中国人群肤纹的主成分分析

近年来 ,我国学者多将中国人群分为南、北两大类群。作者对我国 5 9个人群的肤纹进行主成分分析。结果表明 ,根据肤纹特征 ,可将中国人分为 6个族群 ,除北方族群、南方族群外 ,存在着新疆族群与西藏族群。新疆族群与北方族群相比 ,斗型率低 ,尺箕、桡箕率高 ,小鱼际区与指间区Ⅱ、Ⅲ真实花纹率高。西藏族群斗型率高、尺箕率低。北方族群与南方族群相比 ,指纹嵴线总数、小鱼际区与指间区Ⅲ真实花纹率高。此外 ,还存在南北族群间的过渡族群与南北混合族群。 8个汉族人群未能聚集 ,分散于各族群中。这表明 ,汉族与少数民族间、南北方民族间存在着肤纹基因的交流。将中华民族分为南北两大类群的观点可能过于简单化了。     

Domestication and the distribution of genetic variation in wild and cultivated populations of the Mesoamerican fruit tree Spondias purpurea L. (Anacardiaceae)

Domestication occurs as humans select and cultivate wild plants in agricultural habitats. The amount and structure of variation in contemporary cultivated populations has been shaped, in part, by how genetic material was transferred from one cultivated generation to the next. In some cultivated tree species, domestication involved a shift from sexually reproducing wild populations to vegetatively propagated cultivated populations; however, little is known about how domestication has impacted variation in these species. We employed AFLP data to explore the amount, structure, and distribution of variation in clonally propagated domesticated populations and sexually reproducing wild populations of the Neotropical fruit tree, Spondias purpurea (Anacardiaceae). Cultivated populations from three different agricultural habitats were included: living fences, backyards, and orchards. AFLP data were analysed using measures of genetic diversity (% polymorphic loci, Shannon's diversity index, Nei's gene diversity, panmictic heterozygosity), population structure (F(ST) analogues), and principal components analyses. Levels of genetic variation in cultivated S. purpurea populations are significantly less than variation found in wild populations, although the amount of diversity varies in different agricultural habitats. Cultivated populations have a greater proportion of their genetic variability distributed among populations than wild populations. The genetic structure of backyard populations resembles that of wild populations, but living fence and orchard populations have 1/3 more variability distributed among populations, most likely a reflection of relative levels of vegetative reproduction. Finally, these results suggest that S. purpurea was domesticated in two distinct regions within Mesoamerica.     

中国特有濒危树种毛红椿核心和边缘居群的遗传多样性

选用8对多态的微卫星引物, 研究了毛红椿(Toona ciliata var. pubescens)核心居群和边缘居群的遗传多样性。研究结果显示, 边缘居群的观察等位基因数和有效等位基因数并不比核心居群低, 甚至更高。普通广布和稀有地方等位基因在所有居群中均有分布, 而普通地方和稀有广布等位基因分别仅在5个和3个居群中有分布。从4种类型等位基因总数上看, 边缘居群高于核心居群, 特别是边缘居群的稀有地方等位基因数量明显多于核心居群。边缘居群的平均期望杂合度和观察杂合度都高于核心居群。核心居群间的基因分化系数为0.1520, 边缘居群间为0.3045, 边缘居群与核心居群的遗传分化差异达到显著水平。核心居群间基因流大于1, 而边缘居群间基因流小于1, 说明核心居群间基因交流频繁, 边缘居群由于片段化和地形影响, 基因流较小。Mantel检验结果显示, 居群间遗传距离与地理距离的相关性不显著, 说明地理距离对毛红椿居群遗传分化的影响不显著。     

Microsatellite variation in autochthonous and introduced populations of the Alpine marmot (Marmota marmota) along a European west–east transect

Microsatellite variation was studied in 11 populations of the Alpine marmot along a west–east transect through the present distribution range. The samples represent five autochthonous and six introduced populations. Eleven loci were analysed in nine populations and six loci in the two populations from France. In the populations from the Western Alps, there is no indication for reduced variability as has been assumed in previous studies. However, a decrease of variation in the autochthonous populations was observed from the west to the east. The introduced populations showed a heterogeneous pattern reflecting the geographic origin of the released individuals. The population from the Spanish Pyrenees harbours a high level of variation and is genetically closest to the French populations. In Austria, three of the introduced populations have low variation and are closely related to the autochthonous populations from the western part of Austria. In contrast, two introduced populations from the central part of Austria are highly variable and resemble the populations from France. At least for one of these populations an early introduction of founder individuals from the Western Alps has been documented.     

