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2 Department of Biological Sciences, Southern Illinois University at Edwardsville, Edwardsville, Illinois 62026 USA; 3 Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, Ohio 43210 USA; 4 Department of Biology, Ashland Uiversity, Ashland, Ohio 44805 USA; 5 Department of Higher Plant Systematics and Evolution, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria; 6 Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269 USA; and 7 Departamento de Botánica, Universidad de Concepción, Concepción, Chile
Received for publication February 25, 1998. Accepted for publication July 27, 1999.
ABSTRACT
Random Amplified Polymorphic DNA (RAPD) markers were used to measure genetic diversity within and divergence among species of Dendroseris (Asteraceae: Lactuceae), a genus endemic to the Juan Fernandez Islands, Chile. Results were compared to previous studies employing allozymes. For five of the species, RAPD banding patterns distinguished all individuals examined, and different mutilocus genotypes were found even in species exhibiting no allozyme diversity. RAPD band diversities ranged from 0.003 to 0.022 within species; >90% of total diversity was among species and <10% within them. Relative levels of allozyme and RAPD diversity were similar for some species, particularly those with highest and lowest diversities, but overall there was no significant correlation. Relationships inferred from a neighbor-joining tree generated from RAPD bands were similar to results obtained from morphology, chloroplast DNA (cpDNA) restriction site mutations, and sequences from the internal transcribed spacer regions of nuclear ribosomal DNA (ITS), but somewhat better resolution was achieved. Relationships shown by allozymes differed from trees based on other data; this ostensibly is a result of the sharing of ancestral alleles and the absence of alleles generated subsequent to speciation. Dendroseris represents an example where RAPD markers, because of their greater variability, provide a useful alternative to allozymes for assessing diversity in rare species endemic to oceanic islands and for resolving relationships among the species.
Key Words: allozymes • Asteraceae • Dendroseris • genetic diversity • Juan Fernandez Islands • RAPD markers
Endemic species have, on average, low genetic diversity at allozyme loci relative to vascular plants in general (Hamrick and Godt, 1989, 1996
), and species endemic to oceanic islands have even lower mean diversity (De Joode and Wendel, 1992
; Frankham, 1997
). For some endemic congeners on oceanic islands there is minimal interspecific divergence at allozyme loci, and thus little resolution of relationships among species is achieved with enzyme electrophoresis (Helenurm and Ganders, 1985
; Lowrey and Crawford, 1985
; Francisco-Ortega et al., 1996
). Because allozymes have sometimes proven insufficiently variable for assessing genetic diversity within and among populations of rare endemic plants (e.g., Waller, O'Malley, and Gawler, 1987
; Lesica et al., 1988
; Soltis et al., 1992
; Crawford et al., 1994
), attention has turned to more variable regions of the genome. A more recently employed approach in plant systematics and population biology is random amplified polymorphic DNA (RAPD) markers, a PCR (polymerase chain reaction)-based technique (Hadrys, Balick, and Schierwater, 1992
; Whitkus, Doebley, and Wendel, 1994
; Brunell and Whitkus, 1997
; Spooner, Ugarte, and Skroch, 1997
; Whitkus et al., 1998
; Wolfe and Liston, 1998
).
The genus Dendroseris (Asteraceae: Lactuceae) is endemic to the Juan Fernandez Islands, which are of volcanic origin, located some 600 km west of mainland Chile at 33°S latitude, and consist of two main islands. Masatierra is four million years old and nearer continental Chile, while Masafuera is one to two million years in age and more distant from the continent (Stuessy et al., 1984
). Dendroseris consists of rosette trees and shrubs and is extremely variable morphologically. Sanders et al. (1987)
placed the 11 species (making Dendroseris the largest genus in the archipelago) into three subgenera: (1) subg. Dendroseris consisting of D. litoralis Skottsb., D. macrantha (Bertero & Dcne.) Skottsb., D. macrophylla D. Don, and D. marginata (Bertero & Dcne.) Hook. & Arn.; (2) subg. Phoenicoseris with D. berteroana (Dcne.) Hook. & Arn., D. pinnata (Bertero ex Dcne) Hook & Arn., and D. regia Skottsb.; and (3) subg. Rea composed of D. gigantea Johow, D. micrantha (Bertero & Dcne.) Hook. & Arn., D. neriifolia (Dcne.) Hook. & Arn., and D. pruinata (Johow) Skottsb. Various aspects of the genus have been discussed in earlier papers (Crawford, Stuessy, and Silva O., 1987
; Crawford et al., 1992, 1998
; Sanders et al., 1987
; Sang et al., 1994
), but it should be emphasized that natural populations of Dendroseris are very small (almost always fewer than ten plants), few in number, and widely scattered.
