Spread of exotic plants in the landscape: the role of time,growth habit,and history of invasiveness

We investigated the relative contribution of minimum residence time, growth habit, and history of invasiveness to the spread of exotic plants in Michigan and California. Our data include minimum residence time as estimated by earliest herbarium collection records, growth habit, and history of invasiveness for over 2000 records from two herbaria (MI = 943, CA = 1131). Our data support the hypothesis that minimum residence time is highly associated with landscape spread, explaining 39–44% of variation in the number of counties invaded. In contrast, growth habit and history of invasiveness explained a small fraction of variation in spread in California but not Michigan. Over the past 30 years exotic plant species frequently became established in Michigan and California (≥50 species per decade), suggesting that many more species will become invasive over time. There is an urgent need to develop effective policies for exotic plant management. In both states we found significant positive correlations between minimum residence time and species occurrence on state invasive plant lists. Further, we found historical information on the pest status of a plant species introduced into a similar environment to be relevant in determining landscape spread of exotic plants. We conclude that efforts to predict exotic species spread based on biological characteