Although designating the Night Parrot (Geopsittacus occidentalis) and the Ground Parrot (Pezoporus wallicus) as each other's closest taxonomic relatives is generally accepted, placing this group with respect to other Australo-Pacific parrots has proven problematical. To examine the phylogenetic relationships of these two species, a 924-bp fragment of the cytochrome-b gene was sequenced from single representatives of the following genera: Geopsittacus, Pezoporus, Neophema, Melopsittacus, Platycercus, Polytelis, Strigops, and Calyptorhynchus. Maximum-parsimony, maximum-likelihood, and distance trees all supported a close association between Geopsittacus and Pezoporus. These two genera were also found to be closely linked with Neophema and Melopsittacus. Despite superficial morphological similarities, Geopsittacus and Strigops (Kakapo) were found not to be closely related. Received 21 December 1992, accepted 6 October 1993.
Department of Ornithology, Museum of Victoria, 71 Victoria Crescent,
Abbotsford, Victoria 3067, Australia;
2Department of Genetics and Human Variation, LaTrobe University,
Bundoora, Victoria 3083, Australia; and
3Division of Vertebrate Zoology, Australian Museum, 6 College Street, Sydney, NSW 2000, Australia
THE PSITT^CIFORMES (parrots, lorikeets, and
cockatoos) are distributed throughout the Neo-
tropical, Ethiopian, Oriental and Australasian
regions. Studies based on morphological (Brer-
eton 1963, Smith 1975, Homberger 1980), bio-
chemical (Christidis et al. 1991a), and chro-
mosomal (Christidis 1990, Christidis et al. 1991b)
data have shown that most diversity is centered
within the Australasian region. Although these
studies have identified major groupings among
the Australasian psittaciforms, the placement of
several genera and species is still poorly re-
solved. Two such species are the Night Parrot
(Geopsittacus occidentalis) and the Ground Parrot
(Pezoporus wallicus).
The monotypic genus Geopsittacus often has
been considered to be allied to, or congeneric
with, the monotypic genus Pezoporus (Brereton
1963, Ford 1969, Schodde and Mason 1980). The
paucity of knowledge about the behavior and
biology of Geopsittacus has hampered attempts
to assess its links with Pezoporus. Until 1990,
when a dead specimen was found (Boles et al.
1991, 1994), Geopsittacus had not been reliably
documented since 1912. It is represented in mu-
seum collections by only 22 skins (excluding
the 1990 specimen) and some bones (Forshaw
et al. 1976). Schodde and Mason (1981) regarded
Geopsittacus and Pezoporus as closely related vi-
cariants, replacing each other in inland and wet
coastal habitats of southern Australia, respec-
tively. There is some similarity in the structure
of their preferred low scrubby/heathland hab-
itats. These two parrots share similar green
plumage crossed with bands of black and yel-
low. Both are primarily terrestrial. Geopsittacus
receives its common name from its nocturnal
habits, and Pezoporus is essentially crepuscular
(Forshaw 1981).
Superficially, Geopsittacus and Pezoporus re-
semble diminutive versions of the flightless New
Zealand Kakapo (Strigops habroptilus), a fact com-
mented on by Gould (1861). Like the two Aus-
tralian taxa, Strigops is nocturnal and terrestrial,
and has at least superficially similar green-barred
plumage. Furthermore, Strigops and Geopsittacus
possess enlarged fleshy ceres ringed by fine
"hairlike" feathers. These are pronounced in
the former, but small in the latter. Forshaw (1981,
1989) proposed that Geopsittacus, Pezoporus, and
Strigops were closely related and constituted an
ancient relict group. He also suggested that the
Budgerigar (Melopsittacus undulatus) and Neo-
phema linked this group with the "typical" pla-
tycercines or broad-tailed parrots. In the strict-
est sense, the broad-tailed parrot assemblage
comprises the following Australian genera:
Platycercus, Barnardius, Northiella, Purpureice-
phalus, Lathamus, Psephotus, Pezoporus, Geopsit-
tacus, and Neophema. Cyanoramphus from New
Zealand and the South Pacific is generally in-
cluded (Forshaw 1989), and some authors also
include other South Pacific genera such as Eu-
nymphicus (Smith 1975, Hornberger 1980) and
Prosopeia (Hornberger 1980). Melopsittacus shares
with Pezoporus, Geopsittacus, and Strigops a yel-
low-green plumage marked with dark barring
on the dotsurn. Brereton (1963) placed Geopsit-
tacus and Pezoporus with Melopsittacus in their
own family, the Pezoporidae. Biochemical stud-
ies (Christidis et al. 1991a) do not support a close
association between Melopsittacus and Pezopo-
rus. Smith (1975) included Melopsittacus, Geop-
sittacus, and Pezoporus within the platycercines
and kept Strigops in its own monotypic tribe.
