Effects of cyanogenesis in bracken fern (Pteridium aquilinum) on associated insects

Abstract. 1. The relationship between cyanogenesis in bracken fern and the insect fauna feeding on the plant was investigated over a 3 year period. The most common insects between May and July, while cyanide levels were high, were the sawflies Strongylogaster impressata Provancher, S.multicincta Norton, Aneug-menus fzavipes (Norton), the aphid Macrosiphum euphorbiae (Thomas) and a microlepidopteran species of Monochroa .
2. Collections of insects from cyanogenic and acyanogenic fronds showed significantly fewer sawflies on the cyanogenic fronds. The aphid and the microlepidopteran were randomly distributed with respect to cyanogenicity.
3. Feeding tests for two of the sawfly species ( Simpressata and Smulticincta ) showed that larvae grew more slowly and had a higher mortality when raised on cyanogenic fronds than on acyanogenic ones.
4. Field collected cyanogenic bracken fronds were found to have sustained less damage from chewing herbivores compared with acyanogenic fronds.     

Estimates of gene flow, genetic substructure and population heterogeneity in bracken (Pteridium aquilinum)

Bracken [ Pteridium aquilinum (L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow ( Nm ) at several levels. Gene flow among British populations was extremely high ( Nm = 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) at Nm = 2.47. Trans-Atlantic gene flow was low ( Nm = 0.0926).
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species.     

Assessment of genetic relationships among native and introduced Himalayan balsam (Impatiens glandulifera) plants based on genome profiling

We conducted genomic characterization based on SNP and SilicoDArT markers on the invasive Himalayan balsam (Impatiens glandulifera) plants originating from native and non‐native regions of their distribution. When genetic relationships were explored by PCoA using SNP and SilicoDArT marker data, the first, second, and third principal coordinates explained altogether 37.4% and 31.0% of the variability, respectively. Samples from the UK, Canada, and Pakistan were grouped together, while Indian plants were clearly distinct based on SNP markers but relatively close to the UK–Canada–Pakistan group based on SilicoDArT markers. Constructed trees differentiated individuals into clusters resembling the PCoA patterns. The Bayesian BAPS analysis performed for the SNP data revealed that the individuals were distributed in seven clusters, representing samples from each of the four Finnish populations, India, Pakistan, and the combination of the UK and Canada. Similar clustering was visible in the UPGMA tree. The Indian cluster did not display any ancestral gene flow with the others, while the Pakistani cluster showed ancestral gene flow only with the combined UK and Canada cluster. Furthermore, the latter cluster displayed ancestral gene flow with the Finnish populations varying from 0% to 3.1%. The BAPS analyses conducted for the SilicoDArT data differ slightly: The individuals were distributed in nine clusters, and the Indian cluster exhibited ancestral gene flow with the mixed cluster including Canadian, Pakistani, and UK samples, and one Finnish sample. The AMOVA showed that 45% and 26% of variation was present among the I. glandulifera groups/populations and the rest within them based on SNP and SilicoDArT markers, respectively. The Bayesian BAPS analyses and the gene flow networks were the most informative tools for resolving relationships among native and introduced plants. It is notable that the small sample sizes for non‐Finnish plant materials may affect the accuracy of the gene flow and other estimates.     

Clarification of the taxonomic status and relationships of Pteridium caudatum (Dennstaedtiaceae) in Central and South America

Contemporary systematic treatments of the Central and South American bracken ferns in the genus Pteridium Gled. ex Scop. recognize morphotype caudatum as either a full species or a variety of P. aquilinum (L.) Kuhn. Geographically representative sporophytes of morphotype caudatum , including the type in the Linnaean Herbarium, are shown using spore size, guard-cell length and morphology of the cells of the false indusium to be tetraploid (based on 4 n  = 208). DNA fingerprinting of field-collected Venezuelan samples supports the generalization that morphotype caudatum is a fertile allotetraploid containing genomic elements otherwise distinctive of the southern hemisphere diploid P. arachnoideum (Kaulf.) Maxon, together with elements characteristic of northern hemisphere diploids including the North American P. aquilinum var. pubescens Underw. and P. aquilinum var. pseudocaudatum (Clute) A. Heller. Evidence of genetic isolation from taxa with overlapping distributions, as well as morphological, biochemical and ecological data, validate recognition of P. caudatum (L.) Maxon at species level. Heterogeneity observed within P. caudatum is consistent with multiple origins through independent hybridization events. Pteridium caudatum is strikingly analogous to the tropical Asian/Australasian allotetraploid P. semihastatum (N. Wallich ex J. G. Agardh) S. B. Andrews [= P. yarrabense (Domin) N. A. Wakef.].  © 2002 The Linnean Society of London . Botanical Journal of the Linnean Society , 2002, 140 , 237−248.     

