Dasyurus Research Articles

The original mammal fauna of the Pilbara biogeographic region of north-western Australia

The hills and ranges of the Pilbara contain large numbers of caves, but only a miniscule proportion of these holds mammal remains that can be used to reconstruct the original (i.e. pre-European) fauna. During two field seasons in 1985 and 2004, only 12 sites with bones were discovered. Material from three other sites lodged in the collections of the Western Australian Museum was also used. Thirty-six native mammal species plus the introduced House Mouse were identified from cave surface remains. Compared with the fauna known from live-caught specimen records and the results of the Pilbara Biodiversity Survey, rodent species are comprehensively represented among the remains, dasyurid marsupials and bandicoots are moderately well represented, macropodoids are poorly represented, and bats (except two cave-roosting species) hardly represented at all. Results of this study indicate that the Central Rock-rat (Zyzomys pedunculatus), and probably the Golden-backed Tree-rat (Mesembriomys macrurus), originally occurred throughout the Pilbara ranges. Chuditch (Dasyurus geoffroii) is recorded from the Pilbara for the first time, suggesting that it may have occurred in the lowlands, while Northern Quoll (D. hallucatus) occupied the ranges. New records of Melomys burtoni and Pseudomys fieldi represent substantial extensions of geographic range. Overall, these results confirm the Pilbara as the western outpost of several northern mammal species, but show that the original fauna is less distinctive than previously thought, with a higher proportion of species widespread in the arid zone.

The diet of some New Guinean dasyurid marsupials

We investigated the diets of five forest-dwelling species of dasyurid marsupials endemic to New Guinea by using faecal and gut content analysis and compared the contents with the results of pitfall trapping for terrestrial invertebrates carried out coincidently. In one study area, in montane forest 2060–2340 m above sea level, three dasyurid species were trapped. In another area, in forest 1000–1470 m above sea level, two other species were captured. All five species ate a diverse range of invertebrates but beetles (Coleoptera) and spiders (Araneae) formed the bulk of their diet, followed by grasshoppers and crickets (Orthoptera). Earthworms (Annelida) were eaten by all species and some vertebrate remains were found in samples from four species. We found some significant differences between diets of the sympatric species. Some of the invertebrates commonly collected in pitfall traps, such as isopods (Isopoda) and amphipods (Amphipoda), were rarely detected in the diets of any of the species and millipedes (Diplopoda) and centipedes (Chilopoda) were never detected. Our results are broadly in agreement with what is known about the diets of the small Australian species of dasyurid marsupials.

Impact of Invasive Cane Toads on Australian Birds

The cane toad (Bufo marinus), a large, toxic, American anuran, was introduced to Australia in 1935. Populations of many of Australia's reptiles (snakes, varanid lizards, crocodiles) and carnivorous mammals (dasyurid marsupials) have declined because these predators are killed by the toad's powerful toxins. In contrast to these well-studied species, little is known about the cane toads impacts on Australian birds. We reviewed published and unpublished data on behavioral interactions between Australian avian predators and cane toads and collated distributional and dietary information to identify avian taxa potentially at risk from cane toad invasion. Cane toads are sympatric with 172 frog-eating bird species in Australia, and an additional 8 bird species overlap with the predicted future range of the toad. Although many bird species thus are potentially at risk, behavioral observations suggest the risk level is generally low. Despite occasional reports of Australian birds being killed when they ingest cane toads, most birds either ignore toads or survive the predation event. The apparently higher tolerance of Australian birds to toad toxins, compared with Australian reptiles and marsupials, may reflect genetic exchange between Australian birds and Asian populations that encounter other bufonid species regularly and hence have evolved the capacity to recognize or tolerate this toxic prey.

