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Chromosome morphology in Gilbert’s Potoroo, Potorous gilbertii (Marsupialia: Potoroidae)


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Chromosome morphology was examined for male and female Gilbert’s potoroo, Potorous gilbertii, to infer taxonomic and evolutionary relationships among the extant taxa within the genus Potorous. P. gilbertii has the same number of chromosomes as P. tridactylus, 2n = 12,13. Giemsa-banding patterns were very similar in P. gilbertii and P. tridactylus; however, differences were noted between the sex chromosomes. Given that the relationships among extant Potorous are unresolved, we mapped karyotypes onto two alternative phylogenies to suggest methods of karyotype evolution within this group. Karyotypes and molecular-based information from the now ‘presumed extinct’ P. platyops or sequencing of multiple gene regions for phylogenetic analysis within the Potoroidae would provide valuable information for resolving the issue of rooting, and hence drawing conclusions on the evolution of karyotypes within this group.
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Chromosome morphology in Gilbert’s potoroo,
Potorous gilbertii (Marsupialia : Potoroidae)
E. A. SinclairA, A. R. MurchB, M. Di RenzoB, and M. PalermoB
ADepartment of Zoology, University of Western Australia, Nedlands, WA 6907, Australia.
Present address: Department of Zoology, Brigham Young University, Provo, UT 84602, USA.
BDepartment of Cytogenetics, King Edward Memorial Hospital, Subiaco, WA 6008, Australia.
Chromosome morphology was examined for male and female Gilbert’s potoroo, Potorous gilbertii, to infer
taxonomic and evolutionary relationships among the extant taxa within the genus Potorous. P. gilbertii has
the same number of chromosomes as P. tridactylus, 2n = 12,13. Giemsa-banding patterns were very similar
in P. gilbertii and P. tridactylus; however, differences were noted between the sex chromosomes. Given
that the relationships among extant Potorous are unresolved, we mapped karyotypes onto two alternative
phylogenies to suggest methods of karyotype evolution within this group. Karyotypes and molecular-based
information from the now ‘presumed extinct’ P. platyops or sequencing of multiple gene regions for
phylogenetic analysis within the Potoroidae would provide valuable information for resolving the issue of
rooting, and hence drawing conclusions on the evolution of karyotypes within this group.
Gilbert’s potoroo, Potorous gilbertii, was originally recognised by John Gilbert as a full
species, Hypsiprymnus gilbertii (1840). The description was, however, based on a single
animal. Its taxonomic status was later re-interpreted, and it was synonymised with the long-
nosed potoroo, P. tridactylus, on the basis of morphology (Ride 1970; Johnston and Sharman
1976). The difficulties in determining the correct taxonomic status of Gilbert’s potoroo have
principally arisen through a lack of specimens: less than ten specimens were known to have been
collected (Clem Fisher, personal communication). Some subfossil material has also been
collected (Baynes et al. 1975), but the last known living specimens were collected last century.
Gilbert’s potoroo was rediscovered in 1994 at Two Peoples Bay in Western Australia
(Sinclair et al. 1996). A subsequent study of the genetic relationship between this animal and its
extant relatives in eastern Australia, using allozyme electrophoresis and DNA sequencing, was
carried out by Sinclair and Westerman (1997). Results showed that Gilbert’s potoroo was as
different from the two eastern Australian species (P. tridactylus and the long-footed potoroo, P.
longipes) as these two were from each other. It was concluded that Gilbert’s potoroo should
again be recognised as a full species, but its relationships to other taxa were not fully resolved.
Chromosome morphology of Australian macropods has been extensively studied, and
provides a window into both evolution between the major groups (Rofe 1978; Sharman 1989),
as well as relationships among closely related species (e.g. within the genus Petrogale: Eldridge
et al. 1991a, 1991b). In both American (north and south) and Australian species, the most
common karyotype number is 2n = 14 (Rofe and Hayman 1985). The relative uniformity
(highly conserved G-banding patterns) and wide distribution of this karyotype across
superfamilies and families suggest that it may be the ancestral karyotype for marsupials
(Hayman and Martin 1974; Rofe and Hayman 1985). Several marsupial species have a high
chromosome number, including the rufous bettong, Aepyprymnus rufescens (2n = 32: Hayman
and Martin 1969), the banded hare-wallaby, Lagostrophus fasciatus (2n = 24: Sharman 1961),
and P. longipes (2n = 24: Seebeck and Johnston 1980). It may be inferred that A. rufescens and
L. fasciatus have derived karyotypes (see Hayman and Martin 1974), while Johnston et al.
(1984) concluded that the ancestral Potorous karyotype was similar to 2n = 24 of P. longipes.
Australian Journal of Zoology, 2000, 48, 281–287
10.1071/ZO99049 0004-959X/00/030281
© CSIRO 2000
The higher chromosome numbers observed in the above species would have to result from
fission events. Imai and Crozier (1980) have suggested that fission events played a major role in
mammalian chromosome evolution.
