Allium ampeloprasum var. babingtonii (Alliaceae): an isoclonal plant found across a range of habitats in S.W. England

Despite the widespread distribution and common habitat dominance of clonal plant species the mechanisms for their ecological success often remain uncertain. Allium ampeloprasum var. babingtonii is a sterile plant that reproduces with physiologically independent asexual propagules. The variety is found mainly in the S.W. of England over a wide habitat range including sea cliffs and open woodlands and displays an autumn-spring phenology in common with its close Mediterranean relatives. The role of population genetic structure in the remarkable habitat distribution of the variety is not known. Genetic variation in A. ampeloprasum var. babingtonii was analysed using RAPD markers in single individuals of var. babingtonii from 16 distinct populations and five further individuals from a single population. This analysis revealed no polymorphism suggesting that all sampled individuals are part of a single clone. We offer the conjecture that in the absence of genetic variation an ecological release, due to temporal separation from competing species, may contribute to the ability of var. babingtonii to exploit heterogeneous environmental conditions.     

Adsorption and Degradation of Metolachlor and Metribuzin in a No-Till System Under Three Winter Crop Covers

The objective of this study was to quantify adsorption and degradation of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1 -methylethyl) acetamide] and metribizun [4-amino-6-(1,1 -dimethylethyl)-3-(methylthio)-1,2,4-trazine-5(4H)-one] in a soil planted to winter covers clover (Trifolium sp.), vetch (Vicia villosa), and wheat (Triticum aestivum). Surface soil samples (0 to 5?cm) from Memphis silt loam (fine-silty, mixed, thermic Typic Hapludalf) were collected and equilibrated with herbicide at initial concentrations ranging from 0 to 20?mg L^?1 that were then applied for a batch experiment. Soils were treated either with a single herbicide or a mixture of the two herbicides. For the degradation experiments, herbicides at a concentration of 10?mg kg^?1 soil were applied and incubated for 21?d at ～23°C. Metolachlor and metribuzin adsorptions were described by the Freundlich isotherm. Average Freundlich distribution coefficient (K_f) for metolachlor was significantly higher (p≥0.05) than that of metribuzin in soils under the three crop covers irrespective of method of application. The K_f for metolachlor ranged from 18.38 to 11.18?L kg^?1, and K_f for metribuzin ranged from 1.80 to 0.93?L kg^?1. Average normalized distribution coefficient (K_oc) for metolachlor was significantly higher (p≥0.05) than average K_oc for metribuzin irrespective of crop cover. After 21 days of incubation, average half-life of metolachlor across soil under the three crop covers was significantly higher than the average half-life of metribuzin (p≥0.05). Half-life values ranged from 20.6 to 24.9 days for metolachlor, and 4.4 to 12.4 days for metribuzin. In soils treated with metribuzin, the half-life was highest for soil under wheat and lowest for soil under clover (p≥0.05).     

Sexual dimorphism and synchrony of breeding: variation in polygyny potential among populations in the common brushtail possum, Trichosurus vulpecula

Male-biased sexual dimorphism in both size and body mass isa common characteristic of many polygynous mammals and is oftenattributed to sexual selection favoring large males. The degreeof dimorphism is thought to be related to the potential forsome males to monopolize access to estrous females, which isin turn related to the distribution of receptive females inspace and time. In the present study, we investigated the relationshipbetween the temporal distribution of breeding females and thedegree of mass dimorphism among 11 populations of the commonbrushtail possum from northern Australia. Breeding patternsvaried from complete aseasonality in some populations to a seasonalconcentration of births within 2 or 3 months in others. We predictedthat in populations in which mating opportunities were distributedthroughout the year, dominant males would be able to monopolizeaccess to larger numbers of estrous females than in populationsin which matings were more seasonal, and in such populations,large body size in males would be favored. We found that dimorphismwas related to seasonality of breeding, being greatest in populationswith a more aseasonal pattern. Mean body mass of male possumsalso decreased with increasing population density. Populationdensity may influence the degree of breeding synchrony withinpopulations, particularly in locations with a more seasonalclimate. The present study is the first to demonstrate plasticityin mass dimorphism in response to local variation in the synchronyof breeding in a mammal species.     

Interactions among mycorrhizae, atmospheric CO2 and soil N impact plant community composition

We examined plant community responses to interactions between arbuscular mycorrhizal (AM) fungi and availability of atmospheric CO₂ and soil N. Communities of 14 plant species were grown in mesocosms containing living or killed AM fungal inoculum, ambient or elevated atmospheric CO₂ and low or enriched soil N. After one growing season, significantly different plant communities existed in the different treatments. Plant species richness was lowest in +N mesocosms and highest in +AM + CO₂ mesocosms. At ambient CO₂, AM fungi reduced richness but at elevated CO₂ they increased it. This was caused by changes in mortality rates of several C₃ forbs and may suggest that CO₂ enrichment ameliorates the carbon cost of some AM symbioses. Soil moisture was higher in +CO₂ mesocosms but +AM counteracted this effect. These results suggest that AM symbioses may be important mediators of plant community responses to anthropogenic CO₂ and N enrichment.     

Intramyocellular triacylglycerol in prolonged cycling with high- and low-carbohydrate availability.

Vastus lateralis intramyocellular lipid (IMCL) content was assessed by (1)H-magnetic resonance spectroscopy before and after prolonged time trial cycling bouts of approximately 3-h duration. Six highly trained male cyclists completed a double-blind, randomized, crossover design of two experimental trials after a strenuous exercise bout and 48 h of high (HC) (9.32 +/- 0.08 g. kg(-1). day(-1)) and low (LC) (0.59 +/- 0.21 g. kg(-1). day(-1)) dietary carbohydrate. Resting IMCL content was significantly higher after LC vs. HC (P < 0.01) and was reduced during exercise by 64 and 57%, respectively. IMCL was not different between conditions after exercise (P > 0.05). The approximately twofold increase in IMCL degradation in LC compared with HC suggests that higher rates of whole body lipid metabolism in LC were in part attributable to a greater IMCL utilization. Four subjects experienced reductions of IMCL in excess of 70% during exercise. To our knowledge, this is the first study to report near depletion of IMCL during prolonged cycling, indicating that IMCL, presumably the triacylglycerol component, may be exhausted by prolonged strenuous exercise.     

Mesenteric microvascular inflammatory responses to systemic hypoxia are mediated by PAF and LTB4.

Systemic hypoxia produces a rapid microvascular inflammatory response characterized by increased reactive oxygen species (ROS) levels, leukocyte-endothelial adherence and emigration, and increased vascular permeability. The lipid inflammatory mediator leukotriene B(4) (LTB(4)) is involved in the early hypoxia-induced responses (ROS generation and leukocyte adherence). Whether other lipid inflammatory mediators participate in this phenomenon is not known. The objective of these experiments was to study the role of platelet-activating factor (PAF) in the microvascular inflammatory response to hypoxia and its potential interactions with LTB(4) in this response. Intravital microscopy was used to examine mesenteric venules of anesthetized rats. We found that WEB-2086, a PAF receptor antagonist, completely prevented the increase in ROS levels and leukocyte adherence during a brief reduction in inspired Po(2) to anesthetized rats; administration of either WEB-2086 or the LTB(4) antagonist LTB(4)-DMA attenuated leukocyte emigration and the increase in vascular permeability to the same extent during prolonged systemic hypoxia in conscious rats. Furthermore, no additive effect was observed in either response when both antagonists were administered simultaneously. This study demonstrates a role for PAF in the rapid microvascular inflammatory response to hypoxia, as well as contributions of PAF and LTB(4) to the slowly developing responses observed during sustained hypoxia. The incomplete blockade of the hypoxia-induced increases in vascular permeability and leukocyte emigration by combined administration of both antagonists indicates that factors in addition to LTB(4) and PAF participate in these phenomena.     

Sentenced without trial: reviling and revamping the Resource Dispersion Hypothesis

The resource dispersion hypothesis (RDH) offers a predictive model for how, in heterogeneous environments, some animals may form groups even without any direct benefits from doing so. Revilla (2003) levels a number of criticisms at the RDH, all of which we feel can be easily clarified or resolved (we address them in the order they appear in his critique). We argue that the RDH, despite its long history and despite our own efforts, still lacks convincing evidence to reject it. On the contrary, we see it as having weathered its critics very well. While there is steadily accumulating evidence in support of the RDH, there are very few empirical tests that provide decent evidence against it.     

Growth rate, size, and sex ratio of last-laid, last-hatched offspring in the tree swallow Tachycineta bicolor

In tree swallows Tachycineta bicolor, last‐laid eggs typically hatch one to two days after the other eggs in the clutch hatch, putting last‐hatched offspring at a disadvantage when competing for food delivered by parents. We studied the biology of last‐laid, last‐hatched tree swallow offspring over two years in a Wyoming, USA, population. Our first objective was to compare the growth of last‐hatched offspring to that of their earlier‐hatched nestmates. One previous study had suggested that last‐hatched, competitively disadvantaged offspring grow feathers faster than senior nestmates, even at the expense of other aspects of growth. This may allow last‐hatched offspring to fledge with senior nestmates and avoid abandonment by parents. A second objective was to determine the sex of nestlings from last‐laid eggs. If last‐laid eggs typically produce undersized, weak adults that are poor competitors for resources, and if the fitness costs of being undersized/weak are more severe for males than for females, then selection may favour having offspring from last‐laid eggs to be female. In this study, last‐laid eggs hatched in 63 of 66 (94%) nests and hatched last in 93% of cases. At hatching, offspring from last‐laid eggs weighed, on average, 63% as much as their three heaviest nestmates (range: 26–107%). Offspring from last‐laid eggs fledged from 71% of the nests that produced at least one fledgling and apparently starved to death in remaining nests. Last‐hatched offspring who were presumably at a substantial competitive disadvantage (those whose mass at hatching was no more than about 75% of the mean mass of their three heaviest nestmates), gained mass more slowly than their senior nestmates but they eventually attained the same peak mass before fledging. Last‐hatched offspring grew primary feathers more slowly than their senior nestmates although the difference in growth rate was slight (0.2 mm/d) and only marginally significant. As a group, offspring from last‐laid eggs did not differ from offspring from all other eggs in either maximum mass attained before fledging or tarsus length at fledging. This is atypical for species with asynchronous hatching and is possibly the result of another unusual trait: the tendency of parent tree swallows to distribute food equally among young within broods. The sex ratio of offspring from last‐laid eggs did not deviate from 1:1 (22 males, 21 females). Given that last‐hatched eggs do not routinely produce undersized/weak individuals in our study population, there should be little selection on parent females to bias the sex ratio of last‐laid offspring towards females.     

Stream Water Chemistry in Mixed-Conifer Headwater Basins: Role of Water Sources,Seasonality, Watershed Characteristics,and Disturbances

Ecosystems - Understanding the transport of dissolved organic carbon (DOC) and nitrogen (N) as water flows through headwater basins is important for predicting downstream water quality. With...     

Developing a hybrid weed risk assessment system for countries with open and porous borders: insights from Bhutan

Biological Invasions - Intentional introduction of alien plant species through increased global trade and movement of people worldwide has contributed to the current problem of invasion by alien...