Acrosomal integrity, viability, and DNA damage of sperm from dasyurid marsupials after freezing or freeze drying

Dasyurids are a diverse group of Australian native carnivores and insectivores that contains several threatened species. Despite successful cryopreservation of sperm from several marsupials, only 3% postthaw motility is reported for dasyurid marsupials. This study examined sperm preservation in the fat-tailed dunnart ( Sminthopsis crassicaudata), an experimental model, with supplementary observations on the eastern quoll ( Dasyurus viverrinus) and northern quoll ( Dasyurus hallucatus). In S. crassicaudata, a toxicity trial demonstrated that incubation with up to 40% glycerol did not reduce sperm viability, suggesting that glycerol is not toxic to dasyurids. On the basis of this finding, S. crassicaudata, D. viverrinus, and D. hallucatus sperm were extended to a final concentration of 20% or 40% glycerol in Tris-citrate fructose and frozen in liquid nitrogen vapor. Postthaw sperm from all three species were nonmotile, and vital staining (SYBR14 and propidium iodide) indicated that sperm were nonviable. However, there was no evidence suggesting disruption of normal gross morphology or loss of acrosomal integrity when assessed by Bryan's staining. After freeze drying, Bryan's staining indicated that approximately 80% of S. crassicaudata sperm had normal acrosomes and no head loss. Despite being nonviable, terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling showed that S. crassicaudata sperm frozen in 40% glycerol or freeze-dried had no DNA damage compared with fresh controls. This study has described a method for preservation of the dasyurid sperm nuclei, but continued studies are required to achieve viable motile sperm and establish tools for the long-term storage of dasyurid sperm.

Spatial and Temporal Organization in the Swamp Antechinus: Comparison between Island and Mainland Populations

Comparative analyses of the biology of insular and mainland populations of mammals have demonstrated a number of behavioral differences. Individuals from island populations generally have reduced home-range sizes, increased territory overlaps, and reduced aggressiveness with neighbors in comparison to mainland counterparts. We tested the hypothesis that island and mainland populations of the swamp antechinus (Antechinus minimus maritimus), an insectivorous marsupial, will differ in their use of space. We predicted that the home ranges of individuals on an offshore island are smaller and their territory overlaps greater compared to those of antechinus at an adjacent mainland site in southeastern Australia. We used radiotelemetry to measure home-range areas and overlaps, as well as the temporal activity patterns of 40 individuals in the nonbreeding and breeding seasons at island and mainland sites. These dasyurid marsupials were social animals and nested together at both sites, and a high degree of spatial overlap was recorded in both populations. Island individuals occupied significantly smaller home ranges and were mainly nocturnal, whereas mainland individuals were diurnal and had large home ranges. The small home ranges of island individuals may have been in response to increased food resources, resulting from large allochthonous inputs from seabirds. The nocturnality of island animals was likely a predator-avoidance mechanism to evade diurnal raptors in the open tussock grassland.

Oestrus in the Julia Creek dunnart ( Sminthopsis douglasi) is associated with wheel running behaviour but not necessarily changes in body weight, food consumption or pouch morphology

The Julia Creek dunnart ( Sminthopsis douglasi) is an endangered carnivorous marsupial belonging to the family Dasyuridae. This study investigated the oestrous cycle of this species in terms of its reproductive physiology and behaviour to explore more efficient methods of oestrus detection. Ten sexually mature captive female dunnarts were monitored daily at David Fleay Wildlife Park, Burleigh Heads, Australia, from mid September to late December 2006 for changes in urogenital cytology within the urine (0, 1+, 2+ and 3+), running wheel activity, body weight, uneaten food, faecal steroid metabolites (progesterone and oestradiol) and pouch development. Periods of increased running wheel activity were associated ( p = 0.004) with an increase in the proportion of cornified urogenital epithelial cells found in the urine; periods of decreasing weight ( p < 0.001) and uneaten food ( p < 0.001) were also associated with changes in urogenital cytology but not to the point where they would be useful for oestrus detection. Between 60.3% and 92.0% of peak distances (confidence interval 95%) occurred when the epithelial cell index was 2+ or 3+. Only 15.5–37.5% of peak weights (CI: 95%) and 28.1–49.9% of incidences of uneaten food (CI: 95%) occurred when the epithelial cell index was 2+ or 3+. There was no significant difference in the mean length of the oestrous cycle when measured by urogenital cytology (mean ± SD: 25.0 ± 5.7 days; n = 20) or peak distance travelled (mean ± SD: 25.4 ± 5.7 days; n = 20). Changes in the concentration of oestradiol metabolites in Julia Creek Dunnart faeces were not useful in characterising the oestrous cycle. Wheel running activity declined markedly with increased faecal progestagen concentration. The majority of the pouch variables examined showed maximum development during the inter-oestrus period but as there was considerable variation between animals, the pouch was not considered a useful index of oestrus.

