Damage Function and Economic Threshold for Belonolaimus longicaudatus on Potato

Belonolaimus longicaudatus has long been recognized as a pathogen of potato (Solanum tuberosum). However, a damage function relating expected yield of potato to population densities of B. longicaudatus at planting has not been derived, and the economic threshold for nematicide application is unknown. The objectives of this study were to derive the damage function of B. longicaudatus on potato and to calculate the economic threshold population density. The damage function data for B. longicaudatus on potato were obtained from an ongoing field study to evaluate cropping systems and nematode management practices. Soil samples were collected from experimental field plots, and nematodes were extracted from a 130-cm³ subsample with a centrifugal-flotation method. A damage function was derived by linear regression of potato yield on nematode population density at planting. Based on this derived damage function and published potato prices, the economic threshold for nematicide application was calculated at 2 to 3 B. longicaudatus/130 cm³ of soil, which was near the detection threshold based on methodology used in this study.     

PHASE THREE OF WRIGHT'S SHIFTING-BALANCE THEORY

We examine the third phase of Wright's shifting-balance theory of evolution, the exportation by migration of favorable gene combinations from a fitter subgroup to the rest of the population. The equations are deterministic and are studied numerically. Most of the models studied involve 2–9 loci in which all intermediates between two extreme genotypes are equally unfit. If the favored combination consists of dominant alleles, it is usually fixed even if the migration rate is two orders of magnitude less than the selection coefficient, and if the combination is recessive, one order. Although Wright thought of migration as being essentially one-way, two-way migration does not significantly alter the results. We conclude that, whatever weaknesses the Wright theory may have, they are not in phase III.     

Regulation of product formation during glucose or lactose limitation in nongrowing cells of Streptococcus lactis

Nongrowing cells of Streptococcus lactis in a pH-stat were dosed with sugar to allow fermentation at the maximum rate or were fed a continuous supply of sugar at rates less than the maximum. Under anaerobic conditions, rapid fermentation of either glucose or lactose was essentially homolactic. However, with strain ML3, limiting the fermentation rate diverted approximately half of the pyruvate to formate, acetate, and ethanol. At limiting glucose fermentation rates, cells contained lower concentrations of lactate dehydrogenase activator (fructose 1,6-diphosphate) and pyruvate formate-lyase inhibitors (triose phosphates). As a result, pyruvate formate-lyase and pyruvate dehydrogenase play a greater role in pyruvate metabolism. In contrast to strain ML3, strain ML8 did not give the same diversion of products under anaerobic conditions, and cells retained higher concentrations of the above effector compounds. Lactose metabolism under aerobic conditions resulted in pyruvate excretion by both S. lactis ML3 and ML8. At 7% of the maximum utilization rate, pyruvate accounted for 69 and 35% of the lactose metabolized by ML3 and ML8, respectively. Acetate was also a major product, especially with ML8. The data suggest that NADH oxidase is involved in coenzyme recycling in the presence of oxygen and that pyruvate formate-lyase is inactivated, but the pyruvate dehydrogenase complex still functions.     

The use of cytospin monolayer technique in the cytological diagnosis of vulval and anal disease

This pilot study investigated the use of the non-invasive cytospin monolayer technique in the diagnosis and screening of neoplastic and non-neoplastic vulval disease. Twenty-three patients (age range 34-86 years) attending a vulval disease clinic had brush cytology performed. The samples were prepared with a cytospin monolayer technique and the slides Papanicolaou-stained. Subsequent cytological interpretation and diagnosis were performed without knowledge of the clinical history and correlated with follow-up biopsy histopathology from each patient. Twenty-eight cytospin samples were analysed in total, of which 11 (39%) contained dyskaryotic cells which were assessed and a predicted VIN/AIN grade given. Ten of 11 samples (91%) reported as dyskaryotic had VIN/AIN on biopsy histology. One of 11 samples (9%) was reported as containing occasional squamous cells with borderline nuclear features and, although the corresponding biopsy did not show VIN, basal atypia was reported. One patient had features suggesting invasive carcinoma on cytology which was verified on subsequent biopsy. The 15 cases in which no dyskaryotic cells were identified did not show VIN or AIN on subsequent histology. Two cases were acellular and considered inadequate for cytological interpretation. The cytospin monolayer technique allows the diagnosis of neoplastic from non-neoplastic vulval disease. It is a quick, inexpensive and non-invasive method that may have a role in diagnosis, screening and surveillance of patients.     

Evolving origin-of-transfer sequences on staphylococcal conjugative and mobilizable plasmids—who’s mimicking whom?

In Staphylococcus aureus, most multiresistance plasmids lack conjugation or mobilization genes for horizontal transfer. However, most are mobilizable due to carriage of origin-of-transfer (oriT) sequences mimicking those of conjugative plasmids related to pWBG749. pWBG749-family plasmids have diverged to carry five distinct oriT subtypes and non-conjugative plasmids have been identified that contain mimics of each. The relaxasome accessory factor SmpO, encoded by each conjugative plasmid, determines specificity for its cognate oriT. Here we characterized the binding of SmpO proteins to each oriT. SmpO proteins predominantly formed tetramers in solution and bound 5′-GNNNNC-3′ sites within each oriT. Four of the five SmpO proteins specifically bound their cognate oriT. An F7K substitution in pWBG749 SmpO switched oriT-binding specificity in vitro. In vivo, the F7K substitution reduced but did not abolish self-transfer of pWBG749. Notably, the substitution broadened the oriT subtypes that were mobilized. Thus, this substitution represents a potential evolutionary intermediate with promiscuous DNA-binding specificity that could facilitate a switch between oriT specificities. Phylogenetic analysis suggests pWBG749-family plasmids have switched oriT specificity more than once during evolution. We hypothesize the convergent evolution of oriT specificity in distinct branches of the pWBG749-family phylogeny reflects indirect selection pressure to mobilize plasmids carrying non-cognate oriT-mimics.     

A reassessment of equivalence in yield from marine reserves and traditional fisheries managament

Lively debate continues over whether marine reserves can lead to increased fishery yields when compared to conventional, quota‐based management, apparently driven by differences in the complexity and biological richness of the models being used. In an influential article, Hastings and Botsford used an analytically tractable, spatially implicit, non‐age‐structured model to assert that reserves are typically incapable of increasing yields relative to conventional management, regardless of the type (pre‐ or post‐dispersal, involving adults and/or larvae) or functional form (Ricker or Beverton‐Holt) of density dependence present. A recent numerical (simulation) model by Gaylord et al. concludes that reserves can enhance yield compared to conventional management, a result the authors attribute to their spatially‐explicit evaluation of stage‐structured adult growth, survivability and fecundity; and intercohort (adult‐on‐larvae) post‐dispersal density dependent population dynamics. Here we demonstrate that the increased model complexity is not responsible for the different conclusions. We analyze a spatially‐implicit model without stage structure that incorporates intercohort post‐dispersal density dependence. In this simple model we still find annual extirpation of adult populations outside reserves due to fishing to enhance larval recruitment there, allowing for increased yields compared to those achieved when harvest is evenly spread across the entire domain under conventional management. Consideration of neither spatially‐explicit dispersal dynamics nor stage‐structure in adult demographics is required for reserves to substantially improve yield beyond that attainable under conventional management. In contrast, consideration of within cohort post‐dispersal density dependence among larva during settlement in an otherwise identical model generates equivalence in yield between the two management strategies. These results recast a common message characterizing the relative benefit of reserve versus non‐reserve management from “equivalence at best” to “potentially improved”.