Several authors (e.g. Forshaw 1989, Sibley and
Monroe 1990) have placed Geopsittacus, Pezo-
porus, and Strigops adjacent to each other in lin-
ear sequence, at least implying a relationship.
In an effort to resolve the systematic affinities
of Geopsittacus and Pezoporus, we collected se-
quence data for a 924-base-pair fragment of the
mitochondrial cytochrome-b gene from eight
psittaciform genera, including Strigops and Mel-
opsittacus.
MATERIALS AND METHODS
The following specimens were examined (with ac-
cession number, year of collection, and DNA source,
in parentheses): Geopsittacus occidentalis, Night Parrot
(36246, 1876, feather); Pezoporus wallicus wallicus,
Ground Parrot (R8794, 1924, feather); Strigops habrop-
tilis, Kakapo (R2402, 1907, feather); Neophema petro-
phila petrophila, Rock Parrot (MV254, 1989, frozen liv-
er); Melopsittacus undulatus, Budgerigar (MV1058, 1992,
frozen liver); Platycercus icterotis xanthogenys, Western
Rosella (MV347, 1989, frozen liver); Polytelis antho-
peplus westralis, Regent Parrot (MV340, 1989, frozen
liver); and Calyptorhynchus banksii graptogyne, Red-
tailed Black-Cockatoo (MV1616, 1989, feather). Spec-
imens are lodged in the Museum of Victoria, Mel-
bourne, Australia. The choice of an outgroup was
compounded by the lack of conclusive evidence con-
cerning the nearest relatives of Psittaciformes (sum-
marized in Sibley and Ahlquist 1990). Consequently,
two outgroups were chosen. A gruiform, Grus rubi-
cunda (the Brolga; MV790, 1991, frozen liver) was
sequenced. In addition, published cytochrome-b se-
quences from the passeriform Pitta sordida (the Hood-
ed Pitta; Edwards et al. 1991) were used. The cyto-
chrome-b sequences collected in the present study
have been deposited in GenBank with the accession
numbers U13620 to U13628.
Where feather tips were used, DNA extraction was
performed as described in Leeton et al. (1993). For
frozen liver samples, total DNA was extracted by
grinding 0.I to 0.3 g of tissue in 500 1 of digestion
solution (50 mM Tris HC1, 10 mM EDTA, I00 mM
NaC1, pH 8.0) to which I0 1 proteinase K (10 g/ml)
was added. Digestion was performed at 37øC for 2 h.
DNA was then extracted through two washes with
equal volumes of phenol :chloroform (1:I), and pre-
cipitated following the addition of 2.5 volumes of ice-
cold absolute ethanol. After drying, the DNA was
resuspended in I00/d TE (10 mM Tris, 0. I mM EDTA,
pH 8.0).
The cytochrome-b sequence was amplified as a se-
ries of small segments (300-400 bp) using the primer
pairs LI4841/HI5149 (Kocher et al. 1989), L15114/
H15547, and LI5424/HI5767 (Edwards et al. 1991).
Letters refer to light and heavy strands and numbers
to positions of the 3' nucleotides in the human mtDNA
sequence (Anderson et aL 1981). Double-stranded PCR
amplifications were performed in a 50 1 reaction mix
(25 /M of each appropriate primer, 2.5 mM dNTPs
[Boehringer], i unit of Tth DNA polymerase [Toyobo],
adjusted to appropriate specifications using I0 x Tth
buffer [Toyobo]). Thirty-five rounds of amplification
were performed, with each cycle consisting of de-
naturation at 92øC for 60 s, reannealing at 52øC for 60
s, and extension at 72øC for 60 s. The final product
was cleaned and concentrated using a microcentri-
fuge filter tube (Millipore), and resuspended in 50 1
of TE (pH 8.0).