Inferring ancient Agave cultivation practices from contemporary genetic patterns

Several Agave species have played an important ethnobotanical role since prehistory in Mesoamerica and semiarid areas to the north, including central Arizona. We examined genetic variation in relict Agave parryi populations northeast of the Mogollon Rim in Arizona, remnants from anthropogenic manipulation over 600 years ago. We used both allozymes and microsatellites to compare genetic variability and structure in anthropogenically manipulated populations with putative wild populations, to assess whether they were actively cultivated or the result of inadvertent manipulation, and to determine probable source locations for anthropogenic populations. Wild populations were more genetically diverse than anthropogenic populations, with greater expected heterozygosity, polymorphic loci, effective number of alleles and allelic richness. Anthropogenic populations exhibited many traits indicative of past active cultivation: fixed heterozygosity for several loci in all populations (nonexistent in wild populations); fewer multilocus genotypes, which differed by fewer alleles; and greater differentiation among populations than was characteristic of wild populations. Furthermore, manipulated populations date from a period when changes in the cultural context may have favoured active cultivation near dwellings. Patterns of genetic similarity among populations suggest a complex anthropogenic history. Anthropogenic populations were not simply derived from the closest wild A. parryi stock; instead they evidently came from more distant, often more diverse, wild populations, perhaps obtained through trade networks in existence at the time of cultivation.     

Life-history differentiation in Nymphoides coreana (Menyanthaceae) populations in aquatic habitats with different disturbance regimes in Japan

Different disturbance regimes in aquatic habitats may bring about life-history differentiation in aquatic plants. However, there is little information on this association. Adult longevity, seed size and mass, and seed-germination characteristics were surveyed for Nymphoides coreana populations, which grow in different types of aquatic habitats, to demonstrate life-history differentiation. Seed size and seed mass were significantly greater in paddy-field populations (disturbed habitats) than in irrigation-pond populations (stable habitats). Paddy-field populations were composed of annuals, whereas irrigation-pond populations contained perennials. Seed-germination characteristics were significantly different between paddy-field and irrigation-pond populations. The moist-chilling pretreatment period needed to release innate seeds from dormancy was significantly shorter in paddy-field populations than in irrigation-pond populations. The percentage of seeds that germinated was significantly higher under anaerobic conditions, irrespective of light, and under light aerobic conditions compared to dark aerobic conditions in paddy-field populations. Conversely, in irrigation-pond populations, the percentage of seeds that germinated was highest under light anaerobic conditions. These results show that the reaction norm of seed-germination characteristics was significantly broader in annual populations than in perennial populations. The occurrence of aquatic habitats with different disturbance regimes thus contributes to the maintenance of phenotypic diversity in N. coreana populations.     

Population genetics of Howellia aquatilis (Campanulaceae) in disjunct locations throughout the Pacific Northwest

Howellia aquatilis A.Gray (water howellia) is a federally-listed threatened aquatic plant species with limited distribution in four states: California, Idaho, Montana, and Washington. Previous studies have shown a lack of genetic variation within the species; these studies, however, have excluded samples from one or more states. There have been no published studies on the population biology or genetics of the six known California populations or their evolutionary relationship to the other Pacific Northwest populations. We used Amplified Fragment Length Polymorphisms to identify genetic variation within and among the California populations, and to compare the California populations to the Idaho, Montana, and Washington populations. Analysis of molecular variance of 92 individuals from the six California populations show that 83.8% of genetic variation is found within populations and 16.2% among populations (P < 0.001). All sampled populations from all states provide 83.7% variation within and 16.3% variation among populations (P < 0.001). A UPGMA analysis confirms there is no clear clustering of Howellia aquatilis populations within California, that the Montana populations cluster within the California populations, and, although with limited population sample sizes, the Idaho and Washington populations are distantly related to all other populations. Waterfowl migration patterns support a hypothesis for avian dispersal as a primary factor in gene flow in Howellia aquatilis.     