Small mammal populations in a eucalypt forest affected by fire and drought. I. Long-term patterns in an era of climate change

This paper reports a study of ground-dwelling, small mammals in coastal eucalypt forest in south-eastern Australia from 1970 through 2005. During this time, the study area burnt in an intense fire in December 1972 and was partially burnt in November 1980. Both fires were associated with prolonged drought. The mammals studied comprised two dasyurid marsupials, Antechinus agilis and A. swainsonii, two native murid rodents, Rattus fuscipes and R. lutreolus, and the introduced house mouse Mus musculus. After intensive sampling throughout the year from 1970 through 1972 to establish basic ecological and population parameters of the small mammal community, populations were sampled annually during late autumn and early winter before the onset of breeding. There were marked differences in the annual (autumn/winter) abundances of all species; numbers of A. agilis ranged from 4 to 142 individuals; A. swainsonii 0 to 43; R. fuscipes 4 to 54; R. lutreolus 0 to 11; M. musculus 0 to 23. Following the 1972 fire, numbers fell to the lowest level recorded during the study and each population subsequently disappeared from the plot between the 1973 and 1974 winter censuses. The less intense 1980 fire did not lead to extirpation, but numbers of A. agilis, A. swainsonii and R. fuscipes declined as drought conditions persisted through 1983. R. lutreolus occurred consistently only following the fires, when a grassy ground vegetation favoured by this species developed. Similarly, M. musculus colonised within two years of the fires and persisted on the plot for 3–4 years before disappearing. Following the fires, populations of the omnivorous R. fuscipes recovered first followed by the scansorial, insectivorous A. agilis and last by the fossorial, insectivorous A. swainsonii. Two primary conclusions emerged from this study. First, the intense fire of 1972 did not kill all the animals immediately, but led to the disappearance of each species from the plot over 18 months. Thus, intense fire had a delayed but catastrophic impact on small ground-dwelling mammals. The fluctuations in population levels, covering more than an order of magnitude, demonstrate that factors other than fire, such as rainfall and drought, drive the population dynamics of these small mammals. As stability and recovery are not features of local populations, long-term studies of benchmark populations are necessary to manage forest biodiversity.

Dissociation and preservation of preantral follicles and immature oocytes from female dasyurid marsupials

The mammalian ovary contains numerous immature preantral follicles that are not dependent on endocrine support, unlike the more mature hormone-dependent antral follicles. Preantral follicles can be enzymatically dissociated to yield immature oocytes that survive sub-zero preservation better as they lack a temperature-sensitive meiotic spindle. These techniques are highly applicable to gamete banking, which is an urgent requirement for Australian carnivorous marsupials as several species have rapidly declining populations and risk extinction. The present study developed protocols for the transport, dissociation, preservation and culture of granulosa cell-oocyte complexes (GOC) from the ovaries of dasyurid marsupials. High viability of GOC following enzymatic dissociation is reported and it was demonstrated that GOC are of significantly better quality following refrigerated storage for 24 h compared with storage at room temperature. Oocytes from primary follicles were not damaged by cold shock or the toxicity of vitrification media and following vitrification in liquid nitrogen 69.42+/-2.44% of oocytes were viable. However, the surrounding granulosa cells demonstrated significant damage post-thaw. These granulosa cells proliferated during a 48-h culture period resulting in significant improvements in GOC quality. The present study is a valuable step towards cryostorage of dasyurid gametes and represents fundamentally important methods by which we can contribute to the conservation of Australia's native predators.