Asymmetric PCRs were carried out under similar
conditions, in a reaction volume of I00 1 using I 1
of double-stranded PCR product and 0.25 g of the
appropriate primer (the addition of a limiting primer
was not deemed necessary, due to small amounts of
"carry over" following filtration). The final asym-
metric PCR product was purified and concentrated
following ethanol precipitation. Asymmetric prod-
ucts were sequenced directly by the protocol of Sang-
er et al. (1977) using a commercial kit (Sequenase,
United States Biochemical). Sequences were obtained
for the entire light strand and a portion of the heavy
strand. There was complete congruence between the
heavy- and light-strand sequences.
DNA sequences were aligned relative to the human
mtDNA sequence (Anderson et al. 1981). No base
insertions or deletions were detected. Sequence di-
vergence, transition: transversion ratios, and evolu-
tionary weightings were calculated from the data set.
Following Brown et al. (1982), the transition:trans-
version ratio calculated for the least-diverged species
pairs was used for all the taxa examined because the
saturation of transitions for distantly related com-
parisons obscures the real transition: transversion bias.
Maximum-parsimony trees were constructed using
the exhaustive algorithm in PAUP version 3. I. 1 (Swof-
ford 1993). Initial analyses were based on all the char-
acters without weighting (global parsimony). A series
TABLE 1. Sequence divergence measured between species pairs examined over the 924-bp cytochrome-b
fragment. Above diagonal, Kimura (1980) two-parameter distance; below diagonal, frequency of sequence
divergence.
Taxon 1 2 3 4 5 6 7 8 9 10
1 Geopsittacus -- 0.0903 0.1139 0.1735 0.1105 0.1348 0.1770 0.2340 0.2140 0.2266
2 Pezoporus 0.0840 -- 0.1346 0.1682 0.1163 0.1297 0.1779 0.2378 0.2048 0.2312
3 Melopsittacus 0.1050 0.1220 -- 0.1363 0.1101 0.1065 0.1587 0.2164 0.2076 0.2136
4 Strigops 0.1540 0.1490 0.1230 -- 0.1586 0.1276 0.1405 0.2470 0.2193 0.2439
5 Neophema 0.1020 0.1070 0.1020 0.1420 -- 0.1162 0.1631 0.2341 0.2164 0.2339
6 Platycercus 0.1220 0.1180 0.0980 0.1160 0.1070 -- 0.1312 0.2129 0.2067 0.2222
7 Polytelis 0.1560 0.1570 0.1410 0.1270 0.1450 0.1190 -- 0.1943 0.2300 0.2574
8 Calyptorhynchus 0.1990 0.2010 0.1860 0.2070 0.1990 0.1830 0.1690 -- 0.2704 0.2475
9 Grus 0.1840 0.1770 0.1800 0.1880 0.1860 0.1800 0.1960 0.2250 -- 0.2002
10 Pitta 0.1930 0.1960 0.1830 0.2060 0.1980 0.1890 0.2140 0.2420 0.1730 --
of conditional data sets was also analyzed: (1) weight-
ing for differential evolutionary rates at the three
codon positions (weighted parsimony); (2) excluding
third positions; (3) transversions only (transversion
parsimony). The resolving power of the sequence data
was assessed using the bootstrap procedure (Felsen-
stein 1985) as implemented in PAUP and the jack-
knifing procedure as described by Lanyon (1985).
A maximum-likelihood analysis (Felsenstein 1981)
using the DNAML option of PHYLIP version 3.5 (Fel-
senstein 1993) was performed including 100 bootstrap
replicates. The data set was analyzed both with and
without evolutionary weightings for the three codon
positions. A transition: transversion bias of 4:3, gen-
erated from a consideration of all positions in the
Pezoporus-Geopsittacus comparison, was included.
A distance matrix was constructed using the
DNADIST program of PHYLIP employing Kimura's
(1980) two-parameter method (Table 1). From the ma-
tfix, Fitch-Margoliash (Fitch and Margoliash 1967) and
neighbor-joining (Saitou and Nei 1987) trees were
generated using the FITCH and NEIGHBOR options
of PHYLIP. Bootstrap resampling was implemented
for both trees.
