Population genetics of the koala (Phascolarctos cinereus) in north-eastern New South Wales and south-eastern Queensland

Habitat loss and fragmentation are key threats to local koala (Phascolarctos cinereus) populations. Broad-scale management is suboptimal for koalas because distribution models are not easily generalised across regions. Therefore, it is imperative that data relevant to local management bodies are available. Genetic data provides important information on gene flow and potential habitat barriers, including anthropogenic disturbances. Little genetic data are available for nationally significant koala populations in north-eastern New South Wales, despite reported declines due to urbanisation and habitat loss. In this study, we develop 14 novel microsatellite loci to investigate koala populations in north-eastern New South Wales (Port Macquarie, Coffs Harbour, Tyagarah, Ballina) and south-eastern Queensland (Coomera). All locations were significantly differentiated (FST = 0.096–0.213; FʹST = 0.282–0.582), and this pattern was not consistent with isolation by distance (R2 = 0.228, P = 0.058). Population assignment clustered the more northern populations (Ballina, Tyagarah and Coomera), suggesting contemporary gene flow among these sites. For all locations, low molecular variation among (16%) rather than within (84%) sites suggests historical connectivity. These results suggest that koala populations in north-eastern New South Wales and south-eastern Queensland are experiencing contemporary impediments to gene flow, and highlight the importance of maintaining habitat connectivity across this region.

Genetic differentiation and introgression amongst Thylogale (pademelons) taxa in eastern Australia

Although pademelons (Thylogale) are widespread and common in coastal eastern Australia, they have been largely neglected in population genetic studies. Here we use 10 microsatellite loci and the mitochondrial DNA (mtDNA) cytochrome b (Cytb) gene to examine genetic differentiation amongst populations of the red-necked (Thylogale thetis) and red-legged (T. stigmatica) pademelon in eastern Australia. Evidence of hybridisation was detected between subspecies of T. stigmatica in central Queensland. Specimens sampled between Eungella and Sarina were found to represent a broad (~90 km) zone of introgression, for both nuclear and mtDNA markers, between T. s. stigmatica (Wet Tropics) and T. s. wilcoxi (south-east Queensland). In addition, individuals sampled from around Proserpine were genetically T. s. stigmatica rather than T. s. wilcoxi, as had previously been assumed. This observation raises some intriguing questions about the dispersal ability of T. stigmatica and the phylogeographic history of moist forest taxa in eastern Australia. Only limited evidence of introgression was detected between sympatric populations of T. thetis and T. s. wilcoxi in south-east Queensland.

The distribution of three parapatric, cryptic species of rock-wallaby (Petrogale) in north-east Queensland: P. assimilis, P. mareeba and P. sharmani

Three morphologically indistinguishable rock-wallaby species (Petrogale assimilis, P. sharmani and P. mareeba) have parapatric distributions in a relatively small area of north-east Queensland. Although problematic to identify in the field, each species can be unambiguously identified by the shape and number of its chromosomes. Here we summarise the known distribution of these three species, based on populations whose identity has been confirmed via karyotypic analysis.

Mapping the distribution of the telomeric sequence (T2AG3)n in the Macropodoidea (Marsupialia) by fluorescence in situ hybridization. II. The ancestral 2n = 22 macropodid karyotype

In marsupial karyotypes with little heterochromatin, the telomeric sequence (T(2)AG(3))(n), is involved in chromosome rearrangements. Here we compare the distribution of the (T(2)AG(3))(n) sequence in chromosomes recently derived by fusions and other rearrangements (7-0.5 MYBP) with its distribution in chromosomes derived earlier (24-9 MYBP). We have previously shown that the (T(2)AG(3))(n) sequence is consistently retained during chromosome rearrangements that are recent (7-0.5 MYBP). We suggest that in less recent rearrangements (24-9 MYBP) the pattern observed is initial retention followed by loss or amplification. We also suggest that the presence of interstitial (T(2)AG(3))(n) sequence is related to the evolutionary status of single chromosomes rather than entire karyotypes.