Comparative spatial distribution, size, biomass and growth rate of two varieties of bracken fern (Pteridium aquilinum L. Kuhn) in a neotropical montane habitat

A comparative field study of caudatum and arachnoideum, the two Pteridium aquilinum varieties of the caudatum subspecies known to grow in the neotropics, was performed in a montane savanna habitat of the Venezuelan Andes that was affected by wildfire. Frond size, ramet density and spatial distribution, blade and rhizome biomass, and frond elongation and expansion rates were measured in separate, isolated stands each containing only one bracken variety and covering approximately the same area (540 m²). In addition to clearly discernible morphological differences, caudatum and arachnoideum were found to possess distinct features: caudatum tends to develop open stands of relatively shorter blades of 76.6±0.89 cm (±SE) of rachis length and lower ramet density (1.6 fronds m^-2, max.=7 fronds m^-2) whereas arachnoideum grows into longer, more expanded fronds 124±1.6 cm tall and significantly higher ramet density (5.1 fronds/m², max.=14.6 fronds m^-2). The sum of aerial and underground biomass was found to be notably larger for arachnoideum (8522±614 Kg/ha) than for caudatum (1929±131 Kg ha^-1) in stands growing under the same habitat conditions. Therefore the spatial distribution of arachnoideum appeared considerably more compact than that of caudatum. Blade growth rates and development time were also very different. Newly emerged caudatum croziers developed into mature blades within 42 to 48 days following an inverse exponential curve whereas arachnoideum blades required 70 to 75 days to reach maturity following a linear development. All the above dissimilarities are interpreted as the hitherto unreported indication of diverging growth strategies of two cohabitant bracken varieties following fire.     

A global molecular phylogeny of the fern genus Trichomanes (Hymenophyllaceae) with special reference to stem anatomy

To establish a basis for future taxonomic revisions and to infer the evolutionary traits of Trichomanes s.l. , one of two large filmy fern genera, molecular phylogenetic analyses were conducted using chloroplast rbcL sequences. Sampling covered most of the global distribution range of this genus throughout the tropical and temperate zones, as well as all taxonomically significant species by the addition of 51 samples principally from Asia. The evolution of eight selected characters, which were adopted as taxonomic keys and/or putatively reflect morphological regression, was optimized on the retrieved most parsimonious rbcL trees, together with new observations on the stem anatomy of 45 species. The eight robust clades retrieved within Trichomanes in the rbcL phylogeny conflict with the existing classifications. Our results also suggest that the cup-shaped sorus, the primary diagnostic character of the genus, appears in parallel in the Hymenophyllum lineage, as demonstrated by Pleuromanes (typified by Trichomanes pallidum ) included in the lineage. The suggestion that the regressive character states are homoplastic apomorphies in the evolution of the frond size, stem thickness, root system, and stem anatomy (stele and cortex) probably illustrates a strong tendency towards adaptive evolutionary transition in Trichomanes . © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 1–27.     

Introgression and persistence of cultivar alleles in wild carrot (Daucus carota) populations in the United States

Premise

Cultivated species and their wild relatives often hybridize in the wild, and the hybrids can survive and reproduce in some environments. However, it is unclear whether cultivar alleles are permanently incorporated into the wild genomes or whether they are purged by natural selection. This question is key to accurately assessing the risk of escape and spread of cultivar genes into wild populations.

Methods

We used genomic data and population genomic methods to study hybridization and introgression between cultivated and wild carrot (Daucus carota) in the United States. We used single nucleotide polymorphisms (SNPs) obtained via genotyping by sequencing for 450 wild individuals from 29 wild georeferenced populations in seven states and 144 cultivars from the United States, Europe, and Asia.

Results

Cultivated and wild carrot formed two genetically differentiated groups, and evidence of crop–wild admixture was detected in several but not all wild carrot populations in the United States. Two regions were identified where cultivar alleles were present in wild carrots: California and Nantucket Island (Massachusetts). Surprisingly, there was no evidence of introgression in some populations with a long-known history of sympatry with the crop, suggesting that post-hybridization barriers might prevent introgression in some areas.

