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 TRAGOPOGON SPECIES: ADDITIONAL ORIGINS OF THE ALLOTETRAPLOIDS T. MIRUS AND T. MISCELLUS (COMPOSITAE)

Genetic diversity in the introduced diploids Tragopogon dubius, T. porrifolius, and T. pratensis and their neoallotetraploid derivatives T. mirus and T. miscellus was estimated to assess the numbers of recurrent, independent origins of the two tetraploid species in the Palouse region of eastern Washington and adjacent Idaho. These tetraploid species arose in this region, probably within the past 50–60 yr, and provide one of the best models for the study of polyploidy in plants. The parental species of both T. mirus and T. miscellus have been well documented, and each tetraploid species has apparently formed multiple times. However, a recent survey of the distributions of these allotetraploids revealed that both tetraploid species have expanded their ranges considerably during the past 50 yr, and several new populations of each species were discovered. Therefore, to evaluate the possibility that these recently discovered populations are of recent independent origin, a broad analysis of genetic diversity in T. mirus, T. miscellus, and their diploid progenitors was conducted. Analyses of allozymic and DNA restriction site variation in all known populations of T. mirus and T. miscellus in the Palouse and several populations of each parental diploid species revealed several distinct genotypes in each tetraploid species. Four isozymic multilocus genotypes were observed in T. mirus, and seven were detected in T. miscellus. Tragopogon mirus possesses a single chloroplast genome, that of T. porrifolius, and two distinct repeat types of the 18S-26S ribosomal RNA genes. Populations of T. miscellus from Pullman, Washington, have the chloroplast genome of T. dubius; all other populations of T. miscellus have the chloroplast DNA of T. pratensis. All populations of T. miscellus combine the ribosomal RNA repeat types of T. dubius and T. pratensis, as demonstrated previously. When all current and previously published data are considered, both T. mirus and T. miscellus appear to have formed numerous times even within the small geographic confines of the Palouse, with estimates of five to nine and two to 21 independent origins, respectively. Such recurrent polyploidization appears to characterize most polyploid plant species investigated to date (although this number is small) and may contribute to the genetic diversity and ultimate success of polyploid species.     

FLORAL FLAVONOIDS AND ULTRAVIOLET PATTERNS IN VIGUIERA (COMPOSITAE)

Variation occurs among species of Viguiera series Viguiera for ultraviolet (uv) absorption/reflection patterns of ligules. Floral flavonoids that cause uv absorption occur in epidermal papillae. Flavonoids are further localized to the proximal portion of the ligule in the seven taxa that have only proximal uv absorption. Floral flavonoids involved in uv absorption consist of flavone, flavonol, and anthochlor (chalcone/aurone) glycosides. Quercetin 3-methyl ether glycosides characterize the ligules of 10 taxa occurring in Baja California, Mexico, and nearby areas, and these taxa appear to form one taxonomic group. The anthochlor pair, marein/maritimein, characterizes V. dentata, and the lack of ligule flavonoids distinguishes V. potosina from the remaining taxa. The presence of the anthochlor pair, marein/maritimein, only in V. dentata and the lack of ligule flavonoids in V. potosina concur with other data to indicate that these species are not correctly placed with each other or with the other species currently included in series Viguiera.     

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.     

PATTERNS OF VARIATION IN THE STELLARIA LONGIPES COMPLEX: EFFECTS OF POLYPLOIDY AND NATURAL SELECTION

Patterns of morphological variation were studied in herbarium specimens of Stellaria longipes, an herbaceous perennial and subsequently in a growth chamber experiment using three cytotypes (4x, 6x, 8x) of S. longipes and diploids of its proposed progenitor S. longifolia. Despite extensive phenotypic plasticity in many traits, patterns of variation resulting from ecotypic differentiation within S. longipes could be detected in the field. A distinct form of S. longipes, which is restricted primarily to arctic and alpine tundra locations, shows genetic differentiation for the following traits: few flowers per ramet, a low proportion of flowering ramets, and ovate leaves. The three cytotypes of S. longipes could be distinguished by their mean genotypic value for leaf length and number of flowers per ramet. The extent of phenotypic plasticity in these traits makes it unlikely that the cytotypes could be distinguished in the field. The direction and extent of morphological divergence between S. longifolia and S. longipes suggest an alloploid origin for S. longipes. Variational trends (among-habitat types and cytotypes) in trait means are similar to those reported previously for the pattern of plasticity. This supports the argument that similar forces guide evolution of the mean and pattern of plasticity of a trait.     

