ISOZYME DIVERGENCE BETWEEN EASTERN ASIAN,NORTH AMERICAN,AND TURKISH SPECIES OF LIQUIDAMBAR (HAMAMELIDACEAE)

The deciduous woody genus Liquidambar has four morphologically similar species in eastern and western Asia, eastern North America, and Central America. Liquidambar styraciflua is found in the eastern United States and Central America, L. orientalis is native only to southwest Turkey, and L. formosana and L. acalycina occur in eastern Asia. This genus is one of many that contributes to the floristic similarities observed between these different regions. Allelic variation was scored at 22 isozyme loci from 41 populations. The level of genetic divergence between species on different continents is high. Nei's genetic identity was 0.431 between L. formosana and L. styraciflua, 0.485 between L. acalycina and L. styraciflua, 0.512 between L. orientalis and L. styraciflua, 0.256 between L. formosana and L. orientalis, and 0.305 between L. acalycina and L. orientalis. Estimates of time of divergence from the isozyme data suggest that the current species diverged before or during the Miocene. The pattern of relationships portrayed by the isozyme data suggest a longer period of separation between the eastern and western Asian forms of this genus. In addition, the eastern North American and Turkish species appear to be the most closely related intercontinental pair of species providing evidence for a North Atlantic land bridge as late as the Miocene. It would appear, therefore, that the North American populations were in contact with the Asian populations over the North Pacific and North Atlantic possibly as late as the Miocene, but that the separation between the two Asian populations occurred much earlier. The time of divergence as measured from the isozyme data correlates with an independent assessment of the origin of these disjuncts as determined from the fossil record.     

KARYOTYPES OF EASTERN NORTH AMERICAN PHLOX

The karyotypes of 32 Phlox taxa were studied in many plants representative of populations found throughout eastern North America. Most plants were diploid with 2n = 14, but a few tetraploids and plants with B-chromosomes were also observed. Some species were virtually indistinguishable karyotypically, while others differed. Within and between the Subsections Speciosae, Divaricatae, and Subulatae, strikingly similar karyotypes were observed. Other Subsections differed significantly, with the Ovatae showing strong intrasubsectional variation. Increased karyotype asymmetry is correlated with morphological specialization. Where polyploidy was observed, discordant chromosome sets indicated allopolyploidy.     

VEGETATIVE AND FLORAL RELATIONSHIPS AMONG WESTERN NORTH AMERICAN POPULATIONS OF COLLOMIA LINEARIS NUTTALL (POLEMONIACEAE)

Thirty-seven characters were measured on greenhouse grown progenies of twenty-three populations representing, for Collomia linearis, a broad geographical and ecological distribution in western North America. Twelve vegetative and seventeen floral characters showed significant among-population/within-population variance ratios (F-statistics). Overall, floral characters showed higher F-statistics than did vegetative characters. The F-statistics and character means were used to construct phenograms based on weighted similarity measures and single-linkage clustering. With the exception of a homogeneous cluster comprising northern Rocky Mountain OTUs, relationships based on floral characters were geographically random. No clearly defined morphological trends toward increased autogamy were observed in association with geographical or ecological distribution. Several clustering relationships, based on vegetative characters, were interpreted as representing geographically unrelated genotypes convergent with respect to ecotypic differentiation. The most distinctive clusters of OTUs in the vegetative phenogram were associated with subalpine and wet meadow sites, habitats considered as ecologically marginal for the species. Comparison of the two phenograms revealed considerable disparity between relationships based on floral characters and those based on vegetative characters. This disparity lends support to the hypothesis that floral and vegetative character combinations are subject to independent selective processes. The absence of polyploidy or mitotically detectable chromosomal rearrangements indicates that the observed variation among widely separated populations represents either divergence or convergence via genetic differentiation at the diploid level.     

