AOBPreview originally published online on October 21, 2005
Annals of Botany 2005 96(7):1293-1305; doi:10.1093/aob/mci281
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Nuclear DNA Variation, Chromosome Numbers and Polyploidy in the Endemic and Indigenous Grass Flora of New Zealand
1 School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand, 2 Terrestrial Conservation Unit, Department of Conservation, Private Bag 68908, Newton, Auckland, New Zealand and 3 The Horticulture and Food Research Institute of New Zealand Ltd, Private Bag 92169, Auckland, New Zealand
* For correspondence. E-mail b.murray{at}auckland.ac.nz
Received: 13 March 2005 Returned for revision: 7 June 2005 Accepted: 14 September 2005 Published electronically: 21 October 2005
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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• Background and Aims Little information is available on DNA C-values for the New Zealand flora. Nearly 85 % of the named species of the native vascular flora are endemic, including 157 species of Poaceae, the second most species-rich plant family in New Zealand. Few C-values have been published for New Zealand native grasses, and chromosome numbers have previously been reported for fewer than half of the species. The aim of this research was to determine C-values and chromosome numbers for most of the endemic and indigenous Poaceae from New Zealand.
• Scope To analyse DNA C-values from 155 species and chromosome numbers from 55 species of the endemic and indigenous grass flora of New Zealand.
• Key Results The new C-values increase significantly the number of such measurements for Poaceae worldwide. New chromosome numbers were determined from 55 species. Variation in C-value and percentage polyploidy were analysed in relation to plant distribution. No clear relationship could be demonstrated between these variables.
• Conclusions A wide range of C-values was found in the New Zealand endemic and indigenous grasses. This variation can be related to the phylogenetic position of the genera, plants in the BOP (Bambusoideae, Oryzoideae, Pooideae) clade in general having higher C-values than those in the PACC (Panicoideae, Arundinoideae, Chloridoideae + Centothecoideae) clade. Within genera, polyploids typically have smaller genome sizes (C-value divided by ploidy level) than diploids and there is commonly a progressive decrease with increasing ploidy level. The high frequency of polyploidy in the New Zealand grasses was confirmed by our additional counts, with only approximately 10 % being diploid. No clear relationship between C-value, polyploidy and rarity was evident.
Key words: Chromosome number, C-value, distribution, New Zealand, Poaceae, polyploidy, rarity, taxonomy
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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Variation in the amount of nuclear DNA of the entire chromosome complement or holoploid genome size, here called C-value following Greilhuber et al. (2005)
, together with changes in chromosome number and structure, has been implicated in the diversification and speciation of flowering plants (Levin, 2002). This variation is clearly an important component of adaptation, as variation in C-value affects key parameters of plant growth such as the duration of the cell size, cell cycle and life form (Bennett, 1972, 1987; Gregory, 2005). Correlations have also been made between C-value and plant distribution, with the common observation that plants of more tropical latitudes appear to have lower values than those of temperate latitudes (Bennett, 1976; Levin and Funderburg, 1979). However, other studies, e.g. Grime and Mowforth (1982), report the reverse correlation between C-value and latitude. In a large-scale study on the Californian flora, Knight and Ackerly (2002) demonstrated that species with low C-values predominate in all environments and that in extreme environments species with the highest C-values are poorly represented. There has also recently been the suggestion that high C-values may be maladaptive and lead to plant extinction (Vinogradov, 2003). There also appears to be a clear phylogenetic pattern to C-value variation in the Poaceae, with higher values being most common among the members of the Bambusoideae, Oryzoideae, Pooideae (BOP) clade (Kellogg and Bennetzen, 2004).
Polyploidy is clearly one possible contributor to C-value variation, but the relationship between C-value and ploidy is far from clear-cut (Leitch and Bennett, 2004). In their ‘all angiosperms’ and monocot samples Leitch and Bennett (2004) have shown that the mean amount of 1C DNA does not increase in direct proportion to ploidy and that mean genome size (C-value divided by ploidy level) shows a clear decrease. Nevertheless, polyploidy affects many other genetic and phenotypic characters, and in New Zealand, where 63 % of angiosperms are reported to be polyploid (Hair, 1966), it appears to have played an important role in the evolution of the flora. Polyploids also frequently, though not always, have different distributions to their diploid progenitors, and polyploids are often over-represented among colonizer species (Stebbins, 1971; Thompson and Lumaret, 1992; Levin, 2002; Brochmann et al., 2004).