Restricted mating dispersal and strong breeding group structure in a mid-sized marsupial mammal (Petrogale penicillata)

Ecological genetic studies have demonstrated that spatial patterns of mating dispersal, the dispersal of gametes through mating behaviour, can facilitate inbreeding avoidance and strongly influence the structure of populations, particularly in highly philopatric species. Elements of breeding group dynamics, such as strong structuring and sex-biased dispersal among groups, can also minimize inbreeding and positively influence levels of genetic diversity within populations. Rock-wallabies are highly philopatric mid-sized mammals whose strong dependence on rocky terrain has resulted in series of discreet, small colonies in the landscape. Populations show no signs of inbreeding and maintain high levels of genetic diversity despite strong patterns of limited gene flow within and among colonies. We used this species to investigate the importance of mating dispersal and breeding group structure to inbreeding avoidance within a 'small' population. We examined the spatial patterns of mating dispersal, the extent of kinship within breeding groups, and the degree of relatedness among brush-tailed rock-wallaby breeding pairs within a colony in southeast Queensland. Parentage data revealed remarkably restricted mating dispersal and strong breeding group structuring for a mid-sized mammal. Breeding groups showed significant levels of female kinship with evidence of male dispersal among groups. We found no evidence for inbreeding avoidance through mate choice; however, anecdotal data suggest the importance of life history traits to inbreeding avoidance between first-degree relatives. We suggest that the restricted pattern of mating dispersal and strong breeding group structuring facilitates inbreeding avoidance within colonies. These results provide insight into the population structure and maintenance of genetic diversity within colonies of the threatened brush-tailed rock-wallaby.

Retention of latent centromeres in the Mammalian genome

The centromere is a cytologically defined entity that possesses a conserved and restricted function in the cell: it is the site of kinetochore assembly and spindle attachment. Despite its conserved function, the centromere is a highly mutable portion of the chromosome, carrying little sequence conservation across taxa. This divergence has made studying the movement of a centromere, either within a single karyotype or between species, a challenging endeavor. Several hypotheses have been proposed to explain the permutability of centromere location within a chromosome. This permutability is termed "centromere repositioning" when described in an evolutionary context and "neocentromerization" when abnormalities within an individual karyotype are considered. Both are characterized by a shift in location of the functional centromere within a chromosome without a concomitant change in linear gene order. Evolutionary studies across lineages clearly indicate that centromere repositioning is not a rare event in karyotypic evolution and must be considered when examining the evolution of chromosome structure and syntenic order. This paper examines the theories proposed to explain centromere repositioning in mammals. These theories are interpreted in light of evidence gained in human studies and in our presented data from the marsupial model species Macropus eugenii, the tammar wallaby.

First record of quadruplets in the musky ratkangaroo Hypsiprymnodon moschatus

THE musky rat-kangaroo (Hypsiprymnodon moschatus) is endemic to the tropical rainforests of north-east Queensland (Johnson and Strahan 1982). It is the smallest (510 ? 530 g) and most unusual member of the marsupial superfamily Macropodoidea (Dennis and Johnson 1995). Unlike other macropodoids, H. moschatus is frugivorous, diurnal, has an opposable first digit on the pes, a running quadrupedal gait and possesses a relatively unspecialised digestive tract (Johnson and Strahan 1982; Dennis 2002). It also differs from all other macropodoids in typically giving birth to multiple young, usually twins ? although single young and triplets are regularly reported both in the wild and in captivity (Troughton 1967; Johnson and Strahan 1982; Johnson et al. 1983; Dennis and Marsh 1997; Lloyd 2001). However, the birth of more than three young has not previously been observed in H. moschatus or any other macropodoid, even though all species possess four teats.

Fine-scale spatial genetic correlation analyses reveal strong female philopatry within a brush-tailed rock-wallaby colony in southeast Queensland

We combine spatial data on home ranges of individuals and microsatellite markers to examine patterns of fine-scale spatial genetic structure and dispersal within a brush-tailed rock-wallaby (Petrogale penicillata) colony at Hurdle Creek Valley, Queensland. Brush-tailed rock-wallabies were once abundant and widespread throughout the rocky terrain of southeastern Australia; however, populations are nearly extinct in the south of their range and in decline elsewhere. We use pairwise relatedness measures and a recent multilocus spatial autocorrelation analysis to test the hypotheses that in this species, within-colony dispersal is male-biased and that female philopatry results in spatial clusters of related females within the colony. We provide clear evidence for strong female philopatry and male-biased dispersal within this rock-wallaby colony. There was a strong, significant negative correlation between pairwise relatedness and geographical distance of individual females along only 800 m of cliff line. Spatial genetic autocorrelation analyses showed significant positive correlation for females in close proximity to each other and revealed a genetic neighbourhood size of only 600 m for females. Our study is the first to report on the fine-scale spatial genetic structure within a rock-wallaby colony and we provide the first robust evidence for strong female philopatry and spatial clustering of related females within this taxon. We discuss the ecological and conservation implications of our findings for rock-wallabies, as well as the importance of fine-scale spatial genetic patterns in studies of dispersal behaviour.

