Increased abundance of native and non-native spiders with habitat fragmentation

Habitat fragmentation and invasive species often contribute to the decline of native taxa. Since the penetration of non‐native species into natural habitat may be facilitated by habitat fragmentation, it is important to examine how these two factors interact. Previous research documented that, in contrast to most other arthropod taxa, spiders increased in density and morphospecies richness with decreasing fragment area and increasing fragment age (time since insularization) in urban habitat fragments in San Diego County, California, USA. We tested whether a specific mechanism, an increase in non‐native species with fragmentation, is responsible for this pattern. We found that both native and non‐native taxa contributed to the pattern. Abundance of native spiders per pitfall trap sample increased significantly with decreasing fragment size (i.e. a negative density–area relationship) and abundance of non‐natives increased significantly with increasing fragment age. The proportion of non‐native individuals also increased significantly with age. One non‐native species, Oecobius navus, comprised the majority of non‐native individuals (82.2%) and a significant proportion of total individuals (25.1%). Richness of spider families per sample (family density) increased with fragment age due to an increase in the occurrence of non‐natives in older fragments, however, native family richness did not vary with age or area. Due to increasing dominance by non‐native and some native families, family evenness declined with decreasing fragment size and increasing fragment age. Native and non‐native abundance covaried positively arguing against strong negative interactions between the two groups. O. navus had a strong positive association with another common non‐native arthropod, the Argentine ant (Linepitheme humile), suggesting a possible direct interaction. In contrast, abundance of native spiders was negatively correlated with Argentine ant abundance. We hypothesize that fragmentation in this semiarid habitat increases productivity in smaller and older fragments enhancing the density of both native and non‐native taxa.     

Role of foliar hemibiotrophic and fruit resistance in anthracnose‐resistant strawberry genotypes for annual hill plasticulture systems

Anthracnose fruit rot (AFR) caused by Colletotrichum acutatum is one of the most devastating diseases of strawberry (Fragaria × ananassa) in plasticulture systems in the Southeast US. Host resistance offers the best option to limit crop losses in both nursery and fruiting fields. To evaluate levels of anthracnose resistance and elucidate the role of foliar and fruit resistance in overall field AFR resistance, we tested 14 strawberry genotypes including numerous selections from the North Carolina State University strawberry breeding programme. Inoculations of plug plants with three representative C. acutatum isolates prior to field‐set indicated that the commercially standard cultivar Chandler was highly susceptible, with an average fruit rot incidence of over 72% the following spring. In contrast, breeding lines such as NC C99‐13 and NC C02‐63 showed superior resistance with AFR incidence values of 23.6% and 11.1%, respectively, and showed superior marketable yields. An average hemibiotrophic infection (HI) severity on foliage (percent leaf area covered with acervular growth after paraquat treatment and incubation) did not correlate (r = 0.57) well with in vitro AFR severity on detached fruit, indicating different mechanisms may be operative for resistance to foliar HI and fruit rot resistance. Multiple regression analysis indicated that in vitro fruit rot resistance expressed by lesion diameter and severity of foliar hemibiotrophic infections may be utilized to predict field AFR incidence. Strawberry genotypes bred for resistance against both fruit rot and foliar HI could be effectively selected by using rank‐sum classification methods and this process offers an effective strategy to advance selections for superior AFR field resistance.     

A CAL program to teach the basic principles of genetic engineering—a change from the traditional approach

An interactive computer-assisted learning program written for the BBC microcomputer to teach the basic principles of genetic engineering is described. The pro-gram makes extensive use of colour, graphics, and animation and is aimed at A-level students of biology. Students select, from a menu, to investigate one of a number of identified processes involved in the overall production of a protein, each of which is treated as a self-contained unit. An assessment of how much of the factual information the student has learned is provided in the form of a computer 'adventure game' which is not only challenging but fun to play. Briefly, the student is led into an imaginary laboratory and must choose from shelves those essential items (e.g. reagents, starting materials, techniques) to progress through several stages culminating in the production of genetically engineered bacteria capable of producing a specific protein.     

Burkholderia cepacia Complex as Human Pathogens

Although sporadic human infection due to Burkholderia cepacia has been reported for many years, it has been only during the past few decades that species within the B. cepacia complex have emerged as significant opportunistic human pathogens. Individuals with cystic fibrosis, the most common inherited genetic disease in Caucasian populations, or chronic granulomatous disease, a primary immunodeficiency, are particularly at risk of life-threatening infection. Despite advances in our understanding of the taxonomy, microbiology, and epidemiology of B. cepacia complex, much remains unknown regarding specific human virulence factors. The broad-spectrum antimicrobial resistance demonstrated by most strains limits current therapy of infection. Recent research efforts are aimed at a better appreciation of the pathogenesis of human infection and the development of novel therapeutic and prophylactic strategies.     

Are There Circadian Variations of Polymorphonuclear Phagocytosis in Man?

Eleven male subjects were investigated to detect a possible circadian rhythm of the polymorphonuclear phagocytosis. Both cell activity and serum opsonins were studied for numerical detection of granulocytes having ingested at least one particle and for the mean number of ingested particles per cell. No significant temporal differences (ANOVA and cosinor) were found.     

Preparation and partial characterization of a Lactobacillus lactis bacteriophage

High-titer lysates of a bacteriophage active against Lactobacillus lactis were prepared from liquid cultures as well as from areas of confluent lysis in soft-agar overlayers. Phage concentration and purification were accomplished by means of polyethylene glycol precipitation, differential centrifugation, and cesium chloride gradient centrifugation. The buoyant density of this phagein cesium chloride was 1.4795 g/ml. Characterization of phage growth cycle by one-step growth experiments under optimal conditions showed that the latent period was about 120 min, that the rise period lasted approx. 130 min, and that the average burst-size was about 80.Abbreviations p.f.u. plaque forming units - m.o.i. multiplicity of infection - PEG polyethylene glycol - SSC standard saline citrate solution