Dasyurid Species Research Articles

The Distribution of small mammal species in relation to heath vegetation near Cape Otway, Victoria

A trapping study of small mammals within heath communities near Cape Otway was conducted during April-August 1989. The purpose was to describe the distribution patterns of several small mammals in relation to a floristic and structural description of the vegetation. Two species of rodent (Rattus lutreolus, R. fuscipes), two species of dasyurid (Antechinus stuartii, A. minimus) and one species of bandicoot (Isoodon obesulus) were trapped frequently enough for statistical analysis. A. stuartii was trapped significantly more often in the Heathy Open-forest than in the Closed Heath community, in contrast to A. minimus and R. lutreolus, which were captured significantly more often in Closed Heath. There was no significant difference in the distributions of R. fuscipes and I. obesulus between communities. Within the Closed Heath community only R. fuscipes displayed significant distribution patterns between sub-communities. In the Heathy Open-forest the distribution of captures among sub-communities varied significantly for both species of Antechinus and for R. lutreolus. Floristic and structural cues, as well as ground cover, were associated with the spatial distribution of dasyurid and rodent species. Bandicoot dispersion was associated only with vertical vegetation diversity. The importance of interspecific avoidance in contributing to the observed distribution patterns of both dasyurid and rat species cannot be dismissed.

Dna-Dna Hybridization Studies of Carnivorous Marsupials .2. Relationships Among Dasyurids (Marsupialia, Dasyuridae)

A suite of comparisons among ten radiolabelled dasyurid species and one outgroup bandicoot was generated using the hydroxyapatite chromatography method of DNA-DNA hybridisation; comparisons were also made with four other dasyurid taxa. Square matrices of DELTA-T(m)s, DELTA-Modes, and DELTA-T50H's were complied and corrected for reciprocity, additivity, and, in the case of DELTA-T(m)'s, normalised percentages of hybridisation. These matrices were analysed using the FITCH algorithm in Felsenstein's PHYLIP (Version 3.1), and all distinct topologies were jackknifed to test for internal consistency. Additionally, uncorrected DELTA-T(m), DELTA-Mode, and DELTA-T50H datasets were bootstrapped and subjected to phylogenetic analysis to assess measurement imprecision. FITCH trees from folded matrices including unlabelled species or those for which heteroduplex comparisons were incomplete were also calculated and jack-knifed, both before and after correction. With the exception of limited measurements to Dasyuroides byrnei and Dasykaluta rosamondae, which showed affinities with Dasyurus spp., the final tree was fully resolved: Sminthopsis crassicaudata and S. murina, together with the more distant Planigale maculata, are the sister-group to all other dasyurids examined, which in turn comprise two clades. One of these includes Dasyurus, Dasyuroides, and Dasykaluta; the other, 'true' Antechinus (A. flavipes, A. stuartii, A. swainsonii) as a sister-group to Antechinus melanurus plus Murexia longicaudata, with Phascogale tapoatafa representing a probable sister-group to all Antechinus with Murexia. DNA-DNA hybridisation provides no support for the genus Satanellus: most of the trees linked Dasyurus albopunctatus with D. maculatus instead of D. hallucatus. Similarly, Antechinus flavipes and A. stuartii appear to be closer to each other than either is to A. swainsonii. The historical biogeographic significance of the adopted phylogeny is considered, and it is concluded that the putative early Miocene separation of Australia and New Guinea was probably too early to account for the independent evolution of the New Guinean clade.

Assessment of an Approximate Lethal Dose Technique for Determining the Relative Susceptibility of Non-Target Species to 1080-Toxin

The susceptibility of eight species of dasyurid marsupials and five species of murid rodents from the pastoral areas of Western Australia to the toxin sodium monofluoroacetate (Compound 1080) was assessed. Both LD*5O tests and an increasing dose procedure to determine the approximate lethal dose (ALD) were used. The results ranged from a low ALD of 1.6 mg kg-1 for an island population of Pseudomys hermannsburgensis to a high of 20 mg kg-1 for a mainland population of Notomys mitchelli. Intraspecific and regional variation in sensitivity was evident: three populations of P. hermannsburgensis showed widely different ALDS, and high ALDS were found in the Millstream area relative to elsewhere in the pastoral regions. Where both ALD and LD*5O were available, the dose response curve was steep; all LDSOS were less than a factor of 1.5 above the ALD. LD*5O values and ALDS were significantly correlated for selected dasyurids and murids, using published data. A computer simulation based on sampling a standard number of animals from 10 theoretical populations differing only in their LD~O confirmed that ALD and LD*5O gave similar rankings of sensitivity, although high variance on the LD~O reduced the strength of the correlation. Actual dosing data from eight populations of Rattus fuscipes were also analysed; both LD*5O and ALD gave similar rankings of population sensitivity. Subject to assumptions about the variability of sensitivity within a population, the ALD offers an alternative to LD~O testing that requires fewer animals, and need not cause more than one death per population tested.

