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Vigour
Kinds of Vigour Selected AbstractsEditorial: Vigour, vitiligo and the RPEPIGMENT CELL & MELANOMA RESEARCH, Issue 5 2006Colin Goding No abstract is available for this article. [source] Vine vigour effects on leaf gas exchange and resource utilisationAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 1 2010A. ZERIHUN Abstract Background and Aims:, Variability in vine vigour is a commonly observed feature in vineyard blocks. Although this aspect is well recognised among viticulturalists, impacts of vigour variability on vine function and resource use efficiency are seldom considered in management decision-making. This study examined influences of vine vigour variability on vine physiological performance and resource use in a commercially managed vineyard block. Methods and Results:, The vineyard block was divided into different vigour zones using plant cell density data derived from aerial multi-spectral imaging of the study block. Gas exchange and under-vine soil moisture status were measured in some of the vigour zones. Low vigour vines had consistently lower photosynthesis and stomatal conductance rates than high vigour vines. The differences were evident both during soil-drying and rewetting. Similarly, irrigation water utilisation was markedly lower in low than in high vigour vines. Vine fruit yield was linearly and positively related to vines' capacity to utilise applied water. Conclusions:, Vigour has considerable influence on vine physiological performance and on resource utilisation capacity. Uniform irrigation application to a block with variable vigour (which is the norm currently) leads to spatially inefficient resource use, and consequently to a marked within-block variation in irrigation water productivity. Significance of the Study:, The demonstration that variation in vigour has a corresponding effect on resource utilisation has direct relevance for managing vineyard inputs such as irrigation or fertilisers. [source] Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicityEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2006Rob Westaway Abstract Many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over Quaternary timescales. On the basis of the rheological knowledge gained, it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust. This view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation. It is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity, and by instances of seasonal seismicity that correlates with seasonal climate. Human interference in the environment can affect surface loading: for instance, deforestation for agriculture or urban development can cause increased erosion rates; global warming is expected to cause increased storminess (and thus increased erosion rates) and/or global sea-level rise. The possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment. Copyright © 2006 John Wiley & Sons, Ltd. [source] Cascading effects of variation in plant vigour on the relative performance of insect herbivores and their parasitoidsECOLOGICAL ENTOMOLOGY, Issue 1 2002Tiit Teder Abstract 1. Consequences of variation in food plant quality were estimated for a system consisting of two monophagous noctuid herbivores and three ichneumonid parasitoids. 2. In a natural population, pupal weights of the herbivores in this system, Nonagria typhae and Archanara sparganii, were found to be highly variable. Pupal weights increased strongly and consistently with the increase in the vigour of the host plant, Typha latifolia, providing support for the plant vigour hypothesis. Correspondingly, as the moths do not feed as adults, a strong, positive correlation between host vigour and fecundity of the herbivores would be expected. 3. There were strong and positive relationships between adult body sizes of the parasitoids and the sizes of their lepidopteran hosts. Moreover, a direct, positive link between plant quality and parasitoid size was documented. 4. For all three parasitoids, cascading effects of plant quality on body size were weaker than for the herbivores. Differences in the importance of adult feeding and oviposition behaviour suggest that dependence of fitness on body size is also weaker in the parasitoids than in the moths. It is therefore concluded that the numerical response of the herbivore population to a change in plant quality should exceed the corresponding response in the parasitoids. 5. The results of this work imply that variation in plant variables may affect performance of different trophic levels to a different extent. It is suggested that the importance of adult feeding for the reproductive success (capital vs. income breeding strategies) in both herbivores and parasitoids is an essential aspect to consider when predicting responses of such a system to changes in plant quality. [source] Invasive aliens and sampling biasECOLOGY LETTERS, Issue 4 2003Andrew M. Simons Abstract Two hypotheses have been proposed to explain the observation of increased vigour of invasive alien plants in their nonindigenous ranges: phenotypic plasticity, and the post-invasion evolution of increased competitive ability (EICA). Here I specify how a general pattern of increased vigour may result from sampling bias. Ignoring failed invasions can account for the illusion of increased vigour over a broad range of assumptions. Plasticity and EICA need not be viewed as explanations for a general pattern of increased vigour even if they are the mechanisms underlying every occurrence. [source] Evaluating the impact of pollution on plant,Lepidoptera relationshipsENVIRONMETRICS, Issue 4 2005Christian Mulder Abstract We