Aust. J. Zool., 1983, 31, 723-41
Karyotypic Evolution in Gehyra
(Gekkonidae:Reptilia)
III.* The Gehyra australis Complex
Max King
Department of Population Biology, Research School of Biological Sciences, Australian National
University, Canberra, A.C.T. 2601.
Abstract
A karyotypic analysis of the widely distributed Australian gekko Gehyra australis has revealed a
complex of chromosome races. Each of these is fixed for a particular karyomorph, and is found over a
geographically delimited distribution. The seven chromosome races differ by number, or chromosome
morphology, and are defined as: 2n = 44,2n = 42a, 2n = 42b, 2n = 42c, 2n = 40a, 2n = 40b, 2n = 38. In
addition, a series of animals from these races possess novel chromosome rearrangements. A model for
the evolution of this complex of races is proposed, and the relationship ofthese forms to each other and
to members of the Gehyra variegata-punctata complex is discussed.
Introduction
It is now clear that chromosome evolution in terms of gross chromosomal change has
been far more extensive in some reptilian lineages than in others. In the Iguanidae,
Agamidae and Lacertidae many species share a karyotype format common to that group.
Thus, most iguanids have a 12V 24m karyotype with 2n = 36; most Australian agamids
have 2n = 32 made up of 12V 20m elements, and most Lacertidae have 2n = 38 all
acrocentric chromosomes (see Gorman 1973; King 1981a). However, some species within
these families do show interspecific variation in their karyotype morphology attributable to
fusion, fission or pericentric inversion.
Considerable intraspecific chromosome variation is also present in certain groups of
lizards. This variation is expressed in the form of chromosome races, polymorphisms, sex
chromosome races and rare mutant animals, and is most commonly found in certain iguanid
and gekkonid lizards. Indeed, more chromosome race variation has been encountered in the
Australian Gekkonidae than in any other group of reptiles, with species from the genera
Diplodactylus [D. tessellatus, 2n = 28, 38 (King 1982a); D. vittatus, 2n = 38A, 38B, 38C, 34,
36 (King 1977a)], Phyllodactylus [P. marmoratus, 2n= 36, 36ZW, 34, 32 (King and Rofe
1976; King and King 1977)] and Hemidactylus [H. frenatus, 2n=46, 40 (King 1978)l
providing striking examples of the situation.
Perhaps the most interesting genus in terms of its chromosome race diversity is Gehyra.
In an analysis of the G. variegata-punctata complex, King (1979) found that there were five
chromosome races (2n = 44, 42, 40a, 40b, 38) each of which was allopatrically distributed.
Specimens from these races also showed characteristic differences in their external
morphology. In an analysis of specimens of Gehyra australis from a relatively restricted area,
King (1982b) was able to show that two chromosomally distinct forms were present (2n = 40
and 2n = 42) and that these were morphologically distinguishable.
+
+
* Part 11, Aust. J. Zool., 1982, 30, 93-101.
004-959X/83/050723$02.00
Max King
The present paper presents the results of a detailed karyotypic analysis of Gehyra
australis throughout its Australian distribution; the distributions of the karyoptypic variants
are described; and the evolutionary, phylogenetic and taxonomic implications are
considered.
Materials and Methods
In this study a total of 81 specimens collected from 40 localities were karyotyped (see Fig. 1;
Table 1).
Chromosomes were obtained from each specimen by means of intestinal epithelial preparations. In
males, testis preparations were also made. The air-drying techniques used are described in detail by
King and Rofe (1976). At least 10 cells were examined from each individual to ascertain chromosome
number and morphology.
All specimens used in this study have been preserved for morphometric analysis and will be lodged
in the relevant State museum collections.
EZ8 G.xenopus
Storr
Fig. 1. Map showing the approximate distribution of the chromosome races of G. australis. The
closely related G. xenopus is also included. Precise localities of specimens are shown in Table 1.
Results
Gehyra australis Gray shows considerable karyotypic variation throughout its mainland
distribution. This occurs in two forms. First, a series of chromosome races are present, each
of which is fixed for a particular karyomorph and occurs over a defined geographic
distribution. Second, animals possessing novel chromosome rearrangements occur as
population isolates, as rare mutants, or as a polymorphism.
Karyotypic Evolution in Gehyra. I11
The Chromosome Races
Seven chromosome races were encountered: 2n = 44, 2n = 42a, 2n = 42b, 2n = 42c,
2n = 40a, 2n = 40b and 2n = 38. A description of the karyotypes and their distribution
follows:
Table 1. Localities of specimens of Gehyra australis analysed
2n
d
100 km E. of Mt Isa, Qld
17 km S. of Dismal Crossing, Qld
55 km NW. of Mt Isa, qld
36 km E, of Mt Isa, Qld
5 km NW. of Dajarra, Qld
4 km W, of Cloncurry, Qld
26 km S. of Dajarra, Qld
38 km E. of Georgetown, Qld
7 km E. of Croydon, Qld
Macquarie Marshes, N X W .