ORIGINS OF GENOTYPIC VARIATION IN NORTH AMERICAN DANDELIONS INFERRED FROM RIBOSOMAL DNA AND CHLOROPLAST DNA RESTRICTION ENZYME ANALYSIS

Restriction enzyme analysis of ribosomal DNA (rDNA) and chloroplast DNA (cpDNA) is used to assess the relative contribution of hybridization and mutation as sources of genotypic variation in weedy asexual dandelions, with focus on the dandelion flora of North America. Of 318 North American dandelions surveyed, 145 rDNA-cpDNA clones are detected. The combined rDNA-cpDNA genotypes show that most of the polymorphic rDNA and cpDNA restriction sites or lengths in these plants are also present in weedy asexual dandelions collected from natural populations in Europe and in asexual and diploid taxa (microspecies) chosen to represent diverse Eurasian members of the genus. However, of 222 combined rDNA-cpDNA genotypes found in 427 asexual plants surveyed, only 9 genotypes are found in both North American and Eurasian dandelions. Two rDNA and three cpDNA characters are unique to individual plants in North America and are consistent with mutational origins of genotypic variation in asexual lineages. But the array of genotypic diversity, characterized by different combinations of the rDNA and cpDNA characters, show that multiple hybridization events are a more important source of genotypic variation than mutation in the asexual polyploids. The rDNA and cpDNA data also indicate polyphyletic origin of several asexual Taraxacum taxa.     

MOLECULAR DIVERGENCE BETWEEN ASIAN AND NORTH AMERICAN SPECIES OF LIRIODENDRON (MAGNOLIACEAE) WITH IMPLICATIONS FOR INTERPRETATION OF FOSSIL FLORAS

Botanists have long been aware of the floristic similarities between eastern Asia and eastern North America. Most who have considered this classic disjunction pattern have suggested that it arose through range disruption of a flora that was once more widely distributed in the Northern Hemisphere. There is less agreement on the timing of this process, with suggestions ranging from the Paleocene to the Neogene. In this study, molecular markers from two different plant genomes were used to assess the degree of genetic divergence between the two interfertile, morphologically similar species of the genus Liriodendron, i.e., L. tulipifera and L. chinense. Resulting molecular divergence estimates were translated into approximate dates of separation, independent of evidence from the fossil record. Allozyme data (Nei's genetic identity = 0.434) suggested a divergence time of 10–16 million years before present, whereas sequence divergence in the plastid genomes (1.24%) led to an estimate of approximately 11–14 million years before present. A review of the paleobotanical literature indicated that the fossil floras that included, or might have included Liriodendron could not have survived in Beringia after the late Miocene and the onset of southward-migrating Arctic air masses on the North American continent. This interpretation suggests a minimum time of separation of approximately 13 million years before present. Thus, both molecular data sets and the paleobotanical evidence concur in suggesting a divergence time of 10–16 million years before present. Interspecific compatibility and relative morphological stasis must have, therefore, persisted from at least the late Miocene. We emphasize the need for similar studies in other genera, especially those that have both a reasonable Tertiary fossil history and extant species in mesic temperate refugia in Asia, Europe, and western as well as eastern North America.     

蒿属腺毛蒿组和白苞蒿组的分支分类,生物地理及亲缘关系的研究

菊科蒿属Ａｒｔｅｍｉｓｉａ的腺毛蒿组和白苞蒿组共有２６种８变种,为亚洲特有植物。前主产我国西南中、高海拔地区;后主产秦岭以南横断山脉以东各省区的中、低海拔地区,少数种在亚洲南部、东南部也有分布。除泰国艾Ａ．ｂｏｒｅａｌｉ－ｓｉａｍｅｎｓｉｓ外,其余国内均产。它们在蒿属蒿亚属中进化程度较高,且与其它组有明显的区别。选择亲缘关系最近的艾组为外类群。在外类群比较原则和形态演化原则的基础上,对大量性状     

KARYOTYPIC VARIATION OF EASTERN NORTH AMERICAN CLAYTONIA CHEMICAL RACES

Considerable karyotypic differentiation has occurred within the group of taxa comprising the eastern North American members of the genus Claytonia. Patterns of karyotypic differentiation are congruent with evolutionary groupings based on flavonoid chemistry, particularly at the diploid level. The 2n = 16 diploid chemotype found in both C. caroliniana and C. virginica possesses a karyotype composed entirely of metacentric chromosomes, while acrocentric chromosomes predominate in the karyotypes of the 2n = 12 and 2n = 14 diploid chemotypes of C. virginica. The 2n = 16 diploid also has a karyotype significantly larger than those of the other diploid cytotypes. Polyploid karyotypes of both species show varying degrees of divergence from their presumed diploid progenitors.     