monitored the biodiversity of plants, adult butterflies and leaf-miners in a Dutch nature reserve over a period of six years (1994,1999) within the International Co-operative Programme on Integrated Monitoring on Air Pollution Effects (ICP-IM). Butterfly abundance decreased steadily over the period, indicating a negative diversity trend, while the number of leaf-mining larvae of Microlepidoptera remained fairly constant. Also the concentration of pollutants (NH4, NO3, SO4, Cd, Cu and Zn) was determined in air, leaves, litter, throughfall and stemflow. We have no reason to expect a negative impact of acidification in rainwater or climate change, as temperature and ozone show no significant trends across the six years. It is shown that the nectar-plants of adult butterflies are much more sensitive to heavy metals than the nectar-plants of moths and other pollinating insects. It is hypothesized that the butterfly decline is a secondary effect of heavy metal stress on local plants, not resulting in a decrease in the number of host-plants, but in a selective pressure of pollutants on the plant vigour, subsequently affecting their pollinators (p,<,0.001). An alternative explanation, such as the possible coexistence of a direct effect of xenobiotics on the adult Lepidoptera occurring in the study area, is not supported by our data (p,>,0.05). Copyright © 2005 John Wiley & Sons, Ltd. [source] Associations among symptoms of dieback in even-aged stands of ash (Fraxinus excelsior L.)FOREST PATHOLOGY, Issue 1 2010J. P. Skovsgaard Summary The objective of this study was to establish statistically based associations among macroscopic symptoms of crown dieback, cankers due to Chalara fraxinea, and symptoms caused by other pathogens and pests on Fraxinus excelsior. A total of 454 trees were observed in two plots of a 15-year-old experimental stand. The symptoms included: (i) overall extent of crown dieback; (ii) dieback of upper parts of the crown; (iii) canker in upper parts of the crown; (iv) wilting foliage; (v) cankers and bark proliferations at the lower part of the stem; and (vi) discolouration at stump or stem base. The analysis suggested that the observed symptoms of crown dieback are caused by a primary disease. The macroscopic symptoms attributed to dieback and canker in the crown were strongly associated. Moreover, the disease was associated with symptoms of Armillaria gallica, but no associations were found for symptoms of Neonectria galligena, Pseudomonas syringae subsp. savastanoi pv. fraxini, Hylesinus fraxini or H. varius when considered collectively. Dieback was more frequent on trees of average or below-average size, suggesting that individual tree resistance decreased with decreasing growth potential or tree vigour. The extent of canker in the crown depended on site conditions and possibly on silvicultural practices. The development of phytosanitary prescriptions for silviculture should primarily be targeted towards young stands as these represent the most critical phases of stand development. [source] Effects of drought on avian community structureGLOBAL CHANGE BIOLOGY, Issue 8 2010THOMAS P. ALBRIGHT Abstract Droughts are expected to become more frequent under global climate change. Avifauna depend on precipitation for hydration, cover, and food. While there are indications that avian communities respond negatively to drought, little is known about the response of birds with differing functional and behavioural traits, what time periods and indicators of drought are most relevant, or how response varies geographically at broad spatial scales. Our goals were thus to determine (1) how avian abundance and species richness are related to drought, (2) whether community variations are more related to vegetation vigour or precipitation deviations and at what time periods relationships were strongest, (3) how response varies among avian guilds, and (4) how response varies among ecoregions with different precipitation regimes. Using mixed effect models and 1989,2005 North American Breeding Bird Survey data over the central United States, we examined the response to 10 precipitation- and greenness-based metrics by abundance and species richness of the avian community overall, and of four behavioural guilds. Drought was associated with the most negative impacts on avifauna in the semiarid Great Plains, while positive responses were observed in montane areas. Our models predict that in the plains, Neotropical migrants respond the most negatively to extreme drought, decreasing by 13.2% and 6.0% in abundance and richness, while permanent resident abundance and richness increase by 11.5% and 3.6%, respectively in montane areas. In most cases, response of abundance was greater than richness and models based on precipitation metrics spanning 32-week time periods were more supported than those covering shorter time periods and those based on greenness. While drought is but one of myriad environmental variations birds encounter, our results indicate that drought is capable of imposing sizable shifts in abundance, richness, and composition on avian communities, an important implication of a more climatically variable future. [source] Detection of vegetation change using reconnaissance imageryGLOBAL CHANGE BIOLOGY, Issue 3 2001Herman H. Shugart Summary Vegetation occurs at its highest elevations on equatorial mountains. Inspection of archival and recent high-resolution reconnaissance imagery of tropical mountains shows, in all cases, features indicating an increase in the elevation of mountain vegetation zones and an increase in vigour in the high-elevation vegetation. These changes are consistent with an increased