Thigmonasticity of thistle staminal filaments

Investigations of the longitudinal distribution of the extensibility of staminal filaments of the common thistle (Cirsium horridulum Michx.) showed that the base of the filaments (attachment to corolla) is almost twice as elastic as the apical portion (next to anthers). Boiling leads to a more uniform distribution of extensibility. Using a stress-strain analyzer we investigated the elastic properties of fresh, water-boiled, partially hydrolyzed (acid-boiled), and dehydrated filaments. Stress-strain curves of sinusoidally stretched sets of filaments revealed complex, non-linear behavior with an average modulus of elasticity of 5 MPa·m^–2. The phase angle varied from approximately 18 degrees for 0.01-Hz deformations to 84 degrees at 2 Hz, indicating strong viscoelastic components. The viscoelasticity of the filaments indicates that the cell walls have a high ratio of pectin to cellulose. Boiling does not affect Young's modulus, but dehydration does. The technique of applying sinusoidal loads and the analysis of the stress-strain curves proves useful for the assessment of mechanical properties of cell walls, especially for non-growing or contractile tissues.We thank Dr. Paul Russo, Louisiana State University, for allowing us to use the stress-strain analyzer. This work was supported by National Science Foundation grant IBN-9118094.     

Isolation of polymorphic microsatellites in the stemless thistle (Cirsium acaule) and their utility in other Cirsium species

The genus Cirsium includes species with both widespread and restricted geographical distributions, several of which are serious weeds. Nine polymorphic microsatellite loci were isolated from the stemless thistle Cirsium acaule. Eight were polymorphic in C. acaule, six in C. arvense and seven in C. heterophyllum. One locus monomorphic in C. acaule showed polymorphism in C. heterophyllum. The mean number of alleles per locus was 4.1 in C. acaule, 6.2 in C. arvense and 2.9 in C. heterophyllum. These nine loci were also amplified in C. eriophorum and C. vulgare, suggesting that these markers may be of use throughout the genus.     

Invasion history of North American Canada thistle,Cirsium arvense

Aim Canada thistle (Cirsium arvense– Cardueae, Asteraceae) is one of the worst invasive plants world‐wide. Native to Eurasia, its unintentional introduction into North America now threatens the native flora and is responsible for enormous agricultural losses. The goals of this study are to: (1) reconstruct the evolutionary history of C. arvense and estimate how often it may have colonized North America, (2) compare the genetic diversity between European and North American populations to detect signs of demographic bottlenecks and/or patterns of population admixture, and (3) conduct bioclimatic comparisons to infer eventual niche shifts following this species’ introduction into North America. Location Europe and North America. Methods A total of 1522 individuals from 58 populations were investigated with six microsatellite markers. Estimates of heterozygosity (H_E) and allelic richness (R_S) were quantified for each population, and population structure was inferred via analyses of molecular variance (AMOVAs), principal components analyses (PCAs), Mantel tests and Bayesian clustering analyses. Climatic niche spaces were based on 19 bioclimatic variables extracted from approximately 32,000 locations covering the entire range, and compared using PCA and hierarchical cluster analysis. Results Although there is evidence of multiple introductions from divergent European lineages, North American populations of C. arvense exhibited significantly lower levels of genetic diversity than their putative ancestors. Bioclimatic comparisons pointed to a high degree of niche conservatism during invasion, but indicated that genotypes from the former USSR and Central European mountain chains were probably best adapted to invade North America upon entry into the continent. Main conclusions Genetic and historical data suggest that C. arvense first entered North America from Western Europe with the first European settlers, and was later introduced from Eastern Europe into the prairie states during the agricultural boom. The species went through a significant bottleneck following its introduction into the New World, but the level of genetic diversity remained high owing to admixture between genetically differentiated lineages and to a highly efficient outcrossing breeding system.     

