Fertile Hybrids in Two Genera of Wallabies: Petrogale and Thylogale
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Fertile Hybrids in Two Genera of Wallabies:
Petrogale and Thylogale
R. L. Close and J. N. Bell
Breeding trials between karyotypically distinct species of Petrogale produced a
number of hybrids and backcross hybrids of which some of the females were fer-
tile. The only fertile male hybrid resulted from parents currently considered to be
conspeclflc, but with different karyotypes. To investigate the possibility that hy-
bridizations occur In other genera, we examined three Thylogale species, two of
which, T. thetls and T. stlgmatlca, are sympatrlc over parts of their range In eastern
coastal Australia, while the third, T. blllardlerll, is now found only In Tasmania.
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Female hybrids of T. thetls (female) x T. stlgmatlca (male) were fertile when mated
with T. stlgmatlca, but in male hybrids the testes and seminiferous tubules failed
to reach full-blood size and the tubules contained only primary spermatocytes. In
contrast, the T. stlgmatlca (female) x T. thetls (male) crosses failed to produce
hybrids. However, the only female backcross hybrid to produce young to date mat-
ed with a T. thetls. Female T. blllardlerll have not produced young with either T.
thetls or T. stlgmatlca males and T. blllardlerll males could only be caged with
conspecifics. Presumably behavioral barriers prevent regular gene flow in the wild,
but in unusual conditions of habitat change (such as after fire or forest degradation)
occasional gene transfers could be expected.
Hybrids are relatively common in the mar- netic imprinting. This article describes the
supial family Macropodidae (kangaroos array of hybrids so far obtained from Pe-
and wallabies), particularly in the rock trogale and preliminary results obtained
wallaby genus Petrogale which comprises from a study of hybrids in another closely
15 of the 44 species In the family (Close related macropod genus, Thylogale.
and Lowry 1990; Strahan 1995). Rock wal- Petrogale hybrids were first discovered
labies are small (1-10 kg), acrobatic, and in the wild in 1976 when heterozygotes
form colonies in rocky, often isolated ar- which carried the submetacentric fourth
eas throughout mainland Australia. Of the chromosome of P. herberti and an acrocen-
15 species and 6 subspecies and chromo- tric homologue typical of P. penicillata
somal races in Petrogale, 18 have unique (Figure 2), were collected from a single
karyotypes (Figures 1 and 2; Eldridge and colony at the boundary between the two
Close 1993) and many will mate in captiv- species. Spermatogenesis in a male back-
ity to produce healthy hybrids. The genus, cross hybrid was found to be apparently
therefore, provides an outstanding oppor- unaffected despite formation of a bridge
From the University of Western Sydney, Macarthur, P.O. tunity to examine the effects of different and fragment during meiosis, while female
Box 555, Campbetltown, New South Wales, Australia
2560 (Close), and the School of Biological Sciences, genotypes and karyotypes when com- heterozygotes carried pouch young (Shar-
Macquarie University, New South Wales, Australia bined in a hybrid. man et al. 1990). When next examined 10
(Bell) We thank Macquarie University for facilities and These hybrids can be used to study the years later, heterozygotes were again
R. Claassens and S. McCleod for maintaining the wal-
labies. Breeding stock was supplied by P. Johnson from effects of karyotype differences on fertili- found in the same colony, while only ho-
Queensland National Parks and Wildlife Service, ty, to detect karyotypic differences by mozygotes were obtained in neighboring
Townsvllle; G & C Smith, "Blolac"; Wildlife Park, Uni-
versity of New South Wales; Gorge Wildlife Park, South analysis of synaptonemal complexes colonies (Bee and Close 1993).