47 km W. of Mt Garnet, Qld
Lizard I., Qld
Edward River Mission, Qld
Pilliga Scrub, N X W .
Townsville, Qld
Lions Den Hotel, Helenvale, Qld
Hewcamp Creek, Qld
2.3 km W. Horseshoe Bay, Magnetic I., Qld
Picnic Bay, Magnetic I., Qld
Grosvenor Creek, Qld
7 km N. of Ellis Reach, Cairns, Qld
Batavia Downs, Qld
Mapoon Mission, Qld
Urapunga, N.T.
Cannon Hill, N.T.
Nourlangie Rock, N.T.
Bullo River, N.T.
Manning Gorge, W.A.
32 km E. of Napier Downs turnoff, W.A.
Barnett Range, W.A.
37 km W. of Balbirini Jn, N.T.
4 km S. of Balbirini Jn, N.T.
Dilldoll Rock
Bing Bong HS., N.T.
Kununurra Hotel, W.A.
Timber Creek Inn, N.T.
Liverpool R., N.T.
Lammah Hotel, N.T.
Berrimah CSIRO, N.T.
Nourlangie Camp, N.T.
Yirrkala, Gove, N.T.
42b
426
42b
42b
42b
42b
42b
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42c
42a
42a
42a
42a
44
44
44
38
38
40b
40a
40a
40a
40a
40a
40a
40a
40a
No. of specimens
Imm.
9
1
1
1
Type of variant
1 (Het. C.F. 2n=41)
1
1
3
2
1
-
1 (1 Het. C.F. 2n=41)
3
1
-
1
1
-
-
1
-
-
-
1
-
-
-
-
1
-
-
1
I
1
1
1
-
-
-
1
1
1
1
-
-
1
-
-
1
1
1
1
-
-
-
-
-
1
1
-
-
-
1
3
1
-
-
-
-
-
-
-
-
1
1
1
-
-
-
-
-
1
-
7
1
1
1
1
2
-
1
4
1
1
-
1 (Het. P. inv. 2n =41)
-
1
1
1
2
-
1 (Het. C.F. 2n =41)
1
-
1 (Het. C.F. 2n=41)
1 (Het. C.F. 2n = 37)
1
-
-
-
-
1
1
1
-
-
-
4
2
1 (Het. C.F. 2n= 39)
Z W Het.
Z W Het.
-
Total
Grand total, 81
2n = 44. Specimens from this chromosome race appear to be rock-dwelling, and are
restricted to the central Kimberley district of Western Australia. Their distribution is
bounded by G, xenopus Storr on the west, and by the 2n = 40a race to the east. Only three
specimens from this chromosome race were examined, all of which had 2n =44, with a
basically acrocentric karyotype except for pairs 14 and 17, which were metacentric and submetacentric respectively. A secondary constriction was often observed on chromosome pair
10 (Fig. 2).
Max King
2n=42a. This chromosome race was recently described as Gehyra pamela on
morphological grounds (King 1982b). Specimens with this karyomorph were first thought to
be restricted to the Arnhem Land escarpment. However, it is now clear that this
chromosome race has a wider distribution, occurring in isolated populations as far south as
the Roper River and as far west as the Bullo River (Fig. 1). This is also an essentially
rock-dwelling form. The karyotype is acrocentric, although pair 17 appears to be submetacentric in some preparations; however, it is not certain if this is a product of resolution or a
polymorphism. Size diminishes gradually from the largest to the smallest elements (King
1982b, fig. 3). The short arms on the larger chromosomes appear to be shorter than those in
the 2n = 44 karyotype. Sex chromosomes were not detected.
2n = 42b. A large number of specimens from this rock-dwelling chromosome race have
been analysed. Specimens are restricted in their distribution to the mountain ranges in
central western Queensland including the towns of Mt Isa, Cloncurry, Dismal Crossing and
Dajana (Fig. 1). These animals are morphologically very distinctive and appear to be
allopatrically distributed. Rock outcrops surrounding the above-mentioned sites are
inhabited by small specimens of Gehyra variegata (King 1979). The karyotype of this
chromosome race is very similar to that of the 2n = 42a type, being basically acrocentric but
for pair 17 which is submetacentric. In some cells the centromeric areas on the larger
elements appear to be achromatic (Fig. 3). Heteromorphic sex chromosomes were not
observed.