The benefits of interpopulation hybridization diminish with increasing divergence of small populations

Interpopulation hybridization can increase the viability of small populations suffering from inbreeding and genetic drift, but it can also result in outbreeding depression. The outcome of hybridization can depend on various factors, including the level of genetic divergence between the populations, and the number of source populations. Furthermore, the effects of hybridization can change between generations following the hybridization. We studied the effects of population divergence (low vs. high level of divergence) and the number of source populations (two vs. four source populations) on the viability of hybrid populations using experimental Drosophila littoralis populations. Population viability was measured for seven generations after hybridization as proportion of populations facing extinction and as per capita offspring production. Hybrid populations established at the low level of population divergence were more viable than the inbred source populations and had higher offspring production than the large control population. The positive effects of hybridization lasted for the seven generations. In contrast, at the high level of divergence, the viability of the hybrid populations was not significantly different from the inbred source populations, and offspring production in the hybrid populations was lower than in the large control population. The number of source populations did not have a significant effect at either low or high level of population divergence. The study shows that the benefits of interpopulation hybridization may decrease with increasing divergence of the populations, even when the populations share identical environmental conditions. We discuss the possible genetic mechanisms explaining the results and address the implications for conservation of populations.     

GENE FLOW AND INEFFECTIVE ANTIPREDATOR BEHAVIOR IN A STREAM-BREEDING SALAMANDER

Predators often feed on prey that show ineffective antipredator behavior. Gene flow among populations may constrain evolution of effective antipredator ability in larvae of the streamside salamander, Ambystoma barbouri, a species that occupies distinctly different habitats with conflicting selection pressures. Some streams are ephemeral, where larvae should be active to feed and reach metamorphosis before stream drying. In contrast, other streams are more permanent and contain pools with predatory fish, where larvae should remain inactive to avoid fish predation. Feeding rates and predator escape behavior were assayed for laboratory-reared larvae from 15 populations. Larval survival was also compared among populations in artificial streams with natural predators. Five populations represented streams subjected to fish predation along a gradient of genetic and geographic isolation from populations without fish; the remaining 10 populations were ephemeral and without fish. Individuals from populations with fish had significantly stronger behavioral responses to fish (i.e., decreased feeding rate associated with the presence of fish and increased escape response) than individuals from fishless populations. Larvae from populations containing fish that were more isolated from fishless populations showed stronger antipredator responses than less isolated populations. Further, larvae from more isolated populations survived longer in the predation experiment, indicating that the behaviors measured were related with survival. These results suggest that gene flow between populations with conflicting selection pressures limits local adaptation in some salamander populations with fish. While previous studies have typically focused on the role of gene flow in pairs of populations, the results of this study suggest that gene flow is acting to swamp local adaptation across several populations.     

Experimental Extinction of Garlic Mustard (Alliaria petiolata) Populations: Implications for Weed Science and Conservation Biology

An assumption of weed science and conservation biology is that small populations are more vulnerable to elimination and extinction than large populations. We tested this with the invasive biennial garlic mustard (Alliaria petiolata). We compared 61 experimental populations from which every flowering plant was removed for 4 years, with 56 control populations. Whereas the majority of the control populations continued to expand in size over the 4 years, experimental populations showed a strong experimental effect, remaining stable in size, declining in size, or going extinct. Small populations were far more vulnerable to extinction than large populations: 43% of small experimental populations (initially fewer than 10 individuals) went extinct, but only 7% of large populations (initially more than 50 individuals). However, some small experimental populations persisted, and in a few cases, larger experimental populations continued to expand even though every flowering individual had been removed. These results and a simple population model suggest the importance of buried seeds in allowing this species to persist despite attempts to eradicate it.     

