Melomys Burtoni Research Articles

The Epidemiology of Koala Retrovirus

A novel Gammaretrovirus, named Koala retrovirus (KoRV) was identified in koalas in 2000. Subsequent testing has shown that KoRV appears to be widespread throughout the wild koala population in Australia. KoRV is apparently unique in that it is the only known example of an exogenous retrovirus which is actively undergoing the process of endogenisation. While there is currently little direct evidence that KoRV causes overt disease in koalas, it is possible or even likely that KoRV infection plays a significant role in the pathogenesis of various neoplasms and a variety of immunosuppressive disorders which are commonly diagnosed in koalas. It appears that KoRV may have arisen through the cross species transmission of a closely related retrovirus in a native Australian rodent, the grassland melomys. Both of these viruses are closely related to a third retrovirus, Gibbon ape leukaemia virus (GALV). GALV was first isolated in the late 1960's from captive gibbons in Thailand that were suffering from leukaemia. To date, the source of GALV remains unknown.

Helminth Biodiversity in the Genus Melomys (Murinae: Hydromyini) From Australiaand Newguinea

The rodent subfamily the Murinae (Muridae) has its origins in Southeast Asia. Ancestral rats migrated down the Indonesian Island chain, across Wallace's Line and into the Sahul (Australasian) Region. The genus, Melomys, a mosaic- tailed rat (Uromys Division: Hydromyini), has representatives in both New Guinea, including outlying islands (four species), and Australia (four species). The Australian species are thought to be relatively recent arrivals either using New Guinea as a staging post, or more likely forming part of a radiation in New Guinea prior to migrating to Australia in the Pleistocene. Examination of the helminth parasites of Melomys burtoni =M. lutillus and M. rufescens from New Guinea and M. burtoni and M. cervinipes from Australia, has shown that each host species harbours a diverse fauna. The helminth assemblage of M. cervinipes with 33 helminths was the most speciose and that of M. rufescens with 16 helminths the least. Nematodes of the genus Odilia (Trichostrongylida: Heligmonellidae) were dominant in the helminth assemblage of each host species. Each assemblage comprised the heirloom species Railietina celebensis (Cestoda: Davaineidae) an old souvenir O. mackerrasae together with species new souvenirs or recent aquisitions derived from the local context. The helminth assemblage of the population of M. burtoni from Papua New Guinea was a small subset of the assemblage from Australian hosts and had little commonality with that of M. rufescens. This supports an Australian rather than New Guinean origin for M. burtoni.

Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia

A previous study (Braithwaite & Muller 1997) reported substantial declines in mammal abundance over the period 1986–1993 for a large study area (300 km2) within Kakadu National Park in the tropical savannas of northern Australia. This decline was reported as being a ‘natural’ response to fluctuating groundwater levels, driven by runs of poor wet seasons. We resampled mammals in this area in 1999, following a series of unusually good wet seasons, and examined the prediction that mammal numbers should have recovered. Increases in abundance were evident for four species: the smallest dasyurid (red-cheeked dunnart Sminthopsis virginiae) and the three smallest rodents (delicate mouse Pseudomys delicatulus, western chestnut mouse Pseudomys nanus and grassland melomys Melomys burtoni). In contrast, the abundance of all mammals combined and that for seven individual mammal species (northern quoll Dasyurus hallucatus, fawn antechinus Antechinus bellus, common brushtail possum Trichosurus vulpecula, northern brown bandicoot Isoodon macrourus, dusky rat Rattus colletti, black-footed tree-rat Mesembriomys gouldii and pale field rat Rattus tunneyi) continued to decline. The decline in abundance of these mammal species is consistent with limited observations elsewhere in northern Australia. Although far from conclusive, these observations suggest that the biota of the vast relatively undisturbed tropical savannas can no longer be assumed to be intact nor safe. Further research is needed to test this possible pattern of decline and, if confirmed, to identify and ameliorate the processes contributing to it.

Monanema Australe SP. NOV. (Nematoda: Onchocercidae) from the Lungs and Liver of Native Rodents in North Queensland

Monanema australe sp. nov. is described from the lungs, hepatic blood vessels and lymphatics of the fawn-footed melomys, Melomys cervinipes (Gould, 1852) and from the latter two anatomical sites of the giant white-tailed rat, Uromys caudimaculatus (Krefft, 1867), in north Queensland. Microfilariae of this species have previously been reported in the blood of these hosts and of the grassland melomys, Melomys burtoni (Ram-say, 1887); similar but much longer microfilariae are here recorded from blood films of the black-footed tree rat, Mesembriomys gouldii (Gray, 1843). The species is distinguished from congeners by the size of males and females, the presence of cuticular rugosities on the ventral surface of the body and fine, narrowly-spaced transverse cuticular annulations in both sexes, the length of the spicules, the presence of small caudal alae in males bearing ornamentation only on the proximal (= median) surface of each ala and a pre-cloacal area rugosa. Species belonging to the genus Monanema are now known to occur in sciurids in North America, murids and gerbils in Africa and murids in Australia; all are associated with blood and lymphatic vessels.

