Defence by plant toxins in milkweed bugs (Heteroptera: Lygaeinae) through the evolution of a sophisticated storage compartment

Species of the heteropteran subfamily Lygaeinae possess special subcuticular compartments to store cardiac glycosides, plant‐derived defensive compounds, which they release upon predator attack. In adults of the large milkweed bug, Oncopeltus fasciatus, these storage compartments have previously been described as a modified integument, forming a fluid‐filled dorsolateral space. Here we use three‐dimensional imaging of serial histological sections and synchrotron radiation‐based micro‐computed tomography data to reveal the morphology of these storage compartments and the mechanisms used for the release of a cardiac glycoside‐rich fluid upon attack. Our comparative analysis revealed that the morphology and release mechanism vary among the species investigated. By reconstructing these traits on a recent molecular phylogeny of the Lygaeinae, we demonstrate that the adaptations for the storage and release of cardiac glycosides have evolved in a stepwise manner.     

Starvation endurance in the ant Temnothorax nylanderi depends on group size,body size and access to larvae

Social interactions in animal groups can buffer environmental stress and may enhance survival under unfavourable conditions. In the present study, the impact on starvation endurance of social group, access to larvae and cold shock is studied in the ant Temnothorax nylanderi Förster. Resource sharing is expected to lead to grouped workers surviving longer than isolated ones. Access to larvae may increase longevity if larvae serve as food, or may interfere with survival if they induce caring behaviour in workers. Cold shock serves as a stress factor and a negative influence on survival is expected. The results show that isolated workers have a shorter lifespan than grouped workers, which in turn live for a shorter period than grouped workers with larvae. Beneficial ‘group effects’ contribute to group survival and the presence of larvae increases worker survival because the workers presumably feed on the larvae. Thus, improved starvation endurance may reflect an additional benefit of a social lifestyle. Moreover, variance in survival is lower for grouped workers than for isolated workers: group members not only demonstrate improved survival, but also smaller within‐group differences. Although a negative influence on survival is the expected outcome, this type of thermal stress is found to have no direct impact on starvation endurance other than moderating the differences between isolated and grouped workers.     

Czapek-Dox agar containing iprodione and dicloran as a selective medium for the isolation of Fusarium species

A new selective medium for Fusarium species has been developed using Czapek-Dox agar (CZ) containing the fungicides iprodione (3 mg/1) and dicloran (2 mg/1). This new medium (CZID) is selective against numerous species of Alternaria, Epicoccum, Penicillium and mucoraceous fungi. CZID was compared with CZ using samples of barley, malt, sorghum, bean and pea. Fusarium species produced large and easily recognizable colonies on CZID while isolates of Alternaria, Epicoccum and Rhizopus were significantly restricted on CZID compared with their growth on CZ. The use of CZID thus facilitates the isolation and subculturing of Fusarium species.     

Microsatellite variability in wild populations of the house mouse is not influenced by differences in chromosomal recombination rates

Differences in recombination rates along the chromosomes can influence the evolution of neutral loci via hitchhiking effects. Generally, these effects should be stronger in regions of low recombination than in regions of high recombination. Detailed information on physical and genetic maps in the house mouse now allows an assessment of the correlation between neutral variability and recombination rates at given chromosomal regions. We chose 29 microsatellite loci from chromosomal regions which show differences in recombination rates and tested their variability in samples from five wild populations of Mus musculus musculus and M. m. domesticus . Our results provide no evidence for a correlation between microsatellite variability and recombination rates. This suggests that the high average mutation rate of microsatellites in mammals counterbalances the effects of long-range hitchhiking in the mouse genome.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 629–635.     

Annual basal area increment and growth duration of Pinus taeda in response to eight years of free-air carbon dioxide enrichment

Rising CO₂ is predicted to increase forest productivity, although the duration of the response and how it might be altered by variation in rainfall, temperature and other environmental variables are not well understood. We measured the basal area of rapidly growing Pinus taeda trees exposed to free‐air CO₂ enrichment for 8 years and used these measurements to estimate monthly and annual growth. We used these measurements in a statistical model to estimate the start and end of growth in each year. Elevated CO₂ increased the basal area increment (BAI) of trees by 13–27%. In most years, exposure to elevated CO₂ increased the growth rate but not the duration of the active growth period. With the exception of 1 year following an extreme drought and a severe ice storm, BAI was positively correlated with the amount of rainfall during the active growth period. The interannual variation in the relative enhancement of BAI caused by elevated CO₂ was strongly related to temperature and rainfall, and was greatest in years with high vapor pressure deficit. There was no evidence of a systematic reduction in the stimulation of growth during the first 8 years of this experiment, suggesting that the hypothesized limitation of the CO₂ response caused by nitrogen availability has yet to occur.     

Near-term impacts of elevated CO2, nitrogen and fungal endophyte-infection on Lolium perenne L. growth, chemical composition and alkaloid production

Carbon dioxide has been rapidly accumulating in the atmosphere and is expected to continue to do so. This accumulation is presumed to have important direct effects on plant growth. The interacting affects of a small increase in CO₂ concentration (466 p.p.m., approximately 30% increase from current ambient conditions), nitrogen fertilization and fungal endophyte (Neotyphodium lolii) infection on the growth and chemical composition of perennial ryegrass (Lolium perenne) were investigated. It was found that dry mass production was approximately 50% greater under elevated CO₂ than under ambient CO₂, but only in conditions of high soil N. High molecular weight carbohydrates and total carbohydrates (LMW + HMW CHO) depended on an interaction between CO₂ and endophyte infection. Infected plants contained significantly more carbohydrate than endophyte-free plants, and the difference was greatest in ambient CO₂ conditions. Protein concentrations were also influenced by the interaction between CO₂ and endophyte-infection. Endophyte-free plants had 40% lower concentrations of soluble protein under elevated CO₂ than under ambient CO₂, but this CO₂ effect on soluble protein was largely absent in endophyte-infected plants. CO₂, endophyte-infection and nitrogen interacted to influence the total chlorophyll concentration of the grass such that chlorophyll concentration was always lower in elevated CO₂ but this decline was much greater in endophyte-free plants, particularly in conditions of high soil N. In the endophyte-infected plants, the concentrations of the pyrrolopyrazine alkaloid peramine depended on the interaction between CO₂ and N fertilization such that peramine concentrations declined with increasing N at ambient CO₂ but remained roughly constant across N levels at elevated CO₂. A similar pattern was seen for the ergot alkaloid ergovaline. The biochemical responses of perennial ryegrass to elevated CO₂ are clearly modified by the presence of endophytic fungi.