2n = 42c. This chromosome race is very widespread and animals can live on either rocks,
trees, or human habitations. It is distributed from the tip of Cape York peninsula in
Queensland, south to just over the Queensland border with New South Wales. It also reaches
the Gulf of Carpentaria in the west (Fig. 1). The karyotype is acrocentric but for the
metacentric pair 14 and submetacentric 17. Pair 3 is acrocentric, but has a pronounced short
arm and appears to be the product ofa fusion between pairs 5 and 22 ofthe 2n = 44 karyotype
(Fig. 4). A distinct secondary constriction is present on chromosome pair 10. No
morphologically recognizable sex chromosomes were encountered.
2n = 40a. Specimens from this widespread chromosome race live on trees or human
habitations. They are distributed from Lake Argyle in Western Australia, in a broad band
eastward to Bing Bong station, at the base of the Gulf of Carpentaria (Fig. 1). The
chromosomes are acrocentric with a gradual diminution in size from the largest to the
smallest elements (King 1982b, fig. 2). Sex chromosomes were present in several populations
and will be more fully described below.
2n = 40b. Only two specimens from this geographically remote, rock-dwelling Gehyra
were collected. The specimens were found on an isolated rock outcrop at the base ofthe Gulf
of Carpentaria (Fig. 1). In both cases the karyotype has 2n = 40 chromosomes, the first pair
ofwhich is submetacentric and appear to be the product of a fusion between pairs 5 and 19 of
a 2n=42 ancestral karyotype. The remainder of the karyotype is acrocentric (Fig. 5).
Sex-related differences between chromosomes were not found.
2n = 38. This rock-dwelling chromosome race is also geographically restricted, occurring
in the outcrops and mountain ranges associated with the MacArthur River system at the
base of the Gulf of Carpentaria (Fig. 1). The karyotype has 2n = 38 elements, all of which are
acrocentric but for pairs 5 and 8. Pair 17 is submetacentric (Fig. 6). Chromosome pair 5
appears to be the product of a fusion between pairs 6 and 18 of an ancestral 2n=42
karyotype, whereas pair 8 appear to be the product of a fusion between pairs 16 and 20 in a
similar ancestral karyotype. The submetacentric pair 17 is a marker chromosome found in
this race and in the 2n = 44, 2n = 42b and 2n = 42c chromosome races. No sex-correlated
chromosome heteromorphism was observed.
Karyotypic Evolution in Gehyra. 111
Fig. 2. The 2n = 44 chromosome race karyotype. This complement is very similar to that of members
the G. variegata-punctata complex (King 1979).
Fig. 3. The 2n = 42b chromosome race karyotype. Note the achromatic centromeric areas (arrowed)
pair.s 1 and 2.
Max IOng
Fig. 4. The 2n = 42c chromosome race karyotype. Note chromosome pair 3 (underlined) which is a
presumed fusion product. The pair 10 secondary constriction is arrowed.
Fig. 5. The 2n = 40b chromosome race karyotype. Note the submetacentric pair 1 (underlined) which is
a presumed fusion product.
Karyotypic Evolution in Gehyra. 111
Fig. 6. The 2n = 38 chromosome race karyotype. Note the metacentric pairs 5 and 8 (underlined) which
are presumed fusion products.
Fig. 7. A 2n = 42c karyotype ofan animal heteromorphic for a pair 7 pericentric inversion (underlined),
The pair 10 secondary constrictions are arrowed.
Max King
Variants Within Chromosome Races
This variation takes two forms. First, in the 2n = 40a race certain populations had a
ZZ/Z W sex chromosome heteromorphism. This was more fully described in King (1977b)
and is characterized by a large W-chromosome in female specimens. The Z-chromosome is
typically acrocentric, whereas the Wis larger and submetacentric. The short arm ofthe Wis
C-band positive and appears to represent additional material. The male karyotype, which is
indistinguishable from other members of the 2n=40a race, has normal acrocentric
Z-chromosomes (pair 1).
The second form of variation is quite striking and is relatively frequent. A series of seven
specimens from different chromosome races were heterozygous for previously undetected
chromosome rearrangements. Six of these animals were heterozygous for chromosome
fusions and one for a pericentric inversion. In each case a different size group of
chromosome was involved in the rearrangement (see Figs 7-9); this was observed in four
different chromosome races, namely 2n = 42b, 2n = 42c, 2n = 40a and 2n = 38. Three of
these novel rearrangements were seen at disparate localities in the 2n = 42b race, two in the
2n = 40a race, one in the 2n = 42crace and one in the 2n = 38 race. Only heterozygotes for the
changes, and standard homozygotes, were observed. Homozygotes of the derived form were
not encountered and different chromosomes appeared to be implicated in each fusion.
Although samples were small in most instances, a series of eight animals from a population
of the 2n=38 race on a small isolated rock outcrop were scored, one of which was
heterozygous for a chromosome fusion (2n = 37), all others being normal (Fig. 8).