Within the potoroos, P. tridactylus (2n = 12F,13M: Sharman et al. 1950; Sharman and
Barber 1952) and P. longipes are both clearly distinguishable on the basis of karyotypes, while
the two subspecies of P. tridactylus can not be chromosomally differentiated on the basis of
their karyotypes (Sharman and Barber 1952; Shaw and Krooth 1964). Johnston et al. (1984)
artificially constructed the P. tridactylus karyotype from that of P. longipes and suggested that
the ancestral karyotype was probably similar to that of P. longipes. Therefore, fusions, primarily
centric, had played an important role in the evolution of the Potorous karyotype.
Most marsupials have a typical XY sex-determining mechanism (Sharman and Barber 1952),
in which males are the heterogametic sex. However, several exceptions have been reported: P.
tridactylus, Wallabia bicolor, and Macrotis lagotis all have a second Y chromosome while
Lagorchestes conspicillatus has multiple X chromosomes (Martin and Hayman 1966). In this
study, we obtain karyotypes for male and female P. gilbertii and make comparisons with the two
extant congenerics.We statistically test two alternative hypotheses for relationships within
Potorous. Karyotypes will be mapped onto the phylogenetic trees to make inferences about
their evolutionary history.
Materials and Methods
Fresh peripheral blood was collected from one female and one male P. gilbertii trapped at Two Peoples
Bay, Western Australia (Fig. 1) and from two captive P. tridactylus from the Caversham Wildlife Park,
Western Australia.
282 E. A. Sinclair et al.
Fig. 1. The distribution of Potorous species in Australia (from Strahan 1995). Karyotypes of
the taxa are included (see text for references).
Standard thymidine synchronised lymphocyte cultures were set up and prepared for cytogenetic analysis
using the technique of Wheater and Roberts (1987) with minor modifications. The technique gave an
acceptable yield of good-quality metaphases. The trypsin banding technique of Seabright (1971) was used
for G-banding and the barium hydroxide method of Sumner (1972) with minor modifications for C-banding.
Given that the relationships among these taxa are not fully resolved, we have tested alternative rooting
hypotheses under conditions of maximum likelihood, using PAUP* 4.0b3 (Swofford 1999). The computer
program Modeltest ver. 2.1 (Posada and Crandall 1998) was used to estimate the model of evolution that
best explains the variation in cytochrome bsequences from Sinclair and Westerman (1997). Trees with two
alternative rootings tested the hypotheses that P. gilbertii and P. longipes were sister taxa (consistent with
the cytochrome btree), and that P. gilbertii and P. tridactylus were sister taxa (one possible tree from the
allozyme data). A Kishino–Hasegawa test (Kishino and Hasegawa 1989) was performed to test whether
there was a significant difference between the topology of these two trees. This test compares the log-
likelihood scores for trees with different topologies.
Metaphase spreads for males and females were examined for both species (Fig. 2). P.
gilbertii has a karyotype of 2n = 12 for females and 2n = 13 for males, where the male has two
Y chromosomes, the same arrangement as previously reported by Sharman et al. (1950) for both
subspecies of P. tridactylus. G-banding patterns were similar for P. tridactylus and P. gilbertii.
No consistent differences in the banding patterns of the autosomes or the X chromosomes could
be detected. However, the Y1chromosome in P. gilbertii appears to be about twice the size of
that in P. tridactylus and also appears to have two extra dark G-bands. The Y2chromosomes of
both species appear identical and their banding patterns appear very similar to the pattern seen
on the long arm of the X chromosome.
C-banding was unsuccessful in the P. tridactylus samples, but the C-banding patterns obtained
for P. gilbertii (Fig. 3) were compared with those published for P. tridactylus by Johnston et al.
(1984). Heterochromatin was restricted to small amounts around the centromeres in the autosomes
in both species. There were also similar blocks of heterochromatin in the long arm of the X
283Chromosome morphology in Gilbert’s potoroo
Fig. 2. Comparison of G-banded karyotypes for Potorous gilbertii and Potorous tridactylus for (a) male
and (b) female.
284 E. A. Sinclair et al.
Fig. 3. C-banded karyotypes of Potorous gilbertii: (a) male and (b) female.
Fig. 4. Phylogenetic trees for the two hypotheses on rooting (a) P. gilbertii and P. longipes as sister taxa,
and (b) P. gilbertii and P. tridactylus as sister taxa, with karyotypes mapped onto them.
chromosome. However, P. gilbertii lacked the large block of heterochromatin that makes up most
of the short arm of the X in P. tridactylus. Almost all of Y1is heterochromatin in P. tridactylus,
but P. gilbertii has a euchromatic region distal to the heterochromatin on the long arm.
Alternative hypotheses for tree rooting are presented in Fig. 4. A Tamura and Nei (1993)
plus gamma model was selected as the most appropriate model of evolution by Modeltest
(gamma shape distribution = 0.293). The log-likelihood score for the tree that supported P.
gilbertii and P. longipes as sister taxa was 1060.58, and that where P. gilbertii and P. tridactylus
were sister taxa was 1066.48. The Kishino–Hasegawa test was not significant, P = 0.34,
indicating that there was no significant difference in the topology of these two trees. Therefore,
any discussion on the evolution of chromosome karyotypes within potoroids remains speculative
until the issue of rooting this tree can be resolved.