plant performance from increased levels of carbon dioxide in the atmosphere as well as with a warmer or more favourable climate. [source] Effects of atmospheric CO2 concentration and defoliation on the growth of Themeda triandraGRASS & FORAGE SCIENCE, Issue 3 2004S. J. E. Wand Abstract The effects of elevated atmospheric carbon dioxide (CO2) concentration (700 ,mol mol,1) on defoliated (three clippings at 3-week intervals) and undefoliated plants were determined for the C4 grass Themeda triandra, Forsk. The elevated CO2 concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO2 concentration treatment. The primary effect of the elevated CO2 concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down-regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO2 concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO2 concentration treatment were lost following a final 3-week reversion to ambient CO2 concentration, but occurred in plants exposed to the elevated CO2 concentration for the final 3-week period only. In conclusion, elevated atmospheric CO2 concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO2 responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation. [source] Seed variation among annual ryegrass cultivars in south-eastern USA and the relationship with seedling vigour and forage productionGRASS & FORAGE SCIENCE, Issue 4 2002B. C. Venuto Abstract Annual ryegrass (Lolium multiflorum Lam.) is grown on more than one million ha in the south-eastern USA each year. Recommended and actual seeding rates vary substantially within the region. The objective of this study was to evaluate variation in seed weight, germination, seedling vigour and seasonal yield performance among annual ryegrass cultivars. During 1997, 1998 and 1999, seed from fourteen commercial cultivars was weighed and germinated to determine numbers of pure live seed (PLS) m,2 before yield evaluation at four locations. Seed from ten cultivars was planted at 0·7 and 2·0 cm depth in a greenhouse study to evaluate relative seedling vigour. Cultivar mean single-seed weight ranged from 2·4 to 4·8 mg in 1997, 1·8 to 4·5 mg in 1998, and 2·6 to 4·6 mg in 1999. Seed germination ranged from 78·8% to 98·0% in 1997, 82·3 to 98·3% in 1998 and 77·8 to 98·3% in 1999. Seed number, PLS m,2, ranged from 675 to 1289 in 1997, 710 to 1550 in 1998, and 717 to 1179 in 1999. Among the ten cultivars evaluated for seedling vigour, seedling weight differed between planting depths and a significant cultivar by year interaction was observed. Seedling weight was highly correlated with seed weight at each seeding depth. The effect of increasing number of PLS m,2 on subsequent yield performance, although small, was consistently negative. These results indicate that target plant populations may be obtained more economically by adjusting seeding rates for seed size differences among cultivars and seed lots of annual ryegrass. [source] ,Settling the Hearts and Quieting the Minds of All Good People': The Major-Generals and the Puritan Minoritiesof Interregnum EnglandHISTORY, Issue 278 2000Christopher Durston In 1655 Cromwell dispatched the major-generals to the provinces with the aims of improving security and bringing about a moral reformation. Commissioners for securing the peace of the commonwealth were appointed to work with them in every county. While a few of these commissioners were career politicians, most were zealous Puritans who welcomed the major-generals with open arms and embraced their work with enthusiasm. They imposed the decimation tax on their royalist neighbours with vigour, frequently expressing disappointment if the government exempted any individual from the exaction. In some counties they also participated eagerly in efforts to remove suspect clergymen from the ministry and to suppress immorality by closing down unlicensed alehouses and rounding up the idle and dissolute. While some of them believed that their work was paying dividends, during the election campaign of August 1656 their enemies united against them and returned to parliament members who were deeply hostile to them. In January 1657 the rule of the major-generals came to an abrupt end and the local influence of the Puritan commissioners waned. Their activities between November 1655 and September 1656 had, however, re-opened the wounds of the 1640s and deepened the nation's antipathy to Puritan rule. [source] Epicutaneous immunization converts subsequent and established antigen-specific T helper type 1 (Th1) to Th2-type responsesIMMUNOLOGY, Issue 1 2006Jessica Strid Summary Epicutaneous immunization is a potential novel technique for topical vaccine delivery. It targets the immunologically rich milieu of the skin while having the advantage of being a non-invasive immunization procedure. By disrupting the stratum corneum of the epidermis a natural adjuvant effect can be achieved through activation of resident Langerhans cells. This negates the normal need for co-application of noxious adjuvants. Epicutaneous immunization on barrier-disrupted skin induces potent antigen-specific systemic immunity with a strong T helper type 2 (Th2) bias. We show here that epicutaneous immunization enhances the vigour of a subsequent T-cell response to the same antigen. The induced systemic Th2 response prevents the development of Th1 responses induced through injection of antigen in complete Freund's adjuvant (CFA). Prior epicutaneous immunization results in reduced production of antigen-specific interferon-, and immunoglobulin G2a (IgG2a) and enhanced interleukin-4, IgG1 and IgE responses to immunization with CFA. Moreover, epicutaneous immunization converts an established Th1 