Annals of Botany 87: 83±90, 2001
doi:10.1006/anbo.2000.1307, available online at http://www.idealibrary.com on
Widespread Chromosome Variation in the Endangered Grassland Forb Rutidosis
leptorrhynchoides F. Muell. (Asteraceae: Gnaphalieae)
B . G . M U R R AY{ and A . G . YO U NG *{
{School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand and {Centre
for Plant Biodiversity Research, CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia
Received: 24 May 2000 Returned for revision: 1 August 2000 Accepted: 25 September 2000 Published electronically: 24 November 2000
Rutidosis leptorrhynchoides is an endangered plant endemic to southeastern Australia. Chromosome analysis of 19 of
the 24 known populations of the species has identi®ed 17 di€erent chromosome variants or cytotypes. The most
common cytotypes are a diploid and a tetraploid based on x ˆ 11, and triploid and hexaploid plants with this basic
number were also observed. Diploids, triploids and tetraploids based on a second basic number of x ˆ 13 were also
seen. Plants with 2n ˆ 24 were shown to be hybrids between diploids with the two di€erent basic numbers. Meiotic
chromosome pairing analysis of the plants with 2n ˆ 24 showed a maximum of two trivalents indicating the presence
of extra copies of one pair of large and one pair of small chromosomes in the 2n ˆ 26 plants. In addition, a number of
di€erent aneuploids of the 2n ˆ 22 and 2n ˆ 44 races were found and many of these also showed structural
chromosomal variation. The distribution of the two main chromosome races is disjunct with the tetraploids con®ned
to southern Victoria. To avoid dysgenic e€ects, future re-establishment e€orts for this species should avoid mixing
# 2000 Annals of Botany Company
seed from di€erent chromosome races.
Key words: Aneuploidy, conservation genetics, karyotypes, meiosis, polyploidy.
I N T RO D U C T I O N
Information on the genetic structure of endangered species
is useful when planning management actions for conservation. Patterns of genetic diversity for neutral markers
provide information on historical and contemporary
patterns of gene ¯ow and co-ancestry, while di€erentiation
for adaptive traits may re¯ect environmental variation.
Genetic markers can also be usefully employed to obtain
important ecological information regarding plant breeding
systems, and possible limits to the reproductive potential of
small populations imposed by inbreeding depression
(Raijmann et al., 1994; Young and Brown, 1999). Such
data help to provide an empirical basis for decisions about
how to allocate limited resources for either in situ or ex situ
maintenance of genetic diversity.
Further issues arise when there is intraspeci®c cytological
variation. Alteration in chromosome number and structure
raises questions about the origin, extent and evolutionary
relationships of the chromosome variants. If the populations of cytotypes are spatially separate, then there are
important implications for the conservation of existing
populations. The di€erent cytotypes comprise the total
gene pool of the species and may occupy di€erent
ecological niches thus meriting their separate conservation.
It is also important to try and place these variants in a
relevant time frame as in some cases the mixing of
populations with di€erent chromosome numbers may be
relatively recent and a consequence of habitat disturbance
by humans. Cytological variation also needs to be taken
into account when conservation strategies are planned for
* For correspondence. Fax ‡61 6 246 5249, e-mail andrew.young@
pi.csiro.au
0305-7364/01/010083+08 $35.00/00
the restoration of depleted populations, or the establishment of new ones, as the mixing of cytotypes can lead to
hybrid dysgenesis (Dobzhansky, 1951).
This study examines the cytological structure of 19 natural
populations of the endangered grassland forb Rutidosis
leptorrhynchoides F. Muell. taken from its geographical
range in southeastern Australia. Previous analysis, of both
allozyme variation and cytological diversity, by Leeton and
Fripp (1991) identi®ed only a single diploid cytotype with
2n ˆ 26. However, a recent, more exhaustive survey of
allozyme variation (Young et al., 1999) has indicated the
presence of both diploid and putative tetraploid populations, but with the apparent separation of ploidy levels
between populations. From a chromosome analysis it
should be possible to con®rm whether populations consist
of a single cytotype or two or more di€erent ones and
whether there is the possibility of hybridization between the
chromosome races.
The aims of this study were to: (1) quantify the cytological variation that exists across the geographic range of
R. leptorrhynchoides and speci®cally to test the hypothesis
that tetraploid individuals exist; (2) examine meiotic
chromosome behaviour to determine the likely origin of
any polyploids and any other chromosome variants; and (3)
generate guidelines for sourcing seed material for future
restoration and re-establishment e€orts.