The karyotype of P. gilbertii is essentially the same as for P. tridactylus (2n = 12, 13). The
sex-determining mechanism is also XX : XY1Y2. These karyotypes are clearly distinguishable
from the P. longipes form, which Johnston et al. (1984) hypothesised was ancestral. The 2n =
12, 13 karyotype is widespread, being present in Potorous from eastern and western Australia
and on Tasmania and islands in Bass Strait (see Fig. 1).
We acknowledge that there are problems associated with phylogenies derived from single
mitochondrial trees (see Avise 1994; Krajewski and Woods 1995). However, in the absence of
further data at present, we make the following suggestions. The phylogeny of Sinclair and
Westerman (1997), in which mtDNA sequence data support the idea that P. gilbertii and P. longipes
are sister taxa, indicates that 2n = 24 is the derived karyotype. (The allozyme tree was unrooted so
there are two equally parsimonious trees, depending on the rooting.) This refutes the conclusion of
Johnston et al. (1984) that the ancestral Potorous karyotype was similar to that of P. longipes.
Increases in chromosome number, as a result of chromosomal fissions have been postulated in other
mammalian groups including canids (Todd 1970), primates (Matthay 1973), and kangaroo rats
(Patton and Rogers 1993). Although the mechanisms for an increase in chromosome number have
not yet been demonstrated in marsupials (Sharman 1973), this may be an example.
If, however, P. gilbertii and P. tridactylus are sister taxa, which is supported by the
karyotype data, then 2n = 24 is ancestral, and consistent with Johnston et al. (1984). The 2n =
12, 13 derived karyotype could then be hypothesised to have occurred either once (in eastern
Australia and then dispersed westward) or twice. Maynes (1989) suggests that zones of contact
between the south-west and south-east have resulted in many of the western species, including
Setonix brachyurus, Macropus irma, and Potorous tridactylus (now gilbertii). Given that the
autosomes are very similar in both species, it seems unlikely that the exact same chromosomes
would fuse twice independently. For example, in Macropus species that have a common
karyotype of 2n = 16, G-banding patterns indicate that this karyotype has been derived from no
fewer than eight different fusion events in the autosomes (see Rofe 1978).
Divergence estimates, from cytochrome bsequence data (Sinclair and Westerman 1997), are
much older than the last known ‘contacts’ of the Pleistocene, suggesting that these species (or
their immediate ancestors) have been isolated for a much longer period. During the Pleistocene,
a land bridge was present south of what is now the Nullarbor Plain. A continuous distribution of
potoroos may have been present across this region, consistent with a single fusion event. At the
end of this period, potoroos with the 2n = 12, 13 karyotype could remain in the east and west,
but become isolated. However, there is no evidence from fossil or subfossil material to indicate
that either P. tridactylus or P. gilbertii occurred in central southern Australia. Extant Potorous
spp. first appear in the fossil record during the Pleistocene (Flannery 1984). The broad-faced
potoroo (P. platyops) is the only Potorous species identified from Pleistocene and Holocene
cave deposits in the Nullarbor Plain, which has been dated at between 38 000 and 7500 years
ago (Lundelius and Turnbull 1989). P. platyops (and one other unidentified potoroid) is also
reported from surface deposits between Esperance and the Eyre Peninsula, dated at between 390
285Chromosome morphology in Gilbert’s potoroo
± 210 years ago (Baynes 1987) and 180 ± 76 years ago (Merrilees 1970). So the fossil record,
as it stands presently, provides little support for either explanation.
It seems that two approaches could help resolve this issue of how to root the phylogenetic tree,
and hence draw conclusions on the evolution of karyotypes within this group. Karyotyping and
molecular-based information from the now ‘presumed extinct’ P. platyops would be very
valuable, since it is the only potoroo species that is known to have had a distribution across the
arid parts of southern Australia. It is extremely unlikely, however, that suitable material will ever
become available to karyotype this species, although it may be possible to obtain DNA sequences
from museum material. A more feasible option would be to collect DNA sequence data from
multiple gene regions (nuclear and mitochondrial) and from more taxa to obtain a more robust
phylogeny of the Potoroidae. Known karyotypes (including information on chromosome
painting, such as that provided by Rens et al. 1999) can then be mapped onto this phylogeny.
Thank you to Jeff Middleton, Jackie Courtenay and Leigh Whisson for their help in the field;
the Potoroo Recovery Team; David Thorn at the Caversham Wildlife Park for P. tridactylus
blood samples; Jack Sites, Keith Crandall, Duke Rogers, and two reviewers for their
constructive comments on this manuscript. This work was supported by the University of
Western Australia, ALCOA of Australia, and an Australian Post-graduate Research Award to
Avise, J. C. (1994). ‘Molecular Markers, Natural History and Evolution.’ (Chapman and Hall: New York.)