Mathevotaenia niuguiniensis n. sp. (Cestoda: Anoplocephalidae: Linstowiinae) from the water-rat Parahydromys asper (Thomas) in Papua New Guinea, with a list of species of Mathevotaenia Akumyan, 1946

A new species of cestode, Mathevotaenia niuguiniensis n. sp. (Anoplocephalidae: Linstowiinae), is described from the hydromyine rodent Parahydromys asper (Thomas) in Papua New Guinea. This is the third species of the genus reported from the Australasian region. The new species differs from all congeners in rodents by having an elongate cirrus-sac, which crosses the osmoregulatory canals and extends into the medulla, compared with a short, ovoid cirrus-sac which does not penetrate into the medulla in congeners. It differs from the known Australian species, M. antechini (Beveridge, 1977) and M. nyctophili (Hickman, 1954), found in dasyurid marsupials and bats respectively, by lacking a complex of anastomosing osmoregulatory canals in each segment. A list of all known species of Mathevotaenia Akumyan, 1946, their host genera, host families and geographical distribution is provided. New combinations proposed in this report are: M. dipodomi (Bienek & Grundmann, 1973) n. comb. (transferred from Schizorchodes Bienek & Grundman, 1973), M. genettae (Ortlepp, 1937) n.comb., M. mephitis (Skinker, 1935) n. comb., M. pedunculata (Chandler, 1952) n. comb., M. wallacei (Chandler, 1952) n. comb. (transferred from Oschmarenia Spasskii, 1951) and M. oedipomidatis (Stunkard, 1965) n. comb. (transferred from Paratriotaenia Stunkard, 1965).

Factors Influencing the Occurrence of Small Ground-Dwelling Mammals in Southeastern Mainland Australia

We investigated the occurrence of small, ground-dwelling mammals (marsupial mice and rodents) across 128 forested study sites representing a stratified sample of the climatic, geological, and topographic features of far southeastern mainland Australia. We then developed statistical models for the occurrence of the agile antechinus (Antechinus agilis), dusky antechinus (A. swainsonii), and bush rat (Rattus fuscipes) based on various environmental attributes measured for each site. At a landscape scale, the climatic factor mean minimum temperature of the coldest month was an important explanatory variable for the bush rat, with the likelihood of its occurrence increasing with increasing temperature during that period. Sites with greater precipitation during the driest quarter of the year were more likely to support bush rats and the agile antechinus. At an on-site scale, protected slopes and gullies were more likely to support bush rats, and the occurrence of bush rats and the dusky antechinus increased at sites with a higher number of large fallen trees. In multiple-use forests, increasing the number of large fallen trees after timber harvesting may increase habitat quality for both the dusky antechinus and the bush rat, and retaining habitat on protected slopes and gullies also may be important for the latter species.

Maternal Determinants and the Polarised Marsupial Oocyte.

Cleavage is highly stylised in dasyurid marsupials that have highly polarized oocytes and zygotes. The first three cleavage divisions are meridional along the axis of polarity and the cells appear identical except for the order of cell division, in which the first cell to divide at each cleavage division lies on one side of the conceptus and the last cell to divide lies opposite it. The fourth division is latitudinal and separates the conceptus into 8 smaller pluriblast cells (equivalent to the inner cell mass) and 8 larger trophoblast cells. The axis between 1st and last dividing cells at each division is maintained in both pluriblast and trophoblast cells. No morula is formed, but instead the cells from early cleavage adhere to the zona pellucida and then to each other from the 8-cell stage so that they form a unilaminar blastocyst, which is completed at about the 32- cell stage. Cleavage in other marsupials such as the possum or the opposum is slightly less stylized, in that from the 4 -cell stage some cells begin to divide latitudinally, but the end result is the same with about half the cells at the 16-cell stage being pluriblast and half trophoblast. Such a specific cleavage pattern suggests that determinants leading to pluriblast vs trophoblast might be differentially allocated at the 16-cell stage. Certainly the vesicular products which are mainly located in the pole opposite the pronuclei end up being progressively restricted to the trophoblast cells and continue to be discharged into the cleavage cavity as they contribute to the blastocoel. We have identified one vesicle-associated protein, VAP1, which is produced during oogenesis from early primary oocyte stages onwards. VAP1 is a cystatin-like protein, which acts as a cysteine proteinase inhibitor and probably assists in stabilizing the extracellular matrix of the blastocoel. Immunization with VAP1 in possums results in accumulations of degraded lipid bodies which partially replace vesicles in oocytes, disruption of normal polarity in ovulated oocytes and zygotes and failure of normal development. In addition, in a recent cDNA RDA study we isolated ~180 clones of which 70 have been tested and 49 have been identified as dunnart ovary-specific, using Southern dot blot hybridization. On investigation of 20 randomly selected clones, 5 dunnart ovary-specific genes, which included ZP-2, c-mos and 3 novel genes as determined by comparing expression in several somatic, as well as gonadal and brain dunnart tissues by RT-PCR, have been identified. Most importantly, the 3 novel gene transcripts are present during stages of early development. This strongly suggests that some of these transcripts may be maternal determinants akin to those for the frog and chick, and play a role in patterning in the marsupial embryo. The patterns displayed by the marsupial embryo and the late onset of the zygote genome activation at the 16- cell stage, suggest that any determinants found will be involved in establishing the pluriblast/trophoblast lineages and the embryonic-abembryonic axis, and setting up a putative anterior-posterior axis in both pluriblast and trophoblast. The research was supported by the New Zealand Foundation for Research Science and Technology and the University of Melbourne.

