Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis (Trin.) Tzvel.

Randomly amplified polymorphic DNA (RAPD) analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis (Trin.) Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% (P ＜ 0.04), and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% (P ＜ 0.002). A 21.06% RAPD variation among all 16 populations among two regions was found (P ＜ 0.001), as well as 72.59% variation within populations (P ＜ 0.001). Molecular variation within populations was significantly different among 16 populations.     

Genetics of colonization in Hypochaeris tenuifolia (Asteraceae,Lactuceae) on Volcán Lonquimay,Chile

Understanding the genetics of colonizing populations has been, and continues to remain, an important focus in evolutionary biology. Different theoretical models predict varying levels of genetic variation in colonizing populations depending upon strength of founder effect, gene flow and rate of population growth and immigration following colonization. We analyse overall genetic variation using amplified fragment length polymorphism markers in colonizing populations of Hypochaeris tenuifolia (Asteraceae) in the southern Andes. Volcán Lonquimay newly erupted on 25 December 1988, producing a side cone, La Navidad, and sent lava and ash into surrounding areas. Many domesticated animals (estimated at 10 000) and many natural plant populations were destroyed. Into this new open habitat have come immigrant populations of several angiosperm species, most conspicuously H. tenuifolia that forms leaf rosettes with flowering scapes to 15 cm and orange-yellow heads 1-2 cm in diameter. Genetic diversity in five founder populations in the eruption zone is compared with that from five nearby survivor populations, as well as with eight isolated northern and four southern populations from throughout the entire range of the species in Chile. Results from 477 individuals representing 447 different multilocus phenotypes, yielded 170 DNA fragments of which 144 (85%) were polymorphic. Genetic diversity within founder populations is neither lower than in survivor populations nor in isolated populations throughout the range of the species, but it is lower among founder populations than among other populations immediately and distantly outside the zone of disturbance. Closest genetic similarity occurs between founders and nearby survivor populations as well as those in adjacent southern regions.     

Genetic Variation and Random Drift in Autotetraploid Populations

The rate of decay of genetic variation is determined for randomly mating autotetraploid populations of finite size, and the equilibrium homozygosity under mutation and random drift is calculated. It is shown that heterozygosity is lost at a slower rate than in diploid populations, and that the equilibrium heterozygosity with mutation and random drift is higher than for diploids. Outcrossing populations as well as populations that randomly self are analyzed. A method of comparing genetic variation between autotetraploid and diploid populations is proposed. Our treatment suggests that the ``gametic homozygosity' provides a unified approach for comparing genotypes within a population as well as comparing genetic variation between populations with different levels of ploidy.     

Geographic parthenogenesis in the stream mayfly Eurylophella funeralis in eastern North America

Unisexual populations were found largely at the periphery of the geographic range of the mayfly Eurylophella funeralis in eastern North America. Bisexual populations generally had a normal sex ratio but at least two populations were observed with only about 2–11% males. Hatch success for unfertilized eggs depended on temperature but in general averaged >61% in unisexual populations and < 14% in bisexual populations. Eggs took about 65 d to hatch at 10°C and 19 d at 25°C; no hatching occurred at 5 or 30°C. Successful oviposition was observed for about 97% and 20% of unmated female adults from unisexual and bisexual populations respectively. The hatch success of unfertilized eggs for three geographically distinct bisexual populations was in versely correlated with the proportion of males in the populations. The genetic structure of bisexual and unisexual populations was very similar. Unisexual populations consists of clones, with as few as four recognizable phenotypes being present at a given location. All offspring had the same phenotype as the mother. Tychoparthenogenesis is suggested as the most reasonable working hypothesis concerning the origin of unisexual populations in E. funeralis .     

南方红豆杉迁地保护小种群适应性进化机制研究

为了解南方红豆杉迁地保护种群的适应性进化机制,以南京中山植物园内南方红豆杉迁地保护栽培种群和扩散的衍生种群为材料,以引种初始地江西野生种群为对照,对南方红豆杉群落的结构、遗传多样性及遗传结构进行分析和研究。结果表明,南方红豆杉野生种群和迁地保护种群均维持着较高水平的遗传多样性,其中野生种群遗传多样性稍高于迁地保护小种群,但迁地保护种群中南方红豆杉个体密度大于野生种群。同时,种群内的遗传变异所占比例大于种群间的。整体来看,南方红豆杉迁地保护种群还处于演替早期,存在不明显的奠基者效应,有进一步演替发展的可能。     

