VARIATION IN CHROMATOGRAPHIC PATTERNS IN THE TRAGOPOGON DUBIUS-PRATENSIS-PORRIFOLIUS COMPLEX (COMPOSITAE)

Natural populations of the diploid species, Tragopogon dubius, T. pratensis and T. porrifolius, the F₁ hybrids of these species, and the two amphidiploids, T. mirus and T. miscellus, were obtained from the same localities used for previous morphological and cytological studies of the evolutionary relationships of this complex. Inter- and intra-populational comparisons were made utilizing 2-dimensional chromatograms of these taxa. Members of the complex shared a group of 18 flavonoid-type pattern components, no one of which was completely species specific. Therefore, species patterns were expressed for a population rather than an individual with pattern components being expressed as a frequency. Patterns for F₁ hybrids and amphidiploids, expressed in the same manner, were relatable to the parental species. Diploid species and F₁ hybrid patterns were the most variable in areas of greatest sympatry, indicating considerable genetic interchange between species. The distribution of specific components in certain populations was interpreted as chemical introgression. Evidence was presented for separate origins of T. mirus in two localities. The results confirm previous interpretations of the evolutionary relationships in this complex, and when compared to those obtained for Baptisia, they implicate the different breeding systems as important factors in establishing the kind of variation observed.     

SEED FERTILITY IN TRAGOPOGON HYBRIDS (COMPOSITAE)

The seed fertility of 172 interspecific and 32 intraspecific F₁ hybrids in the genus Tragopogon was determined. Intrageneric barriers to interbreeding were variable; some were weak and others quite strong. Maternal influences on fertility were found in 18 pairs of reciprocal interspecific crosses. It was postulated that cytoplasmic and nuclear factors interacted to determine the level of seed fertility. Although F₁'s were generally sterile or semi-sterile, the proportion of fertile seeds produced in most crosses increased in the F₂ generation. In two cases, however, a significant decrease was observed.     

GENETIC VARIATION IN THE EPIPHYTES TILLANDSIA IONANTHA AND T. RECURVATA (BROMELIACEAE)

The genetic structure of two epiphytic species, Tillandsia ionantha and T. recurvata, was investigated using enzyme electrophoresis. Electrophoretic data suggest that T. ionantha and T. recurvata differ in breeding system, in agreement with predictions based on their strikingly different floral morphologies. Electrophoretic data suggest extremely high levels of inbreeding for T. recurvata, whereas Tillandsia ionantha exhibits characteristics of an outcrossing species. Values of P, H, and mean number of alleles per locus are much higher in T. ionantha than in T. recurvata. The mean value of F_IS for T. ionantha is low (0.056), closely approaching expectations at Hardy-Weinberg equilibrium. In contrast, the mean value of F_IS in T. recurvata (1.000) indicates a complete absence of heterozygotes. The two species also differ in genetic structure. Low F_ST values for T. ionantha indicate little variation in allele frequencies among populations. In contrast, F_ST values are high for T. recurvata, suggesting substantial genetic heterogeneity among populations. In addition, the mean value of I is higher in T. ionantha (0.995) than in T. recurvata (0.931). Population genetic data are in agreement with the suggestion of Benzing (1978), who proposed that extreme epiphytes such as T. recurvata, would be characterized by increased autogamy ensuring high seed set. Due to high chromosome numbers in Bromeliaceae (most taxa have x = 25), the family has been considered polyploid. However, with the exception of an additional isozyme for PGM in T. recurvata, the two species are isozymically diploid.     

VARIATION AND LOCALIZATION OF FLAVONOID AGLYCONES IN HELIANTHUS ANNUUS (COMPOSITAE)

Flavonoid aglycone variation within Helianthus annuus, a species widely distributed throughout North America, was analyzed. Flavonoid aglycones of H. annuus consist of two types, flavones and chalcones. The flavone aglycones are sequestered in glandular trichomes that occur on both leaf surfaces, whereas the chalcone aglycones appear to be incorporated in the waxy leaf cuticle. Considerable variation in flavonoid profile was observed with some plants exhibiting as few as one, and others as many as seven of the eight aglycones detected. No definable phytogeographic patterns were observed for this flavonoid variation. Flavonoid aglycone variation also did not differentiate the infraspecific taxa within H. annuus.     