Monomorphism of isoenzyme loci in natural and cultivated amaranth (Amaranthus L.) populations

Starch gel electrophoresis was used for isozyme analysis of ADH, GDH, MDH, IDH, and ME in populations of amaranth. Experiments were performed with 93 populations and 4 cultivars. Some populations proved to be polymorphic, and this fact allowed analysis of the genetic control of the enzymes listed. The populations examined showed poor allozyme variability. Monomorphism for all loci studied was observed in 73 populations and 4 varieties. Starch gel electrophoresis was used for isozyme analysis ofADH, GDH, MDH, IDH, and ME in populations of amaranth. Experiments were performed with 93 populations and 4 cultivars. Some populations proved to be polymorphic, and this fact allowed analysis of the genetic control of the enzymes listed. The populations examined showed poor allozyme variability. Monomorphism for all loci studied was observed in 73 populations and 4 varieties. Only some populations demonstrated rare polymorphism for a single locus each: Adh, Mdh 2, Gdh, Idh 1, Idh 2, or Mod 2. The results demonstrate genetic monomorphism of amaranth for the studied loci.     

Quantitative genetic differences between populations of Drosophila melanogaster from diverse geographic origins

Crosses were made between each seven populations of Drosophila melanogaster-three of which were laboratory populations and four were recently captured populations-and a line previously selected for low sternopleural bristle number for many generations. In each of six replicate lines from each cross, selection was practised for low sternopleural bristle number; subsequently these replicates were intercrossed and reselected. Introduction of new genetic material from four populations into the selected line was achieved, indicating the presence in these populations of particular alleles which are absent from or rare in the base populations of the selected line. Introduction of new genetic material from three populations into the selected line was not achieved. Consequently, it was possible to establish two groups of populations. In each group, the populations appear to be segregating for essentially the same alleles. Differences in gene frequency rather than the presence or absence of particular alleles are mainly responsible for the differences observed between the populations.In all, 11 populations screened for genetic differences controlling sternopleural bristle number. There are widespread genetic similarities among populations of very different geographic origin. Laboratory populations as a group are not more homogeneous than recently collected populations, although the latter are genetically more variable. Drift alone could account for the reduction of variability in the laboratory populations.     

Higher genetic diversity in introduced than in native populations of the mussel Mytella charruana: evidence of population admixture at introduction sites

Aim  Levels of genetic diversity can be used to determine haplotype frequency, population size and patterns of invasive species distribution. In this study, we sought to investigate the genetic structure of the invasive marine mussel Mytella charruana and compare variation from invasive populations with variation found within three native populations.
Location  Invaded areas in the USA (Florida, Georgia); native areas in Ecuador, Colombia and Brazil.
Methods  We sequenced 722 bp of the mitochondrial COI gene from 83 M. charruana samples from four invasive populations (USA) and 71 samples from two natural populations (Ecuador, Columbia). In addition, we sequenced 31 individuals of a congeneric species, Mytella guyanensis , from Salvador, Brazil. We constructed the phylogenetic relationship among all haplotypes and compared diversity measures among all populations.
Results  We found significantly higher levels of nucleotide diversity in invasive populations than in native populations, although the number of haplotypes was greater in the native populations. Moreover, mismatch distribution analyses resulted in a pattern indicative of population admixture for the invasive populations. Conversely, mismatch distributions of native populations resulted in a pattern indicative of populations in static equilibrium.
Main conclusion  Our data present compelling evidence that the M. charruana invasion resulted from admixture of at least two populations, which combined to form higher levels of genetic diversity in invasive populations. Moreover, our data suggest that one of these populations originated from the Caribbean coast of South America. Overall, this study provides an analysis of genetic diversity within invasive populations and explores how that diversity may be influenced by the genetic structure of native populations and how mass dispersal may lead to invasion success.     

海南粗榧（Cephalotaxus mannii Hook.f.）化学元素含量及变异研究

 利用变异系数和差异显著性检验,对海南坝王岭等五个海南粗榧群体植株及其不同器官的C、H、N、K等15种化学元素分布及变异进行研究。结果表明：1)海南粗榧(Cephalotaxus mannii Hook．f．)中的化学元素含量分布总体呈Ca>K型,但枝、茎、根、种子等不同器官却表现为K>Ca型;2)海南粗榧群体内各化学元素含量的变异系数较大,但群体内和群体间基本无显著差异;3)海南粗榧不同群体同一器官间元素含量相对稳定,变异系数不太大,群体不同器官间则呈现显著甚至极显著的差异,但不同器官的总体平均值却无显著差异。     