One of the key recommendations that arose from the first Angiosperm Genome Size workshop and conference held at the Royal Botanic Gardens, Kew, in September, 1997 [Annals of Botany 82 (Supplement A)] was the need to obtain an improved representation of the world's flora in the DNA C-value database (http://www.rbgkew.org.uk/cval/homepage.html). One under-represented area is Australasia. There have been few studies of Australasian plants, with only 19 out of 465 first authors of papers listed in the database coming from the region (Bennett and Leitch, 2005). Only three studies have been published that include New Zealand native angiosperms (Murray et al., 1992, 2003; Hanson et al., 2003). Thus, it is timely to produce a survey of a large family, the Poaceae, from New Zealand.
Grasses are a significant component of the New Zealand endemic and indigenous flora. Poaceae are the second largest family in terms of species and in the recent flora (Edgar and Connor, 2000) 157 species are described as endemic and 31 as indigenous. The New Zealand flora is significant for its high level of species endemicity, in that approximately 85 % of the approximately 2300 vascular plant species are endemic (Cockayne, 1967; Wardle, 1991; de Lange and Norton, 1997; Wilton and Breitwieser, 2000); in the grasses 87·6 % are considered to be endemic (Wilton and Breitwieser, 2000). Recent studies have shown that many of the species-rich genera are the results of recent speciation following long-distance dispersal, mainly from Australia, Malesia and South America (Wardle, 1978; Pole, 1994, 2001; McGlone et al., 2001; Winkworth et al., 2002).
Grasses occupy a wide variety of habitats in a landmass composed of islands of varying sizes that span almost 25° of latitude and rise to over 3000 m. These plants also show a variety of distribution patterns from species that are widespread to those that are restricted to a small local area. Two recent publications have provided an excellent framework for further investigation of the New Zealand grasses, a new grass flora (Edgar and Connor, 2000) and an updated catalogue of threatened indigenous New Zealand plants (de Lange et al., 2004). A recent review (Murray, 2005) has suggested that intraspecific C-value variation can be an indicator of taxonomic heterogeneity. With a number of grass genera for which species delimitation is unclear (Edgar and Connor, 2000), C-value data could provide useful indicators.
In this paper we report on the C-values of 155 species (plus a further six subspecific taxa) and new chromosome numbers for 55 taxa of grasses from the New Zealand endemic and indigenous flora.
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MATERIALS AND METHODS |
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Plant material
The plant material used in this study is listed in Table 1. The majority of species have been studied from single individuals as many of them are rare, confined to restricted areas or found in remote parts of the New Zealand botanical region. Figure 1 shows the botanical provincial boundaries of the North and South Islands of New Zealand and the principal offshore islands mentioned in Table 1 so that the origin of the plant samples can be located. All plants were collected from natural populations and grown either in the experimental garden or in a glasshouse at the University of Auckland. The plants studied are listed in Table 1. The recent grass flora (Edgar and Connor, 2000
) includes 157 endemic and 31 indigenous species. Here we include a further two species, Paspalum orbiculare and Bromus arenarius, as indigenous although they were treated as naturalized by Edgar and Connor (2000). Voucher specimens of all of the plants used in this study have been deposited either in the herbarium of Auckland Museum (AK), the Allan Herbarium, Landcare Research (CHR) or the Otago University Herbarium (OTA). Chromosome numbers were determined either from root tip meristems or from pollen mother cells using standard preparation techniques. In a small number of species we did not determine the chromosome numbers ourselves but for completeness when determining various statistics additional chromosome numbers were obtained from Dawson (2000) and de Lange and Murray (2002).
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Plant classification and determination of conservation status
Grasses have been grouped into two major clades, BOP (Bambusoideae, Oryzoideae, Pooideae) and PACC (Panicoideae, Arundinoideae, Chloridoideae + Centothecoideae) by the GPWG (2000)
. Within this framework we have grouped the New Zealand genera into tribes and subfamilies following Edgar and Connor (2000).
The conservation status of species was obtained from the most recent classification of threatened plants in New Zealand (de Lange et al., 2004). That paper, which uses the New Zealand Threat Classification System (see Molloy et al., 2002), recognizes nine species as ‘Acutely Threatened’, four as ‘Chronically Threatened’ and 58 as ‘At Risk’. Globally all of these taxa fall within the IUCN category of ‘Threatened’ (IUCN, 2000).