Marsupial Gene Mapping and the Evolution of Mammalian Sex-Chromosome Form and Function

Comparisons between the gene maps of distantly related mammalian species can provide information about the evolution of genome arrangement and function in mammals. Marsupial gene mapping is now being vigorously pursued, using newly developed cell and molecular techniques to complement classic breeding studies of model species. Gene associations and localisations established by all these techniques are tabulated, and the beginnings of gene maps, based on in situ hybridisation, are presented for a macropodid and a dasyurid species. The significance of marsupial gene mapping is apparent even from these limited data, which show that large autosomal regions have been conserved between marsupials and eutherians. However, an ancient X-autosome translocation is revealed, which either removed most of the human X short-arm markers (including the putative sex determining factor) to autosomes or added this region to a smaller ancestral X. The implications of these findings to theories of mammalian sex chromosome evolution and function are discussed, and a hypothesis proposed for a gradual differentiation of the mammalian X and Y chromosome, accompanied by progressive spreading of X chromosome inactivation.

Daily Torpor and Thermoregulation in the Small Dasyurid Marsupials Planigale-Gilesi and Ningaui-Yvonneae

Torpor in endotherms has only been observed in small species, suggesting that body mass determines the occurrence of torpor. The present study investigates the influence of body mass on the occurrence of torpor and also the pattern of torpor (i.e. minimum body temperature, metabolic rate, and the duration of torpor). The two small dasyurid marsupials Planigale gilesi (8.3 g) and Ningaui yvonneae (11.6 g) entered torpor frequently when food was available; withdrawal of food increased the occurrence of torpor to almost 100%. Minimum body temperatures during torpor in both species were lower and the torpor duration was longer than for most larger dasyurid species studied so far. These findings suggest that the thermal stress on these very small species exerts a strong selective pressure to enhance daily torpor episodes for reduction of heat loss to the environment.

An Analysis of Some Predatory Behaviour Patterns in Four Species of Carnivorous Marsupials (Dasyuridae), with Comparative Notes on the Eutherian Cat Felis catus

AbstractTwo aspects of predatory behaviour in five species of carnivorous mammals were studied: four species (Dasyurus viverrinus, Dasyurus hallucatus, Dasyuroides byrnei and Phascogale tapoatafa) of a group of Australian marsupials, Dasyuridae, and an eutherian, the domestic cat, Felis catus. All data were collected from captive animals in laboratory conditions. Using sequences of predatory behaviour recorded on movie film, two aspects of predation were compared: (a) attack strategy, that is, the behavioural patterns leading up to biting the prey, and (2) head shaking movements used during killing.All individual predators of all species but Dasyuroides byrnei exhibited avoidance of attacking prey from the front. Indeed, two of the four individual Dasyuroides used not only did not avoid frontal attack but selected to do so even when attacks from the rear or side were possible (e.g., the prey sat unmoving in the centre of the enclosure). Frontal attacks by Dasyuroides involved the use of the forepaws to grasp and pin prey, and the directing of killing bites to the head. These two behaviour patterns are also present in the other three species of dasyurids. Therefore, the frontal attack employed by this species does not involve the use of novel behaviour patterns.Analysis of head shakes revealed two basic forms. From a downward pointing position the head was rotated in one of two ways: the snout traversed an arc in space, as seen in Felis catus and Dasyurus hallucatus, or the sagittal crest traversed an arc in space, as seen in the other three species of dasyurids. When the prey is held down by the forepaws, either form of head shake enhances penetration of the canines into the prey, whereas, when not held down by the forepaws, both forms of head shake can disorient prey, enabling subsequent killing bites to be applied.

Phallic Morphology of Dasyuroides-Byrnei and Dasycercus-Cristicauda (Marsupialia, Dasyuridae)

On the basis of phallic morphology Dasyuroides byrnei and Dasycercus cristicauda appear to be most similar to Dasykaluta rosamondae among the species of dasyurid marsupials which have been studied in this respect. The anatomy of the penis in all three appears to be primitive. Although the three species group together, there are differences in anatomy which suggest that there is no special relationship between any members of the group. This contrasts with the generally held view that D. byrnei and D. cristicauda are more closely related to each other than to D. rosamondae.

