Species Of Australian Rodents Research Articles

Ghost rodents: Albinism in Australian rodent species

While almost half of all mammal species are rodents, records of albinism in free-ranging rodents are very rare. Australia has a large and diverse assemblage of native rodent species, but there are no records of free-ranging albino rodents in the published literature. In this study, we aim to improve our understanding of the occurrence of albinism in Australian rodent species by collating contemporary and historic records of this condition and providing an estimate of its frequency. We found 23 records of albinism (i.e., a complete loss of pigmentation), representing eight species, in free-ranging rodents native to Australia, with the frequency of albinism being generally <0.1%. Our findings bring the total number of rodent species in which albinism has been recorded globally to 76. While native Australian species represent only 7.8% of the world's murid rodent diversity, they now account for 42.1% of murid rodent species known to exhibit albinism. We also identified multiple concurrent albino records from a small island population of rakali (Hydromys chrysogaster) and discuss the factors that may contribute to the relatively high frequency (2%) of the condition on this island. We suggest that the small number of native albino rodents recorded in mainland Australia over the last 100 years means that traits associated with the condition are likely deleterious within populations and are thus selected against.

The effects of antibiotics and illness on gut microbial composition in the fawn-footed mosaic-tailed rat (Melomys cervinipes).

The gut microbiota are critical for maintaining the health and physiological function of individuals. However, illness and treatment with antibiotics can disrupt bacterial community composition, the consequences of which are largely unknown in wild animals. In this study, we described and quantified the changes in bacterial community composition in response to illness and treatment with antibiotics in a native Australian rodent, the fawn-footed mosaic-tailed rat (Melomys cervinipes). We collected faecal samples during an undiagnosed illness outbreak in a captive colony of animals, and again at least one year later, and quantified the microbiome at each time point using 16s ribosomal rRNA gene sequencing. Gut bacterial composition was quantified at different taxonomic levels, up to family. Gut bacterial composition changed between time periods, indicating that illness, treatment with antibiotics, or a combination affects bacterial communities. While some bacterial groups increased in abundance, others decreased, suggesting differential effects and possible co-adapted and synergistic interactions. Our findings provide a greater understanding of the dynamic nature of the gut microbiome of a native Australian rodent species and provides insights into the management and ethical well-being of animals kept under captive conditions.

Growth and behavioural development of the fawn-footed mosaic-tailed rat (Melomys cervinipes)

The fawn-footed mosaic-tailed rat (Melomys cervinipes) is a common Australian rainforest rodent; however, little is known about the growth or behavioural development of individuals of this species. We raised mosaic-tailed rats in captivity to assess the growth and behavioural development of pups from birth until weaning. Pups developed quickly compared with some other Australian species, and there were no significant differences in growth between males and females, except for anogenital distance. The auditory meatus was open by Postnatal Day 5, and eyes were fully opened by Postnatal Day 9. All behaviours, including righting, locomotion, negative geotaxis, climbing and grip reflex, were fully developed by Postnatal Day 6. These results suggest that mosaic-tailed rats are semiprecocial in their physical and behavioural development compared with some native Australian rodent species that are found in arid environments. As females produce few, relatively well-developed young, the population has a low intrinsic rate of natural increase. This may, however, be offset by mosaic-tailed rats producing more litters per year. Understanding the biology of mosaic-tailed rats in general could provide insights into how rarer precocial species might struggle to increase in population size under increasing disturbances.

Testing the decline of the New Holland mouse (Pseudomys novaehollandiae) in Victoria

Many Australian rodent species have become extinct or undergone substantial range contractions since European invasion. Limited and haphazard survey efforts across much of Australia mean we are unsure of many species’ current and former ranges, hampering our ability to identify and remedy causes of decline. The New Holland Mouse (NHM; Pseudomys novaehollandiae) is an endangered rodent species native to south-east Australia that is suspected of undergoing rapid and dramatic range contractions and local extinctions in recent decades. Here, I reassess the species’ distribution across Victoria using extensive survey efforts and, subsequently, provide a summation of potential key threatening processes. In only 40 years, the NHM has been lost from seven of the 12 isolated areas where it once occurred in Victoria. Habitat loss and fragmentation, invasive predators, and potentially disease and genetic inbreeding have likely contributed to the species’ rapid and continuing decline. Conservation priorities include ongoing monitoring and research, cat and fox control, exclusion of rabbit poison-baiting, targeted fire and habitat management, and reintroduction to historically occupied regions where threatening processes have been mitigated.