Conclusions

Our results provide support for the introgression and long-term persistence of cultivar alleles in wild carrots populations. We thus anticipate that the release of genetically engineered (GE) cultivars would lead to the introduction and spread of GE alleles in wild carrot populations.     

基于微卫星标记的中国枣食芽象甲地理种群遗传多样性分析

【目的】枣食芽象甲Scythropus yasumatsui是我国北方枣树Zizyphus jujuba上的一种重要的灾害性害虫,在陕西、山西、河北、河南等枣树主产区普遍发生。本研究旨在揭示我国枣食芽象甲不同种群间的遗传分化和基因交流规律。【方法】利用枣食芽象甲转录组测序的SSR序列,使用荧光标记PCR及毛细管电泳分型方法,筛选出8个微卫星位点,对我国5个省份(山西、陕西、宁夏、河北和河南)10个地理种群共308头枣食芽象甲样本进行种群遗传多样性分析。【结果】8个SSR位点均存在无效等位基因且偏离哈迪 温伯格平衡。各位点的有效等位基因数(Ne)为2.113~8.016,多态信息含量(PIC)为0.561~0.908,期望杂合度(He)为0.476~0.865;种群间遗传分化系数(Fst)平均值为0.151;基因流(Nm)平均值为1.594。枣食芽象甲种群间遗传分化系数与地理距离之间显著正相关(r=0.596, P=0.0035),基于Nei’s遗传距离和Cavalli-Sforza & Edwards余弦遗传距离的系统进化树将10个地理种群均聚为3个相同的分支。【结论】结果说明,枣食芽象甲种群遗传多样性较高,不同地理种群间存在高度的遗传分化,且有一定的基因交流;地理隔离是影响枣食芽象甲地理种群遗传分化和基因交流的重要因素。     

Microsatellite markers for two species of dampwood termites in the genus Zootermopsis (Isoptera: Termopsidae)

Dampwood termites in the genus Zootermopsis inhabit forested areas in western North America. To better understand the colony composition and breeding structure of Zootermopsis, we identified polymorphic microsatellite loci to use in population analysis. Microsatellite loci were isolated from Zootermopsis nevadensis nevadensis (Hagen); however, all primers amplified homologous loci in Zootermopsis angusticollis (Hagen) and Zootermopsis nevadensis nuttingi (Hagen). Twelve loci were polymorphic in one or more of the above subspecies and species. The number of alleles per locus ranged from one to six, with some allelic differences among subspecies and species. We are currently utilizing the microsatellite markers to investigate the population genetics of Zootermopsis.     

Population genetic structure of Japanese wild soybean (Glycine soja) based on microsatellite variation

The research objectives were to determine aspects of the population dynamics relevant to effective monitoring of gene flow in the soybean crop complex in Japan. Using 20 microsatellite primers, 616 individuals from 77 wild soybean (Glycine soja) populations were analysed. All samples were of small seed size (< 0.03 g), were directly collected in the field and came from all parts of Japan where wild soybeans grow, except Hokkaido. Japanese wild soybean showed significant reduction in observed heterozygosity, low outcrossing rate (mean 3.4%) and strong genetic differentiation among populations. However, the individual assignment test revealed evidence of rare long-distance seed dispersal (> 10 km) events among populations, and spatial autocorrelation analysis revealed that populations within a radius of 100 km showed a close genetic relationship to one another. When analysis of graphical ordination was applied to compare the microsatellite variation of wild soybean with that of 53 widely grown Japanese varieties of cultivated soybean (Glycine max), the primary factor of genetic differentiation was based on differences between wild and cultivated soybeans and the secondary factor was geographical differentiation of wild soybean populations. Admixture analysis revealed that 6.8% of individuals appear to show introgression from cultivated soybeans. These results indicated that population genetic structure of Japanese wild soybean is (i) strongly affected by the founder effect due to seed dispersal and inbreeding strategy, (ii) generally well differentiated from cultivated soybean, but (iii) introgression from cultivated soybean occurs. The implications of the results for the release of transgenic soybeans where wild soybeans grow are discussed.     