In earlier studies (Crawford, Stuessy, and Silva O., 1987
; Crawford et al., 1998
), we reported on allozyme diversity within and divergence among species of Dendroseris; both low diversity and divergence were found. Thus, Dendroseris fits the general (but not universal) pattern of many insular endemics (Helenurm and Ganders, 1985
; Lowrey and Crawford, 1985
; Witter and Carr, 1988
). The purposes of the present study were to use RAPD markers to assess genetic diversity within and divergence among species of Dendroseris and to compare the results with those obtained from allozymes.
MATERIALS AND METHODS
Total DNA was extracted from plants collected in the field; leaves were either dried (placed in sealable plastic bags with silica gel) or placed on ice and retained at 4°C until extracted in the laboratory at The Ohio State University, Columbus, Ohio, USA. A total of 35 individuals from 25 populations and seven species was included in the study (Table 1). The CTAB (hexadecyltri-methylammonium bromide) method of Doyle and Doyle (1987)
was used to extract total DNA. DNAs were purified by banding on cesium chloride-ethidium bromide gradients (Palmer, 1986
). Amplifications, electrophoretic separation of the amplified products, and staining were performed as described by Brauner, Crawford, and Stuessy (1992)
. The 11 primers used were from the "A" kit purchased from Operon Technologies, Alameda, California, USA; these included primers 1, 3, 4, 8, 9, 11, 13, 14, 15, 18, and 20. In most instances, DNA from each plant was amplified with the same primer more than once, and the banding patterns were compared.
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; Whitkus et al., 1998
). Diversity was estimated for each species and across all species. Apportionment of diversity within and between species was determined according to Lewontin (1972)
. The rationale for employing these methods for estimating RAPD locus diversity was given in Whitkus et al. (1998)
. A neighbor-joining tree was constructed from RAPD locus similarities (the coefficient of Dice [1945]
) among species of Dendroseris. Genetic distances among species at allozyme loci (Crawford, Stuessy, and Silva O., 1998
) were used to produce a neighbor-joining tree. RESULTS
A total of 215 loci was scored for the 11 RAPD primers for a mean of 19.5 loci per primer. Diversity within species ranged from 0.003 in D. neriifolia to 0.022 in D. micrantha (Table 2) with a mean of 0.012 for all species. About 90% of the total diversity resided between and 10% within species. For the species D. litoralis, D. marginata, D. micrantha, D. neriifolia, and D. pruinata, each plant had a different array of RAPD loci (multilocus genotype). The five plants of D. berteroana have three different patterns, while the 13 plants of D. pinnata express four different genotypes. Total diversity (Ht; Nei, 1973
) at allozyme loci is also shown in Table 2 (from Crawford et al., 1998
); these values ranged from no diversity in D. berteroana and D. pruinata to 0.071 for D. litoralis. Only one plant of D. marginata was examined for allozymes so Ht was not calculated for it.
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) between species of Dendroseris at allozyme loci ranged from 0.73 for D. marginata and D. pruinata to 0.99 for D. berteroana and D. pinnata (Crawford et al., 1998
). Mean identity values for species within subg. Dendroseris, subg. Phoenicoseris, and subg. Rea were 0.91, 0.99, and 0.85, respectively. Mean identities between subgenera ranged from 0.79 for subg. Dendroseris and subg. Rea to 0.90 for subg. Dendroseris and subg. Phoenicoseris. The neighbor-joining tree based on genetic identities at allozyme loci had Dendroseris micrantha and D. pruinata of subg. Rea, and D. berteroana and D. pinnata of subg. Phoenicoseris each forming groups. However, other groups did not correspond to subgeneric assignments; D. litoralis and D. marginata (subg. Dendroseris) do not occur together and D. neriifolia is not included with the other two species of subg. Rea (Fig. 2).