Correlates of Recent Declines of Rodents in Northern and Southern Australia: Habitat Structure Is Critical.

Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south.

The response of native Australian rodents to predator odours varies seasonally: a by-product of life history variation?

Small mammals are subject to predation from mammalian, avian and reptilian predators. There is an obvious advantage for prey species to detect the presence of predators in their environment, enabling them to make decisions about movement and foraging behaviour based on perceived risk of predation. We examined the effect of faecal odours from marsupial and eutherian predators, and a native reptilian predator, on the behaviour of three endemic Australian rodent species (the fawn-footed melomys, Melomys cervinipes, the bush rat, Rattus fuscipes, and the giant white-tailed rat, Uromys caudimaculatus) in rainforest remnants on the Atherton Tableland, North Queensland, Australia. Infrared camera traps were used to assess visit rates of rodents to odour stations containing faecal and control odours. Rodents avoided odour stations containing predator faeces, but did not avoid herbivore or control odours. The responses of the three prey species differed: in the late wet season U. caudimaculatus avoided predator odours, whereas R. fuscipes and M. cervinipes did not. In contrast, in the late dry season all three species avoided odour stations containing predator odours. We speculate that these different responses may result from variation in life history traits between the species. (c) 2006 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.

Competition between Two Australian Rodent Species: A Regression Analysis

Empirical evidence and observations suggest that competition exists between two native rodents, Rattus lutreolus velutinus and Pseudomys higginsi , living in a wet sclerophyll forest, Tasmania, Australia. We used a standardized regression technique to assess competition between the two species and its temporal changes throughout the year. With our time-series data, we also tested the validity of our estimated competition coefficients by comparing regression residuals for a given species in one season to that in another. Overall, the two species competed asymmetrically for space with R. l. velutinus competitively dominant over P. higginsi . In winter (June-October), competition was low, and it reached a maximum during the breeding season (November-April). In the dispersal period (March-May), intensity of competition decreased, but was still higher than in winter, as subadults entered the trappable population. Estimated competition coefficients are validated by analyzing residuals from those three seasons. Results indicate that competitive ability in ground-dwelling small mammals is correlated positively with habitat specialization, but both may be related to body size. Intensity of competition also depends on the population phase of competing species. Our findings suggest that the standardized regression technique can be used reliably to uncover community patterns.

Transillumination patterns of seminiferous tubules in two species of Australian rodents, Pseudomys australis and Notomys alexis

The transillumination-assisted isolation of segments of seminiferous tubules in defined stages of the wave of the seminiferous epithelium was investigated in Pseudomys australis and Notomys alexis. In P. australis, three different transillumination patterns (pale, spotty and dark) of the seminiferous tubules could be isolated. They corresponded to histological stages 1-2, 3-5 and 6-8 of the wave of the seminiferous epithelium. The dark pattern made up about 40% of the wave, the pale pattern about 31%, and the spotty pattern about 24%. In N. alexis, no such isolation of segments with particular cell associations was possible. In a comparison of P. australis with the laboratory rat, the dark, pale and spotty transillumination patterns of seminiferous tubule segments corresponded to the same cell associations in both species, but the length of the spotty segments in the laboratory rat made it possible to subdivide the spotty region into pale spotty and dark spotty areas and thus to isolate four different transillumination patterns. Further separation into other subgroups to isolate additional types of segments could not be performed repeatedly in any of the studied species because of the gradual change of one subgroup of transillumination pattern into another and the short length of some of the subgroups.

The reproductive rates of Australian rodents.