RESULTS
Within the 924-bp region of cytochrome b
(Appendix), 301 positions were variable over
all psittaciform taxa examined; 59 were at the
first-codon position, 56 at the second, and 186
at the third. These converted to evolutionary
weightings for the first-, second-, and third-
codon positions of 3:3:1. The percent sequence
divergence between psittaciform species pairs
(Table 1) ranged from 8.4% (Geopsittacus and Pe-
zoporus) to 20.7% (Calyptorhynchus and Strigops).
Kimura (1980) two-parameter distances, within
the psittaciforms, ranged from 0.0903 (Geopsit-
tacus and Pezoporus) to 0.2470 (Calyptorhynchus
and Strigops), the pattern of divergences being
similar to that of the percent differences (Table
1). Average percent divergences and two-pa-
rameter distances between the psittaciforms and
the outgroups (Grus, Pitta) were 19.6% and 0.2403,
respectively.
Transition: transversion ratios between spe-
cies pairs varied considerably ranging from 1:1
(Calyptorhynchus : Strigops) to 4:3 (Geopsittacus :
Pezoporus). The highest transition: transversion
ratios occurred between those species that had
the lowest percent divergences and Kimura
(1980) two-parameter distances. The choice of
either Pitta or Grus as the outgroup affected the
topology and resolution of some of the analyses
and, therefore, these are described separately
below.
A global-parsimony analysis, without
weighting and using Grus as the outgroup, pro-
duced two equally most-parsimonious trees of
length 668 steps, which differed from one an-
other only in the relative positioning of Calyp-
torhynchus and Strigops. In one, Polytelis and Ca-
lyptorhynchus were sister taxa and, in the other,
Strigops and Polytelis were sister taxa. Bootstrap
analysis supported only the former topology.
In the bootstrap consensus topology (Fig. 1),
Geopsittacus and Pezoporus were sister taxa, and
these were linked with Neopherna, Melopsittacus,
and Platycercus in a stepwise pattern. Bootstrap
values at each of these nodes were 94, 77, 72,
and 73%, respectively. A consideration of near-
parsimonious trees revealed 4 with 671 steps or
less and their strict consensus was identical in
topology to the above. Weighted parsimony
provided less resolution; the Geopsittacus-Pezo-
porus-Neophema clade was present, and Polytelis
was aligned with Strigops, but with a low boot-
_ Geopsittacus
Pezoporus
72 [ Neophema
73 I Melopsittacus
Platycercus
77
Strigops
Polytelis
Calyptorhynchus
Grus
Fig. 1. PAUP maximum-parsimony analysis based
on unweighted characters for psittaciform genera ex-
amined and using Grus as the outgroup. Length of
two equally most-parsimonious trees, before boot-
strapping, was 668 and consistency index was 0.669.
Bootstrap values greater than 50% indicated at nodes.
strap value of 56%. Global parsimony using Pitta
as the group produced a single most-parsimo-
nious tree with 683 steps (not shown). This to-
pology differed from the above (Fig. 1) in that
Platycercus was now linked with Strigops, al-
though this node was not supported following
bootstrapping. The Pezoporus-Geopsittacus clade
was supported in all of the bootstrap replicates,
while nodes linking Neophema and Melopsitta-
cus to this clade were well supported with boot-
strap values of 91 and 71%, respectively. The
Polytelis-Calyptorhynchus clade was supported by
a bootstrap of 78%. A consideration of near-
parsimonious trees revealed 7 with 687 steps or
less, and their strict consensus was identical in
topology to the above. Weighted parsimony,
with Pitta as outgroup, differed in that Polytelis
was aligned with Strigops, but this node had a
low bootstrap value (55%). Following the jack-
knife procedure, only the Geopsittacus-Pezopo-
rus-Neophema clade was identified in all repli-
cates, regardless of choice of outgroup. More-
over, in all replicates that included Neophema,
both Melopsittacus and Platycercus were aligned
with the Geopsittacus-Pezoporus-Neophema clade.
