The Darwinian stickleback Gasterosteus aculeatus: a history of evolutionary studies*

The history of studies on the taxonomy and evolutionary biology of the three‐spined stickleback Gasterosteus aculeatus from the 18th century to the present is reviewed. After the publication of Darwin's Origin of the Species, four important dates, 1925, 1947, 1967 and 2001, are identified as marking major gains in the understanding of the evolution of the diversity in morphological, life‐history, physiological and behavioural traits that characterizes G. aculeatus. The period 1925–1970 led to the identification of the main themes of research: status and adaptive significance of lateral‐plate morphs; inter and intrapopulation trait variation in freshwater resident G. aculeatus and the adaptive significance of the variation. Between 1970 and 2001, these themes were investigated using variation observed particularly along the Pacific coast of the U.S.A. and Canada, notably in the Cook Inlet region of Alaska and the Haida Gwaii Archipelago. Studies on adaptive radiation and reproductive isolation in lacustrine, ecomorph pairs (limnetics and benthics) discovered in the Strait of Georgia region have been particularly productive. From 2001, the application of genomic studies to these problems began to open up the study of the relationships between genotype, phenotype and selective advantage to causal analysis.     

Expected future plague levels in a wildlife host under different scenarios of climate change

We predicted future plague and black-tailed prairie dog dynamics in the North American prairies under different scenarios of climate change. A climate-driven model for the joint dynamic of the host–parasite system was used. Projections for the regional climate were obtained through empirical–statistical downscaling of global climate scenarios generated by an ensemble of global climate models for the recent Fourth Assessment Report by the IPCC. The study shows the uncertainties involved in predicting future regional climate and climate-driven population dynamics, but reveals that unchanged or lower levels of plague, leading to increased black-tailed prairie dog colonies, can be expected. Less plague is particularly expected for scenarios that assume the highest emission of greenhouse gases associated with the greatest projected future warming. Moreover, under high-emission scenarios, decreased probabilities of extremely high numbers of infected colonies are expected, along with decreased probabilities of extremely low total numbers of colonies. The assumed main underlying mechanism is an inhibiting effect of high temperatures on fleas (dispersal vector) and on flea-mediated transmission of the disease-causing bacterium. Our study highlights the importance of using dynamic ecological (here host–parasite) models together with ensembles of climate projections to investigate the responses of populations and parasites to a changed climate.     

Glycyl-L-proline transport in rabbit enterocyte basolateral-membrane vesicles.

The properties of a peptide-transport system in rabbit enterocyte basolateral membrane were examined with glycyl-L-proline as the substrate. Basolateral-membrane vesicles prepared from rabbit proximal intestine were characterized in terms of both purity and orientation. Marker-enzyme assays show that the basolateral-membrane marker, ouabain-sensitive K(+)-activated phosphatase, is enriched 17-fold with respect to the initial homogenate. The activities of enzymes used as markers for other membranes and organelles are low, and contamination of the final membrane fraction with these is minimal. The use of immunoblotting techniques further confirms the absence of brush-border-membrane contamination. Proteins in the basolateral-membrane vesicle preparation gave no cross-reaction with antibodies against the 140 kDa antigen and the Na+/glucose-symport protein, markers specific to the brush-border membrane of the enterocyte. Conversely, antibodies raised against the classical basolateral-membrane marker, the RLA class I histocompatibility complex, reacted strongly with a 43 kDa basolateral-membrane protein. The orientation of the basolateral-membrane vesicles was shown to be predominantly inside-out on determination by two independent criteria. The uptake of [1-14C]glycyl-L-proline by these vesicles is stimulated by the presence of an inwardly directed pH gradient, and this stimulation can be abolished by the proton ionophores carbonyl cyanide p-trichloromethoxyphenylhydrazone (CCCP) and tetrachlorotrifluoromethylbenzimidazole (TTFB). Transport is also inhibited by HgCl2, thimerosal, Na+ and other glycyl dipeptides.     

Effects of experimental warming on arctic willows (Salix spp.): a comparison of responses from the Canadian High Arctic, Alaskan Arctic, and Swedish Subarctic

Three species of dwarf, prostrate willow ( Salix arctica , S. rotundifolia and S. herbacea ) were subjected to experimental summer warming in high arctic Canada, arctic Alaska, and subarctic Sweden, respectively, as part of the International Tundra Experiment. Phenological and growth responses of these species were compared for the second season of the experiment. Stigmas became receptive and pollen dispersal occurred significantly earlier for S. rotundifolia and S. herbacea in the ITEX open-top chambers, but not for S. arctica . Warming had no effect on the timing of seed dispersal, leaf yellowing, or leaf senescence. The length and dry weight of the largest leaves were greater for warmed plants, and was significant for S. rotundifolia . The number of catkins/plot did not differ among species or treatments, but the fruit : flower ratio was reduced in the experimental plots.     

Egg-release behaviour in Antarctic krill

The process of egg release is a complex and crucial step in the life cycle of euphausiids, especially with regards mortality and recruitment success. We examined this process in Antarctic krill (Euphausia superba) in terms of the functioning of the female genital apparatus and associated swimming behaviour. A tethering technique combined with video analysis was used to make observations of three females during the release process. We found eggs were steadily extruded over a period of up to 10 h, during which time the krill released between 1,600 and 4,000 eggs and the ovary reduced by a half in length and a third in height. Eggs were mainly released individually or, less commonly, in batches of between 2 and 4 eggs. Release rates were between 5 and 30 eggs min⁻¹. The steady release of eggs fits well with histological evidence that mature oocytes must pass individually through tight genital ducts with narrow apertures, before coming in to close contact with the sperm plug for fertilisation, and then expulsion from the thelycum as fertilised eggs. During spawning, the female alternated between slow and rapid rates of pleopod beating with egg release occurring at the moment of beat acceleration. At the point of release, the descent of the egg was accelerated through downward beats of the 7th thoracic leg. The cyclic pattern in pleopod beat-rate during spawning may alter swimming performance and contribute to the widely reported sex- and maturity-based biases within krill swarms.     

Colocalization and interaction of the porcine arterivirus nucleocapsid protein with the small nucleolar RNA-associated protein fibrillarin

Porcine reproductive and respiratory syndrome virus (PRRSV) replicates in the cytoplasm of infected cells, but its nucleocapsid (N) protein localizes specifically to the nucleus and nucleolus. The mechanism of nuclear translocation and whether N associates with particular nucleolar components are unknown. In the present study, we show by confocal microscopy that the PRRSV N protein colocalizes with the small nucleolar RNA (snoRNA)-associated protein fibrillarin. Direct and specific interaction of N with fibrillarin was demonstrated in vivo by the mammalian two-hybrid assay in cells cotransfected with the N and fibrillarin genes and in vitro by the glutathione S-transferase pull-down assay using the expressed fibrillarin protein. Using a series of deletion mutants, the interactive domain of N with fibrillarin was mapped to a region of amino acids 30 to 37. For fibrillarin, the first 80 amino acids, which contain the glycine-arginine-rich region (the GAR domain), was determined to be the domain interactive with N. The N protein was able to bind to the full-length genomic RNA of PRRSV, and the RNA binding domain was identified as the region overlapping with the nuclear localization signal situated at positions 41 to 47. These results suggest that the N protein nuclear transport may be controlled by the binding of RNA to N. The PRRSV N protein was also able to bind to both 28S and 18S ribosomal RNAs. The protein-protein interaction between N and fibrillarin was RNA dependent but independent of N protein phosphorylation. Taken together, our studies demonstrate a specific interaction of the PRRSV nucleocapsid protein with the host cell protein fibrillarin in the nucleolus, and they imply a potential linkage of viral strategies for the modulation of host cell functions, possibly through rRNA precursor processing and ribosome biogenesis.