AN ELECTROPHORETIC AND SEROLOGICAL INVESTIGATION OF SEED PROTEINS IN GALEOPSIS TETRAHIT L. (LABIATAE) AND ITS PUTATIVE PARENTAL SPECIES

Seed proteins from the tetraploid Galeopsis tetrahit L. and its putative parental species G. pubescens Bess. and G. speciosa Mill., were examined using disc gel electrophoresis (PAGE), Ouchterlony double diffusion, and Immunoelectrophoresis. Forty-three inbred cultivated lines of G. speciosa, G. pubescens, and G. tetrahit (both the naturally occurring species and an artificially produced hybrid) and two wild populations of G. tetrahit were examined. PAGE gels were stained for total protein or malate dehydrogenase. Although variability in the total protein pattern was detected within and between lines for all three species, there was much similarity among the taxa. No bands appeared in the hybrid that were not present in the parents. The band pattern for synthetic G. tetrahit was very similar to that of natural G. tetrahit suggesting that G. tetrahit originated from a cross in nature between G. pubescens and G. speciosa. The total protein PAGE results were analyzed using numerical taxonomic techniques. Although these analyses did not clearly separate the three species, the general tendency was toward grouping G. pubescens lines together, natural G. tetrahit lines together, and synthetic G. tetrahit lines together. Natural and synthetic G. tetrahit lines were also interspersed among each other along with some G. speciosa lines. The malate dehydrogenase pattern showed little variation among the three species. Qualitative serological methods did not distingush among the three species, but confirmed the similarity observed among the taxa in the results of electrophoresis.     

PATTERNS OF VARIATION IN FOLIAR TRICHOMES OF EASTERN NORTH AMERICAN QUERCUS

Scanning electron microscopy of leaf trichomes of the forty two native species of oaks in eastern North America indicates five patterns of variability: 1) Eight trichome types are evident among the species and each species possesses a definite complement of trichome types. Certain trichomes are restricted to particular subgenera and series. 2) An obvious seasonal loss of trichomes occurs during leaf maturation. This loss may be both quantitative in terms of trichome density and qualitative in terms of trichome type. 3) There is an obvious difference between the adaxial and abaxial surfaces. The adaxial side of most oak leaves is dark green, lustrous, and glabrous or glabrate. The abaxial surface either remains pubescent, becomes glabrate or glabrous, or maintains trichomes along the midrib or in the axils of major secondary veins. There are also initial quantitative and qualitative trichome differences between the two sides. 4) Geographical and ecological variations are due in part to non-genetic ecophenic modifications, ecotypic differentiation, and random genetic differences not necessarily correlated with environmental conditions. Trichome types are considered to be less affected by environment than is trichome density. 5) Hybridization and introgression within a subgenus leads to localized variability. Trichomes of hybrids are usually a combination of the parental types. These five patterns of variation are predictable and appear to be held within rather narrow limits. The complement of foliar trichomes, therefore, is a reliable character in the taxonomy of the oaks.     

