A three-species model explaining cyclic dominance of Pacific salmon

The four-year oscillations of the number of spawning sockeye salmon (Oncorhynchus nerka) that return to their native stream within the Fraser River basin in Canada are a striking example of population oscillations. The period of the oscillation corresponds to the dominant generation time of these fish. Various—not fully convincing—explanations for these oscillations have been proposed, including stochastic influences, depensatory fishing, or genetic effects. Here, we show that the oscillations can be explained as an attractor of the population dynamics, resulting from a strong resonance near a Neimark Sacker bifurcation. This explains not only the long-term persistence of these oscillations, but also reproduces correctly the empirical sequence of salmon abundance within one period of the oscillations. Furthermore, it explains the observation that these oscillations occur only in sockeye stocks originating from large oligotrophic lakes, and that they are usually not observed in salmon species that have a longer generation time.     

Solution structure by nuclear magnetic resonance of the two lantibiotics 97518 and NAI‐107

Lantibiotics 97518 and NAI‐107, produced by the related genera Planomonospora and Microbispora respectively, are members of a family of nisin‐related compounds. They represent promising compounds to treat infections caused by multiresistant Gram‐positive pathogens. Despite their similar structure and a similar antibacterial spectrum, the two lantibiotics exhibit significant differences in their potency. To gain an insight into the structure–activity relationships, their conformational properties in solution are determined by NMR. After carrying out an NOE analysis of 2D ¹H NMR spectra, high‐resolution 3D structures are determined using molecular dynamics simulations. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Life-stage specific environments in a cichlid fish: implications for inducible maternal effects

Through environmentally induced maternal effects females may fine-tune their offspring’s phenotype to the conditions offspring will encounter after birth. If juvenile and adult ecologies differ, the conditions mothers experienced as juveniles may better predict their offspring’s environment than the adult females’ conditions. Maternal effects induced by the environment experienced by females during their early ontogeny should evolve when three ecological conditions are met: (1) Adult ecology does not predict the postnatal environmental conditions of offspring; (2) Environmental conditions for juveniles are correlated across successive generations; and (3) Juveniles occasionally settle in conditions that differ from the juvenile habitat of their mothers. By combining size-structured population counts, ecological surveys and a genetic analysis of population structure we provide evidence that all three conditions hold for Simochromis pleurospilus, a cichlid fish in which mothers adjust offspring quality to their own juvenile ecology. In particular we show (1) that the spatial niches and the habitat quality differ between juveniles and adults, and we provide genetic evidence (2) that usually fish of successive generations grow up in similar habitats, and (3) that occasional dispersal in populations with a different habitat quality is likely to occur. As adults of many species cannot predict their offspring’s environment from ambient cues, life-stage specific maternal effects are likely to be common in animals. It will therefore be necessary to incorporate parental ontogeny in the study of parental effects when juveniles and adults inhabit different environments.     

Molecular genetic study of human arginase deficiency

We have explored the molecular pathology in 28 individuals homozygous or heterozygous for liver arginase deficiency (hyperargininemia) by a combination of Southern analysis, western blotting, DNA sequencing, and PCR. This cohort represents the majority of arginase-deficient individuals worldwide. Only 2 of 15 homozygous patients on whom red blood cells were available had antigenically cross-reacting material as ascertained by western blot analysis using anti-liver arginase antibody. Southern blots of patient genomic DNAs, cut with a variety of restriction enzymes and probed with a near-full-length (1,450-bp) human liver arginase cDNA clone, detected no gross gene deletions. Loss of a TaqI cleavage site was identified in three individuals: in a homozygous state in a Saudi Arabian patient at one site, at a different site in homozygosity in a German patient, and in heterozygosity in a patient from Australia. The changes in the latter two were localized to exon 8, through amplification of this region by PCR and electrophoretic analysis of the amplified fragment after treatment with TaqI; the precise base changes (Arg291X and Thr290Ser) were confirmed by sequencing. It is interesting that the latter nucleotide variant (Thr290Ser) was found to lie adjacent to the TaqI site rather than within it, though whether such a conservative amino acid substitution represents a true pathologic mutation remains to be determined. We conclude that arginase deficiency, though rare, is a heterogeneous disorder at the genotypic level, generally encompassing a variety of point mutations rather than substantial structural gene deletions.     

Piecing together the transport pathway of aliphatic glucosinolates

Glucosinolates are sulfur-rich secondary metabolites characteristic of the Brassicales order. Transport of glucosinolates was suggested more than 30 years ago through a number of studies which indicated that glucosinolates are produced in maternal tissue and subsequently transported to the seed. These observations laid the foundation for numerous studies on glucosinolate transport which have provided a wealth of information on biochemical properties of glucosinolate transport, source–sink relationships between organs and on the transport routes of glucosinolates. However, most of the conclusions and hypotheses proposed in these studies have not been discussed in context of each other to provide a complete overview of the current state of knowledge on glucosinolate transport. In this review, we are thus piecing together the glucosinolate pathway by presenting and critically analyzing all data on glucosinolate research. Furthermore, the data on glucosinolate transport is considered in the light of the newest findings on glucosinolate synthesis and distribution. The aim is to provide a comprehensive and updated set of hypotheses which may prove useful in directing future research on glucosinolate transport.     

Sponge communities of the Antarctic Peninsula: influence of environmental variables on species composition and richness

Sponge communities on the Antarctic continental shelf currently represent one of the most extensive sponge grounds in the world, and all sponge classes are known to occur in the Southern Ocean. Main objectives of this study conducted at the tip of the Antarctic Peninsula were (1) to identify all sampled sponges and (2) to investigate whether the species composition and species richness of Southern Ocean sponge communities in the area of the Antarctic Peninsula are significantly influenced by environmental variables. The studied material originated from 25 AGT catches and was sampled during the expedition ANT-XXIX/3 of RV Polarstern. Samples were collected in three large-scale areas in the vicinity of the Antarctic Peninsula: Bransfield Strait, Drake Passage and Weddell Sea. The following six environmental variables were measured from bottom water samples (except for sea-ice cover): depth (m), light transmission (%), oxygen (µmol/kg), salinity, sea-ice cover (%) and temperature (°C). Two hundred and sixty-three sponge samples were analyzed, and 81 species of 33 genera from all Porifera classes (Calcarea, Demospongiae, Hexactinellida and Homoscleromorpha) were identified. Total numbers of sponge species per sample station ranged from 1 to 29. A detrended correspondence analysis and a backward-stepwise model selection were performed to check whether species composition and richness were significantly influenced by environmental variables. The analyses revealed that none of the measured environmental variables significantly influenced species composition but that species richness was significantly influenced by (1) temperature and (2) the combination of temperature and depth. Results of this study are of crucial importance for development, performance and assessment of future protection strategies in case of ongoing climatic changes at the Antarctic Peninsula.