Australia; Tasmanlan Wildlife Park, Australia's Wonder- (SCs), and to study the role of chromo- Additional evidence of interspecific hy-
land, Wallacla; and Healesvllle Sanctuary. These stud- somal change on speciation (Close et al. bridization was detected from analysis of
ies were financed by grants to R.LC. from the Austra-
lian Research Council and the University ol Western 1996; Eldridge et al. 1988). Given the de- allozyme data from western Petrogale. Cer-
Sydney, Macarthur. This paper was delivered at a sym- gree of both genetic and karyotypic differ- tain alleles appeared to have crossed the
posium entitled "Interspecies Hybrids In Mammals" In
association with the New Zealand Genetlcal Society ences among Petrogale (Bee and Close chromosomal boundaries of karyotypical-
and Australasian Gene Mapping Workshop In Dunedln, 1993; Eldridge and Close 1993; Sharman et ly and physically distinct species (Briscoe
New Zealand, from November 30-December 1, 1995. al. 1990), the hybrids also provide an op- et al. 1982). Additional electrophoretic
Journal of Heredity 1997;8&393-397; 0022-15O3/97/$5.00 portunity to study gene mapping and ge- studies are consistent with this finding
393tao* 130"
ware
I testes. If male hybrids showed significant
concinna testicular growth, they were then housed
coenensls with a parous, full-blood female. Subse-
godmani quently one testis was removed, prepared
burbidgei
mareeba for sectioning, and compared with testes
from proven sires as described in Close et
sharmani
assimilis
al. (1996). Ovaries from adult females were
persephone obtained whenever possible at death for
histological examination. Many of the
inornata - 20'
young female hybrids were removed from
herberti
the pouch at age 70 days for the study of
SCs from pachytene spreads (Close et al.
1996). Detailed descriptions of these SCs
and also of the histological studies will be
published in a subsequent article.
Where possible, reciprocal crosses were
— 30'S
set up; however, the difficulties in obtain-
ing and maintaining Petrogale breeding
stock sometimes made this difficult. Simi-
larly, we were often unable to obtain mul-
tiple hybrids of the same admixture.
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Results
Figure 1. Distributions of species, subspecies, and chromosome races of Petrogale. Currently hackelti, pearsont,
purpureicollis, W. Klmberley, and MacDonnell Range races are all included In P. laleralis, and celeris Is a subspecies Petrogale
of P xanlhopus.
Tables 1 and 2 give details of the Petrogale
hybrids and backcross hybrids produced,
(Briscoe DA, unpublished data). Subse- dierii, still occurs in Tasmania. Preliminary the number removed for SC analysis and
quent searches of contact zones among results of fertility trials in this study are other studies, the number that survived to
eastern Petrogale have revealed another reported here. maturity, and the fertility of the survivors
boundary marked by chromosomal heter- in terms of the number of pouch young
ozygotes (P. godmani/P. mareeba) and sev- produced. The sex ratio of the F, hybrids
Materials and Methods
eral with allozyme evidence of recent in- was close to 1:1 (31 females:29 males), but
trogression (Bee and Close 1993). Hybrid- Full-blood stock for Petrogale were ob- that in backcross hybrids was skewed (13
ization therefore appears to have had a tained by capture in the field, by hand- females:2 males).
major influence on rock wallaby specia- raising pouch young from animals collect- Of the six categories of cross in which
tlon, with the present distribution of dif- ed for other purposes, and from zoos. Thy- F, female hybrids survived to maturity,
ferent chromosomal arrangements due logale are difficult to trap, so stock were four have produced young. One of these
partly to introgression of some arrange- obtained from zoos or research establish- four hybrids, P. assimilis x P. mareeba,
ments into neighboring taxa (Eldridge and ments. Petrogale were maintained In cov- was fertile despite heterozygoslty involv-
Close 1993; Sharman et al. 1990). ered enclosures described in Close and ing a complex pentavalent involving a cen-
As the extent of hybridization within the Bell (1990), while Thylogale were kept in tric shift, two centric fusions, and a large
genus became more obvious, the question grassed yards 35 m x 10 m. One Petrogale inversion (Figure 2; Eldridge et al. 1988).
