Ecological and landscape effects on genetic distance in an assemblage of headwater fishes

Environmental divergence along hierarchically structured longitudinal gradients may constitute barriers to gene flow in river networks for headwater specialised species. While known, this phenomenon has not been well studied, especially with regard to degree of headwater specialisation. We examined six headwater species that differ in habitat specialisation to assess whether patterns of differentiation vary according to geographic or environmental distance. We also identified regional environmental or anthropogenically induced fragmentation effects by comparing within‐drainage patterns of genetic distance across replicate watersheds. We used a comparative modelling framework to determine whether isolation by distance or isolation by resistance of large river habitats was a better predictor of genetic distance across species. The influence of reservoir presence and regional network characteristics that may influence the hydrology and size of large river habitats were also assessed. Resistance effects from large rivers were closely related to headwater specialisation, with increased specialisation leading to increased resistance and loss of drainagewide population connectivity. These results affirm that dendritic networks naturally fragment headwater specialised species. Further isolation from anthropogenic fragmentation was detected in two of the six drainages, indicating interactions with system‐specific conditions. Landscape variables related to the hydrology of large rivers also affected genetic distance in predicted ways, supporting the importance of large rivers in genetically structuring headwater species in drainage networks.     

Finding suitable growth models for turbot (Scophthalmus maximus L.) in aquaculture 1 (length application)

Growth data of two different commercial turbot (Scophthalmus maximus) strains reared in recirculating aquaculture systems were analysed with the aim to determine the most suitable model for turbot. To assess the model performance three different criteria were used: (1) The mean percentage deviation between the estimated length and actual length; (2) the residual standard error with corresponding degrees of freedom and (3) the Akaike information criterion. The analyses were carried out for each strain separately, for sexes within strains and for a pooled data set containing both strains and sexes. We tested a pre‐selection of six models, containing three to four parameters. Models were of monomolecular shape or sigmoid shape with a flexible point of inflection including the special case of monomolecular shape in defined cases of their parameters. The 4‐parametric Schnute model achieved best fit in 62% of all cases and criteria tested, followed by the also 4‐parametric generalized Michaelis–Menten equation in 48% and the 4‐parametric Janoschek model (38%). The von Bertalanffy growth function achieved only 29%, Brody 24% and a new flexible function 19% best fit. In a 1–1000 day growth‐simulation sigmoid shaped curves were produced by the Schnute model in 71% of cases. The Janoschek and the Michaelis–Menten model each produced sigmoid curves in 57% of all cases. This indicates that a flexible 4‐parametric function reflects the growth curve of turbot the best and that this curve is rather sigmoid than monomolecular shaped.     

Major ascaroside pheromone component asc-C5 influences reproductive plasticity among isolates of the invasive species pinewood nematode

Pheromones are communication chemicals and regulatory signals used by animals and represent unique tools for organisms to mediate behaviors and make “decisions” to maximize their fitness. Phenotypic plasticity refers to the innate capacity of a species to tolerate a greater breadth of environmental conditions across which it adapts to improve its survival, reproduction, and fitness. The pinewood nematode, Bursaphelenchus xylophilus, an invasive nematode species, was accidentally introduced from North America into Japan, China, and Europe; however, few studies have investigated its pheromones and phenotypic plasticity as a natural model. Here, we demonstrated a novel phenomenon, in which nematodes under the condition of pheromone presence triggered increased reproduction in invasive strains (JP1, JP2, CN1, CN2, EU1, and EU2), while it simultaneously decreased reproduction in native strains (US1 and US2). The bidirectional effect on fecundity, mediated by presence/absence of pheromones, is henceforth termed pheromone-regulative reproductive plasticity (PRRP). We further found that synthetic ascaroside asc-C5 (ascr#9), the major pheromone component, plays a leading role in PRRP and identified 2 candidate receptor genes, Bxydaf-38 and Bxysrd-10, involved in perceiving asc-C5. These results suggest that plasticity of reproductive responses to pheromones in pinewood nematode may increase its fitness in novel environments following introduction. This opens up a new perspective for invasion biology and presents a novel strategy of invasion, suggesting that pheromones, in addition to their traditional roles in chemical signaling, can influence the reproductive phenotype among native and invasive isolates. In addition, this novel mechanism could broadly explain, through comparative studies of native and invasive populations of animals, a potential underlying factor behind of the success of other biological invasions.     

Antimicrobial flavonoids from the stem bark of Erythrina burttii

The chloroform extract of the stem bark of Erythrina burttii showed antifungal and antibacterial activities using the disk diffusion method. Flavonoids were identified as the active principles. Activities were observed against fungi and Gram(+) bacteria, but the Gram(-) bacteria Escherichia coli was resistant.     

Factors affecting a sheep vegetation management system in British Columbia, Canada

A silvopastoral agroforestry system involving sheep is an important silvicultural issue. We examined the factors that affect the continuation or discontinuation of sheep vegetation management (SVM) in British Columbia. A questionnaire was used to conduct interviews with a randomly selected sample of contractors and farmers who were involved in SVM in British Columbia (BC). Based on a stepwise discriminant analysis, we found that the profitability of SVM, and the practitioners' commitment (number of ewes owned by the farmer or contractor), experience (number of years the farmer or contractor has practiced SVM on public lands in BC) and trust or confidence (number of years the farmer or contractor has consistently worked for the landlord) contributed to the farmer's or contractor's continuation or discontinuation of SVM practice. The factors we defined seemed to be validated (corroborated) by a complex of determinants voiced by various experts concerning the relationship between SVM and the forestry economy in BC, the scale of sheep farming in BC, the relative absence of an agricultural infrastructure to support sheep farming in BC, and the continuity of SVM from year to year. Further investigation into these factors and others is required to advance our understanding of SVM in British Columbia. This revised version was published online in June 2006 with corrections to the Cover Date.     

Plagiotropism and auxin in Abies nordmanniana

Main branches of Abies nordmanniana Spach. were examined through their first growth season from subapical buds around the leader bud to fully expanded shoots. Plagiotropism was evident in branch orientation, which was almost horizontal, as well as in the orientation of buds developing on the branches. Auxin transport capacity was predominantly basipetal (> 90%) and consistently higher in the middle part of the branch than in the distal and proximal ends. Auxin transport capacity was higher on the dorsal side of the branch during the short initial hyponastic growth phase, but the difference disappeared when the branch became horizontal. No dorsal-ventral differences could be detected in young horizontal branches in concentrations of indole acetic acid, cytokinins, gibberellins or abscisic acid. Branch orientation was unaffected by decapitation of the leader apex or by decapitation and replacement with exogenous auxin. However, decapitation resulted in a less plagiotropic bud arrangement on the branches, and auxin application to the leader bud scar counteracted this effect. Thus, a signal originating in the stem seems to be involved in regulating branch bud positioning, whereas the horizontal branch orientation must rely on a different mechanism, presumably autonomic within the branch.