Centromere Dynamics and Chromosome Evolution in Marsupials

The eukaryotic centromere poses an interesting evolutionary paradox: it is a chromatin entity indispensable to precise chromosome segregation in all eukaryotes, yet the DNA at the heart of the centromere is remarkably variable. Its important role of spindle attachment to the kinetochore during meiosis and mitosis notwithstanding, recent studies implicate the centromere as an active player in chromosome evolution and the divergence of species. This is exemplified by centromeric involvement in translocations, fusions, inversions, and centric shifts. Often species are defined karyotypically simply by the position of the centromere on certain chromosomes. Little is known about how the centromere, either as a functioning unit of chromatin or as a specific block of repetitive DNA sequences, acts in the creation of these types of chromosome rearrangements in an evolutionary context. Macropodine marsupials (kangaroos and wallabies) offer unique insights into current theories expositing centromere emergence during karyotypic diversification and speciation.

Mapping the Distribution of the Telomeric Sequence (T2AG3)nin the 2n = 14 Ancestral Marsupial Complement and in the Macropodines (Marsupialia: Macropodidae) by fluorescence in situ hybridization

In this study we test the theory that the presence of the conserved vertebrate telomeric sequence (T(2)AG(3))(n) at the centromeres of Australian marsupial 2n = 14 complements is evidence that these karyotypes are recently derived, which is contrary to the generally held view that the 2n = 14 karyotype is ancestral for Australasian and American marsupials. Here we compare the distribution of the (T(2)AG(3))( n ) sequence and constitutive heterochromatin in the presumed ancestral 2n = 14 complement and in complements with known rearrangements. We found that where there were moderate to large amounts of constitutive heterochromatin, the distribution of the (T(2)AG(3))(n) sequence reflected its presence as a native component of satellite DNA rather than its involvement in past rearrangements. The presence of centromeric heterochromatin in all Australian 2n = 14 complements therefore suggests that centromeric sites of the (T(2)AG(3))(n) sequence do not represent evidence for recent rearrangements.

Intraspecific variation, sex-biased dispersal and phylogeography of the eastern grey kangaroo (Macropus giganteus)

Genetic information has played an important role in the development of management units by focusing attention on the evolutionary properties and genetics of populations. Wildlife authorities cannot hope to manage species effectively without knowledge of geographical boundaries and demic structure. The present investigation provides an analysis of mitochondrial DNA and microsatellite data, which is used to infer both historical and contemporary patterns of population structuring and dispersal in the eastern grey kangaroo (Macropus giganteus) in Australia. The average level of genetic variation across sample locations was one of the highest observed for marsupials (h=0.95, HE=0.82). Contrary to ecological studies, both genic and genotypic analyses reveal weak genetic structure of populations, where high levels of dispersal may be inferred up to 230 km. The movement of individuals was predominantly male-biased (average Nem=22.61, average Nfm=2.73). However, neither sex showed significant isolation by distance. On a continental scale, there was strong genetic differentiation and phylogeographic distinction between southern (TAS, VIC and NSW) and northern (QLD) populations, indicating a current and/or historical restriction of gene flow. In addition, it is evident that northern populations are historically more recent, and were derived from a small number of southern founders. Phylogenetic comparisons between M. g. giganteus and M. g. tasmaniensis indicated that the current taxonomic status of these subspecies should be revised as there was a lack of genetic differentiation between the populations sampled.

Mapping the distribution of the telomeric sequence (T(2)AG(3))(n) in rock wallabies, Petrogale (Marsupialia: Macropodidae), by fluorescence in situ hybridization. ii. the lateralis complex

The distribution of the conserved vertebrate telomeric sequence (T(2)AG(3))(n) was examined by fluorescence in situ hybridization in the six Petrogale (rock wallabies) taxa of the lateralis complex. As expected, the (T(2)AG(3))(n) sequence was located at the termini of all chromosomes in all taxa. However, the sequence was also present at several nontelomeric (viz., interstitial and centromeric) sites. The signals identified were associated with either ancient rearrangements involved with the formation of the 2n = 22 plesiomorphic macropodine karyotype or more recent rearrangements associated with karyotypes derived from the 2n = 22 karyotype. Interstitial (T(2)AG(3))(n) signals identified on chromosomes 3 and 4 in all six species of the lateralis complex and a large centromeric signal identified on chromosome 7 in the five subspecies/races of P. lateralis appear to be related to the more ancient rearrangements. Subsequent chromosome evolution has seen these signals retained, lost, or amplified in different Petrogale lineages. Within the lateralis complex, in two submetacentric chromosome derived by recent centric fusions, the telomeric sequence was identified at or near the centromere, indicating its retention during the fusion process. In the two taxa where chromosome 3 was rearranged via a recent centromeric transposition to become an acrocentric chromosome, the telomeric signal was located interstitially.

