INTRASPECIFIC VARIATION IN POLLEN YIELD IN BROMEGRASS (POACEAE: BROMUS)

Variation in pollen production was measured within five hermaphrodite species of bromegrass (Bromus). Anther length is an excellent predictor of pollen production in this genus (R² = 0.97). Anther length varied considerably within each of the species, both among and within individual plants. Within plants, most of the variation occurred among florets within spikelets; florets in upper spikelet positions were smaller and produced less pollen. In B. inermis, pollen production was decreased by defoliation and increased in shoots that grew on thatching ant (Formica obscuripes) mounds. Whole-shoot pollen yield was determined by spikelet number, number of florets per spikelet, and pollen production per floret. All of these yield components must be considered in attempts to estimate pollen production accurately.     

POPULATION STRUCTURE AND GENETIC DIFFERENTIATION IN NATIVE AND INTRODUCED POPULATIONS OF DESCHAMPSIA CAESPITOSA (POACEAE) IN THE COLORADO ALPINE

Deschampsia caespitosa is a widespread grass common in moist areas of the alpine tundra of the Rocky Mountains. Enzyme electrophoresis was used to examine population genetic structure along two soil moisture gradients in Rocky Mountain National Park, Colorado. Introduced plants used in a revegetation project were also sampled at one of the sites. At both sites, there were significant differences among subpopulations in allele frequencies, but these differences were distributed in a patchy fashion and were not correlated with the apparent soil moisture gradients. The degree of genetic subdivision differed between the two sites. At one site, gene flow appeared to be high and differences in allele frequencies are attributed to selection in a mosaic environment. At the other site, gene flow appeared more restricted and differences in allele frequencies between subpopulations are attributed to selection and limited gene flow acting simultaneously. Overall, 15% of the genetic variability is between subpopulations and gene flow is high, even between subpopulations separated by up to 1.5 km, but local conditions can apparently limit gene flow and increase the degree of genetic subdivision. The mean genetic distance between introduced plants and the native subpopulations was significantly higher than the mean genetic distance between all other subpopulations. Despite the high gene flow apparent in alpine tundra subpopulations of Deschampsia caespitosa, significant genetic structuring of these subpopulations has developed.     

GENETIC VARIATION AND POPULATION STRUCTURE IN THE FERN BLECHNUM SPICANT (BLECHNACEAE) FROM WESTERN NORTH AMERICA

Population genetic structure in the homosporous fern Blechnum spicant was analyzed in six populations from western North America. Each population was divided into approximately 10 m by 10 m subpopulations, and genetic variation within and among subpopulations was compared using enzyme electrophoresis and F statistics. These analyses indicated that there was no evidence of genetic structure in four of the six populations examined. However, significant genetic heterogeneity among subpopulations was observed for the other two populations. The genetic structure of these populations may be attributable, in part, to family structure resulting from high rates of intragametophytic selling and/or spatial patchiness in the distribution of individuals due to limited habitat availability in these areas. Outcrossing populations of B. spicant generally lack genetic structure, whereas the most highly inbreeding population maintains significant genetic structure. The information obtained in this investigation of population genetic structure in Blechnum spicant is consistent with data for angiosperms and gymnosperms. It appears that the outcrossing mating system and effective mechanism of spore dispersal in B. spicant may account for the general lack of genetic structure within populations of this species.     

GENETIC VARIABILITY AND POPULATION DIFFERENTIATION INFERRED FROM DNA FINGERPRINTING IN SILVEREYES (AVES: ZOSTEROPIDAE)

This study evaluated DNA fingerprinting as a tool for estimating population genetic diversity and differentiation by comparing minisatellite variation in island and mainland populations of silvereyes (Aves: Zosterops lateralis). Three populations with different recent histories were compared: (1) Heron Island and neighboring islands, colonized 3000 to 4000 yr ago; (2) Lady Elliot Island, colonized within the past two decades; and (3) an adjacent mainland population, which presumably has existed for thousands of years. The degree of genetic variability within the three populations reflected both their size and the time since their colonization. Minisatellite diversity was highest in the mainland population, intermediate in the Capricorn Island group (which was shown to represent a single admixture), and lowest in the Lady Elliot Island population, possibly because of a recent population bottleneck during colonization. Mean band sharing between any two populations was less than the mean within either of those populations, and four fingerprint bands common to island birds were rare or absent in the fingerprints of mainland birds. In the absence of significant gene flow between the mainland and the islands, the populations have apparently become distinct at minisatellite loci, as evidenced by differences in both allelic diversity and in the frequencies of specific fragments. Within the Heron Island population, cohort analyses demonstrated the temporal stability of the fingerprint profile over 6 yr. This study demonstrates that length polymorphisms at minisatellite loci may be stable enough over time to retain information about recent historical and demographic effects on the relative genetic variability and differentiation of small, closely related populations.     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. III. CHROMATOGRAPHIC VARIATION