Taxonomic status and relationships of bracken ferns (Pteridium: Dennstaedtiaceae) of Laurasian affinity in Central and North America

Detailed quantitative comparisons confirm and extend the discrimination of four major morphotypes amongst brackens of Laurasian affinity in Central and North America. These are recognized here at subspecies level as: Pteridium aquilinum sspp. feei , pubescens , latiusculum , and pseudocaudatum . Measurements of spore size indicate that sporophytes of P. aquilinum ssp. feei are diploid (2 n  = 104), as are sspp. pubescens , latiusculum , and pseudocaudatum . Phenetic cluster analysis based on DNA fingerprinting by arbitrarily primed polymerase chain reaction groups these four subspecies as genomically more similar to each other than to any taxa from other geographical regions. The chloroplast haplotype of ssp. feei is the same as that of sspp. latiusculum , pseudocaudatum , and pubescens with respect to the absence of both of the short direct repeats in the rps 4– trn S region (haplotype A), whereas the European ssp. aquilinum (haplotype B) has one of these repeats, and the Southern Hemisphere brackens P. arachnoideum and P. esculentum (haplotype C) have the other.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 1–17.     

Geographic variation in Thomas langur (Presbytis thomasi) loud calls

Geographic variation in primate vocalizations has been described at two levels. First, at the level of acoustic variation within the same call type between populations and, second, at the level of presence or absence of certain call types in different populations. Acoustic variation is of interest because there are several factors that can explain this variation, such as gene flow, ecological factors and population density. Here we focus on the first level in a Southeast Asian primate, the Thomas langur. We recorded male loud calls in four populations that differed in their geographic distances from each other and had varying geographic barriers in between them, such as rivers and mountain ranges. The presence of these barriers leads to expectations of loud call variation under the gene flow model, which are examined here. We conducted a principal components analysis to condense the number of acoustic variables. With a subsequent discriminant function analysis on the six principal component scores, we found that the percentage of loud calls that were correctly assigned to a population was relatively high (50.0-76.2%) when three randomly selected loud calls from each male were used. Using the discriminant functions from this analysis to predict population membership of the remainder of the loud calls yielded lower, but still relatively high correct assignment percentages (26.2-66.7%). Analyses to examine the influence of barriers on similarities between populations confirm our expectations. We discuss that differences in loud calls are probably most parsimoniously explained by gene flow (or the lack thereof) between the populations and that future studies of genetic differences are crucial to test this hypothesis.     

Development, characterization and transferability of microsatellite markers for the plant genus Phlox (Polemoniaceae)

In order to study diversification and microevolution in Phlox, we developed nine polymorphic microsatellite loci. In 20 individuals of Phlox pilosa from a single population, the average number of alleles per locus was 10.0 ± 5.1, and average observed and expected heterozygosities were 0.611 ± 0.234 and 0.769 ± 0.170, respectively. Most of these markers amplified successfully in 11 additional species of Phlox, representing a broad diversity of the genus, and some also amplified in more distantly related members of the Polemoniaceae. These microsatellite markers will be valuable for investigation of evolutionary processes in this important study system.     

Understanding population structure and historical demography in a conservation context: population genetics of an endangered fern

The construction of the world's largest hydroelectric scheme across the Yangtze River, the Three Gorges Dams (TGD), in the centre of a southern-central Chinese biodiversity hot spot, the Three Gorges Reservoir Area (TGRA), has attracted international concern and conservation action. To examine whether landscape changes to date have impacted regional flora, and to establish long-term monitoring baselines, we assessed the distribution and dynamics of an endangered and TGRA endemic fern, Adiantum reniforme var. sinense . For eight nuclear microsatellites, high levels of genetic diversity ( H _E = 0.653–0.781) and slightly elevated inbreeding ( F _IS = 0.077–0.197) were found across 13 surveyed populations. The population history of this fern is characterized by a balance of gene flow and genetic drift, where historical dispersal, inferred from coalescent ( F =  0.129) and genetic differentiation ( F _ST = 0.094 and R _ST = 0.180) approaches, is moderate, reflecting an isolation by distance relationship. Importantly, most populations exhibited mutation-drift disequilibrium, suggesting a recent population decline, which is congruent with the known demographic history of the species following dam-related activities. Based on these results, populations of A. reniforme var. sinense are expected to lose genetic diversity and increase genetic structure as dam-related activities decrease size and increase genetic isolation of remnants.     