response to a Th2 response, as demonstrated by the specific reduction of interferon-, and IgG2a and the enhancement of interleukin-4 and IgE. This Th2 dominance of epicutaneous immunization may have direct therapeutic application as an immune-modulating procedure in Th1-dominant diseases such as autoimmune rheumatoid arthritis, type 1 diabetes, Hashimoto's thyroiditis and multiple sclerosis. [source] The arithmetic of defence policyINTERNATIONAL AFFAIRS, Issue 3 2001Michael Alexander The Kosovo campaign of 1999 demonstrated unambiguously the weakness of European military forces. Recognition of the consequences of this lack of capability has put new vigour into the European defence debate. Yet decline in military capability is systemic in every European country. The Helsinki goals will do nothing to address this decline. National defence budgets over the past 15 years have been decreasing in real terms. Even if current aspirations to hold military spending levels were to be achieved, the decline in capabilities would continue. Military equipment and personnel costs rise faster than domestic inflation, and therefore fewer people and weapons systems can be afforded each year. There is no prospect of significant uplifts in defence budgets in Europe, despite the acknowledged need for a range of expensive enabling capabilities for post-Cold War operations. Palliative measures now on trial are unlikely to have a major impact. The only option for European nations is a progressive integration of their forces to realize the economies of scale that would allow effectiveness to be maintained. There are opportunities for initiatives that would produce short-term pay-offs. Despite the severe political difficulties of a long-term plan for integration, the alternative is worse. Trying to maintain sovereignty in defence provision will mean that the nations of Europe will eventually be unable either to meet the requirements of even their most modest security needs or to exercise any influence over US defence and security policies. [source] Distribution and temporal variability of 500 hPa cyclone characteristics in the Southern HemisphereINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2002Murray Keable Abstract A 40 year period (1958,97) of US National Centers for Environmental Prediction reanalysis data has been used to diagnose the behaviour and variability of 500 hPa extratropical cyclones for the Southern Hemisphere using a Lagrangian perspective. The ,finding' and ,tracking' of these systems were performed using a fully automated scheme. Seasonal distributions of system density, cyclone formation (cyclogenesis), decay (cyclolysis), cyclone centre velocity and intensity/strength are presented. System density is shown to exhibit a maximum in the surface circumpolar trough region and over the Antarctic continent. A broad band of enhanced cyclone system density was evident across the South Pacific from southeast Australia to South America in all seasons, most markedly in winter. As this feature appears also at the surface level, strong vertical consistency of these cyclones in the low and middle troposphere is indicated. Velocities of cyclone centres were found to peak in the latitudes 50,55 °S, and 500 hPa systems appeared to move on average in a much more zonal (easterly) direction than their sea-level counterparts. The mean number of midlatitude cyclones per analysis has exhibited a significant downward trend over the record, with particularly low values observed in the early 1980s. Offsetting this trend have been increases in three measures of mean cyclone vigour. Three orographic features, in particular, are seen to influence the behaviour of 500 hPa cyclones: the mountains of New Zealand, the Antarctic Peninsula and the southern Andes. Over most of Antarctica the rate of cyclogenesis exceeds that of cyclolysis, indicating that many of the cyclones being formed in the vortex are actually exported out (i.e. to the north) of the continent. In the subtropics, considerable numbers of systems are formed in the Mozambique Sea region, but these tend to be quasi-stationary features. Copyright © 2002 Royal Meteorological Society. [source] Dynamic capabilities: A review and research agendaINTERNATIONAL JOURNAL OF MANAGEMENT REVIEWS, Issue 1 2007Catherine L. Wang The notion of dynamic capabilities complements the premise of the resource-based view of the firm, and has injected new vigour into empirical research in the last decade. Nonetheless, several issues surrounding its conceptualization remain ambivalent. In light of empirical advancement, this paper aims to clarify the concept of dynamic capabilities, and then identify three component factors which reflect the common features of dynamic capabilities across firms and which may be adopted and further developed into a measurement construct in future research. Further, a research model is developed encompassing antecedents and consequences of dynamic capabilities in an integrated framework. Suggestions for future research and managerial implications are also discussed. [source] Effect of generalist insect herbivores on introduced Lepidium draba (Brassicaceae): implications for the enemy release hypothesisJOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2008K. P. Puliafico Abstract The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem-mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple-species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH. [source] Relative abundance of males to females affects behaviour, condition and immune function in a captive population of dark-eyed juncos Junco hyemalisJOURNAL OF AVIAN BIOLOGY, Issue 3 2007Timothy