Novel rearrangements have also been reported in G. pilbara and in the G. variegatapunctata complex (King 1979; and Table 2).
Table 2. Numbers of specimens of Gehyra species karyotyped, and the degree of chromosomal
divergence
Taxon
G. variegatapunctata
G. pilbara
G, austrahs
Yo. of specimens
karyotyped
250
6
81
No. of chromosome races
No. of novel
rearrangements
6
1
7
Reference
King 1979:
unpublished
Unpublished
This paper
Discussion
Chromosome Evolution
(i) Chromosome race differentiation
The predominant means of gross chromosomal rearrangement observed in most
vertebrate species has involved the evolutionary increase or decrease in chromosome
number. This pattern has been seen in organisms as diverse as the marsupials (Hayman and
Martin 1974), rodents (Matthey 1973; Capanna et al. 1977; Baverstock et al. 1979) and
crocodiles (Cohen and Gans 1970). In the majority of these cases, change in number is the
result of chromosome fusion or fission.
In the lizard species thus far karyotyped both fusion and fission have also been used to
explain many of the chromosome number differences described. Thus, in the North
American iguanid genus Sceloporus, Webster et al. (1972), Hall and Selander (1973) and Paul
et al. (1976) have all argued for chromosome change based on fission, although presumed
instances of chromosome fusion have also been postulated. In contrast, chromosome fusion
has undoubtedly been the predominant mode ofkaryotypic change in the chromosome races
of gekkonids of the genera Hemidactylus, Phyllodactylus, Diplodactylus and Gehyra
analysed by King (summary in King 198la).
The criteria used for assessing the direction of change in these studies have been based on
extensive karyotypic surveys, in which the most common karyotype was regarded as the
Karyotypic Evolution in Gehyra. 111
Fig. 8. A 2n = 37 karyotype of an individual from the 2n = 38 race heteromorphic for a centric fusion
(see elements involved underlined).
Fig. 9. Cells from animals heteromorphic for separate centric fusions (see fusion products arrowed):
(a) 2n = 40a race, het 2n = 39; (b) 2n = 42b race, het 2n = 41; (c) 2n = 38 race, het 2n = 37; (42n = 42b
race, het 2n = 41.
2n=44
G. pilbara
G. australis
2n = 44
2n = 40b
2n = 40a
2n = 38
2n = 42
Race
G'. vanegata-punctata
Species
10sc
Markers
Meta 14
Meta17'
5'
7
3
6
Table 3. Chromosome markers found in a series of Gehyra species
Fusion products
R
3'
2'
5'
8'\
Karyotypic Evolution in Gehyra. 111
ancestral form. The practice of using the dominant karyotype may be open to criticism ifthis
is to be the sole criterion. However, additional supporting information such as the
phylogenies produced by electrophoretic or morphological analyses can assist in
determining the direction of change.
In many of the cases where fusion has been proposed as the means of karyotypic
reorganization the fusions in question have occurred between differing, though closely
related chromosome races, and in a series of genera. In all these instances a number of
different chromosomes have been involved in the rearrangements. If the changes were not
fusion but regarded as fission, and if evolution had gone in the direction of metacentricity to
acrocentricity, all of the most closely related species complexes would necessarily have had a
polyphyletic origin. This is clearly unacceptable when all other criteria are considered (King
1981a, 1982b).
In the genus Gehyra, King (1979) postulated that the 2n = 44 complement was the extant
ancestral karyomorph for this group. This karyotype has a series of chromosome markers,
viz. metacentric pairs 14 and 17, a secondary constriction on chromosome pair 10, and
different short-arm lengths in acrocentric pairs 1-5. Such a karyotype morphology has been
observed in Gehyra nana (King 1979), G. pilbara (King, unpublished), a number of forms of
the G. variegata-punctata complex (King 1979) and, in the present study, in the 2n=44
chromosome race of Gehyra australis from the Kimberley in Western Australia. In the
G. variegata-punctata complex, derived races showed evidence of chromosome fusion
within this ancestral format. That is, additional metacentric chromosomes are present
(fusion products) accompanying the reduction in chromosome number (see Table 3 for
summary).
Ifwe now turn to the chromosome races of G. australis described in this Daver
- we also see
evidence of chromosome fusion being involved in the derivation of particular races. Thus
the 2n=42c race has chromosome markers 14, 17 and the secondary constriction on 10
shared with the 2n = 44 karyotype. An increased arm length in pair 3 (a 5/22 fusion product)
accompanies the reduction in chromosome number to 2n = 42. Similarly, the 2n = 40b race
has an acrocentric karyotype, except for pair 1 which is a presumed 5/19 fusion product
evolving from a 2n = 42 karyotype. The chromosome markers 14 and 17 are not visible in
this karyotype and may have been inverted to an acrocentric condiiion. The site of the
secondary constriction is uncertain. The last example of clear fusion products is seen in the
2n = 38 race. Here, pairs 5 (6/ 18 fusion) and 8 (16/20 fusion) have also presumably evolved
from an ancestral 2n = 42 karyotype. In this case the pair 17 marker is still present, but the
pair 14 metacentrics have been inverted to acrocentrics and the position of the 10 secondary
constriction is uncertain.