Boom and bust: a review of the physiology of the marsupial genus Antechinus

The marsupial genus Antechinus is a group of small carnivorous marsupials from the order Dasyuromorphia (Family Dasyuridae) and is found in eastern Australia. The life history of all species in the genus is characterized by a complex, but highly synchronized life cycle in both sexes, culminating in a short mating period followed by total male mortality (semelparity). The breeding season is defined by a specific rate of increase in photoperiod, which is different for each species. In Antechinus spp., male mortality is due to the effects of high free testosterone and cortisol levels on many organ systems. Unusually, spermatogenesis is complete before testosterone levels begin to rise at the winter solstice. In males, low sperm counts have been compensated for by high proportions of sperm reaching the isthmus of the female reproductive tract and long-term storage in the crypts. The females survive to rear their young and may mate again in their second year. Gestation lasts from 26 to 34 days, depending on the species. However, developmental arrest can occur at several stages during embryogenesis, elongating the apparent gestation duration by several days. Several species have strong female sex biases in their litters. The high degree of life history synchrony and the cascade of endocrine-driven physiological events that result in male death are unusual physiological characteristics for mammals. Suggestions why semelparity may have evolved in Antechinus are discussed.

Acrosome stability in the spermatozoa of dasyurid marsupials

The spermatozoa of most marsupials lack nuclear stabilising disulfide-bonded protamines found in eutherian mammals. However, disulfide stabilisation has been observed in the acrosome of macropodid (Macropus eugenii) and phalangerid (Trichosurus vulpecula) marsupials. As a result this organelle, which is normally fragile in eutherian mammals, is robust and able to withstand physical and chemical challenge in these marsupials. The present study examined acrosomal characteristics of the spermatozoa of three dasyurid marsupials; the fat-tailed dunnart (Sminthopsis crassicaudata), eastern quoll (Dasyurus viverrinus) and northern quoll (Dasyurus hallucatus). In all species examined Bryan's staining demonstrated that significant acrosomal loss occurred following physical challenge with osmotic stress, cryopreservation without cryoprotectant and exposure to detergent (Triton-X). Bromobimane staining indicated that the acrosomes of dasyurids lacked stabilising disulfide bonds. As reported for the wallaby and possum, calcium ionophore (A23187) did not induce the acrosome reaction-like exocytosis in dasyurid spermatozoa but treatment with diacylglycerol (DiC8) caused significant acrosome loss at concentrations similar to those effective for other marsupials. The present study found that the spermatozoa of dasyurids are more sensitive to physical challenge than the previously-studied marsupials and we suggest that this is due to the absence of acrosomal stabilising disulfide bonds.

Expressed sequence tags as a tool for phylogenetic analysis of placental mammal evolution.

