Detrimental effects of latex and cardiac glycosides on survival and growth of first-instar monarch butterfly larvae Danaus plexippus feeding on the sandhill milkweed Asclepias humistrata

1. A novel experimental method was developed to study negative physical and chemical effects of latex and cardiac glycosides on first-instar monarch butterfly larvae in their natural environment in north central Florida. Forceps were used to nibble through the petioles of leaves of the sandhill milkweed Asclepias humistrata, mimicking the behaviour of mature monarch larvae. This notching cut off the supply-of latex to the leaves without significantly reducing either their cardiac glycoside concentration or water content. 2. The mean cardiac glycoside concentration in larvae that fed on intact leaves was nearly two: and a half times greater than in larvae that fed on notched leaves. This was probably because more latex is present in the gut of the larvae that fed on the intact leaves. Supporting this is the fact that the mean concentration of cardiac glycosides in the latex was 34-47 times that in the leaves. 3. Wet weights, dry weights, and growth rates of first-instar larvae that fed on intact leaves over a 72-h period were less than half those of larvae that fed on notched leaves. 4. Mortality due to miring in the latex was 27% on the intact leaves compared with 2% on the notched leaves. 5. Latex, cardiac glycosides, and other as yet undetermined plant factors all have a negative effect on:first-instar larval survival. 6. Video-analyses indicated that ingestion of latex caused the larvae to become cataleptic and increased their chances of being mired on the leaf by the setting latex glue. Dysfunction resulting from latex ingestion may lead to the larvae falling off the plant and being killed by invertebrate predators. 7. The difficulty of neonate monarch larvae surviving on A. humistrata - one of the principal milkweed species fed on each spring as monarchs remigrate from Mexico into the southern U.S.A. - is evidence that a co-evolutionary arms race is operating in this plant-herbivore system.

Phosphate uptake and growth kinetics of Trichodesmium (Cyanobacteria) isolates from the North Atlantic Ocean and the Great Barrier Reef, Australia

We compared inorganic phosphate (P-i) uptake and growth kinetics of two cultures of the diazotrophic cyanobacterium Trichodesmium isolated from the North Atlantic Ocean (IMS101) and from the Great Barrier Reef, Australia (GBRTRLI101). Phosphate-limited cultures had up to six times higher maximum P-i uptake rates than P-replete cultures in both strains. For strain GBRTRLI101, cell-specific P-i uptake rates were nearly twice as high, due to larger cell size, but P-specific maximum uptake rates were similar for both isolates. Half saturation constants were 0.4 and 0.6 muM for P-i uptake and 0.1 and 0.2 muM for growth in IMS101 and GBRTRLI101, respectively. Phosphate uptake in both strains was correlated to growth rates rather than to light or temperature. The cellular phosphorus quota for both strains increased with increasing P-i up to 1.0 muM. The C:P ratios were 340-390 and N:P ratios were 40-45 for both strains under severely P-limited growth conditions, similar to reported values for natural populations from the tropical Atlantic and Pacific Oceans. The C:P and N:P ratios were near Redfield values in medium with >1.0 muM P-i. The North Atlantic strain IMS101 is better adapted to growing on P-i at low concentrations than is GBRTRLI101 from the more P-i-enriched Great Barrier Reef. However, neither strain can achieve appreciable growth at the very low (nanomolar) P-i concentrations found in most oligotrophic regimes. Phosphate could be an important source of phosphorus for Trichodesmium on the Great Barrier Reef, but populations growing in the oligotrophic open ocean must rely primarily on dissolved organic phosphorus sources.

Global assessment of coral bleaching and required rates of adaptation under climate change

Elevated ocean temperatures can cause coral bleaching, the loss of colour from reef-building corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long-term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere-ocean general circulation models (GCMs) to the local conditions around representative coral reefs. Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral Reef Watch bleaching prediction method to the output of a low- and high-climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM-resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985-2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios. The results indicate that bleaching could become an annual or biannual event for the vast majority of the world's coral reefs in the next 30-50 years without an increase in thermal tolerance of 0.2-1.0 degrees C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.

Application of DNA parentage analyses for determining relative growth rates of Penaeus japonicus families reared in commercial ponds

The ability to track large numbers of individuals and families is a key determinant of the power and precision of breeding programs, including the capacity to quantify interactions between genotypes and their environment. Until recently, most family based selective breeding programs for shrimp, and other highly fecund aquaculture species, have been restricted by the number of animals that can be physically tagged and individually selected. Advances in the development of molecular markers, such as microsatellite loci, are now providing the means to track large numbers of individuals and families in commercial production systems. In this study microsatellites, coupled with DNA parentage analyses, were used to determine the relative performance of 22 families of R japonicus reared in commercial production ponds. In the experimental design 6000 post-larvae from each of 22 families, whose maternal parents had been genotyped at 8 microsatellite loci, were stocked into each of four I ha ponds. After 6 months the ponds were harvested and a total of 6000 individuals were randomly weighed from each pond. Mean wet weight of the shrimp from one pond was significantly lower than that of the other three ponds demonstrating a possible pond effect on growth rate. The representation of families in the top 10% of each pond's weight distribution was then determined by randomly genotyping up to 300 individuals from this upper weight class. Parentage analyses based on individual genotypic data demonstrated that some families were over-represented in the top 10% in all ponds, while others were under-represented due to slower growth rates. The results also revealed some weak, but significant, male genotype x environment (G x E) interactions in the expression of shrimp growth for some families. This indicates that G x E effects may need to be factored into future R japonicus selective breeding programs. This study demonstrated the utility of DNA parentage analyses for tracking individual family performance in communally stocked shrimp pond populations and, its application to examining G x E effects on trait expression under commercial culture conditions. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved.