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Although allozymes have been widely and effectively used to assess genetic diversity within and between plant populations (Hamrick and Godt, 1989, 1996
), they are sometimes of limited value for rare plants because of the low level or total lack of variation (Lowrey and Crawford, 1985
; Waller, O'Malley, Gawler, 1987
; Crawford, Stuessy, and Silva O., 1987; Crawford et al., 1994
; Lesica et al., 1988
; Soltis et al., 1992
). Given the paucity of allozyme variation, PCR-based markers have been employed as an alternative with RAPD markers being commonly used (Hadrys, Balick, and Schierwater, 1992
; Whitkus, Doebley, and Wendel, 1994
; Brunell and Whitkus, 1997
; Wolfe and Liston, 1998
). Available data indicate that RAPD marker diversity is usually equal to or greater than allozyme variation in plant species (e.g., Peakall, Smouse, and Huff, 1993
; Szmidt, Wang, and Lu, 1996
; Ayres and Ryan, 1997
: Esselman et al., 1999
). Few studies are available comparing allozyme and RAPD diversity in rare island endemics, but indications are that the latter are more variable than the former; for example, no allozyme variation was found in Lactoris fernandeziana (Lactoridaceae) (Crawford et al., 1994
), whereas RAPD diversity was detected (Brauner, Crawford and Stuessy, 1992
).
Species of Dendroseris are among the very rarest taxa in the Juan Fernandez archipelago (Stuessy et al., 1998
), with D. neriifolia known from only three plants, D. marginata and D. litoralis from several plants and one or two populations, D. pruinata from only one population with more than five plants and three or four smaller populations, and D. berteroana and D. pinnata occurring in very small (usually five or fewer individuals) scattered populations. The relatively small numbers of plants examined in this study are direct reflections of the rarity of the genus. Our results demonstrate the utility of RAPD markers for detecting variation in very rare species. For example, the total lack of allozyme diversity in D. berteroana and D. pruinata (Table 2; Crawford et al., 1998
) might be taken as evidence that the species are genetically homogenous and thus any individual and/or population represents the diversity found in the species as a whole. By contrast, RAPD markers show that each individual of D. pruinata is distinct and 60% of the D. berteroana individuals examined can be distinguished. Every individual of the four species D. litoralis, D. marginata, D. micrantha and D. neriifolia has a unique array of RAPD loci, and four multilocus genotypes were detected among the 13 plants of D. pinnata examined.
Another question is whether allozymes and RAPD markers provide similar estimates of the relative levels of diversity for species of Dendroseris. Because RAPD markers are inherited primarily as dominants, the banding patterns cannot be analyzed routinely by the gene diversity statistics commonly employed for allozyme data unless one can assume populations are in Hardy-Weinberg equilibrium (Swenson et al., 1995
) or segregation can be observed in haploid tissue such as female gametophytes of conifers (Bucci and Menozzi, 1993
; Isabel, Beaulieu, and Bosquet, 1995
; Szmidt, Wang, and Lu, 1996
) so that band frequencies can be directly interpreted as allelic frequencies. Because this was not possible in the present study, the Shannon-Weaver statistic was employed for comparisons to species diversity at allozyme loci. Relative rankings for allozyme and RAPD locus diversity are not correlated (Spearman rank correlation). However, the two species with highest allozyme diversity, D. litoralis and D. micrantha, also exhibit highest RAPD diversity, and D. berteroana has low diversity with both markers (Table 2). There is no correlation between the number of plants examined and the level of RAPD diversity detected (Spearman rank correlation), so the results do not appear to be an artifact of sampling.