GENETIC VARIATION IN SIX SPECIES OF SACOGLOSSAN OPISTHOBRANCHS

Genetic variation in allozymes of six species of Saco-glossa(Mollusca, Opisthobranchia) from Denmark was studied. Nine enzymesrepresenting 11 loci gave reactions that could be used to calculateallele frequencies. Elysia viridis, Limapontia capitata, L.de-pressa, Ercolania nigra, Alderia modesta and Calliopaea oophagaall showed very great variation both within and between species.Levels of polymorphism varied between 0.5 and 0.8, and levelsof observed heterozygosity were between 0.18 and 0.42. Interspecificidentity of alleles in polymorphic loci was only found betweenthe two species of Limapontia. Even in these two species geneticidentity (I) was very low (0.07) for congeneric species. Theresults are discussed in relation to habitat, fertility, developmenttype and geographic range of the species. (Received 28 February 1990; accepted 26 July 1990)     

GENETIC DIVERGENCE AND GEOGRAPHIC SPECIATION IN LAYIA (COMPOSITAE)

Electrophoretic variability was examined in six species of Layia (Compositae), native to California, which have previously been studied by Clausen, Keck, and Hiesey, and are regarded as a classic example of geographic speciation in plants. The study was carried out to test the hypothesis that the extent of divergence in structural genes coding enzymes is concordant with divergence in morphological characteristics, ecological traits, and reproductive isolation. Eleven enzymes specified by 17 loci were analyzed. The genetic identity values were consistent with those expected on the model that the species diverged gradually as they adapted to geographically separate habitats. Thus, the values between the three species complexes proposed by Clausen, Keck, and Hiesey (L. chrysanthemoides/L. fremontii; L. jonesii/L. leucopappa/L. munzii; L. platyglossa) were substantially lower than the values between species within the complexes. The results provide an important contrast to the very high genetic identities between species which originated rapidly from their progenitors. The electrophoretic results also provided evidence that the cytosolic isozyme of phosphoglucomutase and the cytosolic NADP-dependent isocitrate dehydrogenase in the six species are coded by duplicate genes.     

GENETIC VARIATION IN SYMPATRIC AND ALLOPATRIC POPULATIONS OF HYBRIDIZING FRESHWATER SNAIL SPECIES(VIVIPARUS ATER AND V. CONTECTUS)

To estimate the geographical extent of introgression, we studiedthe genetic structure of sympatric and allopatric populationsof hybridizing freshwater snail species Viviparus ater and V.contectus in central Europe. Six allozyme loci which were variablein Lake Garda, Italy in a previous study (five nearly diagnosticloci between the two species and one highly polymorphic locusin V. contectus) were analyzed from ten sympatric locationsand four allopatric populations each for the two species. Presumablyintrogressed genes (low allele frequencies) were found fromat least one locus in seven out of the ten sympatric sites.These seven sites covered most of northern Italy. The data indicatethat introgression has occurred from Viviparus contectus toV. ater and vice versa. Therefore, there is a possibility ofwidespread introgression or mosaic zones in nature. However,we cannot rule out that the observed patterns are due to theshared ancestry. V. ater possessed low genetic variation (thejackknifed mean of Wright's F_ST±S.E. over four loci was0.041±0.004). On the other hand, V. contectus showedhigh genetic differentiation (the jackknifed mean of F_ST±S.E. over six loci was 0.546±0.166). Although introgressionmay have caused evolutionary changes in V. ater and V. contectus,it was not strong enough to level out the genetic differencesbetween the two species, which may have originated from isolationamong populations in V. contectus and a past bottleneck eventin V. ater. (Received 21 June 1996; accepted 31 January 1997)     

ADAPTIVE RADIATION AND GENETIC DIFFERENTIATION IN THE HAWAIIAN SILVERSWORD ALLIANCE (COMPOSITAE: MADIINAE)

The Hawaiian silversword alliance consists of the three genera Dubautia, Argyroxiphium, and Wilkesia, and is a classic example of adaptive radiation in an insular setting. Genetic variation and interspecific genetic differentiation based on ten enzyme loci are described for Dubautia and Wilkesia. Genetic identities among species span the range of values expected from interpopulation comparisons within a single species (I = 0.90–1.00) to those typical of interspecific comparisons . Genetic-identity values correspond to biogeographic distribution and morphological distinctiveness, supporting a correlation of increasing genetic distance associated with the time of separation among lineages. It may be inferred that the high genetic identities observed within the Hawaiian Madiinae and other island plant groups are due to limited time spans available for taxa to accumulate new genetic variation through mutation. It appears that species may remain genetically similar (I > 0.90) even after time spans on the order of magnitude of 1,000,000 years.     

CHROMATOGRAPHIC COMPARISON OF TRAGOPOGON SPECIES AND HYBRIDS

Approximately 1,700 plants representing five species of Tragopogon (Compositae) and their F₁ and F₂ hybrids were analyzed by two-dimensional descending paper chromatography. Each species, or population within a species, was chromatographically distinct. Often, however, the differences were more quantitative than qualitative. The chromatographic data generally supported the species relationships which had been determined from previous morphologic, hybridization, and fertility studies. Inheritance of the flavonoid compounds was usually additive in the F₁'s. Segregation and recombination of the genes controlling the synthesis of these compounds sometimes approximated 3:1 or 9:7 ratios in the F₂'s. Occasionally parental compounds were missing from some of the hybrids. “Hybrid” compounds which had not been found in either parent were absent from the F₁ but did occur in several F₂ populations. Two linkage groups were present. The first contains genes controlling the synthesis of three compounds and the second, four compounds.     

