsupials, the stripe-faced dunnart Sminthopsis macroura (16.6±1.5 g) and the more than six-times larger kowari Dasyuroides byrnei (109.4±16.4 g), during winter in arid Queensland, Australia. Eight dunnarts and six kowaries were surgically implanted with temperature-sensitive radio-transmitters and monitored for 14–59 days. Both species commenced activity shortly after sunset, but while kowaries remained active through most of the night, dunnarts usually returned to their burrows before midnight. In dunnarts, short activity was associated with the frequent use of daily torpor (99.1% of observation days). Torpor often commenced at night, with body temperature (Tb) decreasing to a minimum of 11.3 °C, and torpor lasted up to 26 h. In contrast, only 50% of the kowaries entered torpor and torpor was brief (maximum 4 h), shallow (minimum Tb 25.3 °C) and restricted to the daytime rest-phase. Our study suggests that in winter, the smaller dunnarts can remain active only during the warmer first half of the night and energy-saving torpor becomes part of their daily routine. In contrast, it appears that the larger kowaries are less affected by cold winter nights and can maintain high night-time activity levels and commence reproduction already in winter. Hence, they enter torpor only occasionally and only during the rest phase.

Did dingo control cause the elimination of kowaris through mesopredator release effects? A response to Wallach and O’Neill (2009)

Did dingo control cause the elimination of kowaris through mesopredator release effects? A response to Wallach and O’Neill (2009)

Threatened species indicate hot-spots of top-down regulation

The introduction of alien mesopredators and herbivores has been implicated as the main driver of mammalian extinction in Australia. Recent studies suggest that the devastating effects of invasive species are mitigated by top-order predators. The survival of many threatened species may therefore depend on the presence and ecological functioning of large predators. Australia’s top predator, the dingo (Canis lupus dingo), has been intensively persecuted across the continent and it is extremely rare to find dingo populations that are not being subjected to lethal control. We predicted that the presence of threatened species point out places where dingo populations are relatively intact, and that their absence may indicate that dingoes are either rare or socially fractured. A comparison of a site which harbors a threatened marsupial, the kowari (Dasyuroides byrnei), and a neighboring site where the kowari is absent, offers support for this suggested pattern.

Effects of cold acclimation on shivering intensity in the kowari ( Dasyuroides byrnei), a dasyurid marsupial

1. Heat production, activity, body temperature and shivering tremor were measured in warm acclimated (WA, 25°C) and cold acclimated (CA, 10°C) kowaris ( Dasyuroides byrnei), to determine the role of shivering following cold acclimation. 2. Heat production and conductance were similar in WA and CA kowaris but the level of shivering tremor was significantly lower for CA than for WA kowaris at ambient temperatures from 20°C to 0°C. 3. Some form of nonshivering thermogenesis (NST) occurs in CA kowaris. Cold acclimation in eutherians is accompanied by potentiation of beta-adrenergic noradrenaline-mediated NST in brown adipose tissue (BAT). Morphological studies have failed to find any evidence of BAT in marsupials and the mechanism of the NST that substitutes for shivering in the CA kowari remains to be determined.

Application of a piezoelectric sensor for measuring shivering in a small marsupial

1. A technique using piezoelectric film (PEF) for measuring whole body shivering tremor in unrestrained small mammals (the kowari, Dasyuroides byrnei, and laboratory rats) is described. The PEF converts vibrations from a shivering animal to a discrete voltage, which provides a measure that correlates with ambient temperature below the thermoneutral zone, and physiological parameters such as oxygen consumption and changes in body temperature. 2. Measurement of shivering tremor is recommended as an alternative to electromyography in studies on small mammals, as it does not require restraint, attachment of electrodes or implantation of transmitters.

Anatomy and chromosomes of two intersexual dasyurid marsupials.

