Australian Rattus Research Articles

Jugular vein venepuncture and anatomy in Australian

We describe our experiences collecting blood from Australian Rattus. We found uniform anatomy of the external jugular vein between Australian and exotic Rattus species. Understanding where the maxillary and linguofacial veins join to form the external jugular vein is critical to venepuncture. After locating this union, we consistently achieved successful venepuncture of the external jugular vein; yielding large blood volumes. All other routes of venepuncture yielded minute blood volumes or were unsuccessful. We provide recommendations for venepuncture in Australian rodents and encourage others to share their experiences; such reports facilitate sampling rarely sampled species and promote animal welfare.

Odorants differentiate Australian Rattus with increased complexity in sympatry

Odorants differentiate Australian Rattus with increased complexity in sympatry

New microsatellite markers for the bush rat, Rattus fuscipes greyii: characterization and cross‐species amplification

AbstractWe describe here 16 new microsatellite markers for the bush rat, Rattus fuscipes greyii, and characterize their cross‐species amplification within the Australian Rattus and at a greater level of divergence in Rattus rattus and Rattus norvegicus. Within R. f. greyii, all of the loci are highly polymorphic, with six to 24 alleles per locus across the species range and expected heterozygosity ranging from 0.48 to 0.90 per locus within a sample of 24 rats from a large population on Kangaroo Island. Cross‐species amplification rates were approximately 87% within the Australian Rattus and approximately 50% within R. rattus and R. norvegicus. These loci are highly polymorphic with a high success rate of cross‐species amplification, making them potentially useful for a wide range of genetic studies.

Competition and habitat use in native Australian Rattus: is competition intense, or important?

This study investigates patterns of habitat use and competition in sympatric populations of the bush rat, Rattus fuscipes, and swamp rat, R. lutreolus, in the Blue Mountains National Park, New South Wales, Australia. Radiotracking showed that the home ranges of R. fuscipes tended to occupy woodland more than those of R. lutreolus, whereas use of heath and sedgeland by both species was equal. Home range overlaps were less between the two species than between individuals of R. lutreolus. Trap-captures showed that both species used structurally complex microhabitats, but also that R. fuscipes occupied relatively drier sites with denser leaf litter and taller canopy than R. lutreolus. In a field enclosure containing equal parts dense sedge and woodland, both species spent most time in the sedge. R. lutreolus frequently initiated agonistic behaviour and dominated its smaller congener; subordinate individuals fled or vocalized loudly. To test whether the observed patterns of habitat use of R. fuscipes resulted from habitat selection or competition with R. lutreolus, a field experiment was carried out in which the latter species was removed from two study sites but maintained in two controls. Following removal, the capture rate of R. fuscipes increased some 6.5-fold in sedgeland habitat that had been occupied formerly by R. lutreolus, while capture rates in sedge in the control sites remained unchanged. The rapidity of the habitat shift implicates current or intense competition, mediated by interference. Although interference is a costly process, it may benefit the dominant R. lutreolus by allowing priority of access to preferred moist habitats containing important food or shelter resources. Conversely, R. fuscipes may tolerate interference if it benefits from even temporary access to moist habitats, can reliably detect and avoid R. lutreolus prior to encounters, or has access to drier woodland areas under-used by the dominant species. We suggest finally that extensive gene flow in R. fuscipes may preclude adaptive shifts in habitat preferences in local populations that are sympatric with R. lutreolus, thus reducing the importance of competition but maintaining its intensity over time.

Evolutionary lineages of RT1.Ba in the Australian Rattus.

In this study, the evolutionary history of the variable second exon of RT1.Ba and its adjoining intron b are compared across a number of species and subspecies of the Australian RATTUS: Three lineages are identified in the second intron across a range of Rattus species. Two of these lineages, separated by the insertion of a probable rodent short interspersed nucleotide element and by point mutations outside the indel region, are both found in each of the major clades of the endemic Australian RATTUS: This pattern of ancestral polymorphism is reflected in the adjoining exon 2 sequences, although phylogenetic constraints confirm that the clustering is not identical to that of the associated intron sequences. In addition, the coding sequences show evidence of the retention of ancestral polymorphism, with identical exon sequences found in two divergent species, and some indication of gene conversion detected for the exon sequences.

Reproduction in New-Guinean Rattus and Comparison With Australian Rattus

Reproductive events related to time of breeding and fecundity among species of New Guinean Rattus are examined relative to latitude, altitude, and possible climatological cues. At least half of the 25 subspecies examined can breed in any month, and this capability appears to be unrelated to annual photoperiod fluctuations and ambient temperature at different altitudes. Both rainfall and commensalism may exert strong influence on local breeding regimes. This, the first reproductive analysis of all New Guinean species of this genus, permits comparison with similar events in Australian Rattus, and generalised patterns of breeding in these Australasian species are proposed.

