COMPARISON OF TETRAPLOID AND SINGLE GENE-INDUCED GIGAS VARIANTS IN CHICKPEA (CICER ARIETINUM). II. MORPHOLOGICAL AND ANATOMICAL LEAF CHARACTERS

Two genomic variants of a chickpea (Cicer arietinum L.) parental line have been developed which exhibit gigas characters. The two genotypes were the result of a single-gene mutation (gigas) and induced tetraploidy of a single parental line. The two genotypes plus parental strain were investigated to determine the similarity-of-effect of polyploidy and this single-gene mutation on leaf anatomy and morphology. Leaves consisted of two rows of alternatively arranged leaflets. Both the tetraploid and parental lines had the same mean number of leaflets per leaf while the gigas plants had fewer, but mean total leaf surface area was greater in the gigas plants. Quantitative comparison of mesophyll and vascular tissue and air space volume density (V_v) showed that leaves of the tetraploid plants had the greatest mesophyll cell density (V_vm) and least air space density. Mesophyll cell density was equal in the parental and single-gene mutant while parental leaves had the greatest vascular tissue density. The greater mesophyll cell density values of the polyploid were due to larger mean mesophyll cell size, not to greater cell numbers per unit area. Leaf models based on tissue density and leaflet size showed tetraploid plants had the greatest productivity potential per unit of leaflet surface area. However, if models were based on a whole leaf, gigas plants had the greatest productivity potential since they had larger total leaf area. The effectiveness of using structural models to predict physiological potential in plant tissues will be tested in future studies.     

ENDOCYTOSIS OF LANTHANUM NITRATE IN THE ORGANIC ACID-SECRETING TRICHOMES OF CHICKPEA (CICER ARIETINUM L.)

The organic acid-secreting trichomes of chickpea (Cicer arietinum L.) were exposed to 2.5 mm lanthanum nitrate for 24 hr, and this concentration did not inhibit trichome secretion compared with that of controls. We subsequently used this nontoxic concentration of lanthanum to examine endocytosis. In the stalk cells of these secretory trichomes, exogenously applied lanthanum nitrate was present in cell walls and vacuoles, as well as within both invaginations in the plasma membrane and vesicles in the peripheral cytoplasm between the plasma membrane and the tonoplast. In the head cells, lanthanum nitrate was present in cell walls and in vesicles that form a layer in the cytoplasm around the edge of the head cells, but was not present in vacuoles. We propose that fluid phase endocytosis targeted to the vacuole takes place in the stalk cells and that endocytosis occurs in the head cells to remove excess plasma membrane after the fusion of secretory vesicles with the plasma membrane. This is the first demonstration of endocytosis in secretory trichomes.     

GENETIC STRUCTURE AND MALE-MEDIATED GENE FLOW IN THE GHOST BAT (MACRODERMA GIGAS)

The Australian ghost bat is a large, opportunistic carnivorous species that has undergone a marked range contraction toward more mesic, tropical sites over the past century. Comparison of mitochondrial DNA (mtDNA) control region sequences and six nuclear microsatellite loci in 217 ghost bats from nine populations across subtropical and tropical Australia revealed strong population subdivision (mtDNA φ_ST = 0.80; microsatellites UR_ST = 0.337). Low-latitude (tropical) populations had higher heterozygosity and less marked phylogeographic structure and lower subdivision among sites within regions (within Northern Territory [NT] and within North Queensland [NQ]) than did populations at higher latitudes (subtropical sites; central Queensland [CQ]), although sampling of geographically proximal breeding sites is unavoidably restricted for the latter. Gene flow among populations within each of the northern regions appears to be male biased in that the difference in population subdivision for mtDNA and microsatellites (NT φ_ST = 0.39, UR_ST = 0.02; NQ φ_ST = 0.60, UR_ST = ?0.03) is greater than expected from differences in the effective population size of haploid versus diploid loci. The high level of population subdivision across the range of the ghost bat contrasts with evidence for high gene flow in other chiropteran species and may be due to narrow physiological tolerances and consequent limited availability of roosts for ghost bats, particularly across the subtropical and relatively arid regions. This observation is consistent with the hypothesis that the contraction of the species' range is associated with late Holocene climate change. The extreme isolation among higher-latitude populations may predispose them to additional local extinctions if the processes responsible for the range contraction continue to operate.     

THE ORIGIN AND GENETIC BASIS OF OBLIGATE PARTHENOGENESIS IN DAPHNIA PULEX

Sex in Daphnia is environmentally determined, and some obligately parthenogenetic clones of D. pulex have retained the ability to produce males. In the present study, males from 13 such clones were crossed to sexual females from closely related cyclical parthenogens both to determine whether the males were capable of producing viable hybrids and to determine the mode of reproduction of the hybrids. A total of 178 genetically confirmed hybrids were produced, with each of the 19 attempted crosses resulting in some viable hybrids. On average, only 34% of the hybrid eggs that initiated development survived to the reproductive stage, suggesting some incompatibility between the parents. The absence of any association between survivorship and parental or hybrid genotype indicated, however, that there is no specific genetic incompatibility associated with the marker loci used. The inability of most hybrids to produce normal resting eggs is further evidence of a general genomic incompatibility between the parents. Ten of the hybrids produced viable resting eggs, permitting tests to determine their mode of reproduction. Six of the 10 hybrids reproduced by cyclical parthenogenesis, like their maternal parent. The remaining four hybrids reproduced by obligate parthenogenesis, like their paternal parent, demonstrating that the genes suppressing meiosis can be transmitted by the male parent. These results support a model for the generation of new clones that involves the spread of genes suppressing meiosis and provide evidence that the high genotypic diversity observed in obligately parthenogenetic populations of D. pulex is a result of the multiple origin of new clones from the cyclical parthenogens. Evidence was also obtained suggesting that the obligately parthenogenetic clones carry a load of recessive deleterious genes.     

GENETIC DIVERSITY IN GOSSYPIUM HIRSUTUM AND THE ORIGIN OF UPLAND COTTON

Gossypium hirsutum has a large indigenous range encompassing most of Mesoamerica and the Caribbean, where it exhibits a diverse array of morphological forms spanning the wild-to-domesticated continuum. Modem, highly improved varieties (“Upland cotton”), which currently account for about 90% of world cotton commerce, are day-length neutral annuals derived from subtropical, perennial antecedents. To assess levels and patterns of genetic variation in the species and to elucidate the origin of Upland cotton, 538 accessions representing the full spectrum of morphological and geographical diversity were analyzed forallozyme variation at 50 loci. Levels of variation are modest overall but are low in Upland cotton. Relationships among accessions reflect pre-Columbian influences of aboriginal peoples and later European colonists superimposed on the preagricultural pattern. In contrast to expectations, two centers of diversity are evident, one in southern Mexico-Guatemala and the other in the Caribbean. Introgression of G. barbadense genes into G. hirsutum has been common in a broad area of sympatry in the Caribbean. The germplasm of present cultivars traces to Mexican highland stocks, which, in turn, were derived from material originally from southern Mexico and Guatemala. Despite the widespread belief that germplasm from several other species has been incorporated into modem Upland stocks through intentional breeding efforts, the 50 Upland cultivars examined contain no unique alleles, suggesting that retention of genes from transspecific sources has been minimal. The most recent infraspecific treatment, which recognizes seven races, does not adequately represent genetic relationships.     

云南山茶花四倍体的首次发现及其科学意义

本文对分布于云南和四川金沙江河谷的云南山茶花C. reticulata及其两个近缘种(怒江山茶C.saluenensis和西南山茶C．pitardii)进行了细胞学研究。34个居群的云南山茶花中,21个居群是四倍体类型(2n=60),11个居群是六倍体类型(2n=90),另2个居群为二倍体(2n=30),云南山茶花的四倍体类型为首次发现,并且进行了核形态研究。四倍体和六倍体的花粉母细胞减数分裂染色体构型在大多数居群都为二价体(四倍体中30个二价体,六倍体中45个二价体),少数居群或是个体除二价体为主外还出现单价体和四价体,六倍体类型没有出现六价体构型。根据减数分裂的构型,我们认为,四倍体和六倍体分别为异源四倍体和异源六倍体,少数四价体的存在表明染色体有部分同源性。所有四倍体和六倍体的体细胞间期核特征和前期染色体形态特征基本相似。中海拔(1800m)以上的四倍体的云南山茶花外部形态特征与六倍体类型比较相似,而低海拔(1100～1800 m)的四倍体类型的外部形态特征则有些不同,但核形态结构是比较相似的。四倍体与六倍体类型地理分布是连续的,并与近缘的二倍体种怒江山茶、西南山茶重叠分布。     

黄鳝单条染色体的显微分离及特异性检测

建立了显微分离黄鳝单条染色体及检测其特异性的方法;在Olympus倒置显微镜下用毛细玻璃微针手工分离黄鳝减数分裂Ⅰ终变期3号染色体,将期DNA作模板进行DOP-PCR扩增后,分别以α^-32P-dCTP和Biotin-11-dUTP标记的单条染色体DNAPCR扩增产物及Biotin-11-dUTP标记的大豆18SrRNA基因作探针进行Southern杂交,FISH和Dot杂交来检测其特异性,结果表明：（1）减数分裂Ⅰ终变期染色体标本是进行染色体显微操作的理想材料;（2）DOP-PCR扩增产物片段在200-1000bp之间,平均600bp左右;（3）杂交结果显示,本研究所获得的单条染色体是黄鳝3号染色体;（4）与显微操作仪和微激光分离相比较。该方法不需要昂贵仪器,在常规实验室即可操作,具有广泛的普及应用意义。     

THE QUANTITATIVE GENETICS OF SEXUAL DIMORPHISM IN SILENE LATIFOLIA (CARYOPHYLLACEAE). I. GENETIC VARIATION

It is widely recognized that there are basic conflicts between the resource needs of a plant for paternal versus maternal functions. In dioecious species, these divergent demands, and the selection pressures they impose, can lead to the evolution of sexual dimorphism. The present study was conducted to assess the potential for the evolution of sexual dimorphism in Silene latifolia by evaluating the genetic variation and genetic correlation between characters and between the sexes for a range of growth and reproductive characters. Sexual dimorphism is largely restricted to reproductive characters, particularly flower number and flower size. A canonical correlation analysis revealed considerable intercorrelation between growth characters, such as germination date, height, and leaf size, and reproductive characters; plants that grow fast early on also flower earlier, and plants that produce big leaves also produce big flowers. There was genetic variation for several sexually dimorphic characters; much of the focus in this analysis was on flower size, particularly calyx diameter. Finally, genetic correlations within and between the sexes were found that limit the rate of evolutionary divergence between the sexes. The genetic results suggest that S. latifolia has been subject to divergent selection on the two sexes for a long period of time, bringing about a gradual fixation of sex-limited gene effects, so that the remaining genetic effects are expressed in both sexes. Genetic correlations between the sexes that arise from this residual variation impose limits on further evolutionary change.     

GENETIC AND CONCHOLOGICAL COMPARISON OF SNAILS (HELIX ASPERSA) DIFFERING IN SHELL DEPOSITION OF LEAD

Populations of snails inhabiting areas with different historiesof Pb contamination differed in their deposition of Pb in shellrelative to soft tissues. Genetic variation, measured usingisozymes, was not related to Pb history nor geographic distancebetween populations. Shell characteristics were significantlydifferent among sites; shell dry weight was strongly relatedto soil calcium levels. Shells of snails from areas with longhistories of Pb contamination were significantly more robust(greater shell width/shell height ratio) than snails from otherlocations. H. asprsa adaptation to Pb contamination may involvesignificant changes in shell characteristics but these do notcorrelate with genetic traits assessed with allozymes (Received 29 December 1994; accepted 15 October 1995)     