Four widespread grasses, Andropogon scoparius Michx., A. gerardi Vitman, Sorghastrum nutans (Nash) Hitchc. and Panicum virgatum L., have been studied behaviorally and morphologically. In the present comparison characteristic flavonoid patterns were shown whereby the four grass taxa can be separated at the generic and specific level. The greatest similarity was shown by the two Andropogon species. Panicum was most dissimilar. Although intrapopulational and interpopulational variation was demonstrated within each of the four taxa, both in transplanted material and in native plants of the original transplant site, there was no decisive correlation of biochemical variation with geographic origin, vegetative characteristics or maturity pattern. Early-flowering clones with short flowering culms and glabrous leaves, originating in northern and western areas, were essentially similar biochemically to later-flowering clones with tall flowering culms and extremely pubescent leaves, originating in southeastern areas. Blade samples collected in late fall, 1963, and in early spring, 1964, from the same transplanted clones were similar in flavonoid pattern. In P. virgatum. individual clonal patterns were characteristic of ramets grown under various day-length-thermoperiod conditions. Although biochemical markers for ecotypes would be useful êological tools, partially replacing their cultivation in transplant gardens, geographically correlated patterns were not revealed in this study. However, this study supports the present systematic position of the various morphologically and behaviorally diverse populations within the four taxa.     

GENETIC VARIATION AND DIFFERENTIATION IN THE GENUS MABRYA (SCROPHULARIACEAE-ANTIRRHINEAE): SYSTEMATIC AND EVOLUTIONARY INFERENCES

Nine populations of the five species of Mabrya have been examined for allozyme variation at 22 loci using enzyme electrophoresis. The species are homoploid (n = 12), herbaceous perennials and occur in small populations in canyons and barrancas in North American desert scrub and thorn scrub habitats. Although of ancient polyploid origin, the number of isozymes considered typical for diploids is encountered except for a probable duplication at a TPI locus. The average interspecific pairwise comparisons of genetic identities (range 0.434–0.731) are very dissimilar to intraspecific values (range 0.886–0.968). The uniformly low interspecific genetic divergence estimates (average I value of 0.593), large number of unique alleles (average of five per species), pronounced morphological differences, reduced interspecific cross-compatibilities, and (usually) allopatric distributions support recently proposed specific and infrageneric delimitations and hypotheses of a geographical speciation mode, a long period of reproductive isolation, and relictual endemism. Estimates of populational genetic variation are concordant with previous reproductive observations and suggest an outcrossing breeding system for M. geniculata and a mixed mating system for the other species. Because of approximately similar divergence values, phylogenetic relationships in the genus remain unresolved.     

云南地方稻种的遗传变异和籼粳分化

用７ 个单拷贝探针对８７ 份云南稻地方品种进行了ＲＦＬＰ分析．结果表明∶云南稻（Ｏｒｙｚａｓａｔｉｖａ Ｌ．）地方品种中,籼稻（ｉｎｄｉｃａ）和粳稻（ｊａｐｏｎｉｃａ）都表现出较高水平的变异,粳稻的等位基因数目和遗传多样性水平都高于籼稻,表明粳稻的遗传变异比籼稻丰富． 云南稻地方品种中的籼稻和粳稻间表现出明显的遗传分化,且不同染色体区段分化程度不同． 研究结果支持栽培稻的二系起源学说     

POSTGLACIAL RANGE FLUCTUATION,GENETIC SUBDIVISION AND SPECIATION IN THE WESTERN NORTH AMERICAN SPOTTED FROG COMPLEX,RANA PRETIOSA

The western North American complex of spotted frogs (Rana pretiosa) exhibits isolation-by-distance, genetic subdivision, and speciation in association with its extensive northward range shift in postglacial times. The southern relict populations of R. pretiosa species B existing at high altitudes or in desert springs have been subjected to restricted gene flow, high inbreeding, and bottlenecks to produce significant between-population genetic diversity. The more recently established northern populations, however, show genetic uniformity and isolation-by-distance, as estimated using Slatkin's (1993) statistic M?. Middle latitude populations have higher heterozygosities than populations at either extreme. Fixed differences in allozyme variation separate 21 populations of species B from five populations of R. pretiosa species A found in southwest Washington State and the Cascades Mountains of Oregon. Morphological variation of 20 metric characters among 38 samples, examined using multiple discriminant function analysis, could partially resolve partitioning among populations but specimens from the vicinity of the type series of R. p. pretiosa could not be assigned to either species A or species B. Speciation in these frogs may not be correlated with morphological evolution since comparatively neutral allozyme changes may be established more rapidly than changes in morphology.     