BackgroundWe investigate the usefulness of expressed sequence tags, ESTs, for establishing divergences within the tree of placental mammals. This is done on the example of the established relationships among primates (human), lagomorphs (rabbit), rodents (rat and mouse), artiodactyls (cow), carnivorans (dog) and proboscideans (elephant).Methodology/Principal FindingsWe have produced 2000 ESTs (1.2 mega bases) from a marsupial mouse and characterized the data for their use in phylogenetic analysis. The sequences were used to identify putative orthologous sequences from whole genome projects. Although most ESTs stem from single sequence reads, the frequency of potential sequencing errors was found to be lower than allelic variation. Most of the sequences represented slowly evolving housekeeping-type genes, with an average amino acid distance of 6.6% between human and mouse. Positive Darwinian selection was identified at only a few single sites. Phylogenetic analyses of the EST data yielded trees that were consistent with those established from whole genome projects.ConclusionsThe general quality of EST sequences and the general absence of positive selection in these sequences make ESTs an attractive tool for phylogenetic analysis. The EST approach allows, at reasonable costs, a fast extension of data sampling from species outside the genome projects.

Basking and torpor in a rock-dwelling desert marsupial: survival strategies in a resource-poor environment

Australian deserts are characterized by unpredictability, low primary productivity, and high temperature fluctuations. Despite these adverse conditions the diversity of small insectivorous marsupials of the family Dasyuridae is surprisingly high. We quantified the thermal biology of the dasyurid Pseudantechinus madonnellensis (body mass approximately 30 g) in the wild to gain some understanding of whether the success of dasyurids in the arid zone may be related to some extent to their use of energy conservation strategies. In winter, most free-ranging Pseudantechinus frequently (58.3% of 131 animal days) entered daily torpor after midnight (mean 0157 hours) in rock crevices when outside ambient temperatures (T (a)) were low. Most animals remained torpid until the next morning when they moved while still torpid from rock crevices to sun-exposed basking sites. We visually observed basking during rewarming from torpor (mean commencement at 0943 hours) at body temperatures (T (b)) as low as 19.3 degrees C when radiant heat was high and T (a) was rising. Basking continued for the rest of the day. Torpor use was not strongly correlated with T (a), but the temporal organization of daily torpor and activity were apparently linked to the thermal characteristics of basking sites. Our study suggests that by frequently employing daily torpor and basking and by appropriately coordinating their thermal biology with that of specific locations in their environment, Pseudantechinus can reduce daily energy expenditure and thus can live and reproduce in a challenging environment. It is likely that the success of other small dasyurids and perhaps many other small mammals living in deserts is linked to employment of torpor and basking for energy conservation.

Phylogenetic Relationships of the Dasyurid Marsupial Genus Murexia

Five species of dasyurid marsupials endemic to New Guinea and herein referred to as Murexia longicaudata, M. rothschildi, M. habbema, M. naso, and M. melanurus have a varied taxonomic history. Until 1984, the latter 3 species had been assigned to the otherwise strictly Australian genus Antechinus, but comparisons of phallic morphology showed that this arrangement was untenable. Immunological and DNA hybridization studies of dasyurids suggested that New Guinean “antechinuses” were part of a clade that included M. longicaudata and M. rothschildi, a finding that was confirmed by early DNA sequence comparisons. Comprehensive analyses of cytochrome b, 12S rRNA, and protamine P1 sequences from all recognized dasyurid species led to the recommendation that these 5 species be included in a single genus (Murexia) that, along with Phascogale and Antechinus, constitutes the dasyurid tribe Phascogalini. Recently, however, a morphocladistic study concluded that these species are neither closely related to one another nor to any other dasyurid clade, placing them instead as successive basal branches within the family and assigning each to a distinct genus. Here we report results from an expanded DNA sequence data set that includes 2 additional mitochondrial loci (16S rRNA and control region) and 2 nuclear loci (beta-fibrinogen intron 7 and interphotoreceptor retinoid-binding protein exon 1) from phascogalin species and selected dasyurid and myrmecobiid outgroups. Phylogenetic analyses of these sequences show strong support for the monophyly of Murexia and its placement within Phascogalini, and provide the 1st resolved phylogeny of Murexia and Antechinus species. Reassessment of the morphological data suggests that the apparently primitive cranidental anatomy of Murexia may be an artifact of character polarizations or indicative of extreme homoplasy.

The unique paired retinal vascular pattern in marsupials: structural, functional and evolutionary perspectives based on observations in a range of species

Background:In the few marsupial species studied to date that possess a retinal vasculature, the arterial and venous segments, down to the smallest calibre capillaries, have been shown to occur in...