M AT E R I A L S A N D M E T H O D S
Study species and populations
Rutidosis leptorrhynchoides is a multi-stemmed herbaceous
perennial forb, 20±40 cm in height, which is endemic to
# 2000 Annals of Botany Company
84
Murray and YoungÐCytological Variation in R. leptorrhynchoides
F I G . 1. Distribution of Rutidosis leptorrhynchoides (1871±1999) based on herbarium records.
grassland and grassy woodland communities of southeastern Australia. The species is insect-pollinated, hermaphroditic and has a very ecient sporophytic selfincompatibility system (Young et al., 2000). Flowering is
protracted, lasting from mid-spring until the end of
summer. Although fruit are wind dispersed, dispersal
distances are commonly less than 0.5 m and there is no
long-term storage of fruit in the soil (Morgan, 1995a,b).
Herbarium records suggest that prior to European
settlement, R. leptorrhynchoides was quite widespread and
that there has been a marked reduction in both the number
and size of R. leptorrhynchoides populations since 1874
(Fig. 1). This parallels patterns of loss of the species'
grassland habitat, which has been reduced to about 0.5 %
of its original 2 million ha extent since the mid-1800s, due
mainly to conversion of land for sheep grazing (Kirkpatrick
et al., 1995). The species is currently listed as nationally
endangered (Briggs and Leigh, 1995) and is known from
only 24 populations occupying remnant grassland vegetation mainly along roadsides, railway embankments and in
cemeteries.
Chromosome analysis
Fruit were collected from between three and 37 plants,
depending on availability of ¯owering plants and population size, from each of 19 populations across the geographic
range. To assess variation in chromosome number, a single
seedling from each of these plants was grown in a
greenhouse at 15±258C under natural light. At 3 months,
plants were repotted and 2 weeks later root tips were
sampled. Root tips were treated with 0.05 % colchicine at
48C for 20 h and then ®xed in 3 : 1 absolute ethanol: glacial
actetic acid for 3 h. Root tips were transferred to 70 %
ethanol and stored at ÿ188C. Prior to counting, roots were
hydrolysed in 1 M HCL at 608C for 9 min and then
transferred to 45 % acetic acid before squashing in FLP
orcein (Jackson, 1973). Nucleolar organizer regions were
identi®ed on air-dried chromosome preparations stained
with silver nitrate as outlined in Murray (1994).
Meiotic behaviour
For meiotic analysis, immature in¯orescences were ®xed
in ethanol : chloroform : glacial acetic acid (6 : 3 : 1) for 24 h
and then transferred to 70 % ethanol for storage at 48C.
Observations of diakinesis and metaphase I were made on
pollen mother cells ( pmcs) that had been squashed and
stained in FLP orcein (Jackson, 1973).
Leaf morphological analysis
Previous analysis of leaf morphology by Leeton and
Fripp (1991) indicated signi®cant variation in leaf width to
length ratio that we observed to correlate with the ploidy
variation indicated by allozyme data (Young et al., 1999).
To further explore this relationship, the length and width of
the ®ve lowest leaves from ®ve plants from six populations
of known chromosome number were measured. Three of
the populations were diploid, two from the northern part of
the range and the other from the southern part, and the
other three populations were tetraploids. Similar measurements were then made on herbarium specimens from the
Australian National Herbarium and the National
Herbarium of Victoria representing ®ve extinct populations
from the southern part of the species' range.
R E S U LT S
Chromosome number variation
A total of 333 plants were examined for chromosome
number and karyotype giving an average of 17.5 plants
Murray and YoungÐCytological Variation in R. leptorrhynchoides
85
T A B L E 1. Distribution of cytotypes within and between populations of Rutidosis leptorrhynchoides
2n ˆ
Northern
Barton
Capital Circle
Goulburn
Captains Flat
Letchworth
Poplars
Majura
Queanbeyan
Red Hill
Red Hill B
Stirling Ridge
West Block
Overall
Southern
Bannockburn
Dobies Bridge
Middle Creek
Rokewood
St Albans
Truganina
Wickcli€e
Overall
21
1
2
3
22
12
12
20
12
13
11
20
26
15
16
33
3
193
22t
23
24
26
33
39
43
32
44
44t
45
45u
46
52
66
1
1
2
1
1
1
1
1
1
1
1
1
1
5
3
2
Total
12
12
20
13
14
14
22
29
16
16
37
3
208
2
2
12
20
43t
1
3
1
1
3
5
1
15
17
18
17
1
1
1
2
1
4
1
1
1
1
22
20
20
24
12
20
7
1
1
125
7
1
74
1
1
t indicates replacement of a metacentric chromosome by a telocentric one, and u where one chromosome is of unusual morphology.
studied per population. Thirteen di€erent chromosome
numbers were found in these plants. In addition, a small
number of cases where a metacentric chromosome was
replaced by a telocentric one were also seen (see below).