Elucidating phylogenetic relationships among congeneric species (or closely related genera) on oceanic islands is necessary for understanding adaptive radiation and the evolution of characters in the closely related yet often morphologically and ecologically divergent species (Baldwin et al., 1998
). Exclusive use of morphological characters could be less than optimal for reconstructing phylogenies because of selection for similar character states as different lineages radiate into similar habitats on the islands. Molecular data have been employed in addition to morphology for generating phylogenetic hypotheses for insular groups, but a recurring problem has been poor resolution, usually due to lack of variation (Baldwin et al., 1998
). That is, the commonly employed molecular approaches for resolving relationships among congeneric continental species are often inadequate for insular endemics, ostensibly because radiation and speciation have been too rapid relative to the molecular sequences employed. Dendroseris is typical of various other insular endemics where both chloroplast DNA restriction site mutations (Crawford et al., 1992
) and sequences from the internal transcribed spacer region of nuclear ribosomal DNA (ITS) (Sang et al., 1994
) failed to provide complete resolution of species relationships. Both phylogenies are similar in having an unresolved polytomy at the base with D. neriifolia (subg. Rea), D. micrantha and D. pruinata (subg. Rea), subg. Dendroseris, and subg. Phoenicoseris constituting each of the four lineages.
The neighbor-joining tree from allozymes (Fig. 2) is similar in certain respects to trees based on morphology, cpDNA restriction sites, and ITS sequences. For example, D. micrantha–D. pruinata (subg. Rea), and D. berteroana–D. pinnata (subg. Phoenicoseris) group together. However, the allozyme tree differs in several significant respects from those portrayed by morphology and other molecular data; the two species of subg. Dendroseris do not cluster together because D. marginata joins with subg. Phoenicoseris before D. litoralis (Fig. 2). The high similarities between species of subgenera Dendroseris and Phoenicoseris are probably the result of sharing alleles present in their common ancestors; there are no high-frequency alleles differentiating species of the two subgenera. The position of D. neriifolia in the tree shows it to be quite distinct from all other species, with no support for its inclusion in subg. Rea where it is now placed (Sanders et al., 1987
) (Fig. 2). Dendroseris neriifolia has three unique alleles, whereas only one unique allele was detected in one other species (Crawford et al., 1998
). Allozymes apparently have evolved too slowly during the radiation of Dendroseris to provide useful data for resolving relationships.
RAPD banding patterns have been used for elucidating relationships between subspecies (Wolff and Morgan-Richards, 1998
) and congeneric species (Adams and Demeke, 1993
; Campos, Raelson, and Grant, 1994
; Brummer, Bouton, and Kochert, 1995
; Catalan et al., 1995
; Stammers et al., 1995
; Lannér, Bryngelsson, and Gustafsson, 1996
; Spooner et al., 1996
; Spooner, Ugarte, and Scroch, 1997
). The tree for Dendroseris species produced from RAPD loci is highly concordant with trees from cpDNA restriction sites and ITS sequences (Crawford et al., 1992
; Sang et al., 1994
), with the species of subgenera Dendroseris and Phoenicoseris grouping together, and D. micrantha and D. pruinata of subg. Rea forming a group (Fig. 1). In addition, D. neriifolia of subg. Rea occurs with the two other species of subg. Rea, whereas the cpDNA, allozyme, and ITS data failed to resolve the position of D. neriifolia (Crawford et al., 1992a
; Sang et al., 1994
) (Figs. 1, 2). This suggests that because RAPD loci evolve more rapidly than allozyme loci the common ancestor of the three species of subg. Rea had sufficient time to accumulate mutations prior to the origin of the three species. The fact that the neighbor-joining tree based on RAPD bands is highly concordant with trees generated from morphological and other molecular data indicates that RAPD markers provide an accurate portrayal of relationships in Dendroseris. Judging from the results for Dendroseris, RAPD markers may offer an additional source of data for assessing genetic diversity within and relationships among closely related and rapidly radiating groups of rare plants endemic to oceanic islands. These rare endemics are of concern for conservation, and RAPD loci may prove useful for identifying particular populations or lineages for preservation when other methods fail to detect variation or resolve relationships.