When first- and second-codon positions only
were considered, with Pitta as the outgroup,
Calyptorhynchus was separated from the remain-
ing parrots, but only with a bootstrap value of
51%. The only other resolution was a node link-
ing Polytelis with Strigops with a low bootstrap
value of 62%. When Grus was used as the out-
72
72
-- Geopsittacus
Pezoporus
Neophema
Melopsittacus
Platycercus
Strigops
93 [ Polytelis
Calyptorhynchus
Grus
Fig. 2. Maximum-likelihood tree based on un-
weighted characters for psittaciform genera examined
and using Grus as the outgroup. Log likelihood before
bootstrapping was -4355.78900. Bootstrap values
greater than 50% indicated at nodes.
group, no resolution was obtained following
bootstrapping.
Transversion parsimony using Pitta as the
outgroup (not shown) produced three clades:
(1) Geopsittacus-Pezoporus; (2) Neophema-Platy-
cercus-Melopsittacus; and (3) Polytelis- Strigops. The
first two were sister clades and Calyptorhynchus
pulled out as the most divergent lineage. Fol-
lowing bootstrapping, however, only the Geop-
sittacus-Pezoporus clade (75%) was supported.
When Grus was used as the outgroup, Calyptor-
hynchus was again the most divergent lineage,
Geopsittacus and Pezoporus were linked with
Neophema, Melopsittacus and Platycercus, and
Polytelis was linked with Strigops. Following
bootstrapping, the node separating Calyptor-
hynchus from the rest had a bootstrap of 63%;
the only other nodes with values higher than
50% were Geopsittacus-Pezoporus (68%) and Stri-
gops-Polytelis (55%).
The maximum-likelihood tree (Fig. 2), using
Grus as the outgroup, had a topology compa-
rable to that obtained with global parsimony
(Fig. 1). Polytelis and Calyptorhynchus were linked
with Strigops, although this node had a boot-
strap value of only 40%. All other nodes were
supported by bootstrap values of 72% and high-
er. A consideration of evolutionary weightings
did not alter the topology or resolution of the
maximum-likelihood tree. When Pitta was used
as the outgroup, the position of Platycercus was
not resolved following bootstrapping, but Stri-
gops was linked with Polytelis-Calyptorhynchus
with a bootstrap of 64%.
The Fitch tree, using Grus as the outgroup
(not shown), was identical in topology to the
maximum-likelihood tree, and there was only
one topological difference between the Fitch
and neighbor-joining (Fig. 3) trees. In the latter,
Strigops was aligned with the Geopsittacus-Platy-
cercus clade, and this node was supported by a
bootstrap of 51%. When Pitta was used as the
outgroup, the neighbor-joining tree was iden-
tical in topology to the maximum-likelihood
tree, while in the Fitch tree, Platycercus was
aligned with the Strigops-Calyptorhynchus-Poly-
telis clade and this node was supported by a
bootstrap of 51%.
DISCUSSION
Phylogenetic position of Geopsittacus and Pe-
zoporus.--Cytochrome-b data are unequivocal
and consistent in their linking of Geopsittacus
with Pezoporus. The two genera differ by 8.4%
sequence divergence (Table 1), which is com-
parable to divergences for other congeneric avi-
an species. Edwards et al. (1991) reported values
ranging from 6.2 to 12.0% between congeners
in Pomatostomus, while Smith et al. (1991) re-
corded values of 5.7 to 13.0% within the genus
Laniarius. The present data are consistent with
the conclusions of Ford (1969) and Schodde and
Mason (1980) that Geopsittacus and Pezoporus
should be treated as congeneric species. Geop-
sittacus occidentalis, therefore, becomes Pezoporus
occidentalis. The pattern of distribution and pre-
ferred habitats for these species parallels those
in the genus Neophema, which also has both
inland (bourkii and splendida) and coastal species
( chrysogaster, chrysostoma, pulchella, petrophila, and
elegans).
In concert with the shared patterns of distri-
bution, Geopsittacus and Pezoporus were consis-
tently allied with Neophema by the cytochrome-b
data. Melopsittacus also was aligned with this
assemblage in all analyses. On the basis of mor-
phological characters, such as lack of a nape spot
and presence of barred feathers, Brereton (1963)
linked Melopsittacus with Pezoporus and Geopsit-
tacus; however, lack of a nape spot appears to
be the ancestral condition within the Psittaci-
formes. Only the other Australian platycercine
genera and Cyanoramphus possess a nape spot.