Baynes, A. (1987). The original mammal fauna of the Nullarbor and southern peripheral regions: evidence
from skeletal remains in superficial cave deposits. In ‘A Biological Survey of the Nullarbor Region in
South and Western Australia’. (Eds N. L. McKenzie and A. C. Robinson.) pp. 139–152. (Department of
Environment and Planning: Adelaide.)
Baynes, A., Merrilees, D., and Porter, J. K. (1975). Mammal remains from the upper levels of a late
Pleistocene deposit in Devil’s Lair, Western Australia. Journal of the Royal Society of Western Australia
58, 97–117.
Eldridge, M. D. B., Close, R. L., and Johnston, P. G. (1991a). Chromosomal rearrangements in rock
wallabies, Petrogale (Marsupialia : Macropodidae). IV. G-banding analysis of the Petrogale lateralis
complex. Australian Journal of Zoology 39, 621–627.
Eldridge, M. D. B., Johnston, P. J., and Close, R. L. (1991b). Chromosomal rearrangements in rock
wallabies, Petrogale (Marsulialia : Macropodidae). V. Chromosomal phylogeny of the
lateralis/penicillata group. Australian Journal of Zoology 39, 629–641.
Flannery, T. F. (1984). Kangaroos: 15 million years of Australian bounders. In ‘Vertebrate Zoogeography
and Evolution in Australasia’. (Eds M. Archer and G. Clayton.) pp. 817–835. (Hesperian Press: Perth.)
Hayman, D. L., and Martin, P. G. (1969). Cytogenetics of marsupials. In ‘Comparative Mammalian
Cytogenetics’. (Ed. K. Benirschke.) pp. 191–217. (Springer Verlag: New York.)
Hayman, D. L., and Martin, P. G. (1974). ‘Animal Cytogenetics. Mammalia 1: Monotremata and
Marsupialia.’ (Gebrüder Bornträger: Berlin.)
Imai, H. T., and Crozier, R. H. (1980). Quantitative analysis of directionality in mammalian karyotype
evolution. American Naturalist 116, 537–569.
Johnston, P. G., and Sharman, G. B. (1976). Studies on populations of Potorous Desmarest (Marsupialia). I.
Morphological variation. Australian Journal of Zoology 24, 573–588.
Johnston, P. G., and Sharman, G. B. (1977). Studies on populations of Potorous Desmarest (Marsupialia).
II. Electrophoretic, chromosomal and breeding studies. Australian Journal of Zoology 25, 733–747.
Johnston, P. G., Davey, R. J., and Seebeck, J. H. (1984). Chromosome homologies in Potorous tridactylus
and P. longipes (Marsupialia : Macropodidae) based on G-banding patterns. Australian Journal of
Zoology 32, 319–324.
Kishino, H., and Hasegawa, M. (1989). Evaluation of the maximum likelihood estimate of the evolutionary
tree topologies from DNA sequence data, and the branching order in Hominoidea. Journal of Molecular
Evolution 29, 170–179.
286 E. A. Sinclair et al.
Krajewski, C., and Woods, T. C. (1995). Mitochondrial DNA relationships within the Sarus crane species
group (Gruiformes : Gruidae). Emu 95, 99–105.
Lundelius, E. L., and Turnbull, W. D. (1989). The mammalian fauna of Madura Cave, Western Australia .
Part VII: Macropodidae: Sthenurinae, Macropodinae, with a review of the marsupial portion of the
fauna. Fieldiana, Geology 17, 1–71.
Martin, P. G., and Hayman, D. L. (1966). A complex sex chromosome system in the hare wallaby
Lagorchestes conspicillatus Gould. Chromosoma (Berlin) 19, 159–175.
Matthey, R. (1973). The chromosome formulae of eutherian mammals. In ‘Cytotaxonomy and Vertebrate
Evolution’. (Eds A. B. Chiarelli and E. Capanna.) pp. 531–616. (Academic Press: London.)
Merrilees, D. (1970). A check of the radio-carbon dating of dessicated Thylacine (Marsupial ‘wolf’) and dog
tissue from Thylacine Hole, Nullarbor region, Western Australia. Helictite 8, 39–42.
Patton, D. S., and Rogers, D. L. (1993). Cytogenetics. In ‘Biology of the Heteromyidae’. (Eds H. H.
Genoways and J. H. Brown.) pp. 236–258. (The American Society of Mammalogists.)
Posada, D., and Crandall, K. A. (1998). Modeltest: testing the model of DNA substitution. Bioinformatics
14, 817–818.
Rens, W., O’Brien, P. C. M., Yang, F., Graves, J. A. M., and Ferguson-Smith, M. A. (1999). Karyotype
relationships between four distantly related marsupials revealed by reciprocal chromosome painting.
Chromosome Research 7, 461–474.
Ride, W. D. L. (1970). ‘A Guide to the Native Mammals of Australia.’ (Oxford University Press:
Rofe, R. H. (1978). G-banded chromosomes and the evolution of Macropodidae. Australian Mammalogy 2,
Rofe, R., and Hayman, D. (1985). G-banding evidence for a conserved compliment in the Marsupialia.
Cytogenetics and Cell Genetics 39, 40–50.