J. Greives Relative numbers of males and females in breeding groups may vary from expected values owing to a variety of factors. To determine how sex ratio might influence individual phenotypes in a captive population of dark-eyed juncos Junco hyemalis during the breeding season, we established three treatment groups: a male-biased (2:1), equal (1:1), and female-biased group (1:2). Within-group density (birds/m2) was constant across groups. We assessed the frequency of flight chases (a proxy for social instability), measured changes in body mass and pectoral muscle condition, assayed plasma levels of testosterone (T) and compared cell-mediated immunity of individuals. We found significantly more chases in the male-biased group than in the female-biased group. Birds in the male-biased group lost more mass and displayed poorer pectoral-muscle condition than birds in the equal group. Cell-mediated immune responses were reduced in individuals in the male-biased group in comparison to the female-biased group. Plasma T levels in both sexes did not vary with sex ratio. Collectively, these results suggest that during the breeding season, social instability is greater in male-biased populations, and instability may lead to decreased general health and vigour. [source] Do male hoots betray parasite loads in Tawny Owls?JOURNAL OF AVIAN BIOLOGY, Issue 4 2000Stephen M. Redpath Bird song structure may honestly reveal the health and vigour of individual males to potential mates and competitors. If this is the case then song may reflect the level of parasitic infections in males. We initially examined the relationship between blood parasite infections and the time taken to respond by 22 male Tawny Owls to a broadcast hoot. We then examined the call structure (total length and frequency) in relation to parasite infection, an index of owl condition and an index of food abundance. Owls with higher parasite loads responded more slowly to an intruder, although this relationship was not significant once condition and vole abundance were controlled for. We found no relationship between call length and any of the measured variables. However, the high frequency and the range of frequencies used in calls decreased with increasing parasite load. Thus, there was the potential for individuals to assess male parasite load from the speed of response and the structure of the call. Experimental tests of these relationships are now required. [source] Inbreeding and inbreeding depression in a threatened endemic plant, the African violet (Saintpaulia ionantha ssp. grotei), of the East Usambara Mountains, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Johanna Kolehmainen Abstract Mating among closely-related individuals in small and isolated plant populations may result in reduced vigour of the inbred offspring, i.e. inbreeding depression, especially in naturally outbreeding plants. Occurrence of inbreeding and inbreeding depression was studied in Saintpaulia ionantha ssp. grotei, a threatened endemic plant species with a narrow ecological amplitude from the East Usambara Mountains. The level of inbreeding (measured as the fixation index, F) was investigated in twelve populations by analyzing variation at one microsatellite marker locus. The effect of one generation of selfing and outcrossing on the progeny fitness was studied by controlled crosses in two small patches that differ in the level isolation. The fixation index (F) across the populations was on the average 0.21 and varied among the populations from substantial inbreeding (F = 0.58) to surplus heterozygosity (F = ,0.29). High inbreeding depression (,) was observed at early and late stages of the life-cycle. The isolated patch exhibited lower inbreeding depression than did the non-isolated patch. The results of this study suggest that inbreeding and subsequent inbreeding depression are potential threats to the survival of Saintpaulia populations. Résumé L'accouplement d'individus étroitement liés, dans des petites populations végétales isolées, peut aboutir à une vigueur moindre de la progéniture de même souche, c'est-à-dire une dépression due à l'endogamie, spécialement chez des plantes qui sont naturellement exogames. L'occurrence de l'endogamie et de la dépression qui y est liée a étéétudiée chez le Saintpaulia ionantha spp. grotei, une plante endémique menacée qui n'a qu'une faible amplitude écologique dans l'est des Usambara Mountains. On a recherché le taux d'endogamie (mesuré par l'indice de fixation F) dans 12 populations en analysant la variation d'un locus microsatellite marqueur. L'effet d'une génération d'auto- et d'allofécondation sur l'aptitude (fitness) de la progéniture a étéétudié par des croisements contrôlés dans deux petites parcelles dont le degré d'isolement différait. L'indice de fixation F dans les populations était en moyenne de 0,21 et il variait d'une autofécondation substantielle (F = 0,58) à une hétérozygosité en surplus (F = ,0,29). Une forte dépression due à l'endogamie (,) a été observée aux stades précoce et tardif du cycle vital. La parcelle isolée a présenté une dépression liée à l'endogamie moins forte que celle de la parcelle non isolée. Les résultats de cette étude suggèrent que l'auto-fécondation et la dépression qui en résulte sont des menaces potentielles pour la survie des populations de Saintpaulia. [source] Hybridization dynamics of invasive cattail (Typhaceae) stands in the Western Great Lakes Region of North America: a molecular analysisJOURNAL OF ECOLOGY, Issue 1 2010Steven E. Travis Summary 1.,By increasing vigour and broadening ecological tolerances, hybridization between native and introduced species may serve as a primary driver of invasiveness. 