The inhibitory effects of free nitrous acid on the energy generation and growth processes of an enriched Nitrobacter culture

The inhibitory effects of nitrite (NO2-)/free nitrous acid (HNO2-FNA) on the metabolism of Nitrobacter were investigated using a method allowing the decoupling of the growth and energy generation processes. A lab-scale sequencing batch reactor was operated for the enrichment of a Nitrobacter culture. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population was Nitrobacter. Batch tests were carried out to assess the oxygen and nitrite consumption rates of the enriched culture at low and high nitrite levels, in the presence or absence of inorganic carbon. It was observed that in the absence of CO2, the Nitrobacter culture was able to oxidize nitrite at a rate that is 76% of that in the presence of CO2, with an oxygen consumption rate that is 85% of that measured in the presence of CO2. This enabled the impacts of nitrite/FNA on the catabolic and anabolic processes of Nitrobacter to be assessed separately. FNA rather than nitrite was likely the actual inhibitor to the Nitrobacter metabolism. It was revealed that FNA of up to 0.05 mg HNO2-N center dot L-1 (3.4 mu M), which was the highest FNA concentration used in this study, did not have any inhibitory effect on the catabolic processes of Nitrobacter. However, FNA initiated its inhibition to the anabolic processes of Nitrobacter at approximately 0.011 mg HNO2-N center dot L-1 (0.8 mu M), and completely stopped biomass synthesis at a concentration of approximately 0.023 mg HNO2-N center dot L-1 (1.6 mu M). The inhibitory effect could be described by an empirical inhibitory model proposed in this paper, but the underlying mechanisms remain to be revealed.

Evolution of stress deficit and changing rates of seismicity in cellular automaton models of earthquake faults

We investigate the internal dynamics of two cellular automaton models with heterogeneous strength fields and differing nearest neighbour laws. One model is a crack-like automaton, transferring ail stress from a rupture zone to the surroundings. The other automaton is a partial stress drop automaton, transferring only a fraction of the stress within a rupture zone to the surroundings. To study evolution of stress, the mean spectral density. f(k(r)) of a stress deficit held is: examined prior to, and immediately following ruptures in both models. Both models display a power-law relationship between f(k(r)) and spatial wavenumber (k(r)) of the form f(k(r)) similar tok(r)(-beta). In the crack model, the evolution of stress deficit is consistent with cyclic approach to, and retreat from a critical state in which large events occur. The approach to criticality is driven by tectonic loading. Short-range stress transfer in the model does not affect the approach to criticality of broad regions in the model. The evolution of stress deficit in the partial stress drop model is consistent with small fluctuations about a mean state of high stress, behaviour indicative of a self-organised critical system. Despite statistics similar to natural earthquakes these simplified models lack a physical basis. physically motivated models of earthquakes also display dynamical complexity similar to that of a critical point system. Studies of dynamical complexity in physical models of earthquakes may lead to advancement towards a physical theory for earthquakes.

Testing the relationship between morphological and molecular rates of change along phylogenies

Molecular evolution has been considered to be essentially a stochastic process, little influenced by the pace of phenotypic change. This assumption was challenged by a study that demonstrated an association between rates of morphological and molecular change estimated for total-evidence phylogenies, a finding that led some researchers to challenge molecular date estimates of major evolutionary radiations. Here we show that Omland's (1997) result is probably due to methodological bias, particularly phylogenetic nonindependence, rather than being indicative of an underlying evolutionary phenomenon. We apply three new methods specifically designed to overcome phylogenetic bias to 13 published phylogenetic datasets for vertebrate taxa, each of which includes both morphological characters and DNA sequence data. We find no evidence of an association between rates of molecular and morphological rates of change.

Relationships among the three major lineages of the Acari (Arthropoda : Arachnida) inferred from small subunit rRNA: Paraphyly of the parasitiformes with respect to the opilioacariformes and relative rates of nucleotide substitution

We inferred phylogeny among the three major lineages of the Acari ( mites) from the small subunit rRNA gene. Our phylogeny indicates that the Opilioacariformes is the sister-group to the Ixodida+Holothyrida, not the Ixodida+Mesostigmata+Holothyrida, as previously thought. Support for this relationship increased when sites with the highest rates of nucleotide substitution, and thus the greatest potential for saturation with nucleotide substitutions, were removed. Indeed, the increase in support ( and resolution) was despite a 70% reduction in the number of parsimony-informative sites from 408 to 115. This shows that rather than 'noisy' sites having no impact on resolution of deep branches, 'noisy' sites have the potential to obscure phylogenetic relationships. The arrangement, Ixodida+Holothyrida+Opilioacariformes, however, may be an artefact of long-branch attraction since relative-rate tests showed that the Mesostigmata have significantly faster rates of nucleotide substitution than other parasitiform mites. Thus, the fast rates of nucleotide substitution of the Mesostigmata might have caused the Mesostigmata to be attracted to the outgroup in our trees. We tested the hypothesis that the high rate of nucleotide substitution in some mites was related to their short generation times. The Acari species that have high nucleotide substitution rates usually have short generation times; these mites also tend to be more active and thus have higher metabolic rates than other mites. Therefore, more than one factor may affect the rate of nucleotide substitution in these mites.

Formation and growth mechanism of tungsten oxide microtubules

Tungsten oxide microtubules, arrayed in a radial flower-like structure, were synthesized by simply using W powders reacting with Ni(NO3)(2) center dot 6H(2)O at a elevated temperature. The formed microtubules, with lengths more than 100 pin and outer diameters of 1-5 mu m, have irregular open ends, showing clear grooves along the growth direction on the tubule surface. A novel aggregation mechanism based on chemical-vapor-deposit process was proposed to describe the growth process of the synthesized tubules, and the possible mechanism for the arrangement of the radial flower-like morphology was discussed.