Although Smith (1975) listed Eunymphicus as
possessing a nape spot, our examination found
that it in fact lacks one. If the Geopsittacus-Mel-
opsittacus assemblage, as identified in our study,
100
80
64
92
0.052
0.050
0.049
0.075
78
O.015
0.132
0.138
Geopsittacus
Pezoporus
Neophema
Melopsittacus
Platycercus
Strigops
P01ytelis
Calyptorhynchus
Grus
Fig. 3. Neighbor-joining tree based on the Kimura
(1980) two-parameter distances for psittaciform gen-
era examined, using Grus as the outgroup. Bootstrap
values greater than 50% indicated above nodes. Num-
bers below nodes refer to branch lengths.
is part of the platycercines, then two scenarios
are possible to explain the occurrence of a nape
spot in the various genera. In the first (Fig. 4A),
the nape spot evolved early in the evolution of
the platycercines and has since been lost twice,
in Melopsittacus and in Geopsittacus-Pezoporus. The
alternative scenario (Fig. 4B) is that the nape
spot evolved in the "core" platycercines (sensu
Christidis et al. 1991a) after their divergence
from the lineage, giving rise to the Geopsittacus-
Melopsittacus assemblage, and also evolved in-
dependently in Neophema. There are no data at
present to favor one hypothesis over the other.
The distribution of barred feathers within the
platycercines also has two possible explana-
tions. Barred feathers may have arisen early in
the evolution of the Geopsittacus-Melopsittacus
assemblage and then been lost secondarily in
Neophema (Fig. 4A). Alternatively, barred feath-
ers may have evolved independently in both
Melopsittacus and Geopsittacus-Pezoporus (Fig. 4B).
To differentiate between these two hypotheses,
we examined in detail the barred feathers in
Pezoporus, Geopsittacus, Strigops, Melopsittacus, and
Psittacella. Other than their darker green color,
the barred feathers of Pezoporus are very similar
to those of Geopsittacus, agreeing in details of
pattern on each part of the body. The most ob-
vious difference is the barring of underpart
feathers, which in Pezoporus extends to the bor-
ders of the webs, whereas in Geopsittacus it does
not. Melopsittacus does not exhibit this same
agreement of feather patterns. On no part of
the body does its pattern of barring appear ho-
mologous with that in Pezoporus-Geopsittacus.
a
-- Geopsittacus
Pezoporus
, Neophema
Melopsittacus
"typical" platycercines
b
i I
-- Geopsittacus
Pezoporus
Neophema
, Melopsittacus
"typical" platycercines
Fig. 4. Possible pathways for evolution of nape
spots and barred feathers in platycercines with (A)
character loss, or (B) characters arising more than once.
Closed rectangles represent gain of nape spot; open
rectangles represent loss of nape spot. Closed circles
represent gain of barred feathers; open circles rep-
resent loss of barred feathers.
This adds support to the idea that barred pat-
terns evolved independently in each group. The
barred feathers of Strigops show even more sub-
stantial differences from those of Geopsittacus-
Pezoporus, and are more likely to have been in-
dependently derived. New Guinean Psittacella
is similar to Geopsittacus and Pezoporus in its un-
derparts and to Melopsittacus in its upperparts.
It was shown to be linked with the platycercines
by Christidis et al. (1991a), but was not treated
by Brereton (1963) or included in this study.
The relationship of Psittacella to these other
genera needs to be assessed and further studies
should include it.
Neophema, Melopsittacus, and Geopsittacus share
a Type A-1 carotid formula (no data are avail-
able for Pezoporus), whereas the other platycer-
cines (including Cyanoramphus) are Type A-2
(Garrod 1873, 1874, 1876, Glenny 1957). Apart
from Nestor, Psittrichas, and Prosopeia (which are
Type A-2), other Australasian and Asian genera
examined have a Type A-1 carotid formula. Bed-
dard (1898) listed Eunymphicus (which he called
Nymphicus cornutus) as possessing a Type A-2
carotid formula, citing Garrod (1873, 1874,1876)
as the source. This appears to be in error, as
Garrod (1873, 1874, 1876) did not examine Eu-
nymphicus. Similarly, Smith (1975) listed Psit-
tacella as possessing a Type A-1 carotid formula,
but his cited sources (i.e. Garrod 1874, Beddard
1898, Glenny 1957) did not mention Psittacella.