Characterisation and cross-species utility of microsatellite markers within kangaroos, wallabies and rat kangaroos (Macropodoidea : Marsupialia)

The analysis of DNA using molecular techniques is an important tool for studies of evolutionary relationships, population genetics and genome organisation. The use of microsatellite genetic markers in marsupial studies is primarily limited by their availability and the success of amplification. Within this study, 29 macropodoid (kangaroos, wallabies and rat kangaroos) microsatellite loci were characterised in the tammar wallaby (Macropus eugenii) to evaluate the level of polymorphism and effects of cross-species amplification. Results indicated that 25 primer pairs amplified a single locus, with 21 exhibiting high levels of variability. The success of cross-species amplification was inversely proportional to the evolutionary distance between species. Therefore most macropodoid species can be studied using many of the available microsatellites, since source species are regularly distributed among macropodoid lineages. It was shown that M. eugenii had significantly (P < 0.01) reduced genetic diversity compared with source species. In addition, many microsatellite loci had reduced repeat arrays within M. eugenii, and all monomorphic loci sequenced had interruptions within the repeat arrays. The diversity differences are most likely caused by ascertainment bias in microsatellite selection for both length and purity. The results from this study highlight the need for caution when using genetic distance measures between divergent taxa, as the assumption of a specific mutation rate and/or type may be violated.

Phylogeographic structure within Phascogale (Marsupialia : Dasyuridae) based on partial cytochrome b sequence

The brush-tailed phascogale (Phascogale tapoatafa) is considered locally rare and vulnerable, despite being found in all mainland states of Australia. It is rarely detected in faunal surveys and the two most immediate conservation requirements are a determination of its current range and clarification of its taxonomic status. Measures of genetic differentiation amongst Phascogale tapoatafa populations in eastern, western and northern Australia were estimated using a partial (348 bp) sequence of mitochondrial DNA (cytochrome b gene). Observed sequence divergence within P. tapoatafa was substantial, with an average of 13% separating the allopatric populations in south-eastern, south-western and northern Australia. In comparison, an average of 16% sequence divergence separated the two currently recognised Phascogale species (P. tapoatafa andP. calura). Thus, Phascogale comprises four highly divergent lineages, suggesting that the genus is more diverse than previously thought. These data indicate that further taxonomic research is warranted.

A Significant Range Extension Of The Purple-Necked Petrogale Purpureicollis Rockwallaby

IN 1982, the Queensland subspecies of the blackfooted rock-wallaby Petrogale lateralis purpureicollis was reported to occur around Mt Isa and south to around Dajarra (Briscoe et al. 1982). During 1991, the known range of this taxon was extended 300 km to the north-west when an adult female P. l. purpureicollis was collected from ?Ridgepole Waterhole? in the Musselbrook Resource Reserve near Lawn Hill National Park (Eldridge et al. 1993). In 1994 the range was further extended when P. l. purpureicollis was recorded from the Constance Ranges and the upper reaches of Stockyard and Elizabeth Creeks; around the town of Cloncurry and the following distances from the town: 85 km north west; 60 and 87 km west; 4, 23, 28 and 35 km south and 15 km east (Bell et al. 1995). Approaches by the Cannington Mining operation to the southwest of McKinley in October 1999 to confirm the presence of rock-wallabies on nearby Glenholme Station established the presence of P. l. purpureicollis; a 75 km range extension to the south-east.

