Climate and Demography Dictate the Strength of Predator-Prey Overlap in a Subarctic Marine Ecosystem.

There is growing evidence that climate and anthropogenic influences on marine ecosystems are largely manifested by changes in species spatial dynamics. However, less is known about how shifts in species distributions might alter predator-prey overlap and the dynamics of prey populations. We developed a general approach to quantify species spatial overlap and identify the biotic and abiotic variables that dictate the strength of overlap. We used this method to test the hypothesis that population abundance and temperature have a synergistic effect on the spatial overlap of arrowtooth flounder (predator) and juvenile Alaska walleye pollock (prey, age-1) in the eastern Bering Sea. Our analyses indicate that (1) flounder abundance and temperature are key variables dictating the strength of flounder and pollock overlap, (2) changes in the magnitude of overlap may be largely driven by density-dependent habitat selection of flounder, and (3) species overlap is negatively correlated to juvenile pollock recruitment when flounder biomass is high. Overall, our findings suggest that continued increases in flounder abundance coupled with the predicted long-term warming of ocean temperatures could have important implications for the predator-prey dynamics of arrowtooth flounder and juvenile pollock. The approach used in this study is valuable for identifying potential consequences of climate variability and exploitation on species spatial dynamics and interactions in many marine ecosystems.

Functional responses and scaling in predator-prey interactions of marine fishes: contemporary issues and emerging concepts.

Predator-prey interactions are a primary structuring force vital to the resilience of marine communities and sustainability of the world's oceans. Human influences on marine ecosystems mediate changes in species interactions. This generality is evinced by the cascading effects of overharvesting top predators on the structure and function of marine ecosystems. It follows that ecological forecasting, ecosystem management, and marine spatial planning require a better understanding of food web relationships. Characterising and scaling predator-prey interactions for use in tactical and strategic tools (i.e. multi-species management and ecosystem models) are paramount in this effort. Here, we explore what issues are involved and must be considered to advance the use of predator-prey theory in the context of marine fisheries science. We address pertinent contemporary ecological issues including (1) the approaches and complexities of evaluating predator responses in marine systems; (2) the 'scaling up' of predator-prey interactions to the population, community, and ecosystem level; (3) the role of predator-prey theory in contemporary fisheries and ecosystem modelling approaches; and (4) directions for the future. Our intent is to point out needed research directions that will improve our understanding of predator-prey interactions in the context of the sustainable marine fisheries and ecosystem management.

Comparative analysis of marine ecosystems: workshop on predator-prey interactions.

Climate and human influences on marine ecosystems are largely manifested by changes in predator-prey interactions. It follows that ecosystem-based management of the world's oceans requires a better understanding of food web relationships. An international workshop on predator-prey interactions in marine ecosystems was held at the Oregon State University, Corvallis, OR, USA on 16-18 March 2010. The meeting brought together scientists from diverse fields of expertise including theoretical ecology, animal behaviour, fish and seabird ecology, statistics, fisheries science and ecosystem modelling. The goals of the workshop were to critically examine the methods of scaling-up predator-prey interactions from local observations to systems, the role of shifting ecological processes with scale changes, and the complexity and organizational structure in trophic interactions.

Climate change causing phase transitions of walleye pollock (Theragra chalcogramma) recruitment dynamics.

In 1976 the North Pacific climate shifted, resulting in an average increase of the water temperature. In the Gulf of Alaska the climate shift was followed (i.e. early 1980s) by a gradual but dramatic increase in the abundance of groundfish species that typically prey on pre-recruitment stages of walleye pollock. In the present study we used a previously parameterized model to investigate the effect of these climate and biological changes on the recruitment dynamics of walleye pollock in the Gulf of Alaska. Simulations covered the 1970-2000 time frame and emphasized the medium-to-long temporal scale (i.e. about 5-10 years) of environmental variability. Results showed that during periods characterized by high sea surface temperature and high predation on juvenile pollock stages, recruitment variability and magnitude were below average, and recruitment control was delayed to stages older than the 0-group. Opposite dynamics (i.e. high abundance and variability, and early recruitment control) occurred during periods characterized by low temperature and predation. These results are in general agreement with empirical observations, and allowed us to formulate causal explanations for their occurrence. We interpreted the delay of recruitment control and the reduction of variability as an effect of increased constraint on the abundance of post age-0 stages, in turn imposed by high density dependence and predation mortality. On the other hand, low density-dependence and predation favoured post age-0 survival, and allowed for an unconstrained link between larval and recruitment abundance. Our findings demonstrate that the dominant mechanisms of pollock survival change over contrasting climate regimes. Such changes may in turn cause a phase transition of recruitment dynamics with profound implications for the management of the entire stock.

Development of a method to quantify gene expression levels for glycosylation pathway genes in chinese hamster ovary cell cultures.

Changes in protein glycosylation owing to changes in environmental conditions are not well understood. To better understand these relationships, methods to quantify controlling factors are needed. Because enzymes are translated from genes, the ability to quantify gene expression levels for glycosylation-related enzymes would be advantageous. We developed quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) assays to monitor gene expression in Chinese hamster ovary (CHO) cells for five terminal glycosylation genes. The five enzymes were sialidase, a putative alpha2,3-sialyltransferase, beta1,4-galactosyltransferase, cytosine monophosphate-sialic acid transporter, and uracil diphosphate-galactosyl transporter. Four of these CHO cell genes were publicly available from GenBank; however, the alpha2,3-sialyltransferase gene for Cricetulus griseus (CHO cell species) was not available and, therefore, was sequenced as a part of this work. The qRT-PCR primers and probes (based on the TaqMan chemistry) were designed and validated for these five genes. The gene expression profiles were obtained for CHO cells producing the recombinant interleukin-4/13 cytokine trap molecule in batch reactors.

Gene-expression profiles for five key glycosylation genes for galactose-fed CHO cells expressing recombinant IL-4/13 cytokine trap.

Recombinant protein glycosylation profiles have been shown to affect the in-vivo half-life, and therefore the efficacy and economics, for many therapeutics. While much research has been conducted correlating the effects of various stimuli on recombinant protein glycosylation characteristics, relatively little work has examined glycosylation-related gene-expression profiles. In this study, the effects of galactose feeding on the gene-expression profiles for five key glycosylation-related genes were determined for Chinese hamster ovary cells producing a recombinant IL-4/13 cytokine trap fusion. The genes investigated were sialidase, a putative alpha2,3-sialyltransferase, CMP-sialic acid transporter, beta1,4-galactosyltransferase, and UDP-galactosyltransferase. Additionally, the sialic acid content (sialylation) of the recombinant protein was examined. The peak sialic acid content of the IL-4/13 cytokine trap fusion protein was observed to be similar for the control and galactose-fed cultures. The gene-expression profiles for four of the glycosylation genes were observed to be sensitive to the glucose concentration and not significantly different for the control and galactose-fed cultures prior to glucose depletion. However, the sialidase gene-expression profiles were different for the control and galactose-fed cultures. The sialidase gene-expression profile increased significantly for the galactose-fed cultures prior to glucose depletion, whereas for the control cultures, the sialidase gene-expression profiles did not increase until the late stationary phase. The intracellular sialidase enzyme activity decreased exponentially with time for the control cultures; however, for the galactose-fed cultures, the intracellular sialidase enzyme activity decreased initially and then remained relatively high compared to the control cultures. These results indicate that the galactose feeding may increase the potential for desialylation, which offsets any improvements in the sialylation rate due to increased substrate levels. Thus, galactose feeding is an unnecessary expense for the production of the IL-4/13 cytokine trap fusion protein in a batch process.