The African Psittacini and all South American
genera examined are Type A-2. It can be argued
that the Type A-1 carotid formula is ancestral
for the Australasian genera and that a Type A-2
formula evolved in the "core" platycercines af-
ter this lineage diverged from the one leading
to the Geopsittacus-Melopsittacus assemblage.
Based on 924 bp of cytochrome-b sequences,
no association was apparent between Strigops
and either Geopsittacus or Pezoporus (cf. Forshaw
1989). Thus, the similarities in appearance be-
tween Strigops and Geopsittacus are convergent,
presumably brought about by similar life hab-
its. Predominantly green plumage crossed with
bands of black and yellow may serve as cam-
ouflage for these ground-dwelling species,
which shelter in tussocks or clumps of vege-
tation by day. The "hairlike" feathers present
in both Geopsittacus and Strigops have also
evolved convergently, possibly acting as tactile
sensors when the birds are moving through
thick ground cover.
Deeper relationships within Psittaciformes.--The
platycercine assemblage is generally consid-
ered to include Neophema, Pezoporus, and Mel-
opsittacus (Smith 1975, Hornberger 1980). Al-
though the qualitative and distance analyses
given above generally aligned Platycercus with
the Pezoporus-Melopsittacus clade, bootstrap
analysis revealed that the position of Platycercus
could not be resolved confidently by the cyto-
chrome-b sequences. Moreover, resolution of the
position of Platycercus was affected by the choice
of outgroup. To resolve this inconsistency re-
garding the position of Platycercus, sequence data
are required from other typical platycercines
such as Northiella, Psephotus, and Barnardius. Such
studies are currently in progress. If one assumes
that the Melopsittacus to Pezoporus clade is part
of the platycercine assemblage, it probably rep-
resents a highly divergent group of taxa. Chris-
tidis et al. (1991a), based on allozyme studies,
argued for two successive radiations among the
platycercines. The first involved the divergence
of Pezoporus (and presumably Geopsittacus, which
was not included in that study), Neophema, and
Melopsittacus from the core platycercine group.
The second, more recent one, gave rise to Platy-
cercus, Barnardius, Purpuricephalus, Northiella, La-
thamus, and Psephotus. Christidis et al. (1991a)
also reported a close association between the
polytelitines and platycercines, but this was not
apparent in the present study. Although Poly-
telis was aligned with Calyptorhynchus in most
analyses, the relatively high sequence diver-
gence between the two (17.1%) suggests that an
examination of additional taxa is required to
accurately assess their relationships. Moreover,
bootstrapping and jackknifing indicated that the
relationships of Polytelis, Strigops, and Calyptor-
hynchus could not be resolved from the present
data set.
The patterns of resolution obtained in this
study indicate that the cytochrome-b gene is
particularly useful in determining relation-
ships between closely related genera, but that
for deeper branches, transition bias needs to be
considered. The cockatoos, represented in our
study by Calyptorhynchus, are generally consid-
ered to be the sister group to a large assemblage
that includes all the Australian genera exam-
ined here (Smith 1975, Homberger 1980, Chris-
tidis et al. 1991a, b). Only when the transition
bias was taken into consideration was such a
relationship apparent from the present se-
quence data. Moreover, the levels of sequence
divergence between Calyptorhynchus and the
other psittaciforms examined were of similar
magnitude to those recorded between the psit-
taciforms and the two outgroups Grus and Pitta,
indicating that the level of transition diver-
gence had reached saturation in those compar-
isons.
ACKNOWLEDGMENTS
We thank the Department of Conservation and Land
Management of Western Australia for permission to
collect materiM for this study. We also thank Belinda
Gillies for assistance in the field and Toula Galari-
niotis (Museum of Victoria) for typing the various
drafts of the manuscript. This work was partly funded
by an Australian Research Council Grant (A19031161)
to L.C. and M.W., and by an Australian Geographic
Grant to W.E.B.
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842 LEETON ET ^L. [Auk, Vol. 111
October 1994] Parrot Affinities 843