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.     

CLONAL-DIVERSITY PATTERNS AND BREEDING-SYSTEM VARIATION IN DAPHNIA PULEX,AN ASEXUAL-SEXUAL COMPLEX

Some individuals of the cladoceran crustacean, Daphnia pulex, reproduce by cyclic parthenogenesis, while others are obligate parthenogens. Cyclic parthenogenesis is the primitive breeding system; the transition to obligate parthenogenesis has been linked to sex-limited meiosis-suppression. Detailed study of patterns of breeding-system distribution and clonal diversity is justified because D. pulex is the first species in which the loss of sex has been related to this mechanism. The present study investigated the genotypic characteristics of 10 D. pulex populations from each of 22 sites in the Great Lakes watershed. This analysis revealed that populations reproducing by cyclic parthenogenesis were uncommon and restricted to southern sites. Most populations reproduced by obligate parthenogenesis, with the electrophoretic survey revealing an average of three clones per pond and 145 unique clones over the watershed. A combinatorial analysis was used to examine the relationships between clone discovery in the asexual populations and both sample size and genetic-sampling intensity. This analysis showed that the few clones found in individual ponds were readily discriminated, while diversity on a regional scale was underestimated. These methods provide a quantitative basis for assessing the level of clonal diversity in asexual populations and in asexually transmitted segments of the genome.     

PATTERNS OF CLONAL DIVERSITY IN THE ANTENNARIA ROSEA (ASTERACEAE) POLYPLOID AGAMIC COMPLEX

The perennial herbaceous species, Antennaria rosea, is a large, morphologically diverse, polyploid agamic complex that is widespread in the cordillera of western North America. The species consists of triploid and tetraploid, nonpseudogamous, gametophytic apomicts. Populations of A. rosea are gynoecious, consisting almost entirely of pistillate clones. Clonal diversity among 63 populations of A. rosea was studied over a large portion of its range. Isozyme electrophoresis utilizing four polymorphic enzyme systems detected 192 multilocus genotypes among the populations. Populations of A. rosea tend to be composed of one or a few genotypes (range 1–11; mean 3.5), and these genotypes usually occur in only one or a few localized populations. Geographic patterns of clonal diversity may be a result of frequent genesis of new clones in populations that occur in areas where sexual relatives of A. rosea donate compatible pollen to facultatively sexual apomicts. Populations from previously glaciated regions tend to have fewer clones per population than those from unglaciated portions of the range.     

CHROMATOGRAPHIC DOCUMENTATION OF INTERSPECIFIC HYBRIDIZATION IN VERNONIA: COMPOSITAE

Chromatographic analysis of the flavonoid compounds in leaf extracts support field and morphological studies which lead to the interpretation of Vernonia guadalupensis Heller as a natural hybrid between V. lindheimeri Engelm. and Gray and V. interior Small. Of 16 major flavonoids found in leaf extracts of the parental species, 8 were found only in V. lindheimeri, 3 were found only in V. interior; 5 were common to both. All 16 were found in leaf extracts of V. guadalupensis.     

PATTERNS OF GENETIC VARIATION IN SALIX SECTION LONGIFOLIAE (SALICACEAE)

Enzyme electrophoresis was used to examine genetic relationships within a taxonomically complex group of diploid willows (Salix section Longifoliae). Forty-eight populations representing seven morphogeographic taxa were analyzed for 15 putative enzyme loci. Levels of genetic variation (A, P, H_e, and H_T) differed greatly among populations, but were generally lower than those reported for other species with similar life history traits. In populations and species from southern latitudes, where populations tend to be smaller and more isolated, genetic variation decreased and population differentiation increased. Genetic identity values suggest that the section is divisible into four major elements: 1) Salix interior, 2) S. taxifolia, 3) the S. exigua group, and 4) S. melanopsis. The first three occupy eastern, southern, and western portions of the continent, respectively. Salix melanopsis is sympatric with the S. exigua group in western North America, but is ecologically distinct. The S. exigua group is differentiated into four major geographic entities: S. hindsiana from west of the Sierras in California and southwest Oregon, S. sessilifolia from west of the Cascades in central Oregon to British Columbia, and a northern and southern race of S. exigua in the Intermountain West. The relationships suggested by allozyme data do not agree with traditional taxonomic concepts. Evidence of hybridization was obtained at five points where taxa come into contact, and Salix fluviatilis may be of hybrid origin. Taxonomic confusion appears to be largely the result of frequent hybridization events and overemphasis of a few highly variable morphological traits. The section appears to be a syngameon undergoing geographic speciation, with one taxon gaining reproductive isolation by a shift in habitat preference.     

THE DISTRIBUTION OF LIFE-HISTORY VARIATION IN THE DAPHNIA PULEX COMPLEX

In the midwestern United States the Daphnia pulex complex consists of a mosaic of sexual and asexual populations, providing a useful model system for studying the evolutionary forces underlying the maintenance of sex. One asexual and two sexual populations were surveyed for genetic variation for isozymes, mitochondrial DNA, and life-history characters. While the sexual populations exhibited substantial levels of genetic variance for fitness characters, no variation was detected in the asexual population at any level. However, a parallel survey among asexual clones derived from other ponds revealed large amounts of quantitative variation among clones, even among those with the same molecular profile. As a group, the asexuals are more variable for life histories than are the sexual populations. The molecular data indicate a relatively recent origin for the extant asexual D. pulex. The polyphyletic origin of these clones, combined with their microevolutionary potential, provides an explanation for their broad geographic distribution. The distribution of sex in the complex cannot be explained with the standard models that assume an invariant asexual population in reproductive isolation from the parental species. Although the frequency of asexuality may be driven by the spread of a sex-limited meiosis suppressor through sexual populations, the complete displacement of sexuality may be prevented by ecological distinctions between the two classes of individuals. On average, the asexuals are larger but produce smaller clutches than the sexuals.     

A CHROMATOGRAPHIC STUDY OF RETICULATE EVOLUTION IN THE APPALACHIAN ASPLENIUM COMPLEX

Smith, Dale M. and Donald A. Levin. (U. Illinois, Urbana.) A chromatographic study of reticulate evolution in the Appalachian Asplenium complex. Amer. Jour. Bot. 50(9): 952–958. Ilus. 1963.—The reticulate relationships of the members of the Appalachian Asplenium complex were studied by means of paper chromatography. Substances could be observed with ultraviolet light in the presence of ammonia vapor in all the taxa of the complex. The diploid species (A. montanum, A. platyneuron and A. rhizophyllum) had characteristic biochemical substances. Interspecific hybrids and/or their allotetraploid derivatives showed a complete complementation of all the substances of their known or presumed diploid ancestors. A combination of all the substances of the 3 diploids was found in the hybrids A. X kentuckiense and A. X gravesii. The results agree in all respects with the concept of reticulate evolution in the group which was advanced by Wagner on the basis of comparative morphology, hybridization and karyology.     

ONTOGENETIC VARIATION IN PATTERNS OF PHENOTYPIC INTEGRATION IN THE LABORATORY RAT

I used confirmatory factor analysis to evaluate the ability of causal developmental models to predict observed phenotypic integration in limb and skull measures at five stages of postnatal ontogeny in the laboratory rat. To analyze the dynamics of phenotypic integration, I fit successive age-classes simultaneously to a common model. Growth was the principal developmental explanation of observed phenotypic covariation in the limb and skull. No complex morphogenetic model more adequately reconstructed observed covariance structure. Models that could not be interpreted in embryological terms, coupled with a growth component, provide the best models for observed phenotypic integration. During postnatal growth, some aspects of integration vary in both the skull and limb. The covariance between factors and the proportion of variance unique to each character differ between some sequential age-classes. The factor-pattern is invariant in the limb; however, repatterning in the skull occurs in the interval between eye-opening and weaning. The temporal variation in the structure of covariation suggests that functional interactions among characters may create observed patterns of phenotypic integration. The developmental constraints responsible for evolutionary modification of phenotypes might be equally dynamic and responsive to embryonic functional interactions.     

VARIATION AND EVOLUTION OF BREEDING SYSTEMS IN THE TURNERA ULMIFOLIA L. COMPLEX (TURNERACEAE)

The evolutionary and functional relationships among breeding systems and floral morphology were investigated in the Turnera ulmifolia complex. Predictions of a model of breeding system evolution among distylous and homostylous varieties were tested. Chromosome counts of 73 accessions revealed an association between breeding system and chromosome number. Diploid and tetraploid populations of five taxonomic varieties are distylous and self-incompatible, whereas hexaploid populations of three varieties are homostylous and self-compatible. The latter occur at different margins of the geographical range of the complex. Crossing studies and analyses of pollen and ovule fertility in F₁'s revealed that the three homostylous varieties are intersterile. To test the prediction that, homostylous varieties are long homostyles that have originated by crossing over within the distyly supergene, a crossing program was undertaken among distylous and homostylous plants. Residual incompatibility was observed in styles and pollen of each homostylous variety with patterns consistent with predictions of the cross-over model. The intersterility of hexaploid varieties suggests that long homostyly has arisen on at least three occasions in the complex by recombination within the supergene controlling distyly. Deviation from expected compatibility behavior occurs in populations of var. angustifolia that have the longest styles. These phenotypes displayed the greatest separation between anthers and stigmas (herkogamy) and set little seed in crosses with long- or short-styled plants. This suggests that they are derived from long homostyles with shorter length styles. It is proposed that selection for increased outcrossing has favored the evolution of herkogamy in long homostyles. Estimates of outcrossing rate in a distylous population using allozyme markers confirmed that dimorphic incompatibility enforces complete outcrossing. Significant genetic variation for floral traits likely to influence the mating system, such as stigma-anther separation, occurs within and among homostylous populations of var. angustifolia on Jamaica. Estimates of the mating system of families from a population with varying degrees of stigma-anther separation, using five isozyme loci, were heterogeneous and ranged from t = 0.04–0.79. Families exhibiting the largest mean stigma-anther separation have higher outcrossing rates than those with little separation.     

A COMPARATIVE ANALYSIS OF MORPHOLOGICAL VARIATION PATTERNS IN THE PAPIONINS

Comparative studies of intraspecific variation patterns are important in attempts to reconstruct the differential selection pressures experienced by related species and in assessing the resultant observed interspecific variation. Reconstruction of past selection depends on an assumption of relatively stable patterns of genetic variance and covariance through time and across related species. Models by Lande (1979) and Turelli (1988a, 1988b) lead to contrasting expectations of stability versus lability of variation patterns, respectively, at least for closely related species. I report on a comparative study of phenotypic variance and correlation patterns in seven species of papionins, including macaques, baboons, and mangabeys, in order to determine the stability of variation patterns in this group. The three-dimensional coordinates of 12 bony landmarks on the face were used in a finite-element scaling analysis in order to measure local size variation at each landmark. Variances and correlations for these local size metrics were calculated using pooled sex-specific values. Variation patterns were compared across species using vector and matrix correlations in combination with various randomization-based significance tests. Patterns of variation and correlation were generally quite similar across the seven species, although some differences were also apparent. The overall magnitude of correlation is also similar among species, as only a few interspecific comparisons showed significant differences. Thus, it is concluded that patterns of variation and correlation in facial morphology have tended to remain stable in this group of primates. This result should allow for reconstruction of past differential selection pressures in the clade. The pattern of similarity among correlation structures for these species showed no association with their phylogenetic relationships.     