DIFFERENTIATION AMONG NINE POPULATIONS OF PHLOX. I. ELECTROPHORETIC AND QUANTITATIVE VARIATION

The organization of genetic variation in Phlox drummondii was investigated using both allozyme electrophoresis and quantitative genetics. Variation at five polymorphic enzyme loci was characterized in nine populations, and variation in 16 morphological and life-history characters was examined using an analysis of full- and half-sibs in seven populations. Significant levels of genetic variation were found at enzyme loci and for metric characters. Significant heritabilities were observed for 15 of the 16 characters examined. Genetic differences among populations were revealed both by Nei's genetic distance and by phenotypic differences, summarized by discriminant analysis. Partitioning variance in allozyme frequencies among hierarchical levels of genetic organization indicated that 94% of this variance lay within populations, 4% between populations within varieties, and 2% between varieties. Partitioning phenotypic variance for metric characters indicated that 73% lay within populations, 24% lay between populations within varieties, and 3% lay between varieties. Thus, both electrophoretic and metric characters indicated that despite extensive genetic differentiation among populations, most of the evolutionary potential of the species lies within populations.     

INTROGRESSION OF COYOTE MITOCHONDRIAL DNA INTO SYMPATRIC NORTH AMERICAN GRAY WOLF POPULATIONS

Mitochondrial DNA (mtDNA) genotypes of gray wolves and coyotes from localities throughout North America were determined using restriction fragment length polymorphisms. Of the 13 genotypes found among the wolves, 7 are clearly of coyote origin, indicating that genetic transfer of coyote mtDNA into wolf populations has occurred through hybridization. The transfer of mtDNA appears unidirectional from coyotes into wolves because no coyotes sampled have a wolf-derived mtDNA genotype. Wolves possessing coyote-derived genotypes are confined to a contiguous geographic region in Minnesota, Ontario, and Quebec, and the frequency of coyote-type mtDNA in these wolf populations is high (>50%). The ecological history of the hybrid zone suggests that hybridization is taking place in regions where coyotes have only recently become abundant following conversion of forests to farmlands. Dispersing male wolves unable to find conspecific mates may be pairing with female coyotes in deforested areas bordering wolf territories. Our results demonstrate that closely related species of mobile terrestrial vertebrates have the potential for extensive genetic exchange when ecological conditions change suddenly.     

GENETIC RELATIONSHIPS BETWEEN ONE BRITISH AND SEVERAL NORTH AMERICAN POPULATIONS OF CREPIDULA FORNICATA BASED ON ALLOZYME STUDIES (GASTROPODA: CALYPTRAEIDAE)

Crepidula fornicata(Linné) was introduced into Britainand Europe with oysters early in this century. The source populationswere probably from Long Island Sound of the Northwestern Atlantic,U.S.A. In order to determine the genetic similarity of the introducedand native populations, starch-gel electrophoresis was performedon 6 native populations from Maine to Long Island Sound. Theseresults were compared with those for one population from Portsmouth,England. The degree of similarity among New England sites was not relatedto the geographical distance between sites. There were no clinesin gene frequencies. The year-to-year variation at one sitewas often larger than variation between sites. Ail Nei's D valueswere very small, compared with those between species, rangingfrom 0.003 to 0.016 for New England samples. The English populationhad Nei's D values of 0.002 to 0.012 from the New England samples,and hence was not divergent. At no locus was the Portsmouthpopulation significantly different in gene frequencies fromall the new England samples. Genetic distances between speciesof Crepidula are usually in the range of 1.0–2.0. Thedifferences between New England sites can be attributed to samplingerror or to local variation in gene frequency caused by variationin source of recruitment. The species is unified by its planktoniclarvae and a fairly uniform habitat within New England. Heterozygosity and other measures of genetic variation werelower for the Portsmouth population than for any of the NewEngland samples. The absence of some alleles in the Portsmouthpopulation could be due in part to sampling error associatedwith small sample size or the loss of some rare alleles fromthe population. (Received 8 March 1984;     

INTRASPECIFIC CHLOROPLAST DNA VARIATION AND BIOGEOGRAPHY OF NORTH AMERICAN LIRIODENDRON L. (MAGNOLIACEAE)