2.,Cattails (Typha, Typhaceae) are clonal wetland graminoids that are known to hybridize where anthropogenic influences have resulted in distributional overlap. 3.,In order to gauge the relative performance of hybrid vs. pure Typha, we characterized hybridization and clonal growth where native Typha latifolia and introduced Typha angustifolia occur together in the Western Great Lakes Region of North America. 4.,Based on microsatellite markers, we documented F1 hybrids as the most common class at five intensively sampled sites, constituting up to 90% of the genets and 99% of the ramets. Backcrosses to one or the other parent constituted 5,38% of the genets. Pure T. latifolia was rare and never constituted more than 12% of the genets. 5.,F1 hybrid genets achieved the highest mean ramet numbers at three sites, and were second in size only to T. angustifolia at two sites; however, these differences were not significant based on site-specific one-way anovas. 6.,F1 hybrids exhibited little height advantage over other Typha classes, although there was a general tendency for hybrids in relatively mixed stands to be among the tallest genets in shallow water, but among the shortest genets in deeper water. 7.,Native T. latifolia was found growing at the shallowest water depths at the only site where it was sufficiently abundant to be included in statistical comparisons. 8.,Synthesis. The role of hybridization in plant invasions can be difficult to confirm in the absence of molecular data, particularly for clonal species where the boundaries separating individuals are otherwise difficult to discern. Here, we used molecular markers to document the prevalence and performance of hybrid genets in five invasive Typha stands covering a broad area of the Western Great Lakes Region. We found an extremely high prevalence of F1 hybrids within mixed Typha stands. This, coupled with the typically larger sizes of hybrid genets, suggests that hybrids are capable of outperforming other Typha spp. and that hybridization has played an influential role in the North American cattail invasion. [source] Measuring the components of competition along productivity gradientsJOURNAL OF ECOLOGY, Issue 2 2007MARK V. WILSON Summary 1Controversy surrounds the measurement of competition intensity. Moreover, when biomass varies systematically along productivity and other environmental gradients, common indices of competitive outcome mask important ecological interactions. 2This study presents two indices derived from how neighbours interact with target plants. The first, relative crowding, increases directly with the abundance of neighbours present and decreases inversely with the potential size and vigour of the target plant itself. The second, interaction strength, is the integral of suppression of the target by neighbours over the range of neighbour abundance. Relative crowding and interaction strength are derived independently, but when multiplied produce the commonly used relative competitive index, showing the biological underpinnings of the relative competition index in terms of crowding and strength of interaction. Since the new indices of relative crowding and interaction strength explicitly account for the amount of neighbour biomass, they serve as a valid method to track the effects of changing habitat conditions on the components of competition. 3The new indices are applied to three published data sets. In each case, relative crowding increased with standing crop. In one case competition was reported as unchanged along a productivity gradient, whereas the new indices show that relative crowding and interaction strength both had significant patterns, but their effects were counteracting. These results do not fit current theories of competition. Further empirical studies are needed to see if competition theory needs revision. 4Separating the mechanisms of competition into relative crowding and strength of interaction reveals previously hidden patterns that help bring to light underlying processes of competition along productivity gradients. [source] Resprouting of the Mediterranean-type shrub Erica australis with modified lignotuber carbohydrate contentJOURNAL OF ECOLOGY, Issue 3 2003Alberto Cruz Summary 1The vigour of plant resprouting after fire may be driven by the amount of stored non-structural carbohydrates (NC). However, the extent to which NC reserves limit this response in woody plants has not been established. 2This study analyses the effects of modifying NC concentrations in the lignotuberous Mediterranean-type shrub Erica australis, on resprouting after experimental burning. A factorial experiment with two treatments (shade and burn) was carried out, with three levels per treatment. Plants were shaded (exposure to 100%, 50% or 20% of incident radiation for 1 year), following which they were clipped (control, no fire), or clipped and burned at one of two levels of severity. After this, they were allowed to resprout and grow for 2 years. 3Shading modified NC concentrations in the lignotuber, but not in the roots. Two years after burning, plants subjected to the greatest shading, which reduced their NC concentrations to 44% (sum of NC) or 19% (starch) of that of control plants, had suffered higher mortality after resprouting, had a significantly lower number of resprouts, of shorter length, and had produced lower biomass per plant than less shaded or unshaded plants. However, plants subjected to intermediate shade, which suffered a reduction in NC concentrations to 70% of that of control plants, did not differ in resprouting response from control plants. 