Seabright, M. (1971). A rapid banding technique for human chromosomes. Lancet 2, 971–972
Seebeck, J., and Johnston, P. G. (1980). Potorous longipes (Marsupialia : Macropodidae) a new species from
eastern Victoria. Australian Journal of Zoology 28, 119–134.
Sharman, G. B. (1961). The mitotic chromosomes of marsupials and their bearing on taxonomy and
phylogeny. Australian Journal of Zoology 9, 38–60.
Sharman, G. B. (1973). The chromosomes of non-eutherian mammals. In ‘Cytotaxonomy and Vertebrate
Evolution’. (Eds A. B. Chiarelli and E. Capanna.) pp. 485–530. (Academic Press: London.)
Sharman, G. B. (1989). A chromosome phylogeny of kangaroos. In ‘Kangaroos, Wallabies and Rat-
Kangaroos. Vol. 1’. (Eds G. Grigg, P. Jarman, and I. Hume.) pp. v–vii. (Surrey Beatty: Sydney.)
Sharman, G. B., and Barber, H. N. (1952). Multiple sex chromosomes in the marsupial Potorous. Heredity
6, 345–355.
Sharman, G. B., McIntosh, A. J., and Barber, H. N. (1950). Multiple sex chromosomes in the marsupials.
Nature 166, 996.
Shaw, M. W., and Krooth, R. S. (1964). The chromosomes of the Tasmanian rat-kangaroo (Potorous
tridactylus apicalis). Cytogenetics 3, 19–33.
Sinclair, E. A., and Westerman, M. (1997). Phylogenetic relationships within the genus Potorous
(Marsupialia : Potoroidae) based on allozyme electrophoresis and sequence analysis of the cytochrome b
gene. Journal of Mammalian Evolution 4, 147–161.
Sinclair, E. A., Danks, A., and Wayne, A. F. (1996). Rediscovery of Gilbert’s potoroo, Potorous tridactylus
in Western Australia. Australian Mammalogy 19, 69–72.
Strahan, R. (1995). ‘The Mammals of Australia.’ (Reed Books: Sydney.)
Sumner, A. T. (1972). A simple technique for demonstrating centromeric heterochromatin. Experimental
Cell Research 75, 304–306.
Swofford, D. L. (1999). ‘PAUP*. Phylogenetic Analysis using Parsimony and other Methods.’ (Sinauer
Associates: Sunderland, MA.)
Tamura, K., and Nei, M. (1993). Estimation of the number of nucleotide substitutions in the control region
of mitochondrial DNA in humans and chimpanzees. Molecular Biology and Evolution 10, 512–526.
Wheater R., and Roberts, S. (1987). An improved lymphocyte culture technique: deoxycytidine release of a
thymidine block and use of a constant humidity chamber for slide making. Journal of Medical Genetics
24, 113–115.
Manuscript received 16 August 1999; accepted 19 May 2000
287Chromosome morphology in Gilbert’s potoroo
... Allozyme data indicated a sister relationship between P. tridactylus and P. gilbertii, whilst the Cyt b data indicated a sister relationship between P. longipes and P. gilbertii. Chromosomal studies also supported a sister relationship between P. tridactylus and P. gilbertii, with both having a highly derived chromosome assemblage of 2n = 12 $, 13 #, whereas the karyotype of P. longipes, 2n = 24 (Johnston et al., 1984;Sinclair et al., 2000) appears little changed from the presumed ancestral macropodoid chromosome assemblage of 2n = 22 (Eldridge and Metcalfe, 2006;Westerman et al., 2010). Subsequent analyses of complete 12S rRNA and partial Cyt b sequences for all extant, and the two extinct (P. ...
... unknowingly used in phylogenetic studies, numts can obscure inter-relationships among taxa (Arctander, 1995;Thalmann et al., 2004;Zhang and Hewitt, 1996). Our findings that P. tridactylus and P. gilbertii are sister taxa is consistent with both the allozyme (Sinclair and Westerman, 1997), and chromosome data (Johnston et al., 1984;Sinclair et al., 2000). Although our data demonstrate a close relationship between P. tridactylus and P. gilbertii, it was surprising to find three highly divergent mtDNA lineages within P. tridactylus, which were paraphyletic with P. gilbertii. ...