Restriction fragment length polymorphism (RFLP) analysis of three nuclear genes in rock-wallabies (Petrogale: Marsupialia: Macropodidae): a search for genic markers to identify taxa within the Petrogale lateralis-penicillata group

Many rock-wallaby (Petrogale) species within the lateralis–penicillata complex are morphologically similar and can be distinguished only by their unique karyotypes, frustrating attempts to identify specimens in the field and in museums. As chromosome preparations are not always obtainable from specimens, additional diagnostic molecular markers are required. In this study, restriction fragment length polymorphism (RFLP) analysis of three nuclear genes was undertaken using 100 Petrogale specimens, including representatives of 12 taxa. Eleven novel diagnostic nuclear DNA markers were identified, which enabled the identification of four taxa (P. penicillata, P. purpureicollis, P. lateralis and P. inornata). No markers were found that could reliably distinguish amongst five north-east Queensland species (P. assimilis, P. sharmani, P. mareeba, P. godmani and P. coenensis) or the sampled intraspecific taxa of P. lateralis (P. l . lateralis, P. l. pearsoni, MacDonnell Ranges race). These results are consistent with previous studies in demonstrating that P. penicillata, P. purpureicollis, P. lateralis and P. inornata are genically distinct and that the north-east Queensland species and subspecies/races of P. lateralis form two groups of very closely related taxa. Future research should target more rapidly evolving DNA regions, in order to identify specific molecular markers that distinguish amongst taxa within these two groups. Meanwhile, karyotypic analysis remains the only definitive technique currently available to unambiguously identify all taxa within the lateralis–penicillata group.

Taxonomy of rock-wallabies, Petrogale (Marsupialia : Macropodidae). III. Molecular data confirms the species status of the purple-necked rock-wallaby (Petrogale purpureicollis Le Souef)

Mitochondrial DNA (mtDNA) analysis was undertaken to resolve the systematic uncertainties surrounding the morphologically distinct purple-necked rock-wallaby (P. lateralis purpureicollis) of north-west Queensland, Australia. A comparison of mtDNA sequence divergence using both whole mtDNA restriction site and control-region sequence analyses revealed that P. l. purpureicollis was as well differentiated from other P. lateralis (black-footed rock-wallaby) taxa as P. lateralis was from P. penicillata (brush-tailed rock-wallaby) or P. assimilis (allied rock-wallaby). Phylogenetic analysis of the sequence data suggests thatP. lateralis (sensu lato) is paraphyletic, with P. l. purpureicollis being more closely aligned to P. penicillataand P. assimilis than to P. lateralis (sensu stricto). Data are also presented that demonstrate significant differences in the distribution of the telomeric repeat sequence (TTAGGG)n between the chromosomes of P. l. purpureicollis and the karyotypically similar MacDonnell Ranges race of P. lateralis. In addition, meiosis appears to be severely disrupted in the majority (73%) of oocytes examined from two P. l. purpureicollis MacDonnell Ranges race hybrids. In light of these findings we recommend that the purple-necked rock-wallaby be reinstated as a full species, P. purpureicollis Le Souef 1924.

Restriction Analysis of Mitochondrial DNA from the Yellow-footed Rock-wallaby, Petrogale xanthopus: Implications for Management

The extent of mitochondrial DNA divergence between populations of the vulnerable yellow-footed rock- wallaby, Petrogale xanthopus, was assessed by restriction analysis. Of the 15 restriction endonucleases, five were informative, with a single unique haplotype identified in P. x. celeris from Queensland (Qld) (n = 8) and a further two unique haplotypes in three sampled populations of P. x. xanthopus from New South Wales (NSW) (n = 1) and South Australia (SA) (n = 9). The two subspecies of P. xanthopus were found to be genetically distinct (average sequence divergence = 0·72%). As this divergence is greater than that found between some Petrogale species, it is recommended that populations of P. x. xanthopus and P. x. celeris be managed independently both in captivity and the wild. The NSW population of P. x. xanthopus appears genetically similar to those in SA, although these data are limited.

A genetic study of the Brush-tailed Rock Wallaby Petrogale penicillata in East Gippsland and relevance for management of the species in Victoria

Within the Australian macropod genus Petrogale (rock wallabies) nine chromosomally distinct species occur along the Great Dividing Range of eastern Australia (Sharman et al. 1990; Eldridge et al. 1991a; Eldridge and Close 1992). However, Close et al. (1988) found Petrogale from the Grampians, Victoria and from Jenolan Caves, New South Wales, to be remarkably similar despite their 800 km separation (Fig. 1). Standard and C-banded karyotypes of both populations were typical of Petrogale penicillata and were identical except that one Grampians animal was heterozygous for absence of a C-band on chromosome 2. Apart from their smaller physical size, the only difference was that the Grampians animals were homozygous for a unique Pgm allele.