Flow cytometry
Determinations of nuclear DNA C-values were made using flow cytometry. In most cases only a single plant was available for analysis, but where several accessions were available values were measured on different days. All gave consistent results with little day-to-day variation. Nuclei were extracted by chopping fresh young leaves with a pair of single-edged razor blades into a final volume of 10 mL of ice-cold Galbraith's buffer (Galbraith et al., 1983), containing 3 % (w/v) polyvinylpyrrolidone. The chopped material was filtered through a 32-µm steel mesh filter and centrifuged at 300 g for 4 min to obtain a pellet of nuclei. The pellet was resuspended in 300 µL Galbraith's buffer containing100 µg mL–1 propidium iodide. In our laboratory we have found that RNase treatment has no effect on C-value so we routinely omit this step from our procedure. To obtain stable and repeatable results in Cenchrus it was necessary to wash the pellet of nuclei in 15 mL Galbraith's buffer and re-centrifuge before adding the propidium iodide. After staining on ice for at least 60 min, samples were analysed using an EPICS Elite ESP flow cytometer (Beckman-Coulter, Hialeah, FL, USA) using the air-cooled argon laser emitting light at 488 nm. Excitation of the probe propidium iodide was at 488 nm with fluorescence emitted measured using a 610 ± 10-nm bandpass filter. The instrument was aligned daily with flow check beads (Beckman-Coulter) that are labelled with a defined fluorescence intensity. Three replicates of each sample were prepared and at least 5000 nuclei were measured from each replicate.
An initial pilot study to determine the overall range of C-values for the taxa studied used Hordeum vulgare ‘Sultan’ (2C = 11·12 pg DNA/2C nucleus) as an external standard. Once this range was established, we used three different internal standards, H. vulgare ‘Sultan’, Secale cereale ‘Petkus Spring’ (2C = 16·57 pg) and the indigenous Poa anceps subsp. polyphylla (2C = 5·45 pg), which were co-chopped with the taxa to be determined. Poa anceps subsp. polyphylla was calibrated against H. vulgare to provide a grass standard that was closer to the lower values that we obtained in our preliminary study. The flow profiles of two independent runs of P. anceps subsp. polyphylla and H. vulgare are shown in Fig. 2A, B. Neither Zea mays W64A (2C = 5·47 pg) nor Sorghum bicolor ‘Pioneer’ 8695 (2C = 1·74 pg), both grasses and recommended standards (Johnston et al., 1999; Bennett et al., 2000), was available in New Zealand. C-values were reported previously for 26 of the species reported here using Actinidia chinensis as an external standard (Murray et al., 2003). On repeating the analyses with the grass internal standards we have found that these earlier values showed the same ranking but were approximately 30 % lower than those reported here.
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Following Leitch and Bennett (2004)
we have calculated mean 2C genome size as the amount of 2C DNA in picograms divided by the ploidy level of the species.
Chromosome number determination
Somatic chromosome numbers were determined from root tips that were pretreated with a saturated solution of paradichlorobenzene for 18 h at 4 °C, fixed in 3 : 1. ethanol/acetic acid and stained with FLP-orcein (Jackson, 1973). Meiotic chromosomes were observed in pollen mother cells that were fixed and stained as outlined above.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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C-value variation
C-values were determined for 155 species (161 taxa because in some species two subspecies or forms of a species were measured; Table 1). A wide range of C-values was observed, from 0·97 pg per 2C in Zoysia pauciflora to 32·40 pg per 2C in Poa litorosa (Table 1), representing a 33·4-fold variation. The spread of absolute values within genera varied considerably: some, such as Chionochloa, Cortaderia and Microlaena, showed a narrow range of values whereas others, such as Lachnagrostis and Poa, showed a wide range. When the ranges were expressed in relative terms, the highest over the lowest, Poa with a value of 7·4 was clearly different to the others, such as Chionochloa (1·75), Cortaderia (1·2), Microlaena (1·88) and Lachnagrostis (2·13). There was little evidence of any grouping of values that would result in discontinuities in C-values within genera. At the genus level, measurements were available for ten genera present in both New Zealand and the rest of the world (Table 2). It is difficult to see any clear trends from these comparisons as in some cases, e.g. Elymus, Festuca and Paspalum, the mean genome sizes are remarkably similar in both geographical areas, but in others, e.g. Deschampsia, Imperata and Trisetum, there are large differences. Similarly, comparisons of minimum and maximum C-values for the genera (Table 2) show different patterns. In Agrostis, Festuca, Poa and Trisetum the maximum values for the New Zealand representatives are higher than those from elsewhere but in Bromus, Deschampsia and Imperata they are lower. In Imperata and Koeleria the New Zealand species show lower minimum values than the non-New Zealand samples but the reverse is the case in Deschampsia and Trisetum. However, the limited sizes of the samples must be borne in mind when such comparisons are made.