Although such changes are relatively straightforward, derivation of the 2n=40a
karyotype can be most parsimoniously achieved only by either the loss or the incorporation
of a pair of microchromosomes (i.e. by mechanisms such as tandem fusion) of the 2n = 42a
type from which it probably evolved. Similarly, the 2n = 42b race could have evolved from
the 2n = 42c karyotype by a series of pericentric inversions reducing the size of the short
arms of pairs 1-5 and making pair 14 acrocentric. The 2n = 42a and 2n = 42b chromosome
races are very similar in their chromosome morphology.
The most parsimonious phylogenetic sequence of events, based on the assumption of
centric fusion and a series of simple pericentric inversions, involves the following steps
(Fig. 10):
(1) Ancestral 2n = 44 race;
(2) 2rt = 42c race derived from the 2n = 44 ancestral form by a 5/22 fusion;
(3) 2n = 42a and 2n = 42b ancestral races produced by inversions of the 1-5 group and
the inversion of pair 14 of 2n = 42c race;
(4) 2n = 42a and 2n = 42b races differentiated morphologically yet remained chromosomally similar;
A
Max King
(5) 2n = 40a race produced by the loss of a microchromosome pair of the 2n = 42a
race;
(6) 2n = 40b race produced by a 5/19 fusion of the 2n = 42b race and an inversion of the
metacentric pair 17 to an acrocentric;
(7) 2n = 38 race produced by 6/18 and 16/20 fusions of 2n = 42a race.
Clearly, a detailed description of this series of changes cannot be provided from the
present study. It is possible that a G-banding analysis might provide a more definitive interpretation of the evolution of this complex, and such an analysis is being currently
undertaken.
Fig. 10. A phylogeny showing the relationship of the chromosome races within the G, australis
complex, and the relationship to other Gehyra so far examined.
(ii) Novel rearrangements
Chromosome polymorphism involving fusion, fission, pericentric inversion and the
addition of supernumerary segments has now been recorded in a number of lizard species.
Cole (1970, 1977) has identified locality-specific polymorphisms, involving inversions and
addition, in Sceloporus clarkii, S. melanorhinus and S. undulatus. Other iguanid species
showing polymorphisms are S. grammicus (Hall and Selander 1973), Tropidurus torquatus
Becak et al. (1972) and Anolis monticola (Webster et al. 1972). The varanid Varanus
acanthurus also has a geographically delimited pericentric inversion polymorphism (King et
al. 1982).
There are a number of situations described in the literature, where there is some
uncertainty whether a specimen heterozygous for a chromosomal rearrangement is a rare
mutant animal, or forms part of a balanced polymorphism. Olmo and Odierna (1980)
encountered a specimen of Cordylidae, Cordylus cataphractus, heterozygous for an apparent
fission. Similarly, King (198 1a) described a specimen of Phyllodactylus lanei heteromorphic
for a chromosome fusion. In both cases too few specimens were available to determine the
nature of the variation. In the G. variegata-punctata complex (King 1979),three specimens
heterozygous for presumed pericentric inversions were described. In each ofthese animals a
Karyotypic Evolution in Gehyra. I11
different chromosome was implicated in the change and only heterozygotes were observed.
If an inversion polymorphism was involved, its frequency must have been very low.
In the G. australis complex we see a relatively high incidence of animals heterozygous for
novel rearrangements (7 in 81), yet different chromosomes appeared to be involved in the
rearrangements in each case. Indeed, although it is true that chromosome polymorphisms
involving fusion are not a common phenomenon, once again the sample sizes are not large
enough to eliminate the possibility that these are locality-specific polymorphisms.
Chromosome Race Distribution and the Mode of Speciation
The most striking feature of the distributions of the chromosome races is their relative
integrity. Each of these forms is allopatrically distributed, either geographically or in habitat
preference. Additionally, a number of the distributions are restricted to major land forms.