... A further relevant question to ask is should the reproductively isolated and morphologically divergent entities be labelled as subspecies, full species, or potentially higher level again. Key literature relevant to the taxonomic and nomenclatural conclusions within this paper include Abbott (2008), Amos (1982), Bannister et al. (1988), Bee and Close (1993), Bennett (1993), Bensley (1903), Bougher and Friend (2009), Browning et al. (2001), Bryant and Krosch (2016), Burbidge and Manly (2002), Butler and Merrilees (1970), Byrne et al. (2008Byrne et al. ( , 2011, Claridge et al. (2007Claridge et al. ( , 2010, Courtney (1963), Desmarest (1804), Dexter and Murray (2009), Eldridge (1997), Eldridge and Close (1992), Eldridge and Potter (2020), Eldridge et al. (2001), Finlayson (1938), Ford (2014), Frankham et al. (2011Frankham et al. ( , 2012, Friend (2003), Groves et al. (2005), Guiler (1958, 1960, Guiler and Kitchener (1967, Gould (1841Gould ( , 1844Gould ( , 1851, Gray (1837), Heinsohn (1936), Hoke (1990), Hope (1969), Hoser (1991), Iredale and Troughton (1934), Jackson (2008), Johnson (2003), Johnston (1973), Sharman (1976, 1977), Johnston et al. (1984), Kerr (1792), Kitchener (1973), Lawlor (1979), Linné et al. (1792, Long (2001), Mahoney (1964), Mason (1997), Matschie (1916), Maxwell et al. (1996) Potter et al. (2012aPotter et al. ( , 2012bPotter et al. ( , 2012cPotter et al. ( , 2014, Ride (1970), Ride et al. (1999), Rounsevell et al. (1991), Seebeck (1991), Seebeck and Johnston (1980), Shaw (1800), Short (1998), Shortridge (1910), Sinclair and Westerman (1997), Sinclair et al. (1996Sinclair et al. ( , 2000Sinclair et al. ( , 2002, Spencer (1991), Stead-Richardson et al. (2010), Strahan (1988), Tate (1948), Thomas (1888Thomas ( , 1909, Vaughan et al. (2007), Vaughan (1986), Vaughan-Higgins et al. (2011), Vernes and Jarman (2014), Westerman et ...
ABSTRACT Potoroos within the family Potoroidae are small marsupials which were abundant at the time Europeans first came to Australia (White and Stone 1790). They have severely declined in number since. Three main species groups, all currently placed in the genus Potorous Desmarest, 1804 (type species Didelphis tridactyla Kerr, 1792) have been formally described and named, containing one putative species each based on most recently published classifications. One of these, the Long-nosed Potoroo Potorous tridactylus (Kerr, 1792) was recently subdivided into two species, namely P. gilberti (Gould, 1841) from Western Australia and P. tridactylus from eastern Australia, treated as consisting three subspecies, being the nominate form from the Central Coast of New South Wales, P. tridactylus apicalis (Gould, 1851) from Tasmania and P. tridactylus trisulcatus (McCoy, 1865) from Victoria (Frankham et al. 2012). Molecular studies have shown east Australian P. tridactylus to consist of four main divergent clades and so the unnamed one is formally named in this paper as P. waddahyamin sp. nov. based on well-known morphological divergences. Each of the four clades are also formally elevated to full species based on known dates of divergence being 1.32 and 2.45 MYA from nearest common ancestor. Of the three main species groups within the putative genus Potorous two have generic names available being Potorous and Potoroops Matschie, 1916 for the type species Hypsiprymnus platyops Gould, 1844. The third species group does not. As the molecular studies of Westerman et al. (2004) and Frankham et al. (2012) showed genus-level divergences between the groups, the unnamed one is formally named for the first time. The species Potorous longipes Seebeck and Johnston, 1980 is formally placed in the new genus Rossignolius gen. nov.. Keywords: Taxonomy; nomenclature; classification; Potoroo; Marsupials; Potoroidae; Potorous; Potoroops; Hypsiprymnus; platyops; tridactylus; trisulcatus; gilberti; apicalis; longipes; New genus; Rossignolius; new species; waddahyamin.
... This species was regarded as 'presumed extinct' (Seebeck et al. 1989), until December 1994, when it was rediscovered in the Two Peoples Bay National Park, Western Australia (Sinclair et al. 1996 ). A study of phylogenetic relationships among extant congenerics indicated Gilbert's Potoroo should be given full species status (Sinclair and Westerman 1997), and may be more closely related to P. tridactylus, based on karyotype (Sinclair et al. 2000). P. gilbertii has probably survived at Two Peoples Bay for similar reasons as the noisy scrub-bird (Atrichornis clamosus), a species that was also rediscovered in this area after being believed extinct (Webster 1962). ...
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Gilbert's Potoroo isAustralia's most critically endangeredmarsupial, known from a single population inthe Two Peoples Bay National Park in WesternAustralia. We present results from a study ofgenetic variation in microsatellite andmitochondrial DNA. Mean heterozygosity at fivemicrosatellite loci was 49.3%, and the amountof mtDNA variation was extremely low (π =0.0004). There was evidence for a bottleneckin both sets of markers, and this wasconsistent with a demographic decline. Effective population size was estimated usingtwo different models of mutation formicrosatellites (N e = 243 and 362). The results from this study highlight theconcern for the long-term survival of thisspecies.
... Thus it would seem that P. gilberti and P. longipes are genetically slightly more closely related to one another than either is to the extinct species, P. platyops. Given that P. tridactylus and P. gilberti have very similar karyotypes (2N ¼ 13#; 12$) with virtual G-band identity (Sinclair et al., 2000), the mtDNA sequence data suggest that the highly divergent karyotype seen in P. longipes (2N ¼ 24) must be one derived via a number of chromosomal fissions, and not ''ancestral'' as suggested by Johnston et al. (1984). ...