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C-value and phylogeny
In Table 3 the 35 genera are grouped into the two major clades, BOP and PACC, and then subfamilies and tribes, and the mean 2C value and mean genome size for each genus has been calculated. Many of the genera in the PACC clade had relatively small mean C-values and mean genome sizes. However, there were some interesting exceptions. Pyrrhanthera in Arundinoideae (PACC) had the third largest C-value observed (21·51 pg per 2C) but the high ploidy level in this monotypic genus (26x) means it had a small mean genome size. The genera in Ehrhartoideae and the tribe Stipeae in Pooideae, in the BOP clade, have low values for both of these measurements.
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C-value and ploidy level
The mean, standard deviation and range of C-values for different ploidy levels are given in Table 4. There is a progressive increase in mean C-value with increasing ploidy level, with the exception of the 10x category, but it is clear that there is a large range of values at each level and that there no defined incremental increase with increasing ploidy. Nine of the New Zealand genera show a range of different ploidy levels and in seven of these, Deyeuxia, Elymus, Festuca, Hierachloe, Lachnagrostis, Poa and Puccinellia, there is a progressive decrease, to different degrees, in genome size with increasing ploidy (Table 5). In Rytidosperma the tetraploids have a slightly higher genome size than the diploids and in Agrostis the hexaploids and 12-ploids have almost identical genome sizes (Table 5).
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C-value and rarity
We obtained C-values for a significant proportion of the plants in the various conservation categories and the results are shown in Table 6. We also examined the relationship between rarity and C-value at generic level. Because the numbers of species within genera are much smaller at this level we have grouped the plants classified into the three categories outlined above as a single category ‘Threatened’ and compared their values with those of the non-threatened members of four genera, Chionochloa, Poa, Rytidosperma and Trisetum, for which the chromosome numbers of the plants analysed are the same. In Chionochloa the comparison between threatened and non-threatened is 5·56 (n = 9) to 5·46 (n = 10), in Poa 5·80 (n = 9) to 5·75 (n = 17), in Rytidosperma 8·26 (n = 1) to 6·96 (n = 5) and in Trisetum 11·09 (n = 2) to 11·60 (n = 5).
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Intraspecific C-value variation
Deyeuxia avenoides, Lachnagrostis littoralis, L. lyallii and Rytidosperma thomsonii all appear to show intraspecific C-value variation. In the first three species, the plants all had the same chromosome number but in R. thomsonii two different chromosome numbers were obtained (Table 1). In D. avenoides, the lower C-value was 87 % of the higher value, in L. littoralis it was 88 % and in L. lyallii it was 74 %. In R. thomsonii diploid and tetraploid plants were counted and the tetraploids had 1·84 times the DNA C-value of the diploid.
Chromosome numbers and ploidy levels
The chromosome numbers for 55 species are published here for the first time and, in addition, we report five new chromosome numbers in species for which chromosome numbers have been reported previously. These latter species are Deyeuxia aucklandica, Lachnagrostis pilosa subsp. pilosa, Rytidosperma buchananii, R. thomsonii and Trisetum tenellum (Table 1). With these new counts, chromosome numbers are now known for 186 species of endemic and indigenous grasses (91·6 % of the total of 203 that we have recognized in this paper; Table 7). If infraspecific ranks are included, there are 214 taxa and of these 193 (90·2 %) have been counted.
