Добірка наукової літератури з теми "Dasyurus Genetics"

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.

Carnivorous marsupials are native Australian predators including the highly threatened northern quoll (Dasyurus hallucatus) and Tasmanian devil (Sarcophilus harrisii). These species are currently actively managed in captive populations but assisted reproductive techniques such as gamete banking may also contribute to their conservation. Previous studies on a model dasyurid, the fat tailed dunnart (Sminthopsis crassicaudata), have found that spermatozoa do not survive freezing and thawing using a variety of freezing protocols and cryoprotectants. We have re-examined cold shock to investigate problems with sperm cryopreservation in S. crassicaudata. Epididymal spermatozoa were rapidly cooled to 0.5ºC in a pre-cooled tube held in an iced water slurry and upon re-warming the spermatozoa were non-motile (n=6). The addition of up to 20% egg yolk, which is considered protective to the spermatozoa of cold shock sensitive eutherians, did not improve the outcome (n=6). Similarly when S. crassicaudata spermatozoa were rapidly cooled to 4ºC, just 2% remained motile upon re-warming (n=10). However when spermatozoa were combined with at least 10% egg yolk and rapidly cooled to 4ºC only small reductions in motility were observed upon rewarming (n≥8). In order to achieve motile spermatozoa at 0ºC, controlled rate cooling at 0.5ºC/minute was examined. In the absence of egg yolk there was a decline in the percentage of motile spermatozoa below 4ºC (n=6). However if spermatozoa were combined with at least 10% egg yolk there was no significant loss of motility at temperatures as low as 0ºC (n=6). This study has revealed that at least one species of marsupial is highly susceptible to cold shock. These paradigm shifting findings give direction to future experiments aiming to develop a robust technique for sperm preservation in endangered dasyurids.

Abstract We examine possible ways of functional adjustment of morphologically similar alimentary tracts in rodents with different dietary specializations. We study the structure of stomach and gut epithelial surface as well as the features of its colonization with microorganisms in five gerbil species: Psammomys obesus, Meriones crassus, Gerbillus henleyi, G. andersoni, and G. dasyurus. Data on the morphological diversity of mucosa-associated microbiota have been obtained and confirmed by the results of previous microbiology studies. Species differences in chymus acidity associated with dietary specialization have been determined. Variations in the activity of the endoglucanase microbial enzyme, which is crucial for rodents fed on cellulose-containing food, have also been detected. The importance of microbiota for functional adaptations to various food types in rodents with morphologically similar digestive tracts has been evaluated.

Abstract The northern quoll (Dasyurus hallucatus) is a carnivorous marsupial that has suffered severe population declines over the last 50 years and is now listed as Endangered. The Pilbara region of Western Australia is a semi-arid area that represents an extreme of the northern quoll’s range. The overall objective of this study was to assess population characteristics of northern quolls at two rocky sites in the Pilbara, focusing on body condition, reproductive timing, population size, and sex-specific survival. We interpret these in the context of variation in habitat quality and the harsh climate. We found that reproduction occurred later in the year than in populations at more mesic locations where quolls have been previously studied, although their life history and demography were otherwise similar to that in other parts of their range. Contrary to our expectations, post-mating mortality of males was not complete. Population sizes differed between sites, suggesting that these rocky habitats varied in habitat quality. We suggest that local population size estimates can guide decisions on the relative importance of sites to ensure the long-term conservation of the species, given impacts of mining and the imminent invasion of introduced cane toads (Rhinella marina).

The mammalian ovary contains a rich resource of immature preantral follicles present regardless of cycle stage or seasonality. These follicles can be harvested enzymatically and are preserved more successfully than larger, more mature follicles. Thus, the collection and storage of preantral follicles is an applicable technique for the opportunistic harvesting of ovarian tissue from wildlife for the purpose of genebanking. This study examined the potential of such tools for the conservation of two endangered Australian carnivorous marsupials (dasyurids): the northern quoll, Dasyurus hallucatus, and the Tasmanian devil, Sarcophilus harrisii. The fat-tailed dunnart, Sminthopsis crassicaudata, is a representative model dasyurid with the typical attributes of large gametes (220 μm oocytes) and short polyovular reproductive cycles. Ovarian tissue was dissociated with 0.05–0.1% collagenase and 0.01–0.02% DNase in DMEM (all Sigma-Aldrich, St. Louis, USA) for up to 30 min before being neutralized with DMEM +10% fetal calf serum (FCS, Trace Biosciences, Castle Hill, Australia). Survival was determined using membrane permeability stains targeted to the nucleus (SYBR14 and propidium iodide, Molecular Probes, Carlsbad, CA, USA) or cytoplasm (trypan blue, Sigma) and assessed with a four-level survival score (1 = 100% live, 2 = 50–99% live, 3 = 1–49% live, 4 = 0% live) for each stage of follicular maturation: primordial (PF), early (EF), and late (LF) primary and secondary (SF) follicles (n = 100 each). Dissociated EF and LF (n = 45) from S. crassicaudata were vitrified with a three-step medium composed of up to 18% DMSO and ethylene glycol in 1 m sucrose (all Sigma; Vajta G et al. 1998 Mol. Reprod. Dev. 51, 53–58), and post-thaw viability was confirmed with trypan blue. All experiments were carried out on at least three individuals; values are presented as mean ± SEM and differences were determined with ANOVA and post hoc Tukey tests. In all species, 100% of PF were highly viable (score 1) and there was a significant decrease (P < 0.05) in the percentage of highly viable PF, EF, and LF when compared with SF, which were most commonly observed with minor damage (score 2). An incomplete layer of granulosa cells was observed in 11.92 ± 1.08% of freshly dissociated S. crassicaudata follicles. This increased to 30.34 ± 12.22% after preservation. Of the surrounded follicles, 48.40 ± 14.09% were classified as score 1 or 2 after vitrification. Nonviable staining of the oocyte was observed only in naked oocytes. Although these protocols demonstrate a reliable method for follicle collection and preliminary evidence for tools allowing the preservation of female gametes, further optimization is recommended. The demonstrated techniques are highly applicable to genebanking because they utilize material from unstimulated ovaries, as is regularly seen with tissues collected opportunistically from anestrus, ill, or old wildlife. This study was made possible by the cooperation and collection of tissues by the staff from Territory Wildlife Park, Northern Territory, and Tamara Keeley from Western Plains Zoo, New South Wales.