There appear to be at least two di€erent basic numbers in
R. leptorrhynchoides, x ˆ 11 and x ˆ 13, but ®ve plants
based on x ˆ 12 were also found. The most common
chromosome number was 2n ˆ 22, found in 225 individuals
(68.6 %), followed by 2n ˆ 44 which was found in
75 individuals (22.9 %), together making up 91.5 % of the
plants examined (Table 1). Two triploids with 2n ˆ 33
(Fig. 2A) and one hexaploid with 2n ˆ 66 were observed.
The second grouping of plants, whose chromosome number
is based on x ˆ 13, are relatively rare (3.4 % of the sample)
but several diploids, triploids (Fig. 2B) and a single
tetraploid (Fig. 2C) were found.
The remaining plants had a wide range of di€erent
chromosome numbers: 2n ˆ 21, 23, 43, 45 and 46 (see
Fig. 2F±H for selected examples) and would appear to be
aneuploids based around the diploid and tetraploid forms
of the x ˆ 11 race. Three plants with 2n ˆ 22, 2n ˆ 43 and
2n ˆ 44 were observed to have what appears to be a whole
arm deletion since each contained a telocentric chromosome in place of one of the normal metacentrics seen in
other plants with 2n ˆ 22 (Fig. 2D) or 2n ˆ 44. Three
plants had 21 chromosomes and in all cases had what
appears to be a stable dicentric chromosome (Fig. 2E). A
dicentric chromosome of very similar morphology was also
observed in one of the plants with 2n ˆ 44. A further
variation was seen in one plant with 2n ˆ 45 where there
was an additional small chromosome with a constriction in
the short arm.
Karyotype analysis
The R. leptorrhynchoides karyotype consists of two
groups of chromosomes, large metacentrics that are approx.
6.6±7.5 mm long and small metacentrics that are approx.
3.3±4.2 mm long. No obvious secondary constrictions were
seen, but silver staining indicated that the nucleolar
organizer region was on the largest of the small metacentrics adjacent to the centromere. The 2n ˆ 22 karyotype
was made up of four pairs of large metacentric chromosomes and seven pairs of small metacentrics (Fig. 3A). The
2n ˆ 44 karyotype had twice as many chromosomes in each
of these groups and consisted of eight large and 14 small
pairs of metacentrics (Fig. 3B). The plants based on x ˆ 13
had ®ve large metacentrics and eight small metacentrics
(Fig. 2B and C). It was not possible to identify which, if
any, of these chromosomes were present in the x ˆ 13
plants and absent in the x ˆ 11 ones as there were no
obvious distinguishing features that could be used to
identify individual chromosomes in either of the two
groups. In the 2n ˆ 24 plant that was analysed, there
were nine large metacentrics and 15 small ones (Fig. 2I);
thus it would appear to be an F1 hybrid between a 2n ˆ 22
and a 2n ˆ 26 plant.
Meiotic behaviour
Meiosis was examined in ten plants with 2n ˆ 22 and all
were exclusively bivalent forming and had a mean chiasma
frequency of 19.74 per cell (Fig. 3C). Five plants with
2n ˆ 44 showed frequent quadrivalent formation in
addition to bivalents, a low frequency of trivalents and
86
Murray and YoungÐCytological Variation in R. leptorrhynchoides
F I G . 2. Mitotic and meiotic chromosomes of Rutidosis leptorrhynchoides showing a range of numerical and structural variations. A, Triploid
2n ˆ 33; B, triploid 2n ˆ 39; C, tetraploid 2n ˆ 52; D, diploid 2n ˆ 22 with telocentric chromosome (arrow); E, aneuploid 2n ˆ 21 with dicentric
chromosome (arrow); F, aneuploid 2n ˆ 23; G, aneuploid 2n ˆ 43, chromosome with deletion arrowed; H, aneuploid 2n ˆ 45; I, 2n ˆ 24 with
nine large and 15 small metacentrics; J, diakinesis in a 2n ˆ 24 plant with one trivalent (arrow), one univalent and ten bivalents; K, diakinesis in a
2n ˆ 24 plant with two univalents (arrows) and eleven bivalents.