Inferring recruitment history from spatial genetic structure within populations of the colonizing tree Albizia julibrissin (Fabaceae)

Comparative analyses of spatial genetic structure (SGS) among species, populations, or cohorts give insight into the genetic consequences of seed dispersal in plants. We analysed SGS of a weedy tree in populations with known and unknown recruitment histories to first establish patterns in populations with single vs. multiple founders, and then to infer possible recruitment scenarios in populations with unknown histories. We analysed SGS in six populations of the colonizing tree Albizia julibrissin Durazz. (Fabaceae) in Athens, Georgia. Study sites included two large populations with multiple, known founders, two small populations with a single, known founder, and two large populations with unknown recruitment histories. Eleven allozyme loci were used to genotype 1385 individuals. Insights about the effects of colonization history from the SGS analyses were obtained from correlograms and Sp statistics. Distinct differences in patterns of SGS were identified between populations with multiple founders vs. a single founder. We observed significant, positive SGS, which decayed with increasing distance in the populations with multiple colonists, but little to no SGS in populations founded by one colonist. Because relatedness among individuals is estimated relative to a local reference population, which usually consists of those individuals sampled in the study population, SGS in populations with high background relatedness, such as those with a single founder, may be obscured. We performed additional analyses using a regional reference population and, in populations with a single founder, detected significant, positive SGS at all distances, indicating that these populations consist of highly related descendants and receive little seed immigration. Subsequent analyses of SGS in size cohorts in the four large study populations showed significant SGS in both juveniles and adults, probably because of a relative lack of intraspecific demographic thinning. SGS in populations of this colonizing tree is pronounced and persistent and is determined by the number and relatedness of founding individuals and adjacent seed sources. Patterns of SGS in populations with known histories may be used to indirectly infer possible colonization scenarios for populations where it is unknown.     

Differential admixture shapes morphological variation among invasive populations of the lizard Anolis sagrei

The biological invasion of the lizard Anolis sagrei provides an opportunity to study evolutionary mechanisms that produce morphological differentiation among non-native populations. Because the A. sagrei invasion represents multiple native-range source populations, differential admixture as well as random genetic drift and natural selection, could shape morphological evolution during the invasion. Mitochondrial DNA (mtDNA) analyses reveal seven distinct native-range source populations for 10 introduced A. sagrei populations from Florida, Louisiana and Texas (USA), and Grand Cayman, with 2-5 native-range sources contributing to each non-native population. These introduced populations differ significantly in frequencies of haplotypes from different native-range sources and in body size, toepad-lamella number, and body shape. Variation among introduced populations for both lamella number and body shape is explained by differential admixture of various source populations; mean morphological values of introduced populations are correlated with the relative genetic contributions from different native-range source populations. The number of source populations contributing to an introduced population correlates with body size, which appears independent of the relative contributions of particular source populations. Thus, differential admixture of various native-range source populations explains morphological differences among introduced A. sagrei populations. Morphological differentiation among populations is compatible with the hypothesis of selective neutrality, although we are unable to test the hypothesis of interdemic selection among introductions from different native-range source populations.     

Within and between population variation in plant traits predicts ecosystem functions associated with a dominant plant species

Linking intraspecific variation in plant traits to ecosystem carbon uptake may allow us to better predict how shift in populations shape ecosystem function. We investigated whether plant populations of a dominant old-field plant species (Solidago altissima) differed in carbon dynamics and if variation in plant traits among genotypes and between populations predicted carbon dynamics. We established a common garden experiment with 35 genotypes from three populations of S. altissima from either Tennessee (southern populations) or Connecticut (northern populations) to ask whether: (1) southern and northern Solidago populations will differ in aboveground productivity, leaf area, flowering time and duration, and whole ecosystem carbon uptake, (2) intraspecific trait variation (growth and reproduction) will be related to intraspecific variation in gross ecosystem CO(2) exchange (GEE) and net ecosystem CO(2) exchange (NEE) within and between northern and southern populations. GEE and NEE were 4.8× and 2× greater in southern relative to northern populations. Moreover, southern populations produced 13× more aboveground biomass and 1.4× more inflorescence mass than did northern populations. Flowering dynamics (first- and last-day flowering and flowering duration) varied significantly among genotypes in both the southern and northern populations, but plant performance and ecosystem function did not. Both productivity and inflorescence mass predicted NEE and GEE between S. altissima southern and northern populations. Taken together, our data demonstrate that variation between S. altissima populations in performance and flowering traits are strong predictors of ecosystem function in a dominant old-field species and suggest that populations of the same species might differ substantially in their response to environmental perturbations.     

