Trends in major and trace elements in decomposing needle litters during a long-term experiment in Swedish forests

The dynamics of 47 major and trace elements were examined during a long-term (up to 8 years between 1979 and 1988) litter decomposition experiment in European boreal and nemoboreal forests (Sweden). Litterbags were incubated in 11 monocultural stands at 10 different locations including seven with Norway spruce (Picea abies (L.) H. Karst.) and four with Scots pine (Pinus sylvestris L.). Principal component analysis and manual scatter plots revealed groups of elements behaving in a similar manner. One group consisted mainly of nutrients, but also of the unessential or toxic elements Rb, Sc, Sr and Tl, and had a general trend with decreasing mass-normalised (mn) concentrations during decomposition. Another group contained mostly unessential and potentially toxic elements, whose concentrations generally increased during the decay process. An exception from this increasing trend was found for Cd, Hf, Hg, Ta and Zr, for which the mn-concentrations increased initially followed by a net leaching from the litter. The influence of sea spray was identified in the early stages of the experiment (in particular for Na), and the impact of the anthropogenic component of atmospheric deposition was clearly visible (e.g. Pb, Cd, Hg). A regional northern Sb source is indicated in the pine, but not in the spruce, needles. The fact that the samples were collected at a time of higher atmospheric metal deposition than at present provides additional information and usefulness of the results.     

Intraspecific variation in resistance of frog eggs to fungal infection

Documenting sources of variation in host viability at pathogen exposure within and among populations is an important task in order to predict host-pathogen evolutionary dynamics. In the present study, we investigated family and population variation in the degree of embryonic infection of the pathogenic fungus Saprolegnia spp., by infecting moor frog (Rana arvalis) eggs from six populations and exposing them to two different temperatures. We found a significant family effect on the degree of Saprolegnia-infection of eggs and embryos, suggesting that there is genetic variation in resistance among embryos, or variation among females in some aspect of maternally induced resistance. Furthermore, infection level differed significantly between temperatures, with most families having more infected eggs in the relatively colder temperature. However, eggs and embryos from the different populations showed different degrees of Saprolegnia-infection in the two temperatures, i.e., there was a significant population × temperature interaction on the proportion of infected eggs. Thus, the degree of Saprolegnia-infection is sensitive to variation at the level of the family, population and environmental conditions, suggesting that responses to fungal outbreaks will vary geographically and will be difficult to predict.     

Evolution of condition-dependent dispersal under kin competition

Dispersers often differ in body condition from non-dispersers. The social dominance hypothesis explains dispersal of weak individuals, but it is not yet well understood why strong individuals, which could easily retain their natal site, are sometimes exposed to risky dispersal. Based on the model for dispersal under kin competition by Hamilton and May, we construct a model where dispersal propensity depends on body condition. We consider an annual species that inhabits a patchy environment with varying patch qualities. Offspring body condition corresponds to the quality of the natal patch and competitive ability increases with body condition. Our main general result balances the fitness benefit from not dispersing and retaining the natal patch and the benefit from dispersing and establishing somewhere else. We present four different examples for competition, which all hint that dispersal of strong individuals may be a common outcome under the assumptions of the present model. In three of the examples, the evolutionarily stable dispersal probability is an increasing function of body condition. However, we found an example where, counterintuitively, the evolutionarily stable dispersal probability is a non-monotone function of body condition such that both very weak and very strong individuals disperse with high probability but individuals of intermediate body condition do not disperse at all.     

Phylogenetics of the genus Scaevola (Goodeniaceae): implication for dispersal patterns across the Pacific Basin and colonization of the Hawaiian Islands

Scaevola, the only genus of Goodeniaceae that has extensively radiated outside of Australia, has dispersed throughout the Pacific Basin, with a few species reaching the tropical coastal areas of the Atlantic and Indian Oceans. Five Australian and most of the non-Australian species are placed in Scaevola section Scaevola based on their fleshy fruits, indeterminate inflorescences, and more arborescent habits. Analyses of ITS sequence data demonstrate that Scaevola is a monophyletic group if S. collaris is excluded and Diaspasis filifolia is included. The genus is Australian in origin, but there have been at least six separate dispersal events from Australia. Four of these dispersals each resulted in single extra-Australian species. The remaining two were followed by radiations that gave rise to large groups, each including one of the widespread strand species, S. taccada and S. plumieri. Remarkably, three of the six dispersals established species on the remote Hawaiian Archipelago, representing at present the largest number of colonizations by any flowering plant genus to these islands.     