arose whether hybridization may also be male was housed with one or two Petro- The parental species of this cross are dif-
a feature of other genera in the family. gale females, while several female Thylo- ficult to distinguish in the field and have
Studies were therefore set up with small, gale were housed with each Thylogale adjacent distributions (Eldridge and Close
forest wallabies (genus Thylogale), which male. Females were caught regularly with 1992). By comparison, the chromosome
share with some Petrogale the ancestral hand nets and their pouches inspected for differences between parental species of
autosomal pattern in a 2N = 22 karyotype presence of pouch young. Output of Petro- the fertile P. assimilis x P penicillata cross
(Figure 2), but each species differs in the gale young was increased by transferring are less extreme but the physical differ-
shape of the X chromosome. Of the three pouch young to the pouches of foster ences are greater and there Is a significant
species which formerly occurred in the mothers of another species, the tammar geographic separation. The parental spe-
eastern coastal areas of Australia, now wallaby (Macropus eugenii).Such transfers cies of the third fertile hybrid, P. I. pear-
only two remain. These two, T. thetis and allowed a quiescent blastocyst to develop, soni x P I. MacDonnell Ranges race, are
T. stigmatica, are sympatric for 500 km in resulting in another birth in 30 days. currently placed in the same species yet
northern New South Wales and southern Sexual maturity of females (usually at differ by a single chromosome centric
Queensland, with T. thetis extending south 18-20 months) was indicated by eversion shift (Figure 2) and are physically differ-
and T. stigmatica north. Both inhabit rain of the teats. Fertility of hybrid females was ent. SCs of 70-day-old females of the same
forest and individuals of each species tested by housing them with males of the cross and the reciprocal cross showed
come together in small feeding groups at parental stocks to await progeny. Widths high levels of asynapsis (Dollin AE, unpub-
forest edges (Johnson 1977; Johnson and of the testes of male hybrids were mea- lished data). One male hybrid of the same
Vernes 1994). The third species, T. billar- sured monthly with calipers across both parental type is fertile. Parental species of
3 9 4 The Journal of Heredity 1997 88(5)1 2 3 4 5 6 7 8 9 10 fore the age of 4 years, but produced none
in her last 30 months.
Ancestral autosome karyotype Thylogale
e.g. P.xanthopus, P.x.celerls, Table 3 shows the results of the crosses
P.persephone, P.lateralis, set up among the three species. Only the
P.l.pearsoni and Thylogale species T. thetis x T. stigmatica cross produced
young. Although no young resulted from
cc cc cc T. stigmatica x T. thetis attempts, one mat-
P./.MacDonnell P.l.purpurelcollis ing was observed over a 2 day period.
Both male T. thetis used in the trials sired
young with T. thetis females, and one pro-
(( CC CC (( Ci (I I \ CI ([ CC
P.herberti duced young with a backcross hybrid (T.
thetis x T. stigmatica x T. stigmatica). Hy-
brid females mated successfully with T.
II CC CC CC CC CC CC CC 11 stigmatica males. Male T. billardierii were
P. penicillata harassed by females of the other species
and they could not be housed together. Fe-
male T. billardierii caged with T. thetis or
II CC CC CC A CC CC CC tC T. stigmatica did not produce young and
P. sharmani elicited no further response from the
males after a first examination.
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5-10 Of the 29 F, hybrids produced, 13 were
CC CI CC CC CC II II CC females and 16 were males. Ten were re-
P. mareeba
moved for SC analysis and other studies,
one died in the pouch and four before ma-
turity, while four are still immature. In the
five hybrid females that have reached ma-
CC U CC CC CC II CC
P. asslmilis turity, teats everted at a mean age of 11.5
months and the first births occurred at a
mean age of 16.6 months. This compares
5lnv 6-10 with 12.3 months for teat eversion and
19.1 months for first birth for T. thetis
CC II CI CC IC IC CC CC
P. godmani (Johnson 1977), while T. stigmatica can
produce young at 11 months (Johnson
and Vernes 1994). Seven backcross female
6-10a and two male hybrids have been pro-
duced, of which four females and two im-
II f I CC II IC II mature males have survived. The teats of
P. Inornata the one mature female everted at 11
months, but she has produced no young
Figure 2. Autosomal karyotypes of the species, subspecies, and chromosome races of Petrogale referred to In when paired first with T. stigmatica and
this article. Sex chromosomes that are polymorphic In some taxa are not Included, nor Is the variation that exists then T. thetis males.
among the taxa In the distribution of euchromatlc small arms on some chromosomes (see Eldridge and Close 1992;
Eldridge et al. 1992; Sharman et al. 1990).
