Plant Growth Analysis: Allometry, Growth and Interference in Orchardgrass and Timothy

A multiple regression procedure was used to evaluate allometricresponses to stand age and species population densities in monoculturesand mixtures of orchardgrass (Dactylis glomerata L., also knownas cocksfoot) and timothy (Phleum pratense L.). In each speciesthe allometry between shoot dry weight and either leaf areaor tiller number per plant was studied. Population density treatmentsaffected allometry by changing allometric exponents expressingthe ratio of relative growth rates of different plant characteristics.Allometric relationships changed as growth proceeded, and thetwo species differed in their allometric responses to treatments. Plant growth analysis, allometry, competition, Dactylis glomerata L., Phleum pratense L.     

Macro-zooplankter responses to simulated climate warming in experimental freshwater microcosms

1. We report data collected from 48 replicated microcosm communities created to mimic plant‐dominated shallow lake and pond environments. Over a 2‐year period, the microcosms were subjected to warming treatments (continuous 3 °C above ambient and 3 °C above ambient during summer only), a nutrient addition treatment and the presence or absence of fish. We tracked macro‐zooplankter dynamics, censusing cladoceran populations at the species level, copepods at the order level and ostracods as a class. 2. Responses to warming were subtle. Cladoceran diversity and overall abundance were not significantly affected by warming, although measures of community evenness increased. Warming effects on patterns of population trajectories tended to be strongly seasonal and most apparent during periods of pronounced increase. Populations of the prevalent cladocerans, Chydorus sphaericus and Simocephalus vetulus, displayed idiosyncratic patterns, with evidence in the case of S. vetulus for a negative relationship between warming and body‐size at maturity. Copepod populations were reduced in size by warming, but those of ostracods increased. 3. The effects of the nutrient addition and fish treatments were strong and consistent, interacting little with warming effects in statistical models. Zooplankter abundance tended to be the highest in the fish‐free microcosms receiving additional nutrient inputs and lowest when fish were present and no nutrients were added. Both treatments reduced cladoceran diversity and community evenness. 4. We suggest that warming, independently, is unlikely to supplant the effects of changing nutrient loading and fish predation as the major driver of zooplankter dynamics in shallow lakes and ponds. Moreover, in the situations where warming was of significant influence in our experiment, the distinction between summer‐only warming and year‐around warming was blurred. This suggests that warming effects were most pervasive during the summer, at the upper end of the temperature spectrum.     

Properties of microtubule sliding disintegration in isolated tetrahymena cilia

Properties of the sliding disintegration response of demembranated tetrahymena cilia have been studied by measuring the spectrophotomeric response or turbidity of cilia suspensions at a wavelength of 350 nm relative to changes in the dynein substrate (MgATP(2-)) concentration. The maximum decrease in turbidity occurs in 20 muM ATP, and 90 percent of the decrease occurs in approximately 5.9 s. At lower ATP concentrations (1-20 muM), both the velocity and magnitude of the turbidity decreases are proportional to ATP concentration. The velocity data for 20 muM ATP permit construction of a reaction velocity curve suggesting that changes in turbidity are directly proportional to the extent and velocity of disintegration. At ATP concentrations more than 20 muM (50muM to 5mM), both velocity and magnitude of the turbidimetric response are reduced by approximately 50 percent. This apparent inhibition results in a biphasic response curve that may be related to activation of residual shear resistance or regulatory components at the higher ATP concentrations. The inhibitory effects of elevated ATP can be eliminated by mild trypsin proteolysis, whereupon the reaction goes to completion at any ATP concentration. The turbidimetric responses of the axoneme-substrate suspensions are consistent with the extent and type of axoneme disintegration revealed by electron microscope examination of the various suspensions, suggesting that the turbidimetric assay may prove to be a reliable means for assessing the state of axoneme integrity.     

Effects of DIMBOA levels in wheat on the susceptibility of the grain aphid (Sitobion avenue) to deltamethrin

The effects of DIMBOA in cultivars of wheat on aphid antibiosis and tolerance to the insecticide deltamethrin were investigated for the aphid Sitobion auenae. Over 48 hours the mean relative growth rate differed significantly between nymphs of S. auenae reared on wheat cultivars containing different levels of DIMBOA. Nymphs on the resistant cv. Altar showed a significantly greater susceptibility to deltamethrin, with nearly a three-fold increase in the relative toxicity of deltamethrin, compared with the susceptible cv. Dollarbird. The LC₅₀, adjusted for weight, was reduced by 91% for nymphs reared on the high DIMBOA cultivar. The potential for the enhancement of predation under a reduced pesticide régime is discussed in relation to this research.