Biochemical differentiation among karyotypic forms of Australian Rattus

Isozyme electrophoresis of up to 55 loci, and microcomplement fixation of albumin were used to assess the extent of structural gene divergence among karyotypic forms of Australian Rattus. The results show that the Australian Rattus are monophyletic with respect to R. rattus or R. norvegicus. Within the Australian Rattus, rates of chromosomal evolution have varied enormously, the highest rates being found among members of the R. sordidus group, where extensive chromosomal repatterning has occurred with little or no structural gene divergence.

A Graphical Method for Estimating Length of Gestation and Estrous Cycle Length from Birth Intervals in Rodents

A new method is described to determine length of gestation and estrous cycle in rodents. The method was devised using successive birth intervals for female Rattus lutreolus lutreolus. This technique was tested using data collected later by conventional smearing techniques on the same R. I. lutreolus females. Further tests were made using similar information available in the literature for R. sordidus sordidus and R. tunneyi culmorum (McDougall, 1946), Notomys alexis (Smith et al., 1972), and R. I. velutinus (Green, 1967). The technique can be used only for polyestrous species and is most applicable when a pattern is clearly discernible in the distribution of intervals between births, but is also applicable if approximate estimates of the length of the estrous cycle are available to use with an iterative regression procedure. The method is particularly important when working with native species that may or may not have been bred in captivity before, and may be extremely sensitive to behaviorally stressful experiences such as daily capture for vaginal smearing. Little is known of the breeding biology of the Australian murid rodent Rattus lutreolus lutreolus. There is some limited information on breeding season in the field, from South Australia (Barritt, 1976; Taylor and Horner, 1973a) provided data on ovulation rate and embryo counts from histological studies of field-caught specimens of R. I. lutreolus as part of their review of reproduction in 13 of the 14 subspecies of Australian Rattus that they recognized (Taylor and Horner, 1973b). Breed (1978) examined estrous cycling and ovulation rates for R. I. lutreolus and seven other subspecies of Rattus. Green's (1967) study of the biology of R. I. velutinus provides some information on the number of embryos and litter size for this closely related subspecies. Rattus I. lutreolus proved difficult to breed in the laboratory in the first two years. To minimize disturbance new animals obtained in the third year did not have vaginal smears taken when handled daily. Breeding was then successful and 18 litters, from nine females, were raised for growth studies between October, 1977, and December, 1978 (Fox, 1979). The bulk of the reproductive data were then collected in the form of intervals between births of successive litters, with some observed matings available to supplement these data. Derivation and maintenance of the breeding colony of R. 1. lutreolus were described by Fox (1979). Females were inspected daily between 0800 and 1000 h. Each female was weighed, her reproductive condition noted, and presence of pups recorded. Observations of behavior of paired animals in their home cage were conducted at irregular intervals. A mating was recorded when the male was seen to mount the female and show repeated thrusting and intromission; ejaculation was confirmed by the presence of semen or a copulatory plug in the female. Additionally, mating was recorded when either a copulatory plug was observed at the daily inspection or, in the latter part of the project, when sperm were found in a vaginal smear.

Chromosome evolution in Australian Rattus ? G-banding and hybrid meiosis

The karyotypes of seven species of Australian Rattus were studied by G-banding. When taken in conjunction with molecular data, it is shown that rate of chromosome evolution in the R. sordidus group (R. sordidus, R. villosissimus and R. colletti) has been remarkably rapid and directed entirely towards changes of the Robertsonian type. From data on hybrid fertility it is concluded that the presence of fusions with monobrachial homology contributes more to reduced fertility than fusions per se or genetic differences.

Seasonal Changes in Body Weight and Composition of Australian Bush Rats, Rattus fuscipes, and Adaptation to Winter

A montane population of Australian bush rats, Rattus fuscipes, was studied for 3 years. Bush rats were also kept in captivity in natural conditions of temperature and light during the same period; these rats had food and water ad libitum. The body weights of free-living rats declined in autumn, and those of captive rats in winter. Changes in organ weights and body composition fell into three groups. (1) Testes, heart, spleen and adrenals were lighter in winter than in summer. (2) Hair weight increased gradually from February to a peak in June. The weight of carcass lipid and of brown adipose tissue increased rapidly in late autumn (May). (3) Body weights, and the weights of the lean carcass and the liver, were at a minimum in May, had a minor peak in June, and declined again in July and August. There was no evidence that any of these changes were related to diet or to food supply.