Environmental relationships of the brush‐tailed rabbit‐rat, Conilurus penicillatus, and other small mammals on the Tiwi Islands, northern Australia

AbstractAim To describe the habitat characteristics and status of the brush‐tailed rabbit‐rat, Conilurus penicillatus Gould, 1842, on the Tiwi Islands, northern Australia, as part of a broader programme aimed at the conservation management of this species. In addition, comparable environmental modelling is undertaken for other co‐occurring small native mammals, including the black‐footed tree‐rat, Mesembriomys gouldii Gray, 1843, a taxonomically and ecologically related species. These objectives relate to the significance for mammal conservation of islands generally in Australia, and the recent intensification of plantation forestry on these previously little‐disturbed islands.Location Melville and Bathurst islands (Tiwi Islands), respectively, Australia's second and fifth largest islands.Methods A systematic survey was conducted for mammals across Bathurst (115 sampled quadrats) and Melville Island (236 quadrats). A broad range of environmental variables was recorded for every quadrat. All quadrats were classified by their woody plant species composition. The relative occurrence of individual mammal species across the resulting vegetation groups was examined using Kruskal–Wallis anova. The habitat relationships of C. penicillatus and the most commonly recorded mammal species were described by generalized linear modelling, with separate models for each island, for both islands combined, for all habitats and for only those sites dominated by eucalypts.Results Twelve small mammal species (excluding bats, macropods and feral animals) were recorded in this study. The most notable feature of this survey was the lack of records of M. gouldii from Bathurst Island. In contrast, the proportion of quadrats with C. penicillatus was not significantly different between the two islands. There was no significant tendency for these two species to co‐occur in quadrats on Melville Island more or less commonly than by chance. Conilurus penicillatus was most abundant in eucalypt forest while M. gouldii showed a weak association with eucalypt forests and woodlands and shrub land. The five most commonly recorded species showed highly idiosyncratic relationships with environmental variables, with this relationship showing some variation between the two islands. None showed any significant association with floristic variation within the extensive eucalypt forests, but most showed significant associations with tree height, basal area (especially of large trees), landscape position (distance to watercourse) and fire history.Main conclusions Conilurus penicillatus was most likely to occur in tall eucalypt forest away from watercourses. This habitat is now being targeted for clearance for the development of plantations of the exotic Acacia mangium. Seven of the 12 mammal species examined in this study (C. penicillatus, M. gouldii, Rattus tunneyi Thomas, 1904, Melomys burtoni Ramsay, 1887, Sminthopsis butleri Archer, 1979, Phascogale tapoatafa Meyer, 1793 and Petaurus breviceps Gould, 1842) were not recorded at all in plantations, and these (and other) species are likely to be severely disadvantaged by plantation development. The study also demonstrated that the two medium to large arboreal rodent species (C. penicillatus and M. gouldii) vary in environmental associations and found no evidence that C. penicillatus increased in areas unoccupied by M. gouldii.

The mammals of Croker Island, Northern Territory, Australia.

This is a report on the mammals found in April 2001 during a brief terrestial vertebrate fauna survey on previously unsurveyed Croker Island which is 3 km offshore from the Cobourg Peninusula. Seven mammals were recorded but only 3 were native. These were black flying -fox (Pteropus alecto), grassland melomys (Melomys burtoni) and the dingo (Canis lupus dingo). The remaining 4 species were domestic and feral animals (horse, cat, cattle and pig).

Helminth parasites of the grassland melomys (Muridae : Hydromyinae) from Australia and Papua New Guinea

This study documents the helminth assemblages of grassland melomys: Melomys burtoni (Ramsay, 1887), Melomys sp. cf. burtoni and Melomys lutillus (Thomas, 1913). In total, 22 helminth species comprising one cestode and 21 nematodes from 112 hosts were found. All the specimens of Physaloptera spp. examined proved to be Physaloptera banfieldi Johnston & Mawson, 1941 with P. troughtoni Johnston & Mawson, 1941 the junior synonym. The dominant helminth group was the trichostrongyloid nematodes including Odilia melomyos (Mawson, 1961) and O. mackerrasae (Mawson, 1961). The most prevalent, O. melomyos, occurred in each of the host species across all areas sampled (New South Wales, Northern Territory, Papua New Guinea, Queensland and Western Australia). The helminth assemblage of M. burtoni from hosts from New South Wales and Queensland was the most diverse. The helminths of M. burtoni from the Northern Territory and of M. lutillus from Papua New Guinea were subsets of that assemblage. That of M. cf. burtoni from Western Australia, with only six helminth species, was not dominated by trichostrongyloids, three of the six species were not found in other localities, and, with Sorensen’s Indices of 18.2% when compared with the helminths from Papua New Guinea and the Northern Territory and 24% when compared with Queensland, was the least similar. No substantial differences were found between the helminth assemblages of the grassland melomys group, excluding M. cf. burtoni, and Melomys cervinipes (Gould, 1852), the fawn footed melomys. This was reflected in a Sorensen’s Index of 67.9%. The time between the arrival of Melomys into Australia during the Pleistocene and the present day suggests that the trichostrongyloids O. melomyos, O. mackerrasae and O. mawsonae (Durette-Desset, 1969) may have travelled with their rodent hosts from New Guinea to Australia and other helminths in the assemblage may have been acquired in Australia.

Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia

AbstractA previous study (Braithwaite & Muller 1997) reported substantial declines in mammal abundance over the period 1986–1993 for a large study area (300 km2) within Kakadu National Park in the tropical savannas of northern Australia. This decline was reported as being a ‘natural’ response to fluctuating groundwater levels, driven by runs of poor wet seasons. We resampled mammals in this area in 1999, following a series of unusually good wet seasons, and examined the prediction that mammal numbers should have recovered. Increases in abundance were evident for four species: the smallest dasyurid (red‐cheeked dunnart Sminthopsis virginiae) and the three smallest rodents (delicate mouse Pseudomys delicatulus, western chestnut mouse Pseudomys nanus and grassland melomys Melomys burtoni). In contrast, the abundance of all mammals combined and that for seven individual mammal species (northern quoll Dasyurus hallucatus, fawn antechinus Antechinus bellus, common brushtail possum Trichosurus vulpecula, northern brown bandicoot Isoodon macrourus, dusky rat Rattus colletti, black‐footed tree‐rat Mesembriomys gouldii and pale field rat Rattus tunneyi) continued to decline. The decline in abundance of these mammal species is consistent with limited observations elsewhere in northern Australia. Although far from conclusive, these observations suggest that the biota of the vast relatively undisturbed tropical savannas can no longer be assumed to be intact nor safe. Further research is needed to test this possible pattern of decline and, if confirmed, to identify and ameliorate the processes contributing to it.

A SCRUB TYPHUS VECTORLEPTOTROMBIDIUM DELIENSE(WALCH) (ACARI: TROMBICULIDAE) ON RATS IN LITCHFIELD PARK, NORTHERN TERRITORY, AUSTRALIA

AbstractA scrub typhus vector, Leptotrombidium deliense, is reported from Litchfield Park in the Northern Territory. A small mammal trapping survey in areas of the park visited by two confirmed cases of scrub typhus showed a high prevalence of L. deliense in the three native rat species Rattus tunneyi (Thomas), R. colletti (Thomas) and Melomys burtoni (Ramsay).

Cladistical analysis of primitive G-band sequences for the karyotype of the ancestor of the Cricetidae complex of rodents

Homologous segments identified by G-banding sequences of chromosomes of Peromyscus boylii, Neotoma micropus, Oryzomys capito, (Family Cricetidae) Rattus norvegicus, Melomys burtoni, and Apodemus sylvaticus (Family Muridae) were used to hypothesize a chromosomal condition for the cricetid ancestor. A critical assumption in proposing the primitive G-banding sequences for a given chromosome is that if the outgroup and ingroup taxa have a specific sequence, then the ancestor of the ingroup taxa also had that same sequence. Using this methodology, (chromosome numbers refer to proposed homology to the standardized karyotype for Peromyscus), we propose that: (1) the primitive banding pattern of chromosome 1 was identical to that of Neotoma; (2) the primitive patterns of chromosomes 2, 3, 4, 6, 7, 8, 9, 10, 11, and 12 were primitive banding patterns of 5 and 13 were undetermined; (4) a major portion of the banding patterns of 14 and X were present in the ancestral karyotype. Only the largest 14 autosomes and X were examined because the smaller elements had insufficient G-band definition to ensure reasonable accuracy. The karyotype ancestral to that of Peromyscus, Neotoma, and Oryzomys may be as above and the banding patterns of 5, 13, and 14 were acrocentric and identical to those shown for Peromyscus, Neotoma, and Oryzomys (Fig. 1). In the primitive karyotype, heterochromatin (C-band material) was probably limited to the centromeric regions. If the primitive karyotype is as described above, then it is possible to determine the direction, type, and magnitude of chromosomal evolution evident in the various cricetid lineages. Based on the available data, radiation from the ancestral cytotype is characterized by a nonrandom distribution of types of chromosomal changes. Within many genera, more rearrangements occur in the 14 largest autosomal chromosomes of some congeneric species than distinguish the proposed primitive conditions for the genera Peromyscus, Neotoma, and Oryzomys. It would appear that the extensive morphological radiation from the primitive cricetid ancestor as indicated by the presence of over 100 surviving genera within the family, was not accompanied by extensive karyotypic changes. The magnitude of chromosomal variation that accompanies speciation in these genera appears to range from no detectable chromosomal evolution to a radical reorganization of the genome.

Chromosomal and Electrophorectic Studies of Australian Melomys (Rodentia:Muridae)

We undertook an extensive karyotypic and electrophoretic survey of 24 populations of Melomys in Australia. The taxonomic conclusions are: (1) Small grassland Melomys from Queensland belong to the same species as Northern Territory Melomys, viz. M. burtoni. Melomys from the north of the Wenlock River on Cape York, previously thought to belong to a separate species, also belong to M. burtoni. (2) The large rain-forest Melomys from Queensland belong to two separate biological species, M. cervinipes south of Cooktown and M. capensis north of Cooktown. The population data are used to compare and contrast several methods of assessing the genetic relatedness of populations.