The quolls are among the largest of the remaining carnivorous marsupials in the Australasian region, and thus occupy an important ecological niche as top predators and scavengers. All quolls are currently in decline and threatened to some degree yet the application of molecular information to the conservation and management of quolls has been unexplored until now. In this thesis I use two independent and highly variable genetic marker systems, the mitochondrial DNA (mtDNA) control region and nuclear microsatellites, to explore various aspects of conservation genetics relevant to the management of quolls. These aspects include an examination of the phylogenetic or evolutionary relationships among all six species of quolls, an examination of the genetic diversity within populations and the degree of differentiation between populations of the four Australian species of quolls, and the definition of units for conservation within these species. The development of suitable nuclear markers was a vital first step in defining levels of genetic variability and differentiation within and between the different populations and species. These markers proved to be highly variable and provided a wealth of information of relevance to the conservation of these species, and will be extremely useful in further studies. The use of the mtDNA control region for phylogenetic analyses was a novel approach to examining this question in quolls and also proved to be highly informative. Results from these phylogenetic analyses highlight the necessity of 1) examining more than one exemplar of each species, as well as 2) finally bringing some consensus to the question of the evolutionary relationships among quolls. Results show that northern quolls form the earliest split from all other quolls and that western quolls are closely related to the two New Guinean species. Furthermore, there is evidence for distinct lineages within species, corresponding to geographically separate or isolated populations. Levels of genetic variability within populations were examined using the microsatellites developed previously. Genetic variation was significantly higher in western quolls than in any other species. This was surprising given the long term and widespread decline of this species. There were also significant differences between populations within species in the level of genetic variability. Low levels of variability were usually found in small or captive bred populations or populations in severe decline. Genetic differentiation between populations was also explored using microsatellites. Significant differentiation in allele frequency distributions was found between most pairwise population comparisons, indicating that each of these populations forms a separate management unit (MU) for conservation purposes. One notable exception was found among populations of tiger quolls from a highly localized area in the Barrington Tops region of New South Wales. Using microsatellites, these populations were not significantly subdivided and thus appeared to be one MU. Using mtDNA, however, these populations were significantly subdivided and thus should be considered separate MUs. Differences in the way these two genetic markers are inherited (mtDNA is maternally inherited, microsatellites are biparentally inherited) provides a clue as to the social structure and organization of these cryptic nocturnal species. Consequently, the use of different genetic marker systems shows that there is sex-biased migration within this species. Finally, the degree of genetic differentiation observed within tiger quolls does not conform to the currently recognized subspecific categories within this species. The major genetic split occurs between the Tasmanian and mainland populations of tiger quolls, not between Dasyurus maculatus maculatus and D. m. gracilis. Thus, the Tasmanian and mainland populations form two distinct evolutionarily significant units (ESUs) for conservation purposes, and I propose that the Tasmanian populations should be elevated to the subspecific status to account for this.

Antechinus is an Australian genus of small carnivorous marsupials. Since 2012, the number of described species in the genus has increased by 50% from ten to fifteen. The systematic relationships of these new species and others in the genus have not been well resolved and a broad phylogeographic study of the genus is lacking. Moreover, little ecological information is known about these new species. Therefore, the present thesis examined the evolutionary biology of Antechinus in two complimentary components. The first component aimed to resolve the systematics and phylogeography of the genus Antechinus. The second component, at a finer spatiotemporal scale, aimed to improve understanding of the autecology, habitat use and risk of extinction within the group, with a focus on the recently named buff-footed antechinus, A. mysticus and a partially sympatric congener, A. subtropicus.