A PHYSICAL-CHEMICAL DIFFERENCE IN ANTIBODIES AGAINST THE S AND R VARIANTS OF A SINGLE BACTERIAL STRAIN

1. Rabbits were immunized with Bact. typhosum 0 901 S and 0 901 R, over a long period. Homologous and heterologous strains were sensitized with sera obtained from weekly bleedings. Agglutination titer was recorded, and the isoelectric points of the bacteria maximally sensitized were determined. 2. 0 901 S maximally sensitized with homologous immune serum had isoelectric points which became more alkaline as immunization progressed, covering a range of pH 4.8 to 5.5. 3. Strain 0 901 R maximally sensitized with homologous immune serum had isoelectric points which became more alkaline as immunization progressed, covering the range of pH 5.0 to 5.9. 4. Both 0 901 S and 0 901 R maximally sensitized with heterologous serum had isoelectric points lower than when sensitized with homologous serum. 5. The isoelectric points of both forms sensitized with increasing concentrations of homologous immune serum were determined. Increasing concentrations of homologous immune serum shifted the isoelectric point of 0 901 R from less than 2.2 for the unsensitized bacteria progressively to the alkaline side until the maximum values previously mentioned were reached. Increasing concentrations of homologous immune serum conferred upon 0 901 S isoelectric points which became only slightly more alkaline in maximal sensitization. 6. The electrophoretic mobilities of 0 901 S and 0 901 R, in each case maximally sensitized with homologous hyperimmune serum, were found to differ significantly over the whole range of pH studied.     

COMPARISON OF SINGLE PRODUCT SCALING AND RELATIVE-TO-REFERENCE SCALING IN SENSORY EVALUATION OF DAIRY PRODUCTS

Single product scaling and relative-to-reference scaling were compared on the basis of numbers of significant differences among chocolate milks and among vanilla yogurts using both trained and untrained panels. The study involved 920 comparisons among product means with appearance, flavor and mouthfeel attributes. Although there were a greater number of significant t-tests when the relative-to-reference scales were used by both trained and untrained panels, the differences between scale types were minor. Panels showed no advantage with the type of scale they used first. The two methods may be used with equal efficiency for sensory evaluations.     

HIERARCHICAL COMPARISON OF GENETIC VARIANCE-COVARIANCE MATRICES. I. USING THE FLURY HIERARCHY

The comparison of additive genetic variance-covariance matrices (G-matrices) is an increasingly popular exercise in evolutionary biology because the evolution of the G-matrix is central to the issue of persistence of genetic constraints and to the use of dynamic models in an evolutionary time frame. The comparison of G-matrices is a nontrivial statistical problem because family structure induces nonindependence among the elements in each matrix. Past solutions to the problem of G-matrix comparison have dealt with this problem, with varying success, but have tested a single null hypothesis (matrix equality or matrix dissimilarity). Because matrices can differ in many ways, several hypotheses are of interest in matrix comparisons. Flury (1988) has provided an approach to matrix comparison in which a variety of hypotheses are tested, including the two extreme hypotheses prevalent in the evolutionary literature. The hypotheses are arranged in a hierarchy and involve comparisons of both the principal components (eigenvectors) and eigenvalues of the matrix. We adapt Flury's hierarchy of tests to the problem of comparing G-matrices by using randomization testing to account for nonindependence induced by family structure. Software has been developed for carrying out this analysis for both genetic and phenotypic data. The method is illustrated with a garter snake test case.     

WEEDY ADAPTATION IN SETARIA SPP. I. ISOZYME ANALYSIS OF GENETIC DIVERSITY AND POPULATION GENETIC STRUCTURE IN SETARIA VIRIDIS

Setaria viridis is an important self-pollinating, cosmopolitan weed of temperate regions worldwide. Allozyme markers were used to investigate genetic diversity and structure in 168 accessions (including four S. italica) collected mainly from North America and Eurasia. Genetic diversity in green foxtail, and its population genetic structure, provided important clues about this weed's evolutionary history. Genetic diversity was low, with marked population differentiation: the percentage of polymorphic loci was 25% (0.95 criterion); mean number of alleles per locus was 1.86; mean panmictic heterozygosity was 0.07; and the coefficient of population genetic differentiation was 0.65. A common genotype occurred in 25 accessions distributed in six countries from both the Old World and New World, in a wide variety of ecological situations. Relatively little genetic divergence occurred between Eurasia and North America, with Nei's unbiased genetic identity between the two regions equaling 1.0. Populations from these two continents also had equivalent genetic diversity. Within North America, regional differentiation was indicated by northern and southern groups separated at 43.5° N latitude. No geographic pattern in genetic diversity was found within Eurasia. The size of the geographic range from which populations were sampled was not an accurate indicator of the extent of genetic diversity found among populations from that region. These results suggest that present patterning among green foxtail populations in North America is the consequence of multiple introductions into the New World followed by local adaptation and regional differentiation. Finally, S. italica and several green foxtail varieties did not differ isozymatically from typical forms of green foxtail. This supports the view that S. italica and S. viridis are conspecific, that the former (foxtail millet) is a domesticated form of the latter, and also questions the taxonomic validity of formally recognizing morphological varieties within green foxtail.     

HABITAT CHOICE BY ALLELIC VARIANTS IN XIPHOPHORUS VARIATUS (PISCES; POECILIIDAE) AND IMPLICATIONS FOR MAINTENANCE OF GENETIC POLYMORPHISM

Stream pools in northeastern Mexico exhibit gradients in dissolved oxygen (DO) concentration: low DO at the upstream ends and higher DO at the downstream ends. These pools contain populations of the variable platyfish, Xiphophorus variatus, which are polymorphic at an autosomal locus that affects tailspot pigmentation. Previous work showed that adult males of the cut-crescent morph have a lower metabolic rate than wild type males (Borowsky, 1984). Field collections were made to determine whether the morphs are distributed at random in the pools. As predicted, among adult males, all morphs were found in equal proportions at the upstream and downstream ends of the pools, except cut-crescents, which were distributed preferentially toward the upstream ends. In contrast, the opposite distributional pattern was found among adult females. Habitat choice may contribute to the stability of the tailspot polymorphism, especially so because preferences differing between the sexes can lead to disassortative mating.     

THE EFFECT OF INBREEDING IN DIPLOID AND TETRAPLOID POPULATIONS OF EPILOBIUM ANGUSTIFOLIUM (ONAGRACEAE): IMPLICATIONS FOR THE GENETIC BASIS OF INBREEDING DEPRESSION

The partial dominance model for the evolution of inbreeding depression predicts that tetraploids should exhibit less inbreeding depression than their diploid progenitors. We tested this prediction by comparing the magnitude of inbreeding depression in tetraploid and diploid populations of the herbaceous perennial Epilobium angustifolium (Onagraceae). Inbreeding depression was estimated in the greenhouse for three tetraploid and two diploid populations at four life stages. The mating system of a tetraploid population was estimated and compared to a previous estimate for diploids. Tetraploids showed less inbreeding depression than diploids at all life history stages, and these differences were significant for seed-set and cumulative fitness, but not for germination, survival, or plant dry mass at nine weeks. This result suggests that the genetic basis of inbreeding depression may differ among life stages. The primary selfing rate of the tetraploid population was r = 0.43, which is nearly identical to that of a diploid population (r = 0.45), indicating that differences in inbreeding depression between diploids and tetraploids are probably not due to differences in the mating system. Cumulative inbreeding depression, calculated from the four life history stages, was significantly higher for diploids () than for tetraploids (), supporting the partial dominance model of inbreeding depression.     

THE EVOLUTION OF SELF-FERTILIZATION AND INBREEDING DEPRESSION IN PLANTS. I. GENETIC MODELS

The amounts of inbreeding depression upon selfing and of heterosis upon outcrossing determine the strength of selection on the selfing rate in a population when this evolves polygenically by small steps. Genetic models are constructed which allow inbreeding depression to change with the mean selfing rate in a population by incorporating both mutation to recessive and partially dominant lethal and sublethal alleles at many loci and mutation in quantitative characters under stabilizing selection. The models help to explain observations of high inbreeding depression (> 50%) upon selfing in primarily outcrossing populations, as well as considerable heterosis upon outcrossing in primarily selfing populations. Predominant selfing and predominant outcrossing are found to be alternative stable states of the mating system in most plant populations. Which of these stable states a species approaches depends on the history of its population structure and the magnitude of effect of genes influencing the selfing rate.