Thus, the 2n = 44 race occurs in the mountain ranges of the central Kimberley in Western
Australia, the 2n = 38 race is restricted to the ranges surrounding the Macarthur River at the
base of the Gulf of Carpentaria, the 2n = 42b race is present in the mountain ranges in and
around Mt Isa in central Queensland, and the 2n = 42a race occupies the Arnhem Land
escarpment and certain surrounding ranges. All of these forms are rock-dwelling and do not
appear to have the capacity to live in an arboreal habitat. Indeed, the extent of the
distributions of several of these chromosome races is directly proportional to the area of
mountain range or rock outcrop available. The validity of this argument is strengthened by
the distributions of the less specialized forms, which can readily live on trees and human
habitations (2n = 40a, 2n= 42c) and in some cases also on rocks (2n = 42c). In these
instances the distributions are enormous, the 2n = 42c race occupying a wide area from the
tip of Cape York peninsula to south of the Queensland border. Similarly, the 2n = 40a race
occurs from Western Australia to the middle of the Gulf of Carpentaria. This distribution is
of particular interest, because it overlaps the areas occupied by both the 2n=38 and
2n = 42a races. Nevertheless, the different forms remain allopatric due to the arboreal
preference of the 2n = 40a race and the rock-dwelling habitat of the others.
Although the presence of chromosome races on major geographic features may reflect a
requirement for a certain habitat type, this is not necessarily so. The terrestrial gekko
Diplodactylus vittatus has a 2n=34 fusion race restricted to a region including the
Hinders-Mt Lofty ranges in South Australia (King 19774. This gekko does not require a
montane habitat since it also occurs in adjacent mallee country. It is likely that the mountain
ranges provided a radiation pathway during favourable conditions and a refugium during
less favourable periods.
The complicated central Australian distribution of the G. vanegata-punctata race
complex (King 1979)may be similarly interpreted. Here a series of chromosome races occur
on isolated rock outcrops and on ranges surrounded by sandy desert. The distributions are
erratic and do not always reflect a proximity to direct ancestors. It was proposed that the
present-day distribution is a relic of past radiations, extinctions and recolonization; the
outcrops here also being refugia. In other areas of Australia the chromosome races of
G. vanegata-punctata are also restricted to major land forms or habitat types. For example,
the 2n=40a race is found on the Murray-Darling drainage system in south-eastern
Australia, whereas the 2n = 44 form of G. varzegata occurs in the Flinders-Mt Lofty ranges in
South Australia, occupying an area very similar to that of the 2n=34 form of D.
vittatus.
In the G. australis complex, certain of the derived races are distributed in relatively close
proximity to their presumed ancestors. Thus, the 2n = 40b race is adjacent to the 2n = 42b
race, and the latter is adjacent to the 2n = 42c race. Similarly, the 2n = 42a race is adjacent to
the 2n = 40a race, and the 2n = 38 race is adjacent to the 2n = 42a race. If these distributions
are compared to the proposed phylogeny (see Fig. lo), it is clear that the evolution of this
complex could be interpreted as a series of colonizing radiations, during which the
Max King
individual chromosome races were established, i.e, primary chromosomal allopatry (sensu
King 1981~).
Such an explanation can indeed be applied to the more recent chromosomal changes.
However, the distributions of the 2n = 44 and 2n = 42c races, which are chromosomally
most similar to each other, presents a major problem. These putatively closest relatives are
furthest apart in their distributions; the 2n=44 is in the Kimberley district of Western
Australia and the 2n= 42c on the east coast of Australia. For the 2n= 42c race to have
evolved from the 2n = 44 ancestral karyotype form, one might have expected a relatively
close proximity. The most feasible explanation for the present-day distribution is that the
2n = 44 ancestral form, from which the 2n = 42c evolved, once occurred in eastern Australia
but is now extinct, the 2n = 44 race found in the Kimberley being a relic of a form which
formerly was widespread across the top of northern Australia. This form may have been
eventually restricted to the west, either through being eliminated throughout the eastern and
central sections of its range by environmental changes, or through displacement by other
chromosome races [i.e. stasipatry, sensu White (1978)l.
The concept ofan east-to-west distribution of a 2n = 44 ancestral G. australis in northern
Australia is to some extent supported by the present-day distribution of G. nana. This
species is sympatric with the 2n= 44 form of G. australis and also has 2n= 44. G. nana
is distributed across most of northern Australia except for an area in the vicinity of the Gulf
of Carpentaria. Consequently, its east-to-west distribution must at one time have been
continuous, the two isolates being formed by elimination of intervening populations (King
1981b).
The two chromosomally closest 2n = 42 races of G. australis are also isolated on the east
and west of the Gulfofcarpentaria. It therefore appears likely that the 2n = 42a and 2n = 42b
races may have once been contiguous, but that this distributional continuity has been
disrupted by some environmental change which left isolates in central Queensland and the
Northern Territory. The 2n = 38,40a and 40b races today occupy the intermediate areas of
this once extensive distribution. Moreover, the fact that these chromosomally most highly
modified, and hence recently derived forms, occupy the central area at the base of the Gulf of
Carpentaria, suggests that the colonization of this area has been a relatively recent
event.