THE FEMALE GAMETOPHYTE OF THREE SPECIES OF GRINDELIA AND OF PRIONOPSIS CILIATA (COMPOSITAE)

In the four species studied, Grindelia stricta ssp. blakei, G. arizonica, G. lanceolata, and Prionopsis ciliata (Haplopappus ciliatus), the female gametophyte develops according to the Polygonum (normal) type from the chalazal megaspore of a row of four. In most cases only two antipodal cells are formed, the micropylar one originally containing two nuclei. The number of nuclei increases in both cells; one or both antipodal cells typically grow laterally into the integument, often extending to near the surface of the ovule. This resembles the condition previously reported in Grindelia squarrosa. Since the four species of Grindelia have similar antipodal outgrowths, such outgrowths may be considered typical for this genus. The fact that Prionopsis resembles Grindelia in regard to outgrowths from the antipodal cells and differs in this respect from typical Haplopappus helps to justify its separation from Haplopappus, and perhaps its suggested merger with Grindelia.     

PHENOTYPIC VARIATION IN STEPHANOMERIA EXIGUA SSP. CORONARIA (COMPOSITAE) AND ITS RECENT DERIVATIVE SPECIES “MALHEURENSIS”

Phenotypic variation in 33 quantitative characters was analyzed in Stephanomeria exigua ssp. coronaria (Greene) Gottlieb and its recent derivative species, presently called “Malheurensis,” grown in a series of experimental environments. The study was made to determine whether their high genetic identity, previously revealed by electrophoresis of a sample of their enzymes, was correlated with a high similarity in quantitative traits of morphology, size, growth rates, and fecundity. The electrophoretic evidence provided correct information about the relative variability, similarity, and phylogenetic relationship of the two taxa. Thus, 90% of the between-plant variance components from the analysis of variance were higher in ssp. coronaria and, therefore, concordant with its higher genetic variability. The between-environment variance components in the two species were similar in magnitude and when ordered, from smallest to largest, were nearly identical in ranking. The quantitative study provided important additional evidence. Ssp. coronaria grew more rapidly and produced more florets than Malheurensis in all of the growth conditions and also was found to grow larger than Malheurensis in their native habitat in eastern Oregon where they grow sympatrically. These and other results indicate that the persistence of Malheurensis in nature cannot depend on advantages of size, growth rates, or number of flowers produced per individual. The large differences between the taxa in the size of their seeds was used as the basis for a model to account for the continued persistence of Malheurensis.     

INFRASPECIFIC VARIATION OF SESQUITERPENE LACTONES IN AMBROSIA PSILOSTACHYA (COMPOSITAE)

The distribution of fifteen sesquiterpene lactones in sixty-two populations of Ambrosia psilostachya ranging from Canada to Mexico, and cytological observations for seven populations are reported. Chemical data for four Mexican populations of A. cumanensis Kunth are presented. The origin of chemically unique populations of A. psilostachya which occur on the islands and peninsulas that line the Texas Gulf coast are discussed with respect to the chemical, morphological and cytological data.     

蒿属植物的染色体数目和核型研究（一）

本文报道了我国蒿属６种的染色体核型,它们的核型公式分别为：牡蒿（ＡｒｔｅｍｉｓｉａｊａｐｏｎｉｃａＴｈｕｎｂ．）２ｎ＝１８＝１２ｍ＋６ｓｍ（２ＳＡＴ）;西南牡蒿（Ａ．ｐａｒｖｉｆｌｏｒａＢｕｃｂ．－Ｈａｍ．ｅｘＲｏｘｂ．）２ｎ＝３６＝３０ｍ＋４ｓｍ＋２ｓｔ（６ＳＡＴ）;多花蒿（Ａ．ｍｙｒｉａｎｔｈａＷａｌｌ．ｅｘＢｅｓｓ．）２ｎ＝３６＝３０ｍ＋６ｓｍ：牛尾蒿（Ａ．ｄｕｂｉａＷａｌｌ．ｅｘＢｅｓｓ．）２ｎ＝３６＝２８ｍ＋８ｓｍ（２ＳＡＴ）;野艾蒿（Ａ．ｌａｖａｎｄｕｌａｅｆｏｌｉａＤＣ．）２ｎ＝５４＝４２ｍ＋１２ｓｍ;荚毛蒿（Ａ．ｖｅｌｕｔｉｎａＰａｍｐ．）２ｎ＝５４＝３６ｍ＋１８ｓｍ．