FOOTNOTES
1 The authors thank CONAF of Chile for permission to do field work in Robinson Crusoe Islands National Park, including field guides Alfonso Andauer, Oscar Chamorro, Miguel Garcia, Ivan Laceva, Bernardo Lopez, and Ramon Schiller; Richard Whitkus and Andrea Wolfe for valuable comments on the manuscript, and Bette Hellinger who word processed the manuscript with her usual accuracy. Financial support was provided by the National Science Foundation from grants INT-7721637, BSR-08306436, BSR-8906988, and DEB-9500499 to D. J. Crawford, T. F. Stuessy, and G. J. Anderson, and by FONDECYT of Chile through projects FNC 1996008-22 and 796-00-15 to M. Silva O. 
LITERATURE CITED
Adams, R. P., and T. Demeke. 1993 Systematic relationships in Juniperus based on random amplified polymorphic DNAs (RAPDs). Taxon 42: 553–571. [CrossRef][ISI]
Ayres, D. R., and F. J. Ryan. 1997 The clonal and population structure of a rare endemic plant, Wyethia reticulata (Asteraceae): allozyme and RAPD analysis. Molecular Ecology 6: 761–772. [CrossRef][ISI]
Baldwin, B. G., D. J. Crawford, J. Francisco-Ortega, S.-C. Kim, T. Sang, and T. F. Stuessy. 1998 Molecular phylogenetic insights on the origin and evolution of oceanic island plants. In D. E. Soltis, P. S. Soltis, and J. J. Doyle [eds.], Molecular systematics of plants II, DNA sequencing, 410–444. Kluwer Academic Publishers, New York, New York, USA.
Brauner, S., D. J. Crawford, and T. F. Stuessy. 1992 Ribosomal DNA and RAPD variation in the rare plant family Lactoridaceae. American Journal of Botany 79: 1436–1439. [CrossRef][ISI]
Brummer, E. C., J. H. Bouton, and G. Kochert. 1995 Analysis of annual Medicago species using RAPD markers. Genome 38: 362–367. [Medline]
Brunell, M. S., and R. Whitkus. 1997 RAPD marker variation in Eriastrum densifolium (Polemoniaceae): implications for subspecific delimitation and conservation. Systematic Botany 22: 543–553. [CrossRef][ISI]
Bucci, G., and P. Menozzi. 1993 Segregation analysis of random amplified polymorphic DNA (RAPD) markers in Picea abies Karst. Molecular Ecology 2: 227–232. [Medline]
Campos, L. P., J. V. Raelson, and W. F. Grant. 1994 Genome relationships among Lotus species based on random amplified polymorphic DNA (RAPD). Theoretical and Applied Genetics 88: 417–422. [ISI]
Catalan, P.,Y. Shi, L. Armstrong, J. Draper, and C. A. Stace. 1995 Molecular phylogeny of the grass genus Brachypodium P. Beauv. based on RFLP and RAPD analysis. Botanical Journal of the Linnean Society 117: 263–280. [CrossRef]
Crawford, D. J., T. F. Stuessy, and M. Silva O. 1987 Allozyme divergence and the evolution of Dendroseris (Compositae: Lactuceae) on the Juan Fernandez Islands. Systematic Botany 12: 435–443.
———, ———, and ———. 1988 Allozyme variation in Chenopodium sanctae–clarae, an endemic species of the Juan Fernandez Islands, Chile. Biochemical Systematics and Ecology 16: 279–284. [CrossRef]
———, ———, M. B. Cosner, D. W. Haines, M. Silva O., and M. Baeza. 1992 Evolution of the genus Dendroseris (Asteraceae: Lactuceae) on the Juan Fernandez Islands: evidence from chloroplast and ribosomal DNA. Systematic Botany 17: 675–681.
———, ———, D. W. Haines, M. B. Cosner, D. Wiens, and P. Lopez. 1994 Lactoris fernandeziana on the Juan Fernandez Islands: allozyme uniformity and field observations. Conservation Biology 8: 277–280. [CrossRef][ISI]
———, T. Sang, T. F. Stuessy, S.-C. Kim, and M. Silva O. 1998 Dendroseris (Asteraceae: Lactuceae) and Robinsonia (Asteraceae: Senecioneae) on the Juan Fernandez Islands: Similarities and differences in biology and phylogeny. In T. F. Stuessy and M. Ono [eds.], Evolution and speciation in island plants, 97–119. Cambridge University Press, Cambridge, UK.