Phylogenetic relationships within the Phyllopoda (Crustacea,Branchiopoda) based on mitochondrial and nuclear markers

For several decades the relationships within the Branchiopoda (Anostraca + Phyllopoda) have been a matter of controversy. Interpretations of plesiomorphic or apomorphic character states are a difficult venture, in particular in the Phyllopoda. We explore the relationships within the Phyllopoda at the level of nucleotid comparisons of the two genes 12S rDNA (mitochondrial) and EF1alpha (nuclear), and at a higher molecular level based on introns found in the gene EF1alpha. Within the Phyllopoda our explorations show further evidence for a non-monophyletic Conchostraca (Spinicaudata + Cyclestherida + Laevicaudata). The monotypic Cyclestherida is more closely related to the Cladocera, both together forming the Cladoceromorpha. The Spinicaudata (Leptestheriidae, Limnadiidae, and Cyzicidae) is well supported. Spinicaudata and Cladoceromorpha form a monophylum. The position of the Laevicaudata remains unclear but we find neither support for a sister group relationship to the Spinicaudata nor for a close relationship of Laevicaudata and Cladocera. Within the Cladocera, we favour the Gymnomera concept with the monotypic Haplopoda being the sister group to the monophyletic Onychopoda. The Ctenopoda seems to be the sister group to the Gymnomera, which contradicts the common view of a more basal position of the Ctenopoda.     

黄酮和蕨类植物黄酮的研究进展

简明综述了黄酮的结构及其分类、生理活性与人类健康的关系,以及蕨类植物黄酮的研究进展等等,为了进一步开发蕨类植物黄酮提供了理论依据。     

Assessment of gene flow across a hybrid zone in red-tailed chipmunks (Tamias ruficaudus)

The role of hybridization in animal speciation is controversial and recent research has challenged the long-standing criterion of complete reproductive isolation to attain species status. The speciation-with-gene-flow model posits that the genome is semi-permeable and hybridization may be a phase in the process of divergence. Here, we apply these concepts to a previously identified zone of mtDNA introgression between the two strongly morphologically differentiated subspecies of red-tailed chipmunk ( Tamias ruficaudus ) in the US Inland Northwest. Using multilocus genotype data from the southern, older contact zone, we demonstrate that neutral gene flow is unusually low between the subspecies across the Lochsa River. This is geographically congruent with the discontinuity in bacular morphology, indicating that the cline of mitochondrial DNA (mtDNA) haplotypes is displaced. Furthermore, we elucidate the evolutionary forces responsible by testing hypotheses of lineage sorting and hybridization. We determined that introgressive hybridization is the cause of mtDNA/morphology incongruence because there are non-zero levels of migration and gene flow. Although our estimate of the age of the hybrid zone has wide credibility intervals, the hybridization events occurred in the Late Pleistocene and the divergence occurred in the Middle Pleistocene. Finally, we assessed substructure within and adjacent to the hybrid zone and found that the hybrid zone constitutes a set of populations that are genetically differentiated from parental sets of populations; therefore, hybridization in this system is not likely an evolutionary sink, but has generated novel combinations of genotypes.     

Introduced Scotch broom (Cytisus scoparius) invades the genome of native populations in vulnerable heathland habitats

Cytisus scoparius is a global invasive species that affects local flora and fauna at the intercontinental level. Its natural distribution spans across Europe, but seeds have also been moved among countries, mixing plants of native and non‐native genetic origins. Hybridization between the introduced and native gene pool is likely to threaten both the native gene pool and the local flora. In this study, we address the potential threat of invasive C. scoparius to local gene pools in vulnerable heathlands. We used nuclear single nucleotide polymorphic (SNP) and simple sequence repeat (SSR) markers together with plastid SSR and indel markers to investigate the level and direction of gene flow between invasive and native heathland C. scoparius. Analyses of population structures confirmed the presence of two gene pools: one native and the other invasive. The nuclear genome of the native types was highly introgressed with the invasive genome, and we observed advanced‐generation hybrids, suggesting that hybridization has been occurring for several generations. There is asymmetrical gene flow from the invasive to the native gene pool, which can be attributed to higher fecundity in the invasive individuals, measured by the number of flowers and seed pods. Strong spatial genetic structure in plastid markers and weaker structure in nuclear markers suggest that seeds spread over relatively short distances and that gene flow over longer distances is mainly facilitated by pollen dispersal. We further show that the growth habits of heathland plants become more vigorous with increased introgression from the invaders. Implications of the findings are discussed in relation to future management of invading C. scoparius.