4Burning caused more direct mortality, and a severe reduction in both number or biomass of resprouts, than just clipping. There were no significant shade × burning interaction effects. 5While reductions in NC may limit resprouting, such limitation may only occur when NC is reduced to much lower concentrations than caused by commonly experienced conditions. The role of NC reserves in limiting resprouting of lignotuberous, woody plants such as E. australis might therefore not be as important as is commonly assumed. [source] Synergistic epistasis and alternative hypothesesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2004S. Trouve Abstract Inbreeding generally results in deleterious shifts in mean fitness. If the fitness response to increasing inbreeding coefficient is non-linear, this suggests a contribution of epistasis to inbreeding depression. In a cross-breeding experiment, Salathé & Ebert (2003. J. Evol. Biol. 16: 976,985) tested and found the presence of this non-linearity in Daphnia magna. They argue that epistatic interactions cause this non-linearity. We argue here that their experimental protocol does not allow disentangling the effect of synergistic epistasis from two alternative hypotheses, namely hybrid vigour and statistical non-independence of data. [source] Physiological performance of largemouth bass related to local adaptation and interstock hybridization: implications for conservation and managementJOURNAL OF FISH BIOLOGY, Issue 2001S. J. Cooke Four genetically distinct stocks of age 2+ years largemouth bass Micropterus salmoides were produced using adults collected from two regions in the upper midwest (central Illinois, IL and south-eastern Wisconsin, WI, U.S.A.). Two pure stocks (IL × IL and WI × WI), as well as both of their reciprocal F1 interstock hybrids (IL × WI and WI × IL) were produced in research ponds in Champaign, IL. In general, swimming performance, routine oxygen consumption and activity were highest at 18 × C, intermediate at 12 × C, and lowest at 6. C for all stocks. However, performance indicators varied among stocks at each of the temperatures. The pure Illinois stock (IL × IL) had the lowest activity: cost ratio at 18 × C and the highest at 6_ C (based upon swimming strength, routine activity rates and routine metabolic rates). The opposite pattern was observed for the other pure stock (WI × WI). Although differences were less distinct at lower temperatures, the two pure stocks (IL × IL and WI × WI) outperformed both interstock hybrids. These results indicate that not only do non-native stocks appear to have reduced performance relative to locally adapted stocks, but also that interstock hybrids exhibit performance impairments, not hybrid vigour. [source] Influence of plot characteristics and surrounding vegetation on the intra-plot spatial distribution of Empoasca vitisAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2009Damien Decante Abstract 1Spatial distributions of adults and nymphs of Empoasca vitis were assessed during 3 years inside two adjacent vine plots having considerable intra-plot variability, diversified natural ground cover and surrounding vegetation, and no insecticide application. 2Geostatistical analysis confirmed that, in spite of repeated adult migrations, spatial distributions of summer populations were highly aggregated, similar every year and similar between adults and nymphs. Comparison of insect distribution with intra-plot characteristics, such as vine plant vigour (leaf density and leaf chlorophyll concentration) and phenology, plot topography and surrounding vegetation, revealed that E. vitis clearly aggregates in areas with the most vigorous vine plants. 3Even though the presence of natural enemies in the surrounding vegetation was confirmed by specific observations, we did not observe significant population decrease at the contiguous plot edges. Natural ground cover, together with the absence of insecticide, might allow the spreading and perennial conservation of E. vitis natural enemies inside the plots. 4Clear adult aggregations observed along downwind woodlands suggest that this vegetation acts as a barrier and intercepts the adults flying passively across the plot. However, this surrounding vegetation could also serve as an alternative refuge when vine water deficit and vine foliage temperature increase. [source] Environment and host-plant genotype effects on the seasonal dynamics of a predatory mite on cassava in sub-humid tropical AfricaAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2009Christine Zundel Abstract 1,In tropical dry seasons, survival of small arthropods such as predatory mites is often negatively affected by low relative humidity (RH). For species that do not diapause or migrate to refuges, the ability of the habitat to mitigate climatic conditions becomes crucial. 2,The relative effect of macro-habitat (dry grassland hill, humid multiple cropping area, humid riparian forest) and microhabitat (host-plant genotypes with hairy, semi-hairy and glabrous apices) on the seasonal dynamics of the phytoseiid mite Typhlodromalus aripo, a predator of Mononychellus tanajoa on cassava, was examined in a field experiment during a dry season. The effect of RH and plant genotype on T. aripo egg survival was determined in an environment control chamber. 3,Predator abundance was higher in humid multiple cropping areas and on hairy cassava compared with the other habitat types and cassava genotypes. 4,Discriminant and regression analyses showed that the predator's dry season persistence was related to high RH, high plant vigour and hairy apices, but not to prey abundance. 5,In the controlled climate experiment, the effect of host-plant morphology was evident only at the intermediate RH level of 55%. An effect of apex hairiness was not found. 6,It is concluded that the effect of genotype on T. aripo persistence diminishes under low RH conditions, and that supportive effects of apex hairs become effective only in the field, probably through protection from wind and/or intraguild predation. Humid multiple cropping areas planted with hairy and vigorous cassava genotypes are suitable dry season reservoirs for T. aripo. [source] Oviposition strategies employed by the western spruce budworm: tests of predictions from the phylogenetic constraints hypothesisAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2003Kathryn J. Leyva Abstract 1,Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in an eruptive forest Lepidopteran species, the western spruce budworm. 2,In previous work, we established that western spruce budworm females exhibit oviposition preferences with regard to tree age, tree vigour and host species. However, there was no evidence to support a link between oviposition preference and larval performance, which supports the Phylogenetic Constraints Hypothesis. 3,Our preference data led us to test whether female budworms use oviposition strategies to select the sites where they lay their egg masses. Our experiments were designed to make direct comparisons between latent and eruptive insect herbivores with respect to two oviposition behaviours: egg retention and avoidance of conspecifics. This type of research has not previously been conducted on any eruptive forest Lepidopteran. 4,Female budworms retained eggs instead of laying them on less preferred hosts in two of three experiments, but the percentage of eggs they retained was significantly less compared to latent insect herbivores. 5,In addition, female budworms actively avoided oviposition in areas with the highest density of conspecific egg masses, but they laid egg masses in all the other locations provided. This contrasts with the pattern seen in latent insect herbivores, which consistently avoid laying their eggs near any sites already used by conspecifics. 6,Our research indicates that there are extreme differences between latent and eruptive insect herbivores with respect to egg retention and avoidance of conspecifics, thus supporting the Phylogenetic Constraints Hypothesis. [source] Heritability of Phenols in the Resistance of Theobroma cacao against Phytophthora megakarya, the Causal Agent of Black Pod DiseaseJOURNAL OF PHYTOPATHOLOGY, Issue 9 2007P. F. Djocgoue Abstract The black pod disease caused by Phytophthora megakarya is responsible for 80% of the cocoa production loss in Cameroon. To assess the resistance of cocoa plants against this pathogen, necrotic lesions, phenolic content and qualitative alteration of phenolics were conducted in ICS84 and ICS95 clones (two Trinitario introduced from Trinidad) and their hybrids (families F30 and F25) derived from reciprocal cross breeding between these two parental clones after inoculation. The existence of strong hybrid vigour has been shown. Ninety percentage of the hybrid's genotypes manifested a positive heterosis effect for the development of lesion size. This suggests the existence of hybrid vigour with a genetic additive effect. F3086, F2509, F2552 and F2586 hybrids were characterized by localized lesions. Those hybrids genotypes can be considered as elite clones. In relation to analysis of total phenolics and lesion size, no maternal effect was detected in the transmission of these characters. A significant and negative correlation (r = ,0.683) (P < 0.01) has been observed between necrosis evolution and phenolics accumulation. The values of the heritability of lesion size and the total phenolic content in offsprings did not permit to show the maternal effect. Qualitative analyses of phenolics showed high flavonones content in cocoa leaves. Qualitative analyses of phenolics in ICS84, ICS95 clones and their hybrids showed a modification of the phenolics profiles, notably concerning apigenin and luteolin derivatives due to the inoculation. These compounds, along with others that were not identified, could have a role in the reaction and mechanism of defence of cocoa against P. megakarya. [source] Puccinia romagnoliana Marie & Sacc.JOURNAL OF PHYTOPATHOLOGY, Issue 4-5 2002a Potential Bioherbicide Agent for Biocontrol of Purple Nutsedge (Cyperus rotundus L.) in Mulberry Abstract The ingress, infection process and disease development of Puccinia romagnoliana Marie & Sacc. on purple nutsedge (Cyperus rotundus L.) and its cross-infectivity to an economically important sericultural crop, mulberry (Morus alba L.) were investigated under a scanning electron microscope. The potential of P. romagnoliana as a biocontrol agent was also evaluated for the control of purple nutsedge under greenhouse conditions. Uredinia of P. romagnoliana were paraphysate that bore numerous pedicellate urediniospores, having echinulate spore wall. Urediniospores had 2,3 subequatorial germpores, which gave rise to germtubes. Germtubes were observed to orientate toward stomata and terminated in appressoria, through which infection pegs were formed that penetrated the leaf. Symptoms developed on leaves 10 days after inoculation. P. romagnoliana was highly pathogenic to purple nutsedge, which, when disease was severe, caused death of the shoots and reduced both number and vigour of the tubers. P. romagnoliana did not infect the main commercial crop, mulberry. Thus, the present study demonstrated the potential ofP. romagnoliana as a bioherbicide to control the purple nutsedge in mulberry fields. [source] | |||||||||||||||||||||||||||||||||||||||||||