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The large majority (91 %) of species in the 36 endemic and indigenous genera are polyploid; diploids are confined to six genera, Australopyrum, Deschampsia, Imperata, Puccinellia, Rytidosperma and Spinifex (Table 7). Of the species that are polyploid, 39·8 % were tetraploid and 26·3 % were hexaploid, with smaller percentages at the higher ploidy levels (Table 7). High ploidy levels were seen in Poa, four species were 16x and another was 38x, and the endemic, monotypic Pyrrhanthera was 26x. Of the genera with ten or more species, Chionochloa was unusual in that all 23 species were at the same ploidy level (6x) whereas the other large genera had species at a variety of ploidy levels; for example, Festuca, with ten species, had four ploidy levels.
Polyploidy and rarity
Information is available for eight grass taxa that are classified as ‘Acutely Threatened’, four that are ‘Chronically Threatened’, 49 that are ‘At Risk’ and 117 that are ‘Not Threatened’. The percentage of polyploids in each category is given in Table 6. If the three threatened categories are combined then 94·8 % of these species are polyploid, slightly higher than the 89·7 % for the non-threatened category.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSLITERATURE CITED |
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The present study has increased the representation of grasses in the C-value database by about 30 % and the total number of New Zealand angiosperms to 149. This number includes the first reports for 21 additional genera of Poaceae, five of which, Anemanthele, Pyrrhanthera, Simplicia, Stenostachys and Zotovia, are endemic to New Zealand. The new values show a 33·4-fold variation for the New Zealand plants (0·97–32·40 pg per 2C nucleus), well within the range of values for the family as a whole (0·50–43·25 pg per 2C nucleus). Owing to the high level of endemism in the New Zealand flora, few intraspecific comparisons between New Zealand and non-New Zealand plants can be made, but among indigenous plants some comparisons are possible. An example is Deschampsia cespitosa, a widespread cosmopolitan species that in New Zealand is diploid and has 10·43 pg per 2C. By comparison, Bennett et al. (1982)
, who did not count the chromosomes of the plant from South Georgia that they studied, but assumed that it was diploid, reported a C-value of 8·55 pg per 2C. Unfortunately, there is no voucher specimen associated with the measurement made by Bennett et al. (1982) so the identity of their plant cannot be confirmed. The value for Imperata cheesemanii from New Zealand is lower than the value for the one other Imperata species so far recorded: otherwise, the minimum values obtained for genera present in New Zealand are higher than the minimum values recorded for the same genera elsewhere in the world. In seven such genera the maximum values for New Zealand species are higher than those found elsewhere. Poa flabellata from South Georgia is 4x and has a C-value of 5·45 pg per 2C (Bennett et al., 1982) similar to the New Zealand 4x Poa species. Obtaining C-values for this sample of grasses was relatively straightforward and good, symmetrical peaks with low coefficients of variation were generally obtained. Although in most cases only a single sample was available, when we did have more than one there was good agreement between measurements from different plants made on different days, usually less than 5 % difference. There are four exceptions for which there was a greater than 10 % difference between samples and these are discussed briefly below. One other unexpected result was obtained from among the Poa species that had 2n = 4x = 28. Poa schistacea had a C-value of 11·02 pg but 22 other Poa species had C-values between 4·26 and 6·67 pg, with the P. schistacea value being approximately double the mean value of the other species.
C-values, distribution patterns and rarity
Our measurements, although admittedly limited, provide little evidence to support the contention that large C-values are maladaptive and may be a cause of extinction (Vinogradov, 2003). However, our values are relatively low compared with the global sample used by Vinogradov: the highest C-value that we obtained, 32·24 pg per 2C for Poa litorosa, is below the range of his ‘Global concern’ category but higher than the mean of his ‘Local concern’ category. In our sample, there are no clear differences between species that are rare or with restricted distribution and those species that are widespread. When phylogenetic constraints are reduced, by restricting the analysis to species with the same chromosome number within a single genus, there is again no large difference between the restricted and widespread species in the four genera (Chionochloa, Poa, Rytidosperma and Trisetum) for which such a comparison is possible. There also does not appear to be any correlation between polyploidy and rarity, but it must again be borne in mind that the sample sizes are not large and that the majority of New Zealand grasses are polyploid. It is also interesting that in several genera (Agrostis, Festuca, Poa, Puccinellia) the species with the highest C-values and chromosome numbers are found in the most extreme environments such as the sub-Antarctic [Auckland (Campbell) and Enderby Islands] and Chatham Islands. The genus Elymus has the highest mean C-value of all the grass genera in New Zealand (27·02 pg per 2C) yet it is by no means the most uncommon or threatened (de Lange et al., 2004). Many of the least common or seriously threatened species, such as Poa spania, Amphibromus fluitans and Simplicia laxa, are all within the lower half of C-values for New Zealand grasses. Differences in C-value do appear to reflect the geographical origin of the genera, with five that we have identified (following Clayton and Renvoize, 1986) (Imperata, Isachne, Paspalum, Oplismenus, Zoysia) as being of tropical origin all having C-values in the lowest end of the range we observed. This is in line with previous observations that tropical species of plants typically have lower C-values than temperate species (Bennett, 1976; Levin and Funderburg, 1979).