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Complete 12S rRNA and partial cytochrome b (cytb) gene sequences have been obtained from museum samples of two recently extinct potoroids-Potorous platyops and Caloprymnus campestris. Phylogenetic analyses based on these mitochondrial DNA sequences suggest that the broad-faced potoroo (P. platyops) was a close relative of the recently discovered Potorous longipes and the recently re-discovered Potorous gilberti. Although the extinct desert rat-kangaroo (C. campestris) was clearly resolved as a member of the subfamily Potoroinae, its precise relationships vis a vis other living potoroines are unclear. We confirmed that the rufous rat-kangaroo (Aepyprymnus rufescens) is sister to all living Bettongia species, but the molecular data provide no support for a sister relationship between A. rufescens and C. campestris as suggested by on the basis of four shared morphological characters. Molecular dating analyses suggest that the initial radiation of potoroinae seems to have occurred soon after its origin in the early Miocene. Within Potoroinae, C. campestris diverged from other taxa approximately 16 million years ago. P. platyops diverged from P. longipes+P. gilberti approximately 14-15 million years ago.
Comparative studies require information on phylogenetic relationships, but complete species-level phylogenetic trees of large clades are difficult to produce. One solution is to combine algorithmically many small trees into a single, larger supertree. Here we present a virtually complete, species-level phylogeny of the marsupials (Mammalia: Metatheria), built by combining 158 phylogenetic estimates published since 1980, using matrix representation with parsimony. The supertree is well resolved overall (73.7%), although resolution varies across the tree, indicating variation both in the amount of phylogenetic information available for different taxa, and the degree of conflict among phylogenetic estimates. In particular, the supertree shows poor resolution within the American marsupial taxa, reflecting a relative lack of systematic effort compared to the Australasian taxa. There are also important differences in supertrees based on source phylogenies published before 1995 and those published more recently. The supertree can be viewed as a meta-analysis of marsupial phylogenetic studies, and should be useful as a framework for phylogenetically explicit comparative studies of marsupial evolution and ecology.
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Marsupials are an ancient group of mammals that fill diverse niches in Australia, New Guinea, the East Indies and America. These species separated from eutherians around 150 million years ago and the American species diverged from the Australian species around 70 million years ago. Compared to other mammalian species, the karyotypes of marsupials are highly conserved; their diploid numbers range from 2n = 10–32 but with a predominance of 2n = 14 or 2n = 22. The first chromosome comparative studies were performed mainly by searching for similarities in G-banding patterns leading to hypotheses on the ancestral marsupial karyotype and the chromosome rearrangement mechanisms that resulted in the karyotypes seen in the extant species. The advent of chromosome painting allowed chromosome comparisons to be based on chromosome-wide sequence similarities, which is a more accurate method than the indirect method of banding analysis. This chapter is divided into six sections. The first section describes early marsupial karyotype studies performed by G-banding and introduces hypotheses on marsupial chromosome evolution. The second explains chromosome painting techniques including flow karyotyping and flow sorting, and presents results in the form of chromosome paint images and chromosome homology maps. The third section describes marsupial chromosome evolution in terms of phylogeny, ancestral karyotypes, chromosome conserved regions, and mechanisms of chromosome rearrangements. The fourth section explains the role of centromere dynamics in marsupial chromosome evolution. The fifth section focuses on recent work on the sequenced genome of the opossum. This section is followed by concluding remarks. KeywordsChromosome painting-Chromosome evolution-Centromeres-G-banding-Marsupial
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We report 1.3 kb of mitochondrial DNA (mtDNA) sequence from the cytochrome-b, tRNAThr and tRNAPro genes for Sarus Grus antigone, Brolga Grus rubicunda, White-naped Grus vipio and Japanese Grus japonensis Cranes. Previous morphological, behavioural and molecular studies have shown that the former three taxa comprise a monophyletic species group but have been unable to resolve relationships among them. Phylogenetic analysis of mtDNA sequences demonstrates that the Brolga and Whitenaped Crane haplotypes are most closely related. Estimates of the time between successive speciation events, generation time and effective population sizes suggest that there is potential for the mtDNA gene tree to differ from the species tree due to lineage sorting. Genetic divergences among haplotypes suggest that dispersal of ancestral Brolgas to Australia probably occurred in the early Pleistocene.
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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.
The ancestral mammalian karyotype had been hypothesized to have had 2n ≈ 80 (the "fusion hypothesis"), 2n = 6-14 (the "fission hypothesis") or a diploid number close to the present mode (the "modal hypothesis"). The fusion hypothesis has long been the dominant paradigm in the study of karyotype evolution, but recent evidence favors the fission hypothesis, and our analysis also strongly supports fission as the predominant rearrangement compared to fusion. To formalize our analysis, we first define $\overline A$ chromosomes as a group containing both acrocentrics and telocentrics, and $\overline M$ chromosomes as all the rest. Given this dichotomy, we then divide pericentric inversions into three types according to whether they convert $\overline A$ chromosomes to $\overline M$, $\overline M$ to $\overline A$ or make no interchange. Only the first two types, denoted p.i.$(\overline {AM})$ and p.i.$(\overline {MA})$, are important for the analysis. If fusion predominates, the direction of karyotype evolution...