Restriction site variation in chloroplast DNA (cpDNA) was surveyed to analyze population dynamics in Liriodendron tulipifera L., a woody angiosperm found in eastern North America. Two cpDNA haplotypes, differing by the presence or absence of five restriction site changes (nucleotide sequence divergence estimated as approximately 0.15%) are geographically structured; 61 widespread populations possess the “northern” haplotype and three isolated populations of central Florida possess the “southern” haplotype. This geographic break in cpDNA distribution corresponds to patterns of geographic distribution revealed by a previous survey of allozyme variation, with the exception that analyses of allozyme data further divided the populations containing the northern cpDNA haplotype into two groups, a widespread upland group and a coastal intermediate group. Analyses of these two independent data sets together support the hypothesis that L. tulipifera survived the glacial advances of the Pleistocene in two distinct refugia, possibly as different taxa, and the intermediate coastal group was putatively formed from recent hybridizations between these entities.     

REPRODUCTIVE FEATURES OF DENTARIA LACINIATA AND D. DIPHYLLA (CRUCIFERAE), AND THE IMPLICATIONS IN THE TAXONOMY OF THE EASTERN NORTH AMERICAN DENTARIA COMPLEX

Reproductive features including ovule development, megasporogenesis, megagametogenesis, microsporogenesis, microgametogenesis, pollen tube growth, embryogeny, and natural seed germination were studied in a single population each of Dentaria laciniata Muhl. ex. Willd. and D. diphylla Michx. to test for possible agamospermy. The population of D. laciniata studied is sexual. The archesporial cell functions directly as the megasporocyte. It undergoes two meiotic divisions, but the micropylar cell of the dyad fails to undergo meiosis II, and a linear triplet of three cells is formed. The chalazal megaspore divides to form an eight-nucleate, seven-celled megagametophyte of the Polygonum type. Simultaneous cytokinesis follows the second meiotic division of the microsporocyte yielding a tetrahedral tetrad of microspores. A three-celled pollen grain is formed prior to anther dehiscence. Following apparent fertilization, the Capsella-variation of the Onagrad type of embryogeny results in a conduplicate embryo. Endosperm is initially nuclear, but eventually becomes cellular. Seeds readily germinate in nature. Similar events are documented in one population of D. diphylla up to the organization of the embryo-sac, which disintegrates before cellularization. These reproductive events and other data indicate that the eastern North American species of Dentaria may form a sexual polyploid complex with some sexual populations and some sterile ones.     

PHYSIOLOGICAL VARIATION AND ELECTROPHORETIC BANDING PATTERNS OF GENETICALLY DIFFERENT SEASONAL POPULATIONS OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Clones of Skeletonema costatum (Grev.) Cl. isolated from Narragansett Bay, R.I., during different seasons were grouped according to their electrophoretic banding patterns. The growth rates, pg chlorophyll · cell^?1, carbon uptake · cell^?1· h^?1, and carbon uptake · pg chl^?1· h^?1 were measured at 20°C, in a 14:10 h L:D cycle at 180 μE · m^?2· s^?1. Statistically significant sources of variation were found among groups of clones in growth rate, pg chl · cell^?1, and carbon uptake · pg chl^?1· h^?1. It was concluded that there is a significant relationship between the physiological characteristics of clones isolated from populations in different seasons and patterns of genetic variation inferred from the electrophoretic studies. However, genetic diversity detected by banding patterns tends to underestimate the total genetic diversity in natural populations. The groups of clones most common in summer bloom populations had significantly higher growth rates, lower values of pg chl · cell^?1, and higher rates of carbon uptake · pg chl^?1· h^?1 at 20°C than did the group of clones most common in winter bloom populations. However, differences among groups in these parameters at 20°C alone cannot account for the seasonal cycling of genetically variable populations of Skeletonema in Narragansett Bay. The range of growth rates among clones of this species is 0.1–5.0 divisions · d^?1 under a single set of temperature and light conditions. Chlorophyll concentrations range from 0.2–1.7 pg chl · cell^?1 and carbon uptake · pg chl^?1· h^?1 varies by a factor of 7 among clones. The range of physiological variation in this species means that it is difficult to use laboratory studies of single clones to analyze the responses of natural populations of Skeletonema.