PARTIAL SEMELPARITY IN THE NEOTROPICAL DIDELPHID MARSUPIAL GRACILINANUS MICROTARSUS

Semelparity has been demonstrated in males of several species of Australian dasyurid marsupials. Although semelparity also has been reported in some species of neotropical didelphid marsupials, no study has conclusively demonstrated its occurrence based on survival rate estimates from field studies of marked individuals. In this study, we demonstrate that the survival rates of males of a Neotropical didelphid marsupial, the Brazilian gracile mouse opossum (Gracilinanus microtarsus), decrease sharply after the beginning of the breeding season in a cerrado remnant. However, mortality of the males after mating is not complete and a small percentage of them may survive to breed again in a 2nd breeding season. Examination of the demographic data presented here conclusively demonstrates that G. microtarsus is best described as partially semelparous.

Plasma steroids and steroid-binding capacity in male semelparous dasyurid marsupials ( Phascogale tapoatafa) that survive beyond the breeding season in captivity

The semelparous dasyurids display a unique life history, in that all males die within a few weeks of the completion of the breeding season. Studies of several semelparous species have revealed that the male die-off is stress-related, and accompanied by increased plasma androgen and cortisol levels and decreased corticosteroid binding capacity, resulting in suppression of immune and inflammatory responses. This study examines the endocrine profile of male brush-tailed phascogales ( Phascogale tapoatafa) that survive beyond the breeding season in captivity. Plasma cortisol, corticosteroid binding globulin and albumin levels were monitored in both males and females and steroid partitioning calculated. Captive males surviving beyond the breeding season did not show the elevation in plasma cortisol and decrease in corticosteroid binding capacity reported in wild males. Plasma albumin concentrations also remained constant during the sampling period. These data indicate that captive males do not undergo the same stress response described in wild populations.

Distribution, abundance, and individual strategies: a multi‐scale analysis of dasyurid marsupials in arid central Australia

We investigated the effects of different environmental factors on the distribution and abundance of 6 species of dasyurid marsupials using a multiple‐scale analysis. Data collected in the spinifex dunefields of the Simpson Desert, Australia, were analysed at 3 spatial scales spanning more than 5 orders of magnitude: “metasite” (covering an area of 1000–2000 km2), site (2–12 km2) and grid (0.01 km2). Temporal variability was also investigated, using data collected in March, April, and May in 4 consecutive years from 1997 to 2000. Both abiotic and biotic factors influenced the capture rates of different species at different times and spatial scales. At the coarsest spatial scale, Dasycercus cristicauda (mulgara) was consistently limited in its distribution by the intensity of rainfall, probably as an indirect result of increased grazing pressure from pastoral activity and a higher density of feral predators in high rainfall areas. However, at the finest spatial scale, this partly carnivorous species was scarce in areas of dense spinifex, perhaps because such habitats yield lowest returns during foraging, and was more common in areas where small invertebrate prey were abundant. Factors affecting the distribution of the most abundant dasyurid species in the study area, Sminthopsis youngsoni (lesser hairy‐footed dunnart), could not be identified at any scale; we conclude that this reflects the opportunistic foraging strategies and flexible habitat requirements of this insectivorous species. Both Ningaui ridei (wongai ningaui) and Sminthopsis hirtipes (hairy‐footed dunnart) were less abundant throughout the study region. For N. ridei, a spinifex specialist, predictors of occurrence could be identified only at the finest scale of analysis; at the grid level, a close positive association was detected in 2 of the 4 study years between capture rate and spinifex cover. For S. hirtipes, all 3 levels of spatial analysis revealed a negative association between capture rate and both rainfall and spinifex density. For the rarely‐caught S. crassicaudata (fat‐tailed dunnart) and Planigale tenuirostris (narrow‐nosed planigale), no clear results were obtained at any spatial scale, and we interpret this to indicate that the study region represents sub‐optimal habitat for these species.Given that different factors affected the distribution and abundance of dasyurids at different spatial scales over time, we conclude that a multiple‐scale approach to population and community analysis is vital to accurately identify which environmental processes shape population and community dynamics. Understanding the interplay between regional and local processes will be crucial for management of existing species populations and for prediction of their distributions and abundances in future.