Large mainland populations of South Island robins retain greater genetic diversity than offshore island refuges

For conservation purposes islands are considered safe refuges for many species, particularly in regions where introduced predators form a major threat to the native fauna, but island populations are also known to possess low levels of genetic diversity. The New Zealand archipelago provides an ideal system to compare genetic diversity of large mainland populations where introduced predators are common, to that of smaller offshore islands, which serve as predator-free refuges. We assessed microsatellite variation in South Island robins (Petroica australis australis), and compared large mainland, small mainland, natural island and translocated island populations. Large mainland populations exhibited more polymorphic loci and higher number of alleles than small mainland and natural island populations. Genetic variation did not differ between natural and translocated island populations, even though one of the translocated populations was established with five individuals. Hatching failure was recorded in a subset of the populations and found to be significantly higher in translocated populations than in a large mainland population. Significant population differentiation was largely based on heterogeneity in allele frequencies (including fixation of alleles), as few unique alleles were observed. This study shows that large mainland populations retain higher levels of genetic diversity than natural and translocated island populations. It highlights the importance of protecting these mainland populations and using them as a source for new translocations. In the future, these populations may become extremely valuable for species conservation if existing island populations become adversely affected by low levels of genetic variation and do not persist.     

不同地理区域栓皮栎种群结构及其空间格局

利用径级法和方差/均值法对我国不同地理区域上栓皮栎种群年龄结构及其空间分布格局进行分析.结果表明: 在水平梯度上,中部、北部、南部和西部栓皮栎种群均呈倒J型分布,而东部种群呈衰退型分布.成年树在中部和南部均呈集群分布,而北部区域呈现随机分布;幼树在在北、中和西部区域均为集群分布,而在南部和东部均呈随机分布.在纬向梯度上,幼树聚集强度的纬向趋势为中>北>南,而成年树聚集强度为中>南>北,经向梯度上幼树和成年树的聚集强度均为中>西>东.在垂直梯度上,中、低海拔种群呈倒J型分布,高海拔呈现衰退型.幼树在不同海拔均呈集群分布;成年树在低海拔为随机分布,而在高海拔和中海拔均为集群分布.幼树和成年树的聚集强度均为中海拔>高海拔和低海拔.在不同地理区域上,幼树的聚集强度均高于成年树.因此,栓皮栋种群结构及其分布格局主要是由环境梯度变化及其自身生物学特性决定,证实了“中心-边缘”种群假说.     

Translocation of wild populations: conservation implications for the genetic diversity of the black-lipped pearl oyster Pinctada margaritifera

Translocation has been widely studied as a tool for conservation management to restore or enhance degraded populations. On the contrary, few studies have been conducted on translocation for commercial purposes. In this study, we evaluate the genetic consequences of translocation of wild individuals of Pinctada margaritifera on farmed and adjacent wild populations. We tested the hypotheses that translocations would induce high genetic heterogeneity in farmed populations and this heterogeneity would then leak into the adjacent wild populations. In fact, farmed samples exhibit high levels of heterogeneity and low pairwise relatedness compared to wild populations, highlighting the pooling of genetically divergent populations into farms. We also demonstrate that this heterogeneity is transmitted to adjacent wild populations as a result of interbreeding. Adjacent wild populations tend to have higher genetic diversity values and greater pairwise relatedness coefficient with farmed populations than wild populations. Overall, pearl culture in French Polynesia promotes the mixing of unrelated individuals in farmed locations and reduces genetic divergence among geographically distant populations as well as among farmed and wild populations of a same lagoon. We also studied for the first time a farmed population originating from spat collected in a lagoon where release of hatchery-produced larvae occurred 10 years ago and we were able to identify four distinct genetic groups. These groups contribute highly to reproduction and caused considerable genetic drift in the lagoon, suggesting that hatchery-produced larvae are neither sustainable method for pearl culture nor for conserving the diversity of P. margaritifera in French Polynesia.     

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.     

Genetic differentiation between American and European Drosophila melanogaster populations could be attributed to admixture of African alleles

A total of 48 polymorphic microsatellite loci were characterized in 13 Drosophila melanogaster populations originating from Europe, America, and Africa. Consistent with previous results, the African D. melanogaster populations were the most differentiated populations and harbored most variation. Despite an overall similarity, American and European populations were significantly differentiated. Interestingly, genetic distances based on the proportion of shared alleles as well as FST values suggested that the American D. melanogaster populations are more closely related to the African populations than European ones are. We also detected a higher proportion of putative African alleles in the American populations, indicating recent admixture of African alleles on the American continent.     

Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis （Trin.） Tzvel.

Randomly amplified polymorphic DNA （RAPD） analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis （Trin.） Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% （P 〈 0.04）, and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% （P 〈 0.002）. A 21.06% RAPD variation among all 16 populations among two regions was found （P 〈 0.001）, as well as 72.59% variation within populations （P 〈 0.001）. Molecular variation within populations was significantly different among 16 populations.     

Modeling problems in conservation genetics using captive Drosophila populations: Improvement of reproductive fitness due to immigration of one individual into small partially inbred populations

Immigration into small isolated captive and wild populations is recommended to alleviate inbreeding depression. The effects on reproductive fitness of introducing one immigrant into 10 small partially inbred captive populations of D. melanogaster were evaluated. The relative reproductive fitness of the immigrant populations (0.628) was approximately double that of the isolated populations (0.294) and about halfway between the isolated populations and the outbred base population (1.00). Every replicate population increased in fitness following the introduction of an immigrant. The improvements in reproductive fitness shown by the immigrant populations were not due to F₁ hybrid vigor, as the experimental populations underwent three generations of random mating prior to the fitness tests. These results indicate substantial benefits can be gained by the translocation of as few as a single animal between small, partially inbred populations. © 1992 Wiley-Liss, Inc.     

The extent of complex population changes in nature

Summary Many models of animal populations show complex yet predictable patterns of density changes under simple and plausible assumptions. Yet one previous attempt to determine the extent and importance of complex dynamics concluded that they were likely only in some laboratory populations, but not in field populations. Ecologists have treated changes more complex than a return to a simple equilibrium, such as the cyclical changes in populations of lynx and voles in the arctic, as special cases. Highly variable populations, such as insects, are usually thought to be driven by unpredictable changes in the weather. Here, we assemble 71 populations counted for over 50 years, and suggest that complex yet predictable population changes are more common than previously thought.     

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.     

Chromosomal and cell size analysis of cold tolerant maize

Summary C-band number, guard cell length, and chloroplast number per guard cell were determined for eight maize populations. These populations consisted of maize selected for cold tolerance at the University of Nebraska as well as the original unselected populations. The genome size of these populations had previously been determined. C-band number fluctuated concertedly with the changes in genome size indicating that deletions and additions of constitutive heterochromatin occurred during selection, resulting in altered genome sizes. Guard cell size of all the cold tolerant populations was greater than the cell size of the respective nonselected populations. Chloroplast number per guard cell was also higher in all the cold tolerant populations than in their parental populations, but the increases were not statistically significant. The results indicate that changes in genome size that occurred during selection for cold tolerance are the result of changes in amounts of C-band heterochromatin and that the selection process results in an increase in cell size in the cold tolerant populations.     

Range-edge genetic diversity: locally poor extant southern patches maintain a regionally diverse hotspot in the seagrass Zostera marina

Refugial populations at the rear edge are predicted to contain higher genetic diversity than those resulting from expansion, such as in post-glacial recolonizations. However, peripheral populations are also predicted to have decreased diversity compared to the centre of a species' distribution. We aim to test these predictions by comparing genetic diversity in populations at the limits of distribution of the seagrass Zostera marina, with populations in the species' previously described central diversity 'hotspot'. Zostera marina populations show decreased allelic richness, heterozygosity and genotypic richness in both the 'rear' edge and the 'leading' edge compared to the diversity 'hotspot' in the North Sea/Baltic region. However, when populations are pooled, genetic diversity at the southern range is as high as in the North Sea/Baltic region while the 'leading edge' remains low in genetic diversity. The decreased genetic diversity in these southern Iberian populations compared to more central populations is possibly the effect of drift because of small effective population size, as a result of reduced habitat, low sexual reproduction and low gene flow. However, when considering the whole southern edge of distribution rather than per population, diversity is as high as in the central 'hotspot' in the North Sea/Baltic region. We conclude that diversity patterns assessed per population can mask the real regional richness that is typical of rear edge populations, which have played a key role in the species biogeographical history and as marginal diversity hotspots have very high conservation value.     