Murray and YoungÐCytological Variation in R. leptorrhynchoides
87
A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
13
14
16
17
18
19 20
21
22
B
1
2
3
4
23
24
25
26
5
6
27
28
7
29
8
30
9
10
11
31
32
33
C
12
34
35
36
15
37
16 17
38
39
18 19
20
21 22
40
42
43
41
44
D
F I G . 3. Karyotypes and meiosis in diploid (2n ˆ 22) and tetraploid (2n ˆ 44) races of Rutidosis leptorrhynchoides. A, Karyotype of 2n ˆ 22; B,
karyotype of 2n ˆ 44; C, diakinesis in 2n ˆ 22; D, metaphase I in 2n ˆ 44.
univalents and a mean chiasma frequency per cell of 33.77
(Fig. 3D, Table 2). The di€erence in chiasma frequency is
clearer when expressed on a per chromosome basis: diploids
have 0.90 compared to 0.77 in tetraploids.
In a meiotic analysis of one plant with 2n ˆ 24, pollen
mother cells were observed with two trivalents and nine
bivalents, one trivalent, one univalent and ten bivalents
(Fig. 2J) and two univalents and 11 bivalents (Fig. 2K). The
mean frequency of the various con®gurations was 1.05
trivalents, 9.95 bivalents and 0.95 univalents per cell in a
sample of 20 cells. No cells were seen with more than two
trivalents.
T A B L E 2. Meiotic metaphase I chromosome con®gurations
and chiasma frequency per cell in ®ve plants of Rutidosis
leptorrhynchoides with 2n ˆ 44
Cytotype distribution
New South Wales and the Australian Capital Territory or
southern Victoria (Fig. 1). Cytotype distribution showed a
clear north to south geographical discontinuity (Fig. 4);
R. leptorrhynchoides shows a disjunct distribution of its
remaining populations with populations in either southern
Plant
number
Number
of cells
DB 64
DB 65B
MC 55A
MC 54F
BB 51
6
2
10
5
5
MI chromosome con®gurations
I
II
III
IV
Chiasma
frequency
0.33
1.50
0.20
1.60
0.40
13.17
15.50
13.10
16.40
12.60
0.00
0.50
0.00
0.00
0.40
3.39
3.00
3.80
2.40
4.80
33.66
32.50
35.50
30.00
37.20
88
Murray and YoungÐCytological Variation in R. leptorrhynchoides
F I G . 4. Geographical distribution of the cytotypes of Rutidosis leptorrhynchoides. Extinct populations determined on leaf dimensions. d, Diploid
2n ˆ 22; j, tetraploid 2n ˆ 44.
northern populations were largely diploid with 2n ˆ 22, but
seven of the 12 populations examined contained other
cytotypes. For example, of the 13 plants examined from
Captains Flat, 12 had 2n ˆ 22 and the remaining one had
2n ˆ 33, and at Stirling Ridge and Queanbeyan plants with
24 and 26 chromosomes in addition to the more common
2n ˆ 22 were observed. To the south, in Victoria, the two
eastern populations at St Albans and Truganina were
entirely 2n ˆ 22, while the ®ve western populations were
primarily 2n ˆ 44, although all except Wickcli€e contained
some aneuploids. Diversity of cytotype number was
generally higher in tetraploid populations (mean ˆ 3.3,
s.e. ˆ 0.8) than in diploids (mean ˆ 1.9, s.e. ˆ 0.3).
Leaf morphology
There were no signi®cant di€erences in mean width or
length values among any of the three population groups,
northern diploids, southern diploids or southern tetraploids
(data not shown). Similarly, there was no di€erence in the
width to length ratio between northern diploids and
southern tetraploids. However, southern diploids are
distinguishable from the other two groups by their lower
width to length ratio of 16.1 as against 18.8 for tetraploids
and 17.5 for northern diploids, (P 5 0.06). Four of the ®ve
extinct southern populations for which sucient leaves
were available for analysis (AR, CR, KC and KP) had
mean width to length ratios ranging from 14.8 to 17.3,
which are within the 99 % con®dence limits (CL) for
southern diploid populations (14.4±17.8). The ®fth population (VC) had a mean ratio of 17.9 which was beyond the
diploid 99 % CL, but within the 99 % CL for tetraploids
(17.0±20.5). The geographic distribution of these populations is given in Fig. 4.