Taxonomy of Rock Wallabies, Petrogale (Marsupialia, Macropodidae) .1. A Revision of the Eastern Petrogale With the Description of 3 New Species

The taxonomy of Petrogale has been in a state of flux for many years. The eight chromosome races of the eastern Petrogale radiation are currently placed in four species. However, several of these 'species' contain chromosomally unrelated taxa. In this paper a species definition for Petrogale is proposed that allows for some gene flow between species but requires a species to maintain a substantial and distinct genetic identity. When this definition was applied to the eastern Petrogale eight 'good' species were identified. Thus we now consider the eastern Petrogale complex to consist of P. penicillata, P. herberti (formerly P. penicillata herberti), P. inornata, P. assimilis, P. sharmani, sp. nov. (formerly the Mt Claro race), P. mareeba, sp. nov. (formerly the Mareeba race), P. godmani and P. coenensis, sp. nov. (formerly the Cape York race). Several of these taxa are cryptic species and the primary means of identification used was chromosome number and morphology. However, genic data were useful in establishing whether each taxon should be regarded as a separate species.

Chromosomal Rearrangements in Rock Wallabies, Petrogale (Marsupialia, Macropodidae) .4. G-Banding Analysis of the Petrogale-Lateralis Complex

The karyotypes of Petrogale lateralis lateralis, P. l. purpureicollis and P. l 'Macdonnell Ranges' were examined with G-banding from cultured fibroblasts. P. l. lateralis (2n = 22) was found to retain the plesiomorphic karyotype, whereas P. l. purpureicollis (2n = 22) and P. l. 'Macdonnell Ranges' (2n = 22) were found to share an apomorphic karyotype characterised by an acrocentric chromosome 3 (3a) and an acrocentric X-chromosome (Xp). Both the 3a and Xp can be derived from their respective P. l. lateralis homologues by centric transpositions. Although P. l. purpureicollis and P. l. 'Macdonnell Ranges' appear very similar chromosomally, they are readily distinguishable genically and morphologically, P. l. 'Macdonnell Ranges' being more similar to P. l. lateralis. Thus, in these taxa, genic and morphological divergence have not been associated with significant changes in karyotype.

Chromosomal Rearrangements in Rock Wallabies, Petrogale (Marsupialia, Macropodidae) .5. Chromosomal Phylogeny of the Lateralis-Penicillata Group

Cladistic analysis of G-banded karyotypes was conducted on 11 Petrogale taxa from the lateralis/penicillata group with the genus Thylogale as an outgroup. Within the eastern Petrogale radiation (the penicillata complex), no homoplasy-free phylogenies could be generated and each tree contained character reversals, multiple origins and/or introgression of some chromosome characters. On the basis of the significance of some chromosome rearrangements and the genic relationships of taxa, one tree is favoured as being the most likely, although it is not the most parsimonious. In the lateralis/penicillata group the number of chromosome characters available was insufficient to accurately resolve the inter-relationships of the two complexes. However, the data are consistent with the eastern Petrogale radiation being a monophyletic group that excludes members of the Petrogale lateralis complex. The inter-relationships of the three subspecies of P. lateralis that were examined were not resolved by the chromosome data, although the karyotypes of both P. l. purpureicollis and P. l. 'Macdonnell Ranges' can be readily derived from that of P. l. lateralis.

Chromosomal rearrangements in rock wallabies, Petrogale (Marsupialia: Macropodidae). III. G-banding analysis of Petrogale inornata and P. penicillata

The karyotypes of Petrogale inornata and the two currently recognised races of Petrogale penicillata were examined using G-banding from cultured fibroblasts. Petrogale inornata (2n = 22) was found to retain plesiomorphic chromosomes 3 and 4 but possessed an apomorphic inverted chromosome 5 (5i). This 5i appears identical with the 5i found in two other Queensland taxa, Petrogale assimilis and Petrogale godmani, and can be derived from the ancestral chromosome 5 by an extensive paracentric inversion or a centromeric transposition. Petrogale penicillata penicillata (2n = 22) and Petrogale penicillata herberti (2n = 22) both possess the synapomorphic acrocentric chromosome 3, which appears to differ from the plesiomorphic 3 by a small centromeric transposition. Petrogale p. penicillata was also found to be characterised by an apomorphic acrocentric chromosome 4, while P. p. herberti was characterised by an autapomorphic submetacentric chromosome 4. Both apomorphic chromosomes 4 can be related to the plesiomorphic chromosome 4 by centromeric transpositions. Thus although P. inornata is chromosomally distinct it is more closely related to other north Queensland taxa than it is to either P. p. penicillata or P. p. herberti.Key words: chromosomal rearrangements, G-banding, Marsupialia, Petrogale, Macropodidae.