裂叶沙参与泡沙参种群分布格局分形特征的分析

 裂叶沙参与泡沙参种群在不同海拔区域分布格局的计盒维数与其在群落中占据空间的能力成正比,并且与环境因素密切相关。在裂叶沙参与泡沙参种群较为适生的区域,海拔2700～3100m,两者在群落中占据空间的能力最强,他们的计盒维数达到最高。在低于海拔2700m或高于海拔3100m,环境条件严酷的区域,裂叶沙参种群与泡沙参种群占据空间的能力不同程度的下降。在不同的海拔区域,广布种泡沙参种群占据空间的能力均比裂叶沙参种群高,而其受环境因素影响较弱。在海拔2700m以下地区,泡沙参种群水平分布格局的计盒维数比裂叶沙参种群高4.5倍;在两种群较为适生的区域,海拔2700～3100m,泡沙参计盒维数比裂叶沙参种群高1.5倍,差异最小;在泡沙参与裂叶沙参种群分布的上限,海拔3100m以上地区,两者计盒维数差异又增加,泡沙参计盒维数比裂叶沙参种群高1.8倍。这说明裂叶沙参种群的内在适应力、竞争力比泡沙参种群相对较弱。     

Divergence,gene flow,and the origin of leapfrog geographic distributions: The history of colour pattern variation in Phyllobates poison‐dart frogs

The geographic distribution of phenotypic variation among closely related populations is a valuable source of information about the evolutionary processes that generate and maintain biodiversity. Leapfrog distributions, in which phenotypically similar populations are disjunctly distributed and separated by one or more phenotypically distinct populations, represent geographic replicates for the existence of a phenotype, and are therefore especially informative. These geographic patterns have mostly been studied from phylogenetic perspectives to understand how common ancestry and divergent evolution drive their formation. Other processes, such as gene flow between populations, have not received as much attention. Here, we investigate the roles of divergence and gene flow between populations in the origin and maintenance of a leapfrog distribution in Phyllobates poison frogs. We found evidence for high levels of gene flow between neighbouring populations but not over long distances, indicating that gene flow between populations exhibiting the central phenotype may have a homogenizing effect that maintains their similarity, and that introgression between ‘leapfroging’ taxa has not played a prominent role as a driver of phenotypic diversity in Phyllobates. Although phylogenetic analyses suggest that the leapfrog distribution was formed through independent evolution of the peripheral (i.e. leapfrogging) populations, the elevated levels of gene flow between geographically close populations poise alternative scenarios, such as the history of phenotypic change becoming decoupled from genome‐averaged patterns of divergence, which we cannot rule out. These results highlight the importance of incorporating gene flow between populations into the study of geographic variation in phenotypes, both as a driver of phenotypic diversity and as a confounding factor of phylogeographic inferences.     

Mechanism of effector cell blockade. III. The increased sensitivity of neonatal PFC to effector cell blockade

The response to staphylococcal protein A (SPA) of unfractionated, T-cell-enriched (TCE), and T-cell-depleted (TCD) populations of both adult mononuclear cells (AMC) and cord blood mononuclear cells (CBMC) was studied. Adult unfractionated and TCE populations formed more T-lymphocyte colonies than did similar populations of CBMC. However, TCD populations of CBMC formed B-lymphocyte colonies at least as well as did the TCD population of AMC. These results suggest that B cells from CBMC may be more mature than CBMC T-cell populations.     

Demography and genetics suggest reversal of dolphin source‐sink dynamics,with implications for conservation

The forecast for the viability of populations depends upon metapopulation dynamics: the combination of reproduction and mortality within populations, as well as dispersal between populations. This study focuses on an Indo‐Pacific bottlenose dolphin (Tursiops aduncus) population in coastal waters near Bunbury, Western Australia. Demographic modeling of this population suggested that recent reproductive output was not sufficient to offset mortality. Migrants from adjacent populations might make up this deficit, so that Bunbury would act as a “sink,” or net recipient population. We investigated historical dispersal in and out of Bunbury, using microsatellites and mitochondrial DNA of 193 dolphins across five study locations along the southwestern Australian coastline. Our results indicated limited gene flow between Bunbury and adjacent populations. The data also revealed a net‐dispersal from Bunbury to neighboring populations, with microsatellites showing that more than twice as many individuals per generation dispersed out of Bunbury than into Bunbury. Therefore, in historic times, Bunbury appears to have acted as a source population, supporting nearby populations. In combination with the prior finding that Bunbury is currently not producing surplus offspring to support adjacent populations, this potential reversal of source‐sink dynamics may have serious conservation implications for Bunbury and other populations nearby.