DISCUSSION
It is dicult to ascertain just how common intraspeci®c
variation in chromosome number and karyotype is in plant
populations. Population studies where there is no apparent
variation are not particularly newsworthy and, therefore,
are probably under-reported. On the other hand, there are
many reports of the widespread occurrence of chromosome
races or variants within species (Semple, 1974; Murray,
1976; Ainsworth et al., 1983; Parker et al., 1991; Ebert et al.,
1996). In some cases there is a clear geographic separation
of the races, in others the di€erent chromosome numbers
are due to the variable presence of B or supernumerary
chromosomes, and in a third group di€erences in chromosome number may indicate the need for taxonomic revision.
What is particularly interesting about the Rutidosis example
described here is its surprisingly high cytological variation
Murray and YoungÐCytological Variation in R. leptorrhynchoides
for a species made up of only 24 natural populations, many
of which consist of a few hundred individuals. In the
19 populations surveyed here, there are di€erent basic
numbers, autopolyploids of at least two of these basic
numbers, a variety of aneuploids and several types of
structural mutation. The presence of a total of 17 di€erent
cytotypes in a sample of 333 plants is clearly an example of
a chromosomally highly variable species.
Our observations have established that there are two
major chromosome races based on x ˆ 11. Diploids with
2n ˆ 22 are most common in the north but are also found
in the two most easterly southern populations. Tetraploids
with 2n ˆ 44 were only found in ®ve westerly populations in
the south and, based on their meiotic behaviour, are clearly
the autopolyploid derivatives of the 2n ˆ 22 plants. This
geographical split of the major chromosome races supports
the previously published allozyme data (Young et al., 1999)
and provides an interesting correlation with the observed
variation in leaf dimensions reported by Leeton and Fripp
(1991). However, our chromosome results are at variance
with those of Leeton and Fripp (1991). Our results do not
support their report of 2n ˆ 26 from each of nine populations, ®ve of which we have also studied, from across the
geographic range. The very low frequencies of 2n ˆ 26
plants and their polyploid derivatives with 2n ˆ 39 and
2n ˆ 52 observed here (total 2.5 %) may be due in part to
the ten-fold di€erence in sampling intensity between the
two studies. However it seems unlikely that this can account
entirely for such a large discrepancy. There are two other
di€erences between our work and that of Leeton and Fripp
(1991). Studies on the breeding system of R. leptorrhynchoides have shown that in our populations the
majority of plants are strongly self-incompatible (Young
et al., 2000). In addition, we have not found any karyotype
that corresponds to the one they illustrated, which had a
pair of small strongly acrocentric chromosomes.
Our measurements of leaves from plants of known
chromosome number have shown that width to length
ratios can be used to di€erentiate diploids from tetraploids
in the southern part of the range. However, the lack of a
di€erence between northern diploids and southern tetraploids is another area of disagreement with the results of
Leeton and Fripp (1991). The ®nding that four of the ®ve
extinct populations were probably diploid clearly shows
that this race was previously more widespread, in particular
representing a western range extension relative to the
current distribution. This might account for some of the
previously observed chromosome and allozyme variation
that we have observed in re-established tetraploid populations in western Victoria (Young and Murray, 2000).
From our observations, and those of Leeton and Fripp
(1991), it is clear that there are two basic chromosome
numbers in R. leptorrhynchoides, x ˆ 11 and x ˆ 13.
Karyotype analysis shows that the 2n ˆ 24 plants have
nine large and 14 small metacentrics and therefore combine
the gametic contributions of a 2n ˆ 22 and a 2n ˆ 26 plant
and suggests that the 2n ˆ 24 plants are naturally occurring
hybrids. Meiotic pairing in the 2n ˆ 24 plants clearly
indicates, due to the observed formation of two trivalents
combined with nine bivalents, that one pair of the large and
89
one pair of the small chromosomes is duplicated in the
2n ˆ 26 plants. Since the 2n ˆ 26 plants are signi®cantly
less common than the 2n ˆ 22 ones, we suggest that they
are naturally occurring double trisomics.
The origin of the 2n ˆ 26 plants is unclear but their
presence in both northern and southern populations
suggests that they have been in existence for a long time.