Rat Kappa Chain Allotypes. IV. Monoclonal Antibodies to Distinct RI-1b Specificities

Four hybridomas are described which produce antibodies to the RI-1b rat kappa chain allotype. Three are rat alloantibodies of KG2b isotype, one is a mouse heteroantibody of KG2a isotype. These antibodies were labeled by incorporation of 75Se-selenomethionine and their specificity determined by a plate-binding assay. Inhibition studies using partially cross-reactive sera from Asian and Australian Rattus show that these four hybridomas detect four distinct RI-1b specificities. Differences in the slopes of the inhibition curves indicate that each of the specificities may exist in more than one form. In addition, in the form of 125I-labeled antibodies, two of these hybridomas show a high degree of specificity in binding to Ig-bearing lymphocytes from spleen and lymph nodes. These hybridomas will therefore be useful not only in studies on the phylogenetic distribution of RI-1 specificities but also in replacing conventional antisera for immunochemical and cellular immunological studies.

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.

On the demography of Rattus sordidus colletti in monsoonal Australia

Results of a mark-release study of Rattus sordidus colletti (Gould) on sub-coastal, treeless plains in the monsoonal north of the Northern Territory of Australia are given for 5 years. R. s. colletti is the dominant component of the small mammal fauna of these plains, with only small numbers of Melomys spp. and Planigale maculata also occurring. Two classes of peak densities were observed. Localized peaks resulted from non-breeding adult R. s. colletti refuging onto the marginally higher levees during flooding of the plains, and also from refuging into a lower-lying area at the end of a dry-season drought. Generalized peak densities resulted from peaks in reproductive effort. In 1972 and 1974, reproduction was confined to the period immediately following the monsoons, but in 1973 breeding continued throughout the dry season, following unseasonal rain in June. Thus, generalized peak densities were observed in one year at the beginning of the dry season, and in another at its end. The relatively shallower flooding and mildness of the 1972–3 wet season resulted in commencement of breeding earlier in 1973 than in 1974, while rapid severe flooding of the plains in December 1974 resulted in mass mortality and failure of the refuging populations of adults to recolonize the lower plains in 1975. R. s. colletti remained extremely rare until November 1976, when the study was terminated. The good conditions which allowed reproduction during the dry season of 1973 were reflected in rapid growth rates at that time, compared with rates approaching zero in the 1974 dry season. R. s. colletti is the most fecund form of Australian Rattus species. This high fecundity appears to compensate for the restriction, by dry-season aridity and wet-season flooding, of the breeding season in most years to a short period immediately following the monsoons. In unusual years with rainfall during the dry season, the high fecundity gives R. s. colletti populations the capacity to reach very high densities.

Growth and development of Rattus lutreolus (Rodentia : Muridae) in the laboratory

A laboratory breeding colony of R. l. lutreolus was used to obtain data on the growth in the length of head, hind foot, tail, head and body, and body weight during the first 130 days of life. The development of external body features was compared to that known for other Australian Rattus. The young are blind and naked at birth and are not fully furred until 13 days. Incisors are visible at day 8 (5-11) and erupt about day 12 (8-15) with the eyes opening at 17 days (15-18). Independence was achieved at about 25 days (23-30) with the first signs of reproductive maturity at about 60-70 days. Five stages of growth can be related to developmental features from teeth eruption to puberty and reproductive maturity. The onset of hearing (14-15) days appear to be as important in development as does the opening of the eyes. Body measurements show sigmoid relationships to a linear equivalence of weight (W*0.33), except for head and body length which is linear. R. l. lutreolus belongs to the fast-growing group in Australian murids. Measurements from laboratory-bred animals are in agreement with those for field animals, with head and body length the best single parameter for obtaining approximate ages.

Laboratory hybridization of Australian Rattus fuscipes and Rattus Lutreolus and its karyotypic confirmation

This paper reports successful laboratory hybridization of R. lutreolus lutreolus (2n = 42) and R. fuscipes assimilis (2n = 38). Hybrid offspring grew rapidly (hybrid vigour) to age 24 days. Only one individual survived past 50 days but is fertile. Although intermediate for many characteristics the hybrids resemble R. lutreolus more than R. fuscipes. The hybridization indicates a closer relationship between these species than previously accepted, but there is no evidence of natural hybrids, perhaps due to an ecological separation observed in the field and to behavioural obstacles to mating observed in the laboratory. Hybrid animals (2n = 40) have single fused chromosomes from each of the two pairs of submeta- centrics in the R. fuscipes karyotype. Chromosome arm length measurements and rankings show that one centric fusion (CF1) comprises two longer chromosomes (4 + 8) and the second fusion (CF2) comprises the two shorter chromosomes (10 + 12). These fusions appear to be identical with those we observed in other R. fuscipes populations in New South Wales. The chromosome numbering determined by measurement of unbanded chromosomes in this study appears to differ from the numbering convention currently in use. This emphasizes the need to establish a standard sequence of chromosomes for Australian Rattus.