Clearly, this distributional sequence, if interpreted as a direct reflection of the speciation
process, would support a model of stasipatric speciation. That is, the chromosomally
derived forms occupy the central areas, whereas the ancestral forms occupy peripheral areas.
The derived forms could therefore be seen as actively displacing the parental forms (see
White 1978). However, we know that in a number of periods in northern Australia's
geological history the eastern and western sections of the continent were isolated by repeated
episodes of environmental devastation. Over the past 250 000 years major fluctuations in
sea level are known to have occurred in northern Australia (Chappell and Thom 1977). Over
a longer time scale (i.e. the Pliocene to Recent) increased aridity has induced significant
vegetational changes in this area (Gill 1975). Even the use of fire by aboriginal man over the
past 40 000 years may have been a significant agent in modifying faunal distributions.
It is, therefore, not surprising that the region which appears to have undergone a series of
population extinctions is situated at the base of the Gulf of Carpentaria. Today, this is one of
the more environmentally fragile areas. A narrow belt of rock outcrops extends from east to
west. This is bordered on one side by the flat coastal scrubland extending to the Gulf, and on
the other by the treeless Savannah Grasslands of the Barkly Tablelands. Both of these areas
are prone to fire and partial inundation. Major environmental fluctuations of the type
outlined above could be expected to have readily eliminated populations from this region.
Taxa which were previously distributed continuously from west to east may therefore have
been eliminated over a large part of their ranges, leaving eastern and western isolates.
Subsequent periods may have produced a favourable habitat in which population radiations
could once again successfully occur. That is, speciation processes involving the parental
Karyotypic Evolution in Gehyra. 111
species being displaced by chromosomally derived forms (stasipatry) are much less likely
than that the chromosomally derived forms evolved during population radiations into
essentially uninhabited areas (primary chromosomal allopatry).
That the area at the base of the Gulf of Carpentaria has produced a series of population
extinctions is seen in the present-day distribution of certain northern Australian reptiles. For
many species a narrow corridor across the base of the Gulf joins eastern and western
populations (see Cogger 1975). Most significantly, some 14 species show a complete break in
this comdor, leaving eastern and western isolates of each species (see Table 4 for
examples).
Table 4. Species of reptiles in northern Australia separated into eastern and western isolates by
the Gulf of Carpentaria
Family
Sauria
Scincidae
Varanidae
Serpentes
Gekkonidae
Typhlopidae
Colubridae
Elapidae
Species
Carlia fusca (Dumeril & Bibron)
Egernia frerei Gunther
Sphenomorphus crassicaudus (Dumeril)
Varanus indicus ( ~ a u d i n ) ~
Varanus semiremex petersA
Gehyra nana (Storr)
Typhlina aftinis ( ~ o u l e n ~ e r ) ~
Typhlina wiedii ( ~ e t e r s ) ~
Amphiesma mairi~(Gray)
Dendrelaphis punctulatus (Gray)
Enhydris polylepis (Fischer)
Stegonotus cucullatus (Dumeril, Bibron & Durneril)
Demansia atra (Macleay)
Oxyuranus scutellatus (Peters)
Simoselaps sem&sciatus (Gunther)
A ~ e c a u s of
e specialised habitat or lifestyle the absence of these species from the Gulf region may be due
to inadequate collection.
A possible evolutionary sequence of events leading to the diversity and distributions that
we see today, and based on the most parsimonious phylogenetic model, follows:
(1) The 2n = 44 ancestral Gehyra australis radiated from west to east across the north of
Australia;
(2) In the course of this radiation the 2n=42c race was established and this, in turn,
radiated along the east coast of Australia occupying much of its present-day
distribution;
(3) Environmental changes in the Gulf area eliminated the 2n = 44 race from the central
part of its distribution, leaving an isolate in Western Australia;
(4) A population radiation from east to west originated on the periphery of the 2n = 42c
race. The chromosomally modified forms were of the ancestral 2n = 42a and 2n = 42b
types and occupied the area between the 2n=42c and 2n=44 races;
(5) Environmental changes affecting the Gulf area eliminated these ancestral 2n=42
forms from the central part of their distribution, leaving an uninhabited void, and
producing eastern and western isolates, i.e. the 2n = 42a and 2n = 42b races;
( 6 ) Subsequent, more recent population radiations of chromosomally derived forms
(2n =40b and 2n = 38) occurred in the Gulf area, radiating from the 2n = 42b and
2n = 42a races respectively;
( 7 ) The 2n=40a race arose on the periphery of distribution of the 2n=42a race,
coinciding with a change in habitat preference. This race then radiated throughout the
north of the Northern Temtory and into the Gulf area.