De Joode, D. R., and J. F. Wendel. 1992 Genetic diversity and origin of the Hawaiian Islands cotton, Gossypium tomentosum. American Journal of Botany 79: 1311–1319. [CrossRef][ISI]
Dice, L. R. 1945 Measures of the amount of ecologic association between species. Ecology 26: 297–302. [CrossRef][ISI]
Doyle, J. J., and J. L. Doyle. 1987 A rapid DNA isolation procedure for small quantities of fresh leaf material. Phytochemical Bulletin 19: 11–15.
Esselman, E. J., L. Jianqiang, D. J. Crawford, J. L. Windus, and A. D. Wolfe. 1999 Clonal diversity in the rare Calamagrostis porteri ssp. insperata (Poaceae): comparative results for allozymes and random amplified polymorphic DNA and intersimple sequence repeat markers. Molecular Ecology 8: 443–453. [CrossRef][ISI]
Francisco-Ortega, J., D. J. Crawford, A. Santos-Guerra, and J. A. Carvalho. 1996 Isozyme differentiation in the endemic genus Argyranthemun (Asteraceae: Anthemideae) in the Macaronesian Islands. Plant Systematics and Evolution 202: 137–152. [CrossRef][ISI]
Frankham, R. 1997 Do island populations have less genetic variation than mainland populations? Heredity 78: 311–327.
Hadrys, H., M. Balick, and B. Schierwater. 1992 Applications of random amplified polymorphic DNA (RAPD) in molecular ecology. Molecular Ecology 1: 55–63. [Medline]
Hamrick, J. L., and M. J. W. Godt. 1989 Allozyme diversity in plant species. In H. D. Brown et al. [eds.], Plant population genetics, breeding, and genetic resources, 43–63. Sinauer, Sunderland, Massachusetts, USA.
———, and ———. 1996 Conservation genetics of endemic plant species. In J. C. Avise and J. L. Hamrick [eds.], Conservation genetics: case studies from nature, 281–304. Chapman and Hall, New York, New York, USA.
Helenurm, K., and F. R. Ganders. 1985 Adaptive radiation and genetic differentiation in Hawaiian Bidens. Evolution 39: 753–765. [CrossRef][ISI]
Isabel, N., J. Beaulieu, and J. Bosquet. 1995 Complete congruence between gene diversity estimates derived from genotypic data at enzyme and random amplified DNA loci in black spruce. Proceedings of the National Academy of Sciences, USA 92: 6369–6373.
Lannér, C. T., Bryngelsson, and M. Gustafsson. 1996 Genetic validity of RAPD markers at the intra- and inter-specific level in wild Brassica species with n = 9. Theoretical and Applied Genetics 93: 9–14. [CrossRef][ISI]
Lesica, P., R. F. Leary, F. R. Allendorf, and D. E. Bilderbecl. 1988 Lack of genetic diversity within and among populations of an endangered plant, Hawellia aquatilis. Conservation Biology 2: 275–282.
Lewontin, R. C. 1972 The apportionment of human diversity. Evolutionary Biology 6: 381–398.
Lowrey, T. K., and D. J. Crawford. 1985 Allozyme divergence and evolution in Tetramolopium (Compositae: Astereae) on the Hawaiian Islands. Systematic Botany 10: 64–72. [CrossRef][ISI]
Nei, M., 1972. Genetic distance between populations. American Naturalist 106: 283–292.
———. 1973 Analysis of gene diversity in subdivided populations. Proceedings of the National Academy of Sciences, USA. 70: 3321–3323.
Palmer, J. D. 1986 Isolation and structural analysis of chloroplast DNA. Methods in Enzymology 118: 167–186. [ISI]
Peakall, R., P. E. Smouse, and D. R. Huff. 1993 Evolutionary implications of allozyme and RAPD variation in diploid populations of dioecious buffalo grass Buchloe dactyloides. Molecular Ecology 4: 135–147.
Peet, R. K. 1974 The measurement of species diversity. Annual Review of Ecology and Systematics 5: 285–307.