For three hybrid males, testes reached
maximum size at 13, 16, and 20 months
but final testes dimensions were smaller
the fourth cross, P. persephone X P. xan- grandsire to produce two female offspring, than for full-blood T. thetis and T. stigmati-
thopus, have more extreme physical differ- still immature (Table 1). ca which are mature at 11 and 13 months,
ences than do the other parental species Despite the production of fertile hybrids respectively (Johnson 1977; Johnson and
and ecologically are quite distinct; P. per- from a variety of parental types, female Vernes 1994). At 16 months the scrotal
sephone resides in moist, forested areas fertility was not universal. Only one of the widths of two hybrids were 25 and 24 mm
on the Queensland coast, while P. xantho- two P. assimilis x P. mareeba females pro- and showed no further increase, com-
pus is a creature of the dry inland. Both duced young; the other, age 6 years, was pared to 29 mm for a full-blood T. stigma-
parental species, however, share the an- found to have two large cysts in one ovary tica which increased to 34 mm at age 25
cestral karyotype and differ only In their and polyps on the other. Another nonpa- months. Light microscope analysis of sem-
sex chromosomes and in P. xanthopus hav- rous female (P. inornata x P purpureicol- iniferous tubules in the hybrids showed
ing small C-banding regions in chromo- Us), age 60 months, had ovaries with cor- only a few primary spermatocytes, and
somes 6 and 8 (Sharman et al. 1990). pora lutea but mainly consisted of connec- mean diameters of the tubules for three
The two fertile female offspring of the tive tissue (Rodgers JC, unpublished hybrids were 0.12, 0.12, and 0.13 mm.
latter F, hybrid produced six young when data). Parous hybrids may not have been These diameters are significantly different
backcrossed to their own father. One of fully fertile; the P. persephone x P. xantho- from values for T. stigmatica (0.22 mm) and
these young has now mated with its pus female produced her three young be- T. thetis (0.22 mm, 0.23 mm) full-bloods.
Close and Bell • Wallaby Hybridization 3 9 5Table 1. Petrogale hybrid* produced and resultant fertility
No. of offspring No. surviving
Female parent Male parent (Female/Male/?) (Female/Male) Fertility
assimilis mareeba 3(1 rem-)/0 2/0 (36 mo) 2 py; (72 mo) 0 py
mareeba assimilis 0/5(3 rem) 0/1 Infertile*
mareeba sharmani 3/2 0/1 Infertile*4
assimilis sharmani 0/2(1 rem) 0/1 Infertile**
assimilis X mareeba assimilis 1/0 0/0
inomata assimilis 0/1 0/1 Infertile*
assimilis inornata 0/1 0/1 Still Immature
inomata purpureicollis 1/0 1/0 (60 mo) 0 py
assimilis X mareeba penicillala 0/0/1 0/0
mareeba penicillata 6(4 renr)/7/l 0/2 Both Infertile
mareeba herberti 0/2 0/1 Infertile
assimilis penicillata 5(4 renr)/l 1/1 F(48 mo) 2 py; M Infertile
assimilis x penicillata penicillata 2/1 0/0
herberti penicillata 2 rem72/3 0/0
purpureicollis penicillata 2 renv/O 0/0
purpureicollis L MacD 2 renr/0 0/0
I MacD assimilis 1/1 1/1 F(22 mo) 0 py; M Infertile
/. MacD L pearsom 3(1 renr)/2/5 2/2 2F(32/24 mo) 0 py
2M(60/30 mo); 1 fertile
/ pearsoni X / MacD inomata 0/0/1 0/0/1 Immature
/ pearsoni L MacD. 1 rem73(l rem) 0/0
I pearsoni L pearsom X /. MacD 1/0/1 0/0
persephone xanthopus 2/0 1/0 (78 mo) 3 py
persephone X xanthopus x celens 2/1 2/0 2F(42/36 mo) 3 py each
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persephone X xanthopus X celens x celeris 5/0/1 2/0 (22 mo) 2 py; 1 Immature
persephone X xanthopus X celeris X celens x celens 2/0 2/0 Both Immature
° Published in Eldridge et al. (1988).
' Close etal. (1996).
c
Germ tissue taken for SC analysis.
? = disappeared from pouch before sex could be determined; py = pouch young; rem = pouch young removed from pouch; (xx mo) = age in months at death, or current
age.
Discussion rare, or absent, then that sex will be the Only one male hybrid has produced
heterogametlc one (Haldane 1922). These young. SC analysis of oocytes from female
These studies of hybridization In two gen-
results conformed to Haldane's law in two hybrids of the same cross (P. I. pearsoni x
era of macropod demonstrate that fertile ways. First, although sex ratios for F,
hybrids may result from parental species P. I. MacDonnell Ranges race) showed high
crosses were not significantly different rates of asynapsis (Dollin AE, unpublished
that differ markedly in genotype and from 1:1, the ratios for backcross hybrids
karyotype. In Petrogale, the parental spe- data), a feature associated with infertility
in both genera favored females, that is, 13: in male Petrogale (Close et al. 1996) and in
cies were all parapatric or sympatric, 2 for Petrogale and 7:2 for Thylogale. Al-
whereas in Thylogale, the parental species other species (Gustavsson et al. 1988; Lu-
though the mortality of hybrid young was ciani et al. 1984). One mature female hy-
were sympatric. However, the only back- high among those allowed to develop to
cross hybrids that have produced surviv- brid of the same cross produced her first
maturity, no particular sex was favored young at age 26 months, while another
ing, fertile young were those involving P. among the survivors. Second, in crosses
persephone, P. xanthopus, and P. x. celeris. (age 37 months) has not yet produced
between recognized species where a hy-
These taxa share similar autosomes and young. This instance of apparent female
brid was fertile, that hybrid was female.