Local variation in the thistle species Cirsium grayanum affects its utilization by the herbivorous ladybird beetle Henosepilachna niponica

Host plants are the most critical environmental factor for phytophagous arthropods. Adaptation to a novel host will alter the distributional range of an herbivore to include the area the novel host covers, and might promote divergence between populations utilizing the old and new hosts. On the Oshima Peninsula, Hokkaido Island, northern Japan, the ladybird beetle Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae) usually occurs exclusively on the thistle Cirsium alpicola Nakai (Asteraceae), which is distributed in the southernmost part of the island, although some other Cirsium species often grow in sympatry. At least at one site (Assabu), however, H. niponica depends on another thistle, Cirsium grayanum (Maxim.) Nakai, the most abundant and widely distributed thistle species on the Oshima Peninsula. We examined adult feeding acceptance and preference, and larval performance, in two populations of H. niponica that utilize different species of thistles (the Assabu population occurs on C. grayanum; the Shiriuchi population, on C. alpicola) by testing three kinds of thistles (C. grayanum from Assabu, C. grayanum from Shiriuchi, and C. alpicola from Shiriuchi). Results strongly suggested that among the three plants tested, C. grayanum from Assabu was the most suitable host for H. niponica. We concluded that local differences in C. grayanum mainly explain why it is not used at Shiriuchi, but that there are also local differences in host use among the beetle populations, suggesting some degree of local adaptation. This suggests that different selective regimes associated with different host plants might promote divergence among beetle populations. We conclude that H. niponica is at present unlikely to expand its range to the whole range of C. grayanum.     

Translocation in the staminal hairs ofSetcreasea purpurea

Summary Investigations into plant intercellular communication were initiated through an examination of plasmodesmata and cell-to-cell passage of molecular probes in the staminal hairs ofSetcreasea purpurea. Plasmodesmata connecting staminal hair cells of small buds are filled with an electron-opaque homogenous material. To examine the permeation selectivity of plasmodesmata, molecular probes made up of fluorescein isothiocyanate (FITC) complexed with amino acids and peptides were injected into the staminal hair cells and the spread of these fluorescent molecules through the symplast, was monitored. Molecules composed of FITC complexed to single amino acids with polar and aliphatic R groups travel rapidly, while those which include peptides travel slowly. Dye molecules composed of an amino acid with an aromatic side group do not pass from cell to cell at all. It is hypothesized that the material occluding the plasmodesmata constitutes the diffusion barrier, by presenting a hydrophilic environment which allows passage of molecules with maximum molecular weights of 700–800 daltons, but which retains those with aromatic side groups.     

Translocation in the staminal hairs ofSetcreasea purpurea

Summary Previously reported studies of cell ultrastructure and molecular probe passage in immature staminal hairs were extended to kinetic studies. The rate of transport of carboxyfluorescein into the cytoplasm in individual cells was monitored with a video analyzer and transport coefficients were determined. Carboxyfluorescein was found to traverse 5 cells in less than 5 minutes. The values of transport coefficients differed between cells and this was taken to mean that some cells are more closely coupled than others.     

Azide treatment enhances cell-to-cell diffusion in staminal hairs ofSetcreasea purpurea

Summary The effect of azide on the diffusion of fluorescent molecular probes was examined in staminal hairs ofSetcreasea purpurea. Staminal hairs were treated with azide before being microinjected with fluorescent molecular probes of different size, charge, and structure. The cell-to-cell movement of these fluorescent molecules was videotaped, analyzed, and coefficients of diffusion through plasmodesmata (D) and coefficients of diffusion across the tonoplast (k₁) were calculated and compared to those of untreated cells. The D was larger and the k₁ was smaller for many fluorescent probes in azide treated cells compared to normal, untreated cells. In addition, the cell-to-cell diffusion selectivity based on molecule structure, size and charge no longer existed in azide treated cells. An average D of 3.3×10^–8cm²/s and an average k₁ of 2.9×10^–7/m²/s was calculated for the molecular probes tested. New size limits for permeation were observed indicating that the plasmodesmata had become enlarged.Abbreviations CF carboxyfluorescein - D diffusion coefficient for molecular probes in intercellular pores - FITC-Ang fluorescein isothiocyanate-angiotensin II - k₁ coefficient of diffusive loss across the tonoplast     

Cryptic local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa in the ability to use the thistle Cirsium boreale

Local adaptation to different host plants is important in the diversification of phytophagous insects. Thus far, much evidence of the local adaptation of insects with respect to host use at the physiological level has been gathered from systems involving less mobile insects and/or divergent hosts such as plants belonging to different families or genera. On the other hand, the prevalence of such local adaptation of insects with moderate or high dispersal ability to the intraspecific variation of herbaceous hosts is largely unknown. In the present study, we examined the occurrence and degree of local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa (Kôno) (Coleoptera: Coccinellidae) to its primary host, the thistle Cirsium boreale Kitam. (Asteraceae), through reciprocal laboratory experiments using beetles and thistles from three locations with a range of approximately 200 km. Concerning the larval developmental ability, obvious patterns of local adaptation to the thistles from respective natal locations were detected, at least in some combinations of beetle populations. Similar tendencies were detected concerning adult feeding acceptance, although the statistical support was somewhat obscure. Overall, our results indicate that the degree of local adaptation of insect species with moderate dispersal ability to conspecific herbaceous hosts is occasionally as strong as that involving less mobile insects and/or heterospecific hosts, indicating the potential of such cryptic local adaptation to promote ecological/genetic differentiation of phytophagous insect populations.     

The timing of nectar secretion in staminal and staminodial glands in Lauraceae

The flowers of many Lauraceae have two kinds of glandular organ: paired glands at the base of the filaments of the third androecial whorl, and staminodes with a glandular head, corresponding to a fourth, sterile androecial whorl. So far, it is unknown why there are two different kinds of organ with apparently the same function. Observations now show that the staminal and the staminodial glands secrete nectar at different times in the heterodichogamous flowering cycle, and are therefore essential for the pollination of bisexual Lauraceae flowers.     

A new species of Castanopsis (Fagaceae) from the upper Pliocene of West Yunnan,China and its biogeographical implications

Two fossil leaves identified as Castanopsis presclerophylla n. sp. collected from a diatomite bed in the upper Pliocene (3.3–2.8 Ma) in Tengchong County, Yunnan Province, Southwest China, are characterized by elliptic laminar shapes with acuminate apex, convex base, simple trichome bases and cyclocytic stomata. The cuticles of extant leaves from six selected Castanopsis species that are similar to the Pliocene fossil leaves in laminar shape were examined in detail for the comparison. Based on the analysis of leaf architecture and cuticular characteristics, the present fossil leaves most closely resemble the extant leaves of Castanopsis sclerophylla (Lindl.) Schott., which prefers a subtropical climate. The published fossil records of Castanopsis also indicate that it was once widely distributed in North America, Europe and Asia before the Pliocene, and then rapidly retreated to the East and Southeast Asia as a result of the Pleistocene glaciation.     

A new okanin glycoside from the flowers of Coreopsis tinctoria Nutt.

Phytochemical investigation on the water-soluable portions of the EtOH extracts of the flowers of Coreopsis tinctoria Nutt. led to the isolation of six flavonoids, including a new okanin glycoside. The structures of these compounds were identified by spectroscopic analysis, chemical method, and comparison with the literature.     

Taxonomic characters of the staminal tube and epicalyx in Brazilian Pavonia (Malvaceae)

This study was based on the analysis of staminal tube and epicalyx morphology of species ofPavonia (Malvaceae) from northeastern and southeastern Brazil. The importance of characters in the infrageneric taxonomy is discussed. In general, the variability in staminal tube and epicalyx characters are useful mainly in separating closely related species and a few sections; these characters, however, cannot be used to separate subgenera.     

Organization of the cuticle of an aquatic fly larva

The aquatic, apneustic larva of the midge, Chironomus riparius, has a very thin (up to 5 micrometers), readily deformable, post-cephalic cuticle. The ultrastructure of this cuticle from newly moulted and older final instar animals, and exuvia shed at pupation, has been examined using routine methods and also after the extraction of proteins with formamide and acetic acid. From the results described, and using established criteria, it is inferred that an exocuticle is present and represents about 25% of the thickness of the mature procuticle, the remainder being endocuticle. Therefore, it would seem that this exceptionally delicate cuticle conforms to the conventional plan of tanned or sclerotized solid cuticles, unlike those reported in the larvae of cyclorrhaphous dipterans such as blowflies or other soft-bodied insects. This is the first account, using experimental techniques, of the fine structure of sectioned cuticle from nematocerous dipteran larvae. It also indicates the value of the exuvium as a source of information about cuticle structure.     

Warming increases the spread of an invasive thistle

Background

Global warming and shifted precipitation regimes increasingly affect species abundances and distributions worldwide. Despite a large literature on species'' physiological, phenological, growth, and reproductive responses to such climate change, dispersal is rarely examined. Our study aims to test whether the dispersal ability of a non-native, wind-dispersed plant species is affected by climate change, and to quantify the ramifications for future invasion spread rates.

Methodology/Principal Findings

We experimentally increased temperature and precipitation in a two-cohort, factorial field study (n = 80). We found an overwhelming warming effect on plant life history: warming not only improved emergence, survival, and reproduction of the thistle Carduus nutans, but also elevated plant height, which increased seed dispersal distances. Using spatial population models, we demonstrate that these empirical warming effects on demographic vital rates, and dispersal parameters, greatly exacerbate spatial spread. Predicted levels of elevated winter precipitation decreased seed production per capitulum, but this only slightly offset the warming effect on spread. Using a spread rate decomposition technique (c*-LTRE), we also found that plant height-mediated changes in dispersal contribute most to increased spread rate under climate change.

Conclusions/Significance

We found that both dispersal and spread of this wind-dispersed plant species were strongly impacted by climate change. Dispersal responses to climate change can improve, or diminish, a species'' ability to track climate change spatially, and should not be overlooked. Methods that combine both demographic and dispersal responses thus will be an invaluable complement to projections of suitable habitat under climate change.     

Involvement of Yellow-y in the cuticle pigmentation of the larvae,pupae and adults in Henosepilachna vigintioctopunctata

Yellow-y (Y-y) contributes to the accumulation of melanins in insect cuticle. However, the underlining mechanism requires further investigation. Two classical hypotheses have been proposed: Y-y acts as a dopachrome conversion enzyme (DCE) to accelerate biosynthesis of melanins; alternatively, Y-y serves as a cuticular anchor for pigments. Henosepilachna vigintioctopunctata is a serious defoliator attacking Solanaceae and Cucurbitaceae plants. The beetle shows a species-specific pigmentation pattern: stage-dependent dark patches are distributed on pale-yellow background. Here we noted that RNA interference (RNAi)-aided knockdown of Hvyellow-y at the newly-ecdysed second- and third-instar larval, and 1-day-old prepupal stages changed coloration in both dark patches and pale-yellow background. Black pigmentation was lightened in the Hvy-y hypomorphs, including various body portions such as larval heads, antennae, mouthparts, scoli, strumae, legs and exuviae, pupal and adult thoraces and abdomens, and adult elytra and hindwings. Moreover, the coloration background was yellowed in the RNAi beetles. Specifically, more yellow pigments were observed to deposit around the black dorsal markings in the hypomorphic pupal metathorax. Furthermore, the boundaries between black patches and yellow background were distinct in the resultant ladybirds. Similarly, the margins around bristle follicles and droplet spots were not fuzzy within the RNAi pupal black patches. In summary, even though Y-y facilitates the pigmentation in H. vigintioctopunctata exocuticle, our data did not support the pigment anchor hypothesis.