The reproductive rates of about 50 species of Australian rodents were studied by calculating allometric equations for the relationships between female body weight, litter size, length of gestation and weaning periods as well as age of sexual maturity.Members of the subfamily Hydromyinae, which invaded Australia 5-10 million years ago, are characterised by small litters, long gestation and weaning periods and late maturity. The opposite is true for the Murinae (Rattus and Mus) which invaded Australia during the Pleistocene. Among the species of this latter group, those which invaded earlier have reproductive rates closer to the old invaders, while those which arrived with the Europeans during the last 200 years have the highest reproductive rates.Possible reasons for the low reproductive rates of Australian rodents are discussed. It is concluded that the rain forest origin of the hydromyinids is one of the factors responsible for their low reproductive rate. They maintained this rate to the present time because of the unpredictability of the climate and the low productivity of many Australian habitats.

An Autoradiographic Study of Visual Pathways of the Australian Rodents Notomys Alexis, Pseudomys Australis and Rattus Villosissimus.

In three species of Australian rodents, Notomys alexis, Pseudomys australis and Rattus villosissimus, primary optic centres were mapped by observing the distribution of autoradiographic label in the brain following injection of one eye with 3*H-proline or 3*H-leucine. Five regions receive a primary optic input in the three species: the lateral geniculate complex, the pretectum, the superior colliculus, the hypothalamus and the three terminal nuclei of the accessory optic system. The retinal projections are generally similar in the three species, except that in N. alexis and P. australis the dorsal lateral geniculate nucleus (LGNd) is subdivided into two, and the pattern of ipsilateral retinal input to it is similar; but in R. villosissimus the LGNd is not apparently subdivided, and the pattern is slightly different. It is concluded that the pattern of primary optic inputs is likely to be similar in other Australian rodents. Two secondary optic centres were shown in Notomys alexis, using the method of transneuronal transport of 3*H-proline. Autoradiographic label was observed in the visual cortex and in the parabigeminal nucleus 20-25 days after eye injection.

The Foods Eaten by Some Australian Rodents (Muridae).

From microscopic examination of faeces found in live-traps, the diets of 21 species of Australian rodents were studied. Results are tabulated for species and subspecies, and for different places of origin throughout Australia, for 1 to 14 rodents of the main species Rattus colletti, R. fuscipes, R. leucopus, R. lutreolus, R. rattus, R. sordidus, R. tunneyi, R. villosissimus, Melomys littoralis, Mesembriomys gouldi, Pseudomys gracilicandatus, P. nanus, Uromys candimaculatus, Zyzomys argurus and Z. woodwardi and their subspecies. The text gives results for 1 or 2 rodents each of Conilurus penicillatus, Mastacomys fuscus, Notomys alexis, Pseudomys delicatulus, P. occidentalis and P. shortridgei. The Rattus spp. were separated into 3 groups by diet; R. tumeyi and R. sordidus ate 80% grass and under 5% insects by volume. R. villosissimus, R. colletti and R. lutreolus ate 20 to 50% grass and 5 to 20% insects; R. rattus may be of that group. R. leucopus and R. fuscipes ate less than 10% grass and 20 to 90% insects. For the last 2 groups seeds were important.

The karyotes of some Australian Rodents (Rodentia : Muridae)

The number and morphology of the chromosomes of 11 species of Australian rodents have been described. It is suggested that Rattus lutreolus (2n = 42) is derived from an ancestor closely related to R. norvegicus (2n = 42) and that the former gave rise, in Australia, to R. fuscipes (2n = 38). R. fuscipes then gave rise to R. greyi (2n = 38) and R. assimilis (2n = 38) with both of which it is conspecific. Pseudomys minnie (2n = 48) and two species of Leggadina (2n = 48) have very similar karyotypes which differ from the karyotypes of two species of Notomys (2n = 48). The latter have apparently identical chromosomes. Within the Pseudomys group, marked changes in the heteromorphic pair of chromosomes have been involved in the evolution of karyotypes.