the karyotypes of the latter two are iden- subfertility and male fertility may be an
Some female hybrids, however, failed to
tical (Sharman et al. 1990). Furthermore, produce young. Although conditions of exception to Haldane's law and will be ex-
only female backcrosses have survived to captivity may inhibit conception in other- amined more closely. As the parental taxa
maturity. Hence the long-term transmis- wise fertile female hybrids, two nonparous are considered to be subspecies, the phys-
sion of alleles after hybridization of taxa females had abnormalities of the ovaries, ical differences being small and the karyo-
which differ markedly in karyotypes is not and a fertile female bred only when young. typic differences relatively minor, further
known. This finding is consistent with field obser- examination of the relationship between
Most of the results were consistent with vations in which female backcross hybrids asynapsis in female meiosis and fertility in
Haldane's law which holds that if in a of P. godmani x P. mareeba were subfertile the hybrids could also shed light on the
cross between two taxa, one sex is sterile, (Briscoe et al. 1982). role of chromosome changes in specia-
tion. SCs will also be examined from the
male hybrids.
Table 2. Summary of Petrogale hybrid* produced
Results from the Thylogale crosses were
Sex Died consistent with Haldane's law; that is, only
Died In alter Sam-
No. Females Males Unknown Survived pouch pouch pled the female hybrids were fertile and the
males produced no sperm. This is in con-
F, hybrid 69 31 29 9 20 22 5 22
trast to some of the Petrogale hybrids in
Backcross (generation 2, 3, 4) 19 13 2 4 7 8 4 0
Full-blood 32 13 14 5 11 12 7 2 which spermatogenesis proceeded to dif-
ferent stages depending on the parental
3 9 6 The Journal of Heredity 199788(5)Table 3. Breeding of Thyiogale species
Female parent Male parent No. of females used Fertility of hybrids
T. thelis T. stigmatica 6 13 F, 16 M hybrids; females fertile; males Infertile
T. stigmatica T. thetis 6 0 hybrids produced
T. billardierii T. stigmalica 1 0 hybrids produced
T. billardierii T. thetis 1 0 hybrids produced
T. stigmatica T. billardierii 3 0 hybrids produced
T. thelis T. billardterit 3 0 hybrids produced
T. thetis x T. stigmatica T. stigmatica 5 7 F, 2 M hybrids; fertility not yet known
T. thetis X T. stigmatica X T. stigmatica T. stigmatica 1 0 hybrids produced
T thetis X T. stigmatica X T. stigmatica T. thetis 1 1 hybrid produced
species, and the extent of dysfunction was considered more seriously as a manage- Close RL and Lowry PS, 1990 Hybrids In marsupial re-
search. Austral J Zool 37:259-267.
associated with the degree of chromosom- ment tool for wild and captive manage-
al heterozygosity (Close et al. 1996). Infer- ment of species. There has been a tenden- Eldridge MDB and Close RL, 1992. Taxonomy of rock
wallabies, Petrogale (Marsuplalla: Macropodidae). 1. A
tility in the Thyiogale male hybrids, how- cy for zoos to reject hybrids when per- revision of the eastern Petrogale with the description
ever, cannot be associated with autosomal haps they should be viewing them as res- of three new species. Austral J Zool 40:605-625.
heterozygosity unless internal karyotypic ervoirs of genetic variation and safeguards Eldridge MDB and Close RL, 1993. Radiation of chro-
changes have occurred which are not de- against genetic bottlenecks. Similarly, rein- mosome shulOes. Curr Opln Genet Dev 3:915-922.
tectable in the gross or G-banded karyo- troductions to the wild may be more suc- Eldridge MDB, Dollln AE, Johnston PG, Close RL, and
type (Eldridge et al. 1992). Murray JD, 1988. Chromosomal rearrangements In rock
cessful if the founding stock is heterozy- wallabies, Petrogale (Marsuplalia, Macropodidae). I.