Leitch and Bennett (2004), in a survey of amounts of nuclear DNA, have pointed out that in angiosperms the mean genome size of polyploids was significantly lower than that of diploids. We have performed a similar analysis of the nine genera of New Zealand grasses that contain species with different ploidy levels and have found that most also show smaller genome sizes in polyploids compared with diploids. In some cases the differences are not great and it is possible that this reflects the recent nature of speciation/polyploidization that is commonly found in the New Zealand angiosperm flora (Wagstaff and Garnock-Jones, 1998; Heenan et al., 2002) and that genome diminution in some genera may reflect a longer timescale since speciation.
Taxonomic implications of C-value and chromosome variation
Four examples of putative intraspecific C-value variation have been observed. Three of these species (Deyeuxia avenoides, Lachnagrostis littoralis and L. lyallii) have been long recognized as being highly variable, showing differences in habit and distribution (Edgar, 1995). We also found examples of intraspecific variation in chromosome number in two species of Rytidosperma but were only able to measure C-values in one of them, R. thomsonii. This latter species is reported to have robust and small-statured races that related to the observed differences in chromosome number and C-value (B. P. J. Molloy, personal communication).
In line with previous studies (summarized by Dawson in Edgar and Connor, 2000) the majority of new chromosome counts confirm further examples of polyploidy with diploids confined to six genera, Australopyrum, Deschampsia, Imperata, Puccinellia, Rytidosperma and Spinifex. There may be some debate as to what is a diploid in some of these genera because the basic number (x) is 13 in Deschampsia, 10 in Imperata and 12 in Rytidosperma. We have assumed that 2n = 26, 2n = 20 and 2n = 24 are diploid numbers in these three genera as these are the lowest numbers that are found and the plants are bivalent forming. In addition to the new count of 2n = 48 for Rytidosperma thomsonii, we have obtained new counts for four other species that have been studied previously. In Deyeuxia aucklandica, de Lange and Murray (2002) reported 2n = 42 whereas the new material had 2n = 56. de Lange and Murray (2002) found 2n = 56 for Lachnagrostis pilosa subsp. pilosa compared with 2n = 98 here and they, together with Calder (1937), found 2n = 72 for Rytidosperma buchananii compared with 2n = 48 reported here. The final example is Trisetum tenellum with a count of 2n = 28 obtained here compared with 2n = 56 reported by de Lange and Murray (2002). There are relatively few examples of intraspecific chromosome number variation in the New Zealand flora; Murray et al. (1989) reported that only approximately 2 % of the species for which chromosome numbers were known had different chromosome races. Further investigation of these new examples is needed to ascertain whether the chromosome races and putative C-value variants are sufficiently distinct for them to be recognized as distinct taxa.
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ACKNOWLEDGEMENTS |
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We thank Dean Baigent-Mercer, Amanda Baird, John Barkla, Steve Benham, Jonathon Boow, John Braggins, Andrea Brandon, Jim Clarkson, Shannel Courtney, Geoff Davidson, Lisa Forester, Rhys Gardner, Bridget Gibb, Terry Hatch, Graham Jane, Peter Johnson, Phil Knightbridge, Kelvin Lloyd, Geoff McCauley, Brian Molloy, David Norton, Colin Ogle, Brian and Chris Rance, Matt Renner, Nick Singers, Mike Thorsen and Matt von Konrat for their help in obtaining plant material for this study, Mei Nee Lee for her help with accessioning the voucher specimens at the Auckland Museum Herbarium, Alison Duffy for assistance in preparing flow cytometry samples, Jingli Zhang for operation of the flow cytometer, and Henry Connor, Peter Heenan and Ilia Leitch for their comments on an earlier draft of the manuscript.
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LITERATURE CITED |
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