In plants like Haplopappus and Gibasis, for example,
di€erences in basic number within a species can be
demonstrated to be due to Robertsonian translocations
where one metacentric splits to give rise to two telocentrics
or vice versa (Jackson, 1965; Jones 1974, 1977). From the
karyotypes of the two races of Rutidosis, there is no
suggestion of a simple Robertsonian relationship, since all
the chromosomes are metacentrics. An origin via hybridization with other Rutidosis species also seems unlikely as
neither of the two other species in southeastern Australia,
R. leiolepis F. Muell. and R. heterogama Philipson, has a
sympatric range. Both these species are, in addition, diploid
with 2n ˆ 22 and have the same basic karyotype (Murray
and Young unpubl. res.). Thus, at this stage, we can only
speculate on the origin and evolutionary relationships of
the di€erent basic numbers in R. leptorrhynchoides. Aneuploidy as a consequence of meiotic non-disjunction seems
most likely, although naturally occurring aneuploids are
exceedingly rare in plants. However, we do see a signi®cant
frequency of aneuploids in our sample, all be it more
commonly at the higher ploidy level, but plants with less
than the normal diploid chromosome complement were
also seen. It is possible that Rutidosis, like Dahlia and
probably many other species (Lagercrantz and Lydiate,
1996; Gatt et al., 1999), is an ancient polyploid and that this
provides a level of tolerance for aneuploid chromosome
variation.
The observed aneuploids are presumably either the result
of disjunctional errors at meiosis resulting in the production
of unbalanced gametes or from backcrossing of hybrid
triploids to the 2n ˆ 22 and 2n ˆ 44 parents. The higher
frequency of aneuploids in the tetraploid populations
probably re¯ects a higher propensity for such errors to
occur associated with multivalent formation at meiotic
metaphase I. The presence of triploids and aneuploids may
indicate that a low level of genetic exchange is being
maintained between the diploid and tetraploid lineages.
This is supported by the recent results of an analysis of
allozyme variation in both diploid and tetraploid populations by Brown and Young (2000). This showed that
tetraploid populations share many of the same alleles as
diploids and that, in an UPMGA cluster analysis based
on Nei's genetic distance, tetraploids are nested within
diploid populations rather than clustering in a separate
group. The presence of telocentric and dicentric chromosomes in aneuploids as well as euploids indicates that
structural rearrangements are also fairly common in these
populations.
High levels of cytological diversity in restricted populations of plants, similar to those described here, do not
appear to be common, although broadly similar results
have been obtained for Rumex acetosa (Parker and Wilby,
1989) from a small isolated, island population. Parker and
90
Murray and YoungÐCytological Variation in R. leptorrhynchoides
Wilby (1989) suggest that biparental inbreeding in this
normally outbreeding species may be responsible for the
elevated level of chromosome variation. Increased chromosome instability that results in high levels of spontaneous
breakage and reunion of chromosomes and a reduction in
chiasma frequency with an increase in univalent formation
has been observed following enforced inbreeding in a
variety of plants (Rees, 1961; Jones, 1969; Parker, 1975;
Tease and Jones, 1976). There is no evidence for signi®cant
levels of inbreeding in any of the Rutidosis populations
examined here (Young et al., 1999).
CO N C L U S I O N S A N D CO N S E RVAT I O N
I M P L I CAT I O N S
The results show that R. leptorrhynchoides maintains
considerable intraspeci®c variation in chromosome number
and that this is largely based around the diploid number
2n ˆ 22, its derivative 2n ˆ 44 autotetraploid and associated triploids and aneuploids. The restriction of tetraploids
to the southern part of the range and the potential for
dysgenesis in hybrid triploids suggest that deliberate mixing
of ploidy levels should generally be avoided when undertaking replanting for conservation purposes. However, the
evidence from allozyme data (Brown and Young, 2000)
suggests ongoing genetic contact between the diploid and
tetraploid lineages, and it may be that in large populations
negative ®tness consequences of such hybridization may be
tolerated without loss of overall population viability.
Indeed, in such cases it may provide a source of novel
recombinants. In small populations, however, the advantages of potentially increased diversity due to interploidy
gene ¯ow are likely to be outweighed by reduced individual
®tness.
AC K N OW L E D G E M E N T S
We thank John Morgan, the NSW National Parks and Wildlife Service, Environment ACT and the Victorian Department
of Natural Resources for assistance with fruit collections.
L I T E R AT U R E C I T E D
Ainsworth CC, Parker JS, Horton DM. 1983. Chromosome variation
and evolution in Scilla autumnalis. In: Brandham PE, Bennett
MD, eds. Kew chromosome conference II. London: Allen and
Unwin, 261±268.
Briggs JD, Leigh JH. 1995. Rare or threatened Australian plants.
Melbourne: CSIRO Publishing.
Brown AHD, Young AG. 2000. Genetic diversity in tetraploid populations of the endangered daisy Rutidosis leptorrhynchoides and
implications for its conservation. Heredity (in press).
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