The intersexual phenotypes of marsupials with XXY and XO chromosome constitutions imply that not all sexual dimorphisms are under the control of testicular hormones and, ultimately, the SRY gene on the Y chromosome. It has been hypothesised that there is a gene on the X chromosome that determines whether either a scrotum will form (one copy of the gene) or a pouch with teats (two copies of the gene). Here, we describe the anatomy and chromosomes of two intersexual dasyurid marsupials. One, a Dasyuroides byrnei, had a pouch, but the reproductive tract was essentially male. The other, a Sminthopsis douglasi, had a hemipouch and a hemiscrotum and the reproductive tract was essentially female. The S. douglasi was a mosaic for cells with an apparently normal 2n = 14, XX female karyotype and cells with 2n = 14 plus (usually) two dot-like supernumerary elements 2n = 14, XX + 2B. The D. byrnei cells examined also had a 2n = 14, XX + 2B karyotype. In fibroblasts from the male and female sides of the S. douglasi, it was possible to assign the 2n = 14, XX karyotype to the male side and the 2n = 14, XX + 2B to the female side.

Isolation and partial characterization of tammar wallaby luteinizing hormone and development of a radioimmunoassay.

Tammar wallaby (Macropus eugenii) luteinizing hormone (LH) was purified from pituitaries collected from wild and captive populations by salt sequential precipitation, ion exchange chromatography and gel filtration. Pituitary tissue (5 g) yielded 1.8 mg of purified wallaby luteinizing hormone (ME-14B), as verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). A heterologous radioimmunoassay has been developed for measurement of LH in plasma of marsupials using a monoclonal antibody raised against bovine LH (518B7). This assay system was able to measure basal LH concentrations in male and female tammars and detected a significant rise in plasma LH in response to oestradiol benzoate in female tammars and luteinizing hormone-releasing hormone (LHRH) in males. Parallel dose-response curves were also obtained from pituitary extracts from four other species of marsupial (brushtail possum, Trichosurus vulpecula; brown antechinus, Antechinus stuartii; kowari, Dasyuroides byrnei; and Eastern pygmy possum, Cercartetus nanus) in this assay, which suggests its usefulness in the measurement of LH in other marsupial species.

The Blood of Carnivorous Marsupials: Low Hemoglobin Oxygen Affinity

We examined the blood of four dasyurid marsupials, all small, active insectivores and/or carnivores, to establish if there were any specializations in oxygen transport. All four species had hemoglobins with a low affinity for oxygen. This was demonstrated by high P50's (the partialpressure of oxygen [PO₂] at which the hemoglobin is half-saturated with oxygen) of the whole blood (means of 38.3-59.8 mmHg) and of red cells suspended in a physiological buffer (means of 41.6-49.0 mmHg) at a CO₂ tension of 43 mmHg. There was a strong correlation betuween increase in body mass over three orders of magnitude and increase in the oxygen affinity of the whole blood. The effects of changing CO₂ tensions on the oxygen affinity of whole blood were measured as △log P50/Δlog PCO₂; mean values ranged from 0.25 to 0.373. Values for △log P50/ΔpH wuere measured for red-cell suspensions; means values ranged from -0.40 to -0.481. The introduction of 2,3-diphosphoglycerate significantly decreased the oxygen affinity, of the hemoglobin of Dasyuroides byrnei. The blood of D. byrnei and Dasyurus viverrinus had high hematocrits and high concentrations of hemoglobin. We conclude that hemoglobins with a low affinity for oxygen, an adaptation to an active lifestyle, are a characteristic of dasyurid marsupials generally.

A comparison of the molar efficiency of two insect‐eating mammals

The extent to which the different molar morphologies of two similar‐sized mammals, Petaurus breviceps (sugar glider) and Dasyuroides byrnei (kowari), could affect the digestion of larval insect nitrogen was investigated. Nitrogen digestibility of Tenebrio larvae treated with a proteolytic enzyme (trypsin) increased with decreasing larval piece size. However, it was found that the molars of P. breviceps, with their minimal shearing capacity compared with D. byrnei, can only compress rather than finely comminute Tenebrio larvae. As a result, P. breviceps have less efficient nitrogen digestibility than D. byrnei whose shearing molars can finely comminute larvae. Petaurus breviceps molars are inefficient at breaking down insects possibly because of functional constraints, where the molars must perform several different tasks with competing morphological demands, or because of phylogenetic constraints.