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Behavioral cues appear to prevent mat- gous for many alleles. Most reintroduc- The Petrogale assimihs species complex: G-bandlng and
ing between T. billardierii and congenerics. tions will occur in places where the origi- synaptonemal complex analysis. Cytogenet Cell Genet
48:228-232.
Although T. billardierii is now confined to nal genetic stock is extinct and the new
Tasmania and smaller islands, it once stock is only a genetic approximation, at Eldridge MDB, Johnston PG, and Close RL, 1992. Chro-
mosomal rearrangements In rock wallabies, Petrogale
lived on the mainland and may have had best, of the original animals. The replace- (Marsupialia- Macropodidae). VI. Determination of the
contact with T. thetis and T. stigmatica. The ment animals will be released into an en- pleslomorphlc karyotype: C-banding comparison of
Thyiogale with Petrogale persephone, P. xanthopus, and
latter two species remain in contact over vironment that is probably different from P. I. lateralis. Cytogenet Cell Genet 6129-33.
500 km, yet behavioral reproductive iso- that to which the original stock was adapt-
lating mechanisms have not developed to Gustavsson I, Switoflsld M, Larsson K, and PI6en L,
ed. Perhaps we should be giving the new 1988. Synaptonemal complex analysis of spermato-
the same degree as those for T. billardierii. pioneers the maximum genetic chance. cytes In hybrids of silver and blue fox. J Hered 79:338-
Although conditions of captivity may Natural selection will surely use the more 343
mask isolating mechanisms that usually colorful palette to produce its own picture Haldane JBS, 1922. Sex-ratio and unisexual sterility In
operate in the wild, the ecology of the two of the new survivors. hybrid animals J Genet 12:101-109.
species is such that conditions resembling Johnson KA, 1977. Ecology and management of the red-
captivity may occasionally arise. That is, necked pademelon, Thyiogale thetis, on the Dorrlgo pla-
teau of northern New South Wales (PhD dissertation).
both species are known to inhabit the Reference* Armidale, New South Wales: University of New England.
same forest, and in conditions of forest Bee CA and Close RL, 1993. Mltochondrlal DNA analysis Johnson PM and Vernes K, 1994 Reproduction In the
diminution such as may occur after fires, of introgression between adjacent taxa of rock-walla- red-legged pademelon, Thyiogale stigmatica Gould
bles, Petrogale specie* (Marsuplalla: Macropodidae). (Marsupialia: Macropodidae), and age estimation and
climate change, or human intervention, Genet Res (Cambr) 61:21-37. development of pouch young. Wlldl Res 21:553-558.
small numbers of each species might be Briscoe DAB, Calaby JH, Close RL, Maynes GM, Mur-
forced together. Similarly, individuals of tagh CE, and Sharman GB, 1982. Isolation, Introgression Luclanl JM, Gulchaoua MR, Mattel A, and Morarzanl
MR, 1984. Pachytene analysis of a man with a 13q,14q
two Petrogale species may occasionally be and genetic variation In rock-wallabies. In: Species at translocatlon and Infertility. Behaviour of the trlvalent
risk: research In Australia (Groves RH and Ride WDR,
isolated together on small rock outcrops. eds). Canberra: Australian Academy of Science; 73-87. and non-random association with the sex vesicle. Cy-
Under such conditions of ecological up- Close RL and Bell JN, 1990. Age estimation of pouch togenet Cell Genet 38:14-22.
heaval and low population size, an occa- young of the allied rock-wallaby (Petrogale assimilis~) in Sharman GB, Close RL, and Maynes GM, 1990. Chro-
sional hybridization may actually benefit captivity. Austral Wlldl Res 17359-367. mosome evolution, phylogeny and speciatlon of rock
wallabies (Petrogale: Macropodidae). Austral J Zool 37:
the local population and perhaps the spe- Close RL, Bell JN, Dollln AE, and Harding HR, 1996. 351-363.
Spermatogenesls and synaptonemal complexes of hy-
cies itself. brid rock wallabies, Petrogale (Marsuplalia: Macropod- Strahan R (ed.), 1995. The mammals of Australia. Syd-
It is perhaps time that hybridization be idae). J Hered 8756-107. ney: Australian Museum/Reed Books.
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