Systematics and chromosomes of New Guinea Rattus

Karyotypes of six endemic New Guinea Rattus species are described. They fall into two distinct types. The R. leucopus group, which is a compact group morphologically, have very similar karyotypes of 32 or 34 chromosomes and are distinct from the Australian Rattus. The karyotypes of the second type, the R. sordidus group, are related to Australian members of the same group. What has previously been regarded as a single species of the sordidus group, R. sordidus gestroi, is shown to consist of two distinct populations with different karyotypes and skull parameters; we consider that they should be regarded as two species.

Chromosome evolution in Australian rodents. II. The Rattus group.

A total of 219 wild caught specimens representing 12 of the currently recognised 13 species and subspecies of Australian Rattus have been karyotyped. No two species possessed karyotypes in common, most species and several subspecies differing markedly in chromosome number. While the diploid number varied from 2n=32 to 2n=50, the fundamental number (FN) varied only from 60 to 62, suggesting that Robertsonian rearrangements have played a major role in karyotypic evolution in the group. — Karyotypically the Australian species of Rattus fall into two groups. — the R. lutreolus group and the R. sordidus group. Of the karyotypic forms encountered in the former group, that of R. lutreolus is probably most ancestral because it is identical to that of many Asian species of Rattus. Other karyotypic forms in the R. lutreolus group can be derived as follows: That of (1) R. tunneyi tunneyi and R. t. culmorum by a single fixed pericentric inversion; (2) R. fuscipes fuscipes, R. f. greyi, R. f. assimilis and R. f. coracius by two fixed fusions; (3) R. leucopus cooktownensis by three fixed fusions; and (4) R. leucopus leucopus by four fixed fusions. Of the R. sordidus group, R. s. villosissimus may possess the most ancestral karyotype with 2n=50 (FN=60), from which R. s. colletti (2n=42; FN=60) is derived by four fusions and R. s. sordidus (2n=32; FN=60) by nine fusions, four of which appear to be homologous with those R. s. colletti. — The karyotypic data are in accord with Taylor and Horner's (1973) suggestions that (1) R. t. tunneyi and R. t. culmorum belong to one species; (2) R. lut. lutreolus and R. lut. velutinus belong to one species; (3) R. leu. leucopus and R. leu. cooktownensis belong to one species and (4) R. f. fuscipes, R. f. greyi, R. f. assimilis and R. f. coracius belong to one species. However, the large karyotypic difference between R. s. sordidus and R. s. colletti and R. s. villosissimus may indicate that these groups belong to different biological species. — Supernumerary or B-chromosomes were found in R. f. assimilis and R. t. tunneyi. A single R. t. culmorum was heterozygous for a centric fusion.

The ecological significance of thermoregulatory responses to heat stress shown by two populations of an Australian murid, Rattus fuscipes

1. 1. Both populations of Rattus fuscipes thermoregulate well at ambient temperatures below their lower critical temperatures, being assisted by low thermal conductances that vary directly with ambient temperature. 2. 2. All animals remain normothermic when subjected to temperatures within their thermoneutral zones, although they become hyperthermic at higher temperatures. Evaporative cooling is less effective as a means of delaying lethal hyperthermia than in other Australian Rattus species. 3. 3. The two populations of R. fuscipes studied show minor differences in thermoregulatory ability which correlate well with differences in their environments. 4. 4. The absence of R. fuscipes from relatively hot parts of northern Australia, whilst being abundant in cooler, southern areas, can be explained in terms of the thermoregulatory physiology of this species.

Studies on the Metabolism, Thermoregulation, and Evaporative Water Losses of Two Species of Australian Rats, Rattus villosissimus and Rattus rattus

Studies on the Metabolism, Thermoregulation, and Evaporative Water Losses of Two Species of Australian Rats, Rattus villosissimus and Rattus rattus

Reproductive characteristics of wild native Australian Rattus (Rodentia: Muridae).

Reproduction in field populations of the five species and 13 of 14 subspecies of native Australian Rattus is compared, using both materials personally collected and museum specimens. We have separated each subspecies into juvenile and adult categories, the dividing point reflecting the approximate size at which sexual maturity is reached. Occurrence of pregnancies and juveniles, treated monthly, permit estimates of time and length of seasonal breeding for each subspecies. Information on gonads and accessory sex glands is given for both breeding and non-breeding adults and for juveniles. All Australian subspecies of Rattus have a fundamentally similar mechanism of reproduction. Those attaining high densities have the highest ovulation rates, the largest litter sizes, and the greatest number of teats. Furthermore, in the two subspecies of high reproductive potential for which we have evidence, females can be precocious in attaining sexual maturity under field conditions.