This sequence of events is summarized in Fig. 11.
Max King
Taxonomic Implications
(i) Specijc relationships
It is now clear that, in gekkos at least, chromosome analysis at a population level can be of
considerable taxonomic value. Taxonomically 'awkward' species can be unambiguously
categorized into chromosomal races on the basis of karyotypes. Morphological comparisons
within and between these chromosome races may then provide diagnostic characteristics
permitting a taxonomic revision.
Fig. 11. A presumed sequential series of chromosome race distributions producing the present-day
distribution. Arrows indicate chromosome race radiations. Maps B and D show distributions during
populations extinction in the area at the base of the Gulf of Carpentaria.
Such an approach has been successfullyused in the Diplodactylus vittatus complex, where
five allopatrically distributed chromosome races and their morphological difference were
described by King (1 977a). Subsequently, Storr (1979) was able to describe a series of new
species and resurrect a number of older taxa, producing a complex of five species. Similarly,
Gehyra pamela was recently described as a new species after a chromosomal and
morphometric analysis showed it to be clearly distinguishable from G. australis (King
1982b).
Karyotypic Evolution in Gehyra. I11
One ofthe major problems with Gehyra specimens lodged in museums is that coloration
and back pattern fade with the passage of time. In life, the variation in colouring and back
pattern is spectacular, and in most cases is directly correlated with chromosome race
distribution. In this group it is thus important to observe live specimens. A second difficulty
which has hampered traditional taxonomists is that, in groups such as the G. australis
complex, where many undescribed species are present, too few specimens from too few
localities have been examined. Diagnostic characters have therefore been overlooked, and
the 'species' is simply regarded as being highly variable (see Mitchell 1965).
There is good reason to believe that the majority of chromosome races in the G. australis
complex are good biological species. Specimens from each race are chromosomally and
morphologically consistent throughout their range. There is no evidence of introgression of
one form into another when distributions are sympatric or when allopatric races appear to
abut. The major problem at the moment is that too few specimens have been analysed in
certain of the chromosome races (such as 2n=40b) to make a morphometric analysis. Such
an analysis has been performed on the 2n =40a, 2n =42a, 2n= 42b, 2n = 42c and 2n = 38
chromosome races, and all show significant morphological differences. A taxonomic
revision of this complex of species has been made and will be published separately (King
1983).
(ii) The relationship between the G. australis and G, variegata-punctata complexes
In his osteological and morphological study of Australian Gehyra species, Mitchell (1965)
suggested that there were two species-groups within Australia. The first of these was an
Indo-Australian group containing G. australzs and G. oceanica (the status of the latter being
uncertain in Australia). The second contained a series of endemic Australian forms
recognized at that time: G. varzegata, G. pzlbara, G. punctata and G. fenestra. The basis of
this dichotomy was the sternal rib structure: the Indo-Australian group having two sternal
ribs, the endemic group having three. Mitchell (1965) felt that this provided strong evidence
for dividing Gehyra into two genera: an endemic Australian genus Dactyloperus Fitzinger,
1843, and an Indo-Australian genus Gehyra Gray, sensu stricto. A final decision on this
matter was deferred.
The chromosomal data, however, suggest that the Australian Gehyra are a continuum of
genetically related forms. In both the G. varzegata-punctata complex (King 1979) and the
G. australis complex particular chromosome markers and ancestral karyotypes are shared.
This indicates that the G. australis complex is part of an endemic Australian group rather
than an Indo-Australian group, and that it is intrinsically related to other Australian Gehyra.
Indeed, both the chromosome data and the consequent phylogeny suggest that the
G. australis complex has evolved from an ancestral 2n=44 state common to both the
G. australis and G. variegata-punctata complexes. The relative, evolutionary independence
of the complexes since this initial divergence is no more than evidence for a dichotomy into
species-groups. These data in no way support a generic subdivision into endemic and
non-endemic forms, but suggest that in reality both complexes are endemic and belong to
one genus.
Mitchell's proposed generic subdivision of Australian Gehyra was based on only six
cleared specimens of G. australis. The distribution data provided by Mitchell (1 965) suggest
that these specimens were from just two of the seven known chromosome races. Clearly, a
detailed osteological analysis of all the forms of G. australis and of the more recently
described Gehyra species is necessary to establish the sternal rib structure, before the
universality of this structural dichotomy can be accepted.
Acknowledgments
The author is grateful to the many people who helped in this study collecting specimens,
in particular Pamela King, Dennis King, Robert Jenkins, Gregory Mengden, John Wombey,
Max King
Hal Cogger and Craig Moritz. Thanks to Bernard John for his helpful comments on the
manuscript.
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Manuscript received 31 May 1982; accepted 2 1 January 1983