GENETIC VARIATION IN APHANIZOMENON (CYANOBACTERIA) COLONIES FROM THE BALTIC SEA AND NORTH AMERICA

Aphanizomenon Morren is an important member of the cyanobacterial community in the Baltic Sea, but studies of this genus have been hampered by the difficulty of growing it in laboratory culture. PCR amplification of DNA from colonies picked directly from water samples has circumvented this problem and made it possible to carry out an analysis of genetic diversity within the Baltic Sea and in two small North American lakes separated by just a few kilometers. The nucleotide sequence of the phycocyanin intergenic spacer and partial flanking coding regions of cpcB and cpcA was determined for 32 colonies of Aphanizomenon , 26 from the Baltic Sea, and 6 from the North American lakes. No variation was detected among the 26 Baltic Sea colonies, but two alleles, differing at 19 nucleotide positions (5.4%), were found in the North American lake colonies. Surprisingly, the two North American types were less closely related to each other than to the Baltic Sea genotype. The Baltic Sea Aphanizomenon is clearly distinct from A. flos-aquae at both the cpcB–cpcA and 16S rDNA loci, which lends phylogenetic support to their tentative separation based on ultrastructural analysis. We conclude that although there is significant genetic diversity in the genus Aphanizomenon , the population in the Baltic Sea is, in contrast to the Nodularia population, genetically homogeneous.     

ENVIRONMENTAL AND GENETIC CONSTRAINTS ON ADAPTIVE POPULATION DIFFERENTIATION IN ANTHOXANTHUM ODORATUM

Maximum-likelihood estimates of environmental and broad sense genetic (co)variance components were obtained for the growth and reproductive output of clones of the grass Anthoxanthum odoratum. The clones were transplanted between a mesic and a xeric field site and across-environment genetic correlations were used to estimate the strength of genotype-environment interaction. Significant across-environment clonal covariance matrices were found for several traits, including lifetime reproductive output in one population. None of the matrices differed significantly between populations. Significant within-site clonal variation was found, but there was no significant across-environment clonal covariation. Most broad sense heritability estimates of character states within sites were small (median = 0.12), suggesting that only a slow response to selection is possible. All significant within-site clonal correlations between growth and reproductive output were positive, although the pattern of negative clonal correlations suggests that there may be a cost to first year reproduction, which might constrain future selection response.     

八面山银杉林的遗传多样性和群体分化

采用水平淀粉凝胶电泳技术对分布于湖南八面山的濒危植物银杉(cathaya argyrophylla Chun etKuang)的遗传多样性和群体分化进行了初步研究。对13个酶系统25个等位酶位点的检测表明,该地区的银杉林群体遗传变异水平很低,多态位点比率 P=0.28,等位基因平均数 A=1.36,平均期望杂合度He=0.100;但3个小群体间存在着明显的遗传分化,基因分化系数高达G_ST=0.26,明显不同于其它裸子植物的报道。八面山银杉林低水平的遗传变异和明显的群体分化,一方面反映了银杉的古老性和残遗性,另一方面也说明在银杉的进化过程中可能发生了严重的遗传漂变,而且群体之间的基因流明显受阻。     

ALLOZYME VARIATION IN OLD WORLD RACES OF SORGHUM BICOLOR (POACEAE)

A survey of allozyme variation in cultivated races of sorghum (Sorghum bicolor) was undertaken. Eight plants each of 83 accessions representing the five primary races and five of the intermediate races of sorghum were analyzed for 15 enzyme systems encoded by 27 loci. Low levels of variation were found within accessions, which is typical of self-pollinating species. Little variation was also found among accessions. Compared with other cereals, S. bicolor is depauperate in allozyme variation. We found an average of 1.81 alleles per locus with a mean expected heterozygosity of 0.008 for the accessions and total panmictic heterozygosity of 0.093. Only 9% of the variation present was found within accessions, while 91% was among accessions. Most of the variation present is attributable to differences in geographic origin of the accessions rather than racial differences. Western and eastern Africa have the highest levels of total heterozygosity (0.108 and 0.088, respectively), while southern Africa has the lowest (0.008). Principal component analysis revealed continuous variation among races and geographic regions with the accessions failing to segregate into discrete racial or geographic clusters.     

RECONSTRUCTING ORIGINS OF LOSS OF SELF‐INCOMPATIBILITY AND SELFING IN NORTH AMERICAN ARABIDOPSIS LYRATA: A POPULATION GENETIC CONTEXT

Theoretical and empirical comparisons of molecular diversity in selfing and outcrossing plants have primarily focused on long‐term consequences of differences in mating system (between species). However, improving our understanding of the causes of mating system evolution requires ecological and genetic studies of the early stages of mating system transition. Here, we examine nuclear and chloroplast DNA sequences and microsatellite variation in a large sample of populations of Arabidopsis lyrata from the Great Lakes region of Eastern North American that show intra‐ and interpopulation variation in the degree of self‐incompatibility and realized outcrossing rates. Populations show strong geographic clustering irrespective of mating system, suggesting that selfing either evolved multiple times or has spread to multiple genetic backgrounds. Diversity is reduced in selfing populations, but not to the extent of the severe loss of variation expected if selfing evolved due to selection for reproductive assurance in connection with strong founder events. The spread of self‐compatibility in this region may have been favored as colonization bottlenecks following glaciation or migration from Europe reduced standing levels of inbreeding depression. However, our results do not suggest a single transition to selfing in this system, as has been suggested for some other species in the Brassicaceae.