The diploid chromosome number of P. tridactylus is 2n = 12 boys, 13 girls, whereas P. longipes is 2n = 24. G-banding analysis revealed that the P. tridactylus karyotype can be artificially constructed from P. longipes chromosomes by assuming one tandem fusion, five centric fusions and one pericentric inversion. It is concluded that the ancestral Potorous karyotype was similar to P. longipes (2n = 24) and that fusion events have been important in the evolution of the P. tridactylus karyotype.
Potorous longipes, sp. nov., is described from east Gippsland, Vic. It is distinguished from P. tridactylus on the basis of cranial and pedal morphology, the presence of 24 chromosomes in both sexes (cf. P. tridactylus, 12 males, 13 females ) and electrophoretic differences in blood proteins. Descriptions of its open forest habitat are provided and its distribution relative to P. tridactylus in eastern Victoria is mapped. Brief notes on maintenance of the species in captivity are given.
Considerable morphological variation exists in potoroos (genus Potorous) from south-eastern and south-western Australia. This has resulted in as many as five species being named by various workers. Univariate morphometric analyses on potoroos other than P. platyops revealed longitudinal clinal variation in body size across northern Tasmania and latitudinal clinal variation in muzzle proportions in populations from southern Queensland to southern Tasmania. Two multivariate techniques, the Penrose measure of distance and canonical analysis, based on 10 skull and dental measurements, supported the univariate analyses and also suggested the occurrence of clinal variation. On morphological grounds, it was not possible to distinguish separate taxa from south-eastern or south-western Australia. It is concluded that apart from P. platyops all potoroos belong to a single highly variable species, P. tridactylus.
Chromosome numbers of marsupials vary between 2n = 11 B 10 @ and 2n =24. Most species have 14 or 22 chromosomes. There is no evidence that polyploidy has occurred in marsupial evolution. The Dasyuridae have 12 metacentric autosomes, a small metacentric X-chromosome and a very small Y-chromosome (20% of living species have been studied) and the chromosomes of Myrmecobius fasciatus are typically like those of other Dasyuridae. The Peramelidae (30% of species have been studied) have chromosomes like the Dasyuridae except that X- and Y-chromosomes are much larger. The occurrence of similar chromosome numbers in Dasyuridae and Peramelidae is not necessarily evidence of affinity. The chromosomes of the Phascolomidae are similar in number and morphology to those of the Peramelidae and the resemblances are, almost certainly, due to parallel evolution. The chromosomes of Phascolarctos are unlike those of any of the Phalangeridae and this genus might be just as easily grouped with the Phascolomidae. The Phalangeridae have considerable chromosomal heterogeneity but less than 20% of species have been studied. Two species of Cercaertus have 12 metacentric autosomes and small sex chromosomes like all members of the Dasyuridae. This suggests that the primitive phalangers may have retained the chromosome number and morphology of possible dasyurid ancestors but the resemblances may be due to parallel evolution of similar chromosome number and morphology in separate groups. The chromosomes have been studied in more than 50% of Macropodinae. Cytological evidence suggests that Thylogale (3 species studied), Petrogale (2 species studied), and probably Lagorchestes (1 species studied), all with 22 chromosomes, are a related group. Onychogalea unguifer, with 20 chromosomes, may be derived from this group. There is no justification for the placing of Thylogale billardierii in the genus Protemnodon. Lagostrophus fasciatus has 2n = 24 and its placement in a monotypic genus is justified. Macropus major and all species of Protentnodon, except P. bicolor, are a related group with 16 chromosomes. M. robustus is possibly included in this group. M. rufus has 20 chromosomes and should perhaps be placed in the separate genus Megaleia. P. bicolor, with 11 chromosomes in the male and 10 in the female, differs from all other species of Protemnodon and this genus, as at present constituted, may be diphyletic. The relationships of P. bicolor are unknown. Setonix brachyurus has 22, mostly metacentric, chromosomes and its affinities are at present unknown. Three species of Bettongia (Potoroinae) have 22 chromosomes which are mostly metacentric. Hypsiprymnodon moschatus has 22 chromosomes which are mostly acrocentric. Both genera are very different cytologically from Potorous tridactylus.
Geographic variation in potoroos (genus Potorous) from south-eastern Australia and Tasmania was investigated by electrophoretic and chromosomal techniques. Six of the 10 potoroo blood proteins examined showed electrophoretic variation and the genetic basis of three of these was established by breeding studies. Levels of genic heterozygosity were similar in Tasmanian and mainland populations. Coefficients of genetic similarity based on 10 loci indicated that potoroos from Tasmania and the Bass Strait islands are similar to each other but different from those of mainland Australia. No chromosomal variation was observed in potoroos examined from south-eastern Australia and Tasmania. Crosses between animals from these regions produced fertile offspring. It is concluded from this study and a related investigation on morphological variation that the genus Potorous should be separated into two species, P. platyops and P. tridactylus, with the further subdivision of the latter species into P.t. tridactylus from mainland Australia (including P. gilberti) and P.t. apicalis from Tasmania and the Bass Strait islands.