祁连山两侧中国沙棘不同居群的遗传多样性研究

应用RAPD技术研究了祁连山中段中国沙棘(Hippophae rhamnoidoes ssp．sinensis)4个居群和1个对照居群的遗传多样性水平,探讨中国沙棘边缘居群的遗传变异以及天然屏障祁连山对中国沙棘居群遗传结构的影响。结果显示,祁连山地区中国沙棘居群水平的Nei’基因多样度(h)和Shannon多态信息指数(I)分别为0．2070和 0．297 4,基因分化系数(Gst)为0．319 3,均高于中国沙棘整个分布区的平均值,表明该地中国沙棘边缘居群遗传多样性水平及居群间的遗传分化都有增加的趋势;居群间每代迁移数(Nm=1．065 9)显著低于异交风媒植物(Nm= 5．380),表明祁连山的隔离对中国沙棘居群间的基因交流有限制作用,造成了该地中国沙棘边缘居群间较高的遗传分化。     

Reproductive biology and genetic structure in Lloydia serotina

Concern regarding the conservation status of small, isolated populations of the arctic-alpine plant species Lloydia serotina prompted research to establish the status and performance of this species in Wales, in comparison with large populations in its more typical alpine habitat. Relationships between reproductive strategies and genetic variation were investigated in a number of populations, representing a wide habitat, geographic and population size range. In all populations, vegetative reproduction predominates over sexual reproduction, but seed produced is viable and germinates readily under controlled conditions. Smaller, peripheral populations produced fewer flowers and seeds than the larger ones, but all populations studied supported significant percentages (>30%) of male plants, due to either the occurrence of androdioecy in this species or to a resource limited breeding system. Analysis of allozyme variation in sixteen populations from North America, the European Alps and Wales showed lower levels of genetic variation in smaller populations which averaged 1.1–1.2 alleles per locus and 10–20% of loci polymorphic, whereas larger populations averaged 1.4 alleles per locus and 30–40% polymorphic loci. This applied especially to the most northerly and southerly populations in North America, suggesting the occurrence of genetic drift in these small, peripheral populations. F-statistics suggest relatively high levels of differentiation among smaller populations, even among those closely related geographically, but genetic variation has been retained in all but one population, possibly due to infrequent sexual reproduction by long lived clones. RAPD analysis of four small populations in Wales provided further evidence of clonal growth and possible inbreeding dominating a mixed mating reproductive system with consequent genetic structuring in these populations.     

Genetic diversity and gene flow in the endangered dwarf bear poppy, Arctomecon humilis (Papaveraceae)

Arctomecon humilis is a critically endangered species endemic to the Moenkopi shale of Washington County, Utah. Recovery plans for the species would be improved by an understanding of genetic diversity and gene flow among its remaining populations. Ten variable isozyme loci were used to calculate genetic diversity statistics for study populations. Westerly populations possessed higher levels of genetic variability than other populations at the same isozyme loci. Three of the populations exhibited significant deviations from Hardy-Weinberg expectations. No correlation existed between genetic distance and geographic distance. Most of the genetic diversity was distributed among populations with little gene flow between populations, suggesting that observed genetic differences may arise from genetic drift. For the westerly populations, similar genotypes were observed in the seedling and old age classes, while intermediate age classes typically possessed an alternate set of genotypes at Pgi-2. Mean heterozygosity increased with age class across populations. Westerly populations of A. humilis shared more alleles with the nearest geographic population of A. californica than other populations. Since the westerly populations contained more genetic variability and more alleles in common with a near relative, they may be relictual. Other populations may contain less genetic diversity due to founder effects and/or genetic drift.