Global gene expression analysis by combinatorial optimization

Generally, there is a trade-off between methods of gene expression analysis that are precise but labor-intensive, e.g. RT-PCR, and methods that scale up to global coverage but are not quite as quantitative, e.g. microarrays. In the present paper, we show how how a known method of gene expression profiling (K. Kato, Nucleic Acids Res. 23, 3685-3690 (1995)), which relies on a fairly small number of steps, can be turned into a global gene expression measurement by advanced data post-processing, with potentially little loss of accuracy. Post-processing here entails solving an ancillary combinatorial optimization problem. Validation is performed on in silico experiments generated from the FANTOM data base of full-length mouse cDNA. We present two variants of the method. One uses state-of-the-art commercial software for solving problems of this kind, the other a code developed by us specifically for this purpose, released in the public domain under GPL license.     

Dilute-acid hydrolysis for fermentation of the Bolivian straw material Paja Brava

Hydrolysis of the straw material Paja Brava, a sturdy grass characteristic for the high plains of Bolivia, was studied in order to find suitable conditions for hydrolysis of the hemicellulose and cellulose parts. Dried Paja Brava material was pre-steamed, impregnated with dilute sulfuric acid (0.5% or 1.0% by wt), and subsequently hydrolyzed in a reactor at temperatures between 170 and 230 degrees C for a reaction time between 3 and 10 min. The highest yield of xylose (indicating efficient hydrolysis of hemicellulose) were found at a temperature of 190 degrees C, and a reaction time of 5-10 min, whereas considerably higher temperatures (230 degrees C) were needed for hydrolysis of cellulose. Fermentability of hemicellulose hydrolyzates was tested using the xylose-fermenting yeast species Pichia stipitis, Candida shehatae and Pachysolen tannophilus. The fermentability of hydrolyzates decreased strongly for hydrolyzates produced at temperatures higher than 200 degrees C.     

Use of genome-scale microbial models for metabolic engineering

Metabolic engineering serves as an integrated approach to design new cell factories by providing rational design procedures and valuable mathematical and experimental tools. Mathematical models have an important role for phenotypic analysis, but can also be used for the design of optimal metabolic network structures. The major challenge for metabolic engineering in the post-genomic era is to broaden its design methodologies to incorporate genome-scale biological data. Genome-scale stoichiometric models of microorganisms represent a first step in this direction.     

No female mate choice in Mallee dragon lizards, Ctenophorus fordi

Aspects of sexual selection were studied in a sexually monomorphic Australian agamid lizard (Ctenophorus fordi), in particular with respect to the sensory exploitation hypothesis. In enclosure trials, females were offered the choice between large vs. small males and, in a different experiment, males with blue vs. normal head color. The rationale for these experiments was: firstly, to establish if females actively solicit copulations; secondly, if so, do females solicit copulations non-randomly with respect to male size (because large males may have access to food resources); thirdly, if male coloration is manipulated to match traits of congeneric, conspicuous and sexually dimorphic species, do females show preference for this novel trait (in accordance with the sensory exploitation hypothesis). The corresponding manipulations were also made in a free-living population where the distribution of females on the home ranges of color-manipulated males were monitored. Blue-headed males were accepted as mating partners both in the staged mating trials and in the natural population. Females appeared not to express any kind of active or passive mate choice (rejection); in only one out of 62 trials did a female approach a male herself rather than being approached by the male(s). There was no discrimination against any male category regardless of size or color within a female's receptive period and the manipulation of male head color in the natural population did not result in spatial re-distribution of females. Thus, a female appears to mate unselectively within her receptive period. Rejection behaviors were used only outside of the receptive period to communicate, to all males, that the female is not receptive.