Ventilatory Accommodation of Changing Oxygen Consumption in Dasyurid Marsupials

Little is known about how the mammalian ventilatory system accommodates the large change in rates of O₂ consumption V̇o2 between minimal and maximal aerobic metabolism. These changes are expected to be particularly large in marsupials, which have a substantially greater aerobic scope than similar-sized placental mammals. We measured ventilation and V̇o2 at metabolic rates between basal metabolism (BMR) and maximal O₂ consumption during thermogenesis V̇o2max in three dasyurid marsupials: Planigale tenuirostrus (5.7 g), Sminthopsis crassicaudata (14.2 g), and Antechinus swainsoni (66.9 g). Comparative data on a fourth dasyurid species, Dasyuroides byrnei (144 g), were obtained from the literature. Thermogenic aerobic scopes (V̇o2 /BMR) were 9.2, 9.0, 8.7, and 10.4, respectively. Ventilatory accommodation of changing V̇o2 was qualitatively similar in the four species, with most accommodation resulting from changes in minute volume V̇i. However, there were differences in the relative importance of frequency (f), tidal volume (Vt), and O₂ extraction (Eo₂) in accommodation. In all species, f and V̇i were strongly correlated with V̇o2 . Tidal volume was significantly correlated with V̇o2 in S. crassicaudata, A. swainsoni, and D. byrnei, while Eo₂ was significantly correlated with V̇o2 only in A. swainsoni. Analysis of factorial ventilation changes across a standardized eightfold change in V̇o2 revealed overall similarity between the four species in Vt and V̇i with significant differences in f and Eo₂. For the latter two parameters, there was no difference between P. tenuirostrus and S. crassicaudata, whereas A. swainsoni and D. byrnei differed significantly from other species. As size increases in dasyurids, Eo₂ increases, mass-specific Vt decreases, and the importance of Vt changes in accommodation increases. When compared with a generalized allometry for ventilation in resting placental mammals, dasyurids had much lower f and greater Vt than predicted; in the two smaller species, resting Eo₂ was lower than predicted. However, when the dasyurid data were compared with data obtained from 10 placental mammals measured without the use of restraints or invasive procedures, there were no differences between the two taxa. We found no indication that ventilation constrained thermogenic V̇o2max.

Fine structure of the parotid gland in the crest-tailed marsupial-rat (Dasyuroides byrnei).

The parotid gland of Dasyuroides byrnei was examined by light microscopy, and transmission and scanning electron microscopy. The acini were composed predominantly of seromucous cells with a few mucous cells. The seromucous cells were light or dark cells containing acidophilic spherical granules of moderate to high electron density and had well-developed cytoplasmic organelles-ordinary mitochondria and large mitochondria with tubular cristae, RER with vesicular or tubular elements, and Golgi apparatus with lamellae, vesicles and vacuoles. The mucous cells had basophilic amorphous granules of low electron density, like those of ordinary mucous cells. The intercalated ducts were composed of simple cuboidal light cells having a few electron-dense granules. The striated ducts consisted of tall columnar light cells containing numerous vesicles and mitochondria with tubular cristae, the same as found in acinar seromucous cells.

Restricted feeding entrains circadian wheel-running activity rhythms of the kowari

The effect of daily restricted feeding (RF) on the circadian wheel-running rhythms of the kowari, Dasyuroides byrnei, was examined in two experiments. Kowaris were presented with a preferred food (determined in a pilot study) during a daily 2-h meal in the light period of a 14:10 light-dark (LD) cycle (expts 1 and 2), during constant dark (DD) immediately after termination of the LD cycle (expt 1), and during DD when kowaris were free running (expt 1). Results showed that 1) RF elicited anticipatory activity similar in duration and phasing to that observed in the rat; 2) cycles of meal-associated activity free ran for up to 6 days after the termination of RF; 3) activity persists at a phase near that of the former mealtime during periods of food deprivation; and 4) activity indicative of beating between two pacemakers occurred when feeding was restricted to the L period of LD cycles. Together these observations suggest that the activity rhythms of the kowari may be controlled by separate, but possibly coupled, light-entrainable and food-entrainable pacemakers, as are those of the rat.

Significance of cation transport in control of energy metabolism and thermogenesis.

Significance of cation transport in control of energy metabolism and thermogenesis.