Sanders, R. M., T. F. Stuessy, C. Marticorena, and M. Silva O. 1987 Phytogeography and evolution of Dendroseris and Robinsonia, tree Compositae of the Juan Fernandez Islands. Opera Botanica 92: 195–215.
Sang T., D. J. Crawford, S.-C. Kim, and T. F. Stuessy. 1994 Radiation of the endemic genus Dendrosersis (Asteraceae) in the Juan Fernandez Islands: evidence from sequences of the ITS regions of nuclear ribosomal DNA. American Journal of Botany 81: 1494–1501. [CrossRef][ISI]
Soltis, P. S., D. E. Soltis, T. L. Tucker, and F. A. Lang. 1992 Allozyme variability is absent in the narrow endemic Bensoniella oregona (Saifragaceae). Conservation Biology 6: 131–134.
Spooner, D. M., J. Tivang, J. Nienhujs, T. T. Miller, D. S. Douches, and A. Contreras-a. 1996 Comparison of four molecular markers in measuring relationships among the wild potato relatives Solanum section Eutuberosum (Subgenus Potato). Theoretical and Applied Genetics 92: 532–540. [CrossRef][ISI]
———, M. L. Ugarte, and P. W. Scroch. 1997 Species boundaries and interrelationships of two closely related sympatric diploid wild potato species, Solanum astleyl and S. bollviense, based on RAPDs. Theoretical and Applied Genetics 96: 764–771.
Stammers, J., J. Harris, G. M. Evans, M. D. Hayward, and J. W. Forster. 1995 Use of random PCR (RAPD) technology to analyze phylogenetic relationships in the Lolium/Festuca complex. Heredity 74: 19–27.
Stuessy, T. F., K. A. Foland, J. F. Sutter, R. W. Sanders, and M. Silva O. 1984 Botanical and geological significance of potassium-argon dates from the Juan Fernandez Islands. Science 225: 49–51.
———, U. Swenson, D. J. Crawford, G. Anderson, and M. Silva O. 1998 Plant conservation in the Juan Fernandez Archipelago, Chile. Aliso 16: 89–101.
Swenson, S. M., G. J. Allen, M. Howe, W. J. Elisens, S. Junak, and L. H. Rieseberg. 1995 Genetic analysis of the endangered island endemic Malacothamnus fasciculatus (Nutt.) Greene var. nesioticus (Rob.) Kern. (Malvaceae). Conservation Biology 9: 404–415. [CrossRef][ISI]
Szmidt, A. E., X.-R. Wang, and M.-Z. Lu. 1996 Empirical assessmentofallozyme and RAPD variation in Pinus sylvestris (L.) using haploid tissue analysis. Heredity 6: 412–420.
Waller, D. M., D. M. O'malley, and S. C. Gawler. 1987 Genetic variation in the extreme endemic Pedicularis furbishiae (Scrophulariaceae). Conservation Biology 1: 335–340. [CrossRef]
Whitkus, R., J. Doebley, and J. F. Wendel. 1994 Nuclear DNA markers in systematics and evolution. In R. L. Phillips and I. K. Vasil [eds.], DNA-based markers in plants, 116–141. Kluwer Academic Publishers, The Netherlands.
———, M. De La Cruz, L. Mota-Bravo, and A. Gomez-Pompa. 1998 Genetic diversity and relationships of cacao (Theobroma cacao L.) in southern Mexico. Theoretical and Applied Genetics 96: 621–627. [CrossRef][ISI]
Witter, M. S., and G. D. Carr. 1988 Adaptive radiation and genetic differentiation in the Hawaiian silversword alliance (Compositae: Madiinae). Evolution 42: 1278–1287. [CrossRef][ISI]
Wolfe, A. D., and A. Liston. 1998 Contributions of PCR-based methods to plant systematics and evolutionary biology. In D. E. Soltis, P. S. Soltis, and J. J. Doyle [eds.], Molecular systematics of plants II, DNA sequencing, 43–86. Kluwer Academic Publishers, New York, New York, USA.
Wolff, K., and M. Morgan-Richards. 1998 PCR markers distinguish Plantago major subspecies. Theoretical and Applied Genetics 96: 282–286. [CrossRef][ISI]
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