Modelling the dynamic spatio-temporal response of predators to transient prey patches in the field

The spatio-temporal dynamics of two aphid species ( Metopolophium dirhodum and Sitobion avenae ) and a generalist predator ( Pterostichus melanarius ) were observed in a field-scale study using a grid of 256 sampling locations with a 12-m spacing. Using Spatial Analysis by Distance Indices we demonstrate that populations show ephemeral spatial pattern at the field scale. We observed a positive, lagged beetle response to this aphid pattern; conversely, the aphids displayed a negative, lagged response to beetle spatial pattern. Examination of the local structure of the spatio-temporal dynamics revealed a strong response by the beetle population to aphid patches. The temporal structure of spatial associations between the species shows a strong correspondence with those from a conceptual model of predator–prey spatial interaction. The spatially coupled dynamics were sufficiently strong for the predator to have a negative effect on the intrinsic rate of increase of their prey.     

Distribution of plant‐dwelling spiders: Inflorescences versus vegetative branches

Abstract The influence of the architecture of vegetative branches on the distribution of plant‐dwelling spiders has been intensively studied, and the effects on the aggregation of individuals in several spider species on plants include variation in prey abundance, availability of predator‐free refuges and smoother microclimate conditions. The emergence of inflorescences at the reproductive time of the plants changes branch architecture, and could provide higher prey abundance for the spiders. The distribution of spiders between inflorescences and vegetative branches was compared on four widespread plant species in a Brazilian savannah‐like system. Inflorescences attracted more spiders than vegetative branches for all plant species sampled. The influence of branch type (inflorescence and vegetative) on spider distribution was also evaluated by monitoring branches of Baccharis dracunculifolia DC. in vegetative and flowering periods for 1 year, and through a field experiment carried out during the same period where artificial inflorescences were available for spider colonization. Artificial inflorescences attached to B. dracunculifolia branches attracted more spiders than non‐manipulated vegetative branches for most of the year. However, this pattern differed among spider guilds. Foliage‐runners and stalkers occurred preferentially on artificial inflorescences relative to control branches. The frequencies of ambushers and web‐builders were not significantly different between treatment and control branches. However, most ambush spiders (65%) occurred only during the flowering period of B. dracunculifolia, suggesting that this guild was influenced only by natural inflorescences. The experimental treatment also influenced the size distribution of spiders: larger spiders were more abundant on artificial inflorescences than on vegetative branches. The hypothesis that habitat architecture can influence the spider assemblage was supported. In addition, our observational and experimental data strongly suggest that inflorescences can be a higher quality microhabitat than non‐reproductive branches for most plant‐dwelling spiders.     

Shoot P status regulates cluster-root growth and citrate exudation in Lupinus albus grown with a divided root system

The present study was carried out to investigate whether the P concentration in the roots or the shoots controls the growth and citrate exudation of cluster roots in white lupin (Lupinus albus L). Foliar P application indicated that low P concentration in the shoots enhanced cluster‐root growth and citrate‐exudation rate more so than low P concentration in the roots. In the split‐root study, the P concentration in the shoots increased with increased P supply (1, 25 or 75 mmol m^?3 P), to the ‘privileged’ root halves. Roots ‘deprived’ of P invariably had the same low P concentrations, whereas those in the ‘privileged’ roots increased with increasing P supply (1, 25 or 75 mmol m^?3 P). Nevertheless, the proportion of the total root mass allocated to cluster roots, and the citrate‐exudation rates from the root halves were always similar on both root halves, irrespective of P supply, and decreased with increasing shoot P concentrations. Peak citrate exudation rates from developing cluster roots were significantly faster from cluster roots on the ‘deprived’ root halves when the ‘privileged’ half was exposed to 1 mmol m^?3 P as compared with 25 or 75 mmol m^?3 P. The possibility that changes in the concentrations of P fractions in the root halves influenced cluster‐root growth and citrate exudation was discounted, because there were no significant differences in insoluble organic P, ester‐P and inorganic P among all ‘deprived’ root halves. The results indicate that cluster‐root proportions and citrate exudation rates were regulated systemically by the P status of the shoot, and that P concentrations in the roots had little influence on growth and citrate exudation of cluster roots in L. albus.     

Secretory hairs in Gentiana and allied genera (Gentianaceae, subtribe Gentianinae) from the Iberian Peninsula

Eleven species from six different sections of the genus Gentiana , as well as one species each of genera Gentianella (G. campestris), Gentianopsis (G. ciliata), Comastoma (C. tenellum) and Swertia (S. perennis) have been studied by light microscopy for the presence of hairs in floral as well as in vegetative parts. Hairs are produced in the calyx and vegetative leaves of all of them, and also in the corollae of the last three species. They fall into two different types: those found in the corolla of Gentianopsis ciliata are non-secretory, while in the rest of the species studied, and also in the calyx and leaves of G. ciliata , they produce a mucilaginous secretion. Calycine and foliar hairs are always produced in the adaxial epidermis at the base of the foliar organ, and are considered as mucilage secreting colleters. The presence of colleters in vegetative organs has not been adequately considered in previous taxonomic accounts, in spite of their presumed significance.     

An anion-selective analogue of the channel-forming peptide alamethicin.

The peptide alamethicin self-assembles to form helix bundle ion channels in membranes. Previous macroscopic measurements have shown that these channels are mildly cation-selective. Models indicate that a source of cation selectivity is a zone of partial negative charge toward the C-terminal end of the peptide. We synthesized an alamethicin derivative with a lysine in this zone (replacing the glutamine at position 18 in the sequence). Microscopic (single-channel) measurements demonstrate that dimeric alamethicin-lysine18 (alm-K18) forms mildly anion-selective channels under conditions where channels formed by the parent peptide are cation-selective. Long-range electrostatic interactions can explain the inversion of ion selectivity and the conductance properties of alamethicin channels.     

Evaluation of histochemical methods for the detection of intracytoplasmic mucin in serous effusions

We have studied 25 serous effusions containing definitive morphologic evidence of adenocarcinoma to evaluate the ability of two mucin stains (Mayer's mucicarmine, D-PAS) to detect intracytoplasmic mucin in both cytologic (cytospin) and corresponding histological (cell block) preparations. Mucicarmine stain was positive in six of 25 (24%) cytospins and 13 of 25 (52%) cell blocks. D-PAS was positive in 19 of 25 (76%) cytospins and 20 of 25 (80%) cell blocks. Eight cases were identified which showed mucicarmine positivity in the cell block but not the corresponding cytospin; prolonging incubation time resulted in a positive mucicarmine in cytospin preparations for seven of these cases. We conclude that: (i) D-PAS is a more sensitive stain for the detection of intracytoplasmic mucin in all preparations; (ii) mucicarmine shows preferential staining for cell blocks; (iii) alterations in the staining protocol may permit mucin detection by mucicarmine staining in cytologic preparations in a significant number of cases.