Do invasive ants respond more strongly to carbohydrate availability than co‐occurring non‐invasive ants? A test along an active Anoplolepis gracilipes invasion front

Invasions by non‐native insects can have important ecological impacts, particularly on island ecosystems. However, the factors that promote the success of invaders relative to co‐occurring non‐invasive species remain unresolved. For invasive ants, access to carbohydrate resources via interactions with both extrafloral nectary‐bearing plants and honeydew‐excreting insects may accelerate the invasion process. A first step towards testing this hypothesis is to determine whether invasive ants respond to variation in the availability of carbohydrate resources, and whether this response differs from that of co‐occurring, non‐invasive ants. We investigated the effect of carbohydrate subsidies on the short‐term foraging and hemipteran‐tending behaviours of the invasive ant Anoplolepis gracilipes (Formicidae) and co‐occurring ant species on an extrafloral nectary‐bearing plant by experimentally manipulating carbohydrate levels and tracking ant recruitment. We conducted experiments in 2 years at two sites: one site was invaded by A. gracilipes prior to 2007 and the other became invaded during the course of our study, allowing pre‐ (2007) and post‐invasion (2009) comparisons. Short‐term increases in carbohydrate availability increased the density of A. gracilipes workers on plants by as much as 400% and reduced tending of honeydew‐excreting insects by this species by up to 89%, with similar responses across years. In contrast, ants at the uninvaded site in 2007 showed a weak and non‐significant forager recruitment response. Across all sites, A. gracilipes workers were the only ants that responded to carbohydrate manipulations in 2009. Furthermore, ant–carbohydrate dynamics at a site newly invaded by A. gracilipes quickly diverged from dynamics at uninvaded sites and converged on those of the site with an established invasion. These findings suggest that carbohydrate resources may be particularly important for A. gracilipes invasions, and underscore the importance of species interactions, particularly putative mutualisms, in facilitating exotic species invasions.     

The influence of plant age on resistance of radish to cabbage root fly egg-laying

Cabbage root fly ( Delia brassicae ) egg-laying around radish plants ranging in age from newly emerged seedlings to plants with flowering shoots was studied in the field and laboratory. The attractiveness of radish changed with age, one peak in egg-laying occurring just before plants were of marketable size and further peaks as they produced flowering shoots. The pattern of egg-laying was similar for the six radish cultivars tested, both in the field and laboratory, irrespective of whether flies did or did not have a choice of plants of different ages. At any one age, there was no correlation between egg-laying and plant size. Selection within radish cultivars for the extremes of the range of egg-laying preference appeared to alter the cycle of attractiveness of different radish stocks to cabbage root fly, the response being influenced by environmental conditions.     

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water‐limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (θ), soil respiration (R_s), along with leaf‐level photosynthesis (A_net), predawn leaf water potential (Ψ_pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C₄ grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil θ which corresponded with a significant increase in R_s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.     

Cyclic AMP increases the Adhesion of Fibroblasts to Substratum

THE interaction between the cell surface and the substratum is very important in determining several characteristics of cells growing in tissue culture. Transformed cells are less adherent to the substratum than untransformed cells¹ and this reduced interaction with the substratum may be responsible for abnormal properties such as the loss of contact or density dependent inhibition of growth² and the ability to form colonies in agar and to grow in suspension culture.     

The effect of red light in the high irradiance reaction of phytochrome:

Abstract. A proposal has recently been made (Johnson & Tasker, 1979) that phytochrome acts through the multiplicative effect of two components of the phytochrome system, only one of them being Pfr and the other a product of the photoconversion reaction Pr → Pfr . It has been shown previously that HIR action spectra based on this assumption show a good resemblance to the observed responses with the possible exception of the red region of the spectrum. There, a greater response is predicted than is often observed and fluence rate dependency is predicted, on which matter there is disagreement in the literature.
The experiments reported here show that, because chlorophyll is formed in red light but not in far-red, chlorophyll screening lowers the effective fluence rate in red light with respect to phytochrome. When such screening is eliminated the observed responses show strong fluence rate dependency, as predicted. Evidence is also presented to support the conclusion that the two proposed effectors must act together multiplicatively.