VERBESINA SECTION XIMENESIA (COMPOSITAE): BIOSYSTEMATICS AND ADAPTIVE VARIATION

Section Ximenesia is native to the southwestern United States and northern Mexico. Two of its taxa, Verbesina encelioides subsp. exauriculata and V. nana, are more western and occur in arid or semiarid regions, whereas the third taxon, V. encelioides subsp. encelioides, is more eastern and occurs in relatively moist regions. A crossing program revealed the absence of isolating barriers between the subspecies of V. encelioides. It is suggested that V. encelioides and V. nana are effectively isolated genetically by differences in ploidy. The study of several morphological characters of both field-collected and garden-grown populations indicates that differential adaptation for aridity has been of primary importance in the evolution of section Ximenesia. The taxa occupying arid regions show a reduction of transpiring surface, reduced reproductive capacity, and reduced dispersibility.     

UNUSUAL CYTOLOGICAL PATTERNS IN MICROSPOROGENESIS AND POLLEN DEVELOPMENT OF EVOLUTIONARY SIGNIFICANCE IN THE MIMULUS GLABRATUS COMPLEX (SCROPHULARIACEAE)

Four populations of Mimulus glabratus var. utahensis Pennell from the Great Basin and seven of M. glabratus var. fremontii (Bentham) Grant from the New Mexico–Texas–northeastern Mexico area were intercrossed and their F₁ hybrids grown. Cytology and fertility of both the parental populations and the F₁ hybrids were studied. The following cytological abnormalities were observed in microsporogenesis: cytomixis, the stretching of one or more chromosomes from cell to cell; multipolar divisions, separation of the chromosome complement into two or more parts; unequal disjunction; spontaneous polyploidization; and the production of encapsulated pollen tetrads. Typically, these abnormalities were rare or not observed in the parents, were rare in the intravarietal hybrids, but were more common in the intervarietal hybrids. They were closely associated with, in fact were the probably causes of, barriers to gene exchange between these two diploid (n = 15) varieties. Thus, the apparent causes of barriers to gene exchange in intervarietal hybrids are the likely mechanisms for the evolution of aneuploidy and polyploidy so characteristic of the rest of the Mimulus glabratus complex.     

THE HERITABLE BASIS OF VARIATION IN LARVAL DEVELOPMENTAL PATTERNS WITHIN POPULATIONS OF THE WOOD FROG (RANA SYLVATICA)

This study compares the heritable basis of variation in larval developmental patterns of mountain and lowland populations of the wood frog, Rana sylvatica. Additive genetic variances, heritabilities, and genetic correlations for larval developmental time and size at metamorphosis are estimated from half-sib and full-sib crosses. Considerable additive-genetic variances and high heritabilities are revealed for developmental time in both the mountain and the lowland population. There was a high level of additive-genetic variance and high heritability for body size at metamorphosis in the mountain population, but these were very low in the lowland population. The genetic correlations between developmental rate and larval body size are negative for the mountain population and near zero for the lowland population. It is argued that the differences in genetic structure between these two populations reflect differences in the selective regimes of their respective environments.     

ARTIFICIAL HYBRIDIZATIONS IN THE SUBTRIBE PERITYLANAE (COMPOSITAE–HELENIEAE)

Artificial hybridizations were conducted with 37 species of four genera of the subtribe Peritylanae (Compositae). Crossability, pollen stainability, and meiotic behavior were examined for most of the resulting 61 F₁ hybrid combinations. Intergeneric hybrids involving Amauria, Eutetras, Pericome, and Perityle, and infrageneric hybrids involving Perityle were readily obtained. Lower crossability and hybrid fertility were displayed by intergeneric crosses. The infrageneric crosses of Perityle were organized into two categories, intersectional and infrasectional, based upon the taxonomic sections that are recognized for the genus; sect. Pappothrix, sect. Laphamia, and sect. Perityle. In general, the crossability and hybrid fertility of intersectional crosses was markedly higher than that of intergeneric crosses. The results suggest a closer relationship between the three taxonomic sections of Perityle than between Perityle and other genera of the subtribe.