Gene mapping in marsupials and monotremes

Somatic cell hybrids have been obtained between HPRT Chinese hamster cells and cells from several dasyurid marsupial species. These hybrids show the extensive loss of marsupial chromosomes characteristic of the majority of marsupial-eutherian somatic cell hybrids. Although all of the hybrids expressed the selected marsupial marker, <i>HPRT, </i>the only other markers observed were <i>PGK, GLA, </i>and <i>G6PD, </i>consistent with the conservation of X-linked genes extending to this major group of marsupials. Counterselection confirmed the synteny of <i>PGK </i>and <i>GLA </i>with <i>HPRT, </i>whereas <i>G6PD </i>showed decreased concordance.

Effects of photoperiod and endogenous control on timing of reproduction in the marsupial genus Antechinus

The timing of reproduction was investigated and compared in natural pop ulations and laboratory colonies of three species of dasyurid marsupials, Antechinus stuartii, A. swainsonii and A. flavipes. In the natural populations, reproductive events occurred only during the austral winter (July‐September), and began at almost exactly the same time each year. The mating period lasted–3 weeks, and coincided with the onset of pouch changes (oestrus) in females. In males, spermatozoa appeared in the urine up to five weeks before the first matings occurred, but sexual activity tended to be suppressed during this time by female aggression. In the laboratory colonies, most individuals were paired (females with males) and housed under 12L: 12D or ambient light. Irrespective of the light regime, all first‐year animals entered reproductive condition at the same time or only slightly earlier than those in the natural populations. However, in females housed for two years under 12L: 12D, oestrus occurred–5 weeks earlier, on average, than in field individuals, and–5 weeks earlier than in equivalent individuals housed under ambient light. Males again achieved reproductive condition before females, and may have stimulated and helped to synchronize oestrus. These findings showed that the timing of reproduction is controlled by an endogenous circannual rhythm, which is probably entrained by some component of the photoperiod. The timing mechanism ensures that all young are nursed and weaned in spring and summer when food is most predictably abundant, and hence maximizes individual reproductive success.

Confirmation of a New Species of Small Dasyurid Marsupial by Electrophoretic Analysis of Enzymes and Proteins

Eight species of dasyurid marsupials have been typed for the electrophoretic mobility of 18 of their enzymes and proteins. The species were the Ningbing antechinus (Pseudantechinus sp.), Pseudantechinus macdonnellensis (formerly Antechinus macdonnellensis), Parantechinus apicalis (formerly Antechinus apicalis), Parantechinus bilarni (formerly Antechinus bilarni), Antechinus stuartii, Dasykaluta rosamondae (formerly Antechinus rosamondae), Dasycercus cristicauda and Planigale maculata. The results show that the Ningbing antechinus is a probable new species. The data suggest that its nearest relative is Dasycercus cristicauda. Analysis of the results by calculation of a modified x2 and an approximation to Nei's genetic distance indicates that all species have been the product of one radiation, possibly in the late Miocene or early Pliocene. Two races of P. macdonnellensis probably exist, separable by their transferrin types.

Endocrine changes in dasyurid marsupials with differing mortality patterns

A comparison was made between the breeding-related endocrine changes in two species of dasyurid marsupial ( Antechinus swainsonii and A. flavipes), which exhibit a catastrophic male mortality after a brief mating period; and those of another dasyurid species ( Sminthopsis crassicaudata), the males of which survive an extended breeding period. In the males of both Antechinus species, the mating period was preceded by a rapid rinse in plasma androgen concentration and accompanied by a marked fall in plasma corticosteroid-binding globulin (CBG) concentration, to less than the total glucocorticoid concentration, which itself rose. As a consequence plasma free glucocorticoid concentration rose approximately 10-fold just before the males disappeared from the populations. Severe hemorrhagic ulceration of the upper digestive tract was consistently found soon after capture near the time of mating. In females, CBG concentration was always well in excess of total glucocorticoid concentration and free glucocorticoid concentration remained low. There was a significant negative correlation between plasma androgen and CBG concentrations in male Antechinus species from the natural populations. In laboratory-held castrate male A. swainsonii, injection of either testosterone or dihydrotestosterone caused a dose-related fall in CBG. In contrast to the above, the CBG concentration was always well in excess of total glucocorticoid concentration in the plasma of male S. crassicaudata and there was no evidence of interaction between plasma androgen and CBG concentration. These findings support the hypothesis that, in those species with a breeding-related mortality of males, an androgen-dependent fall in plasma CBG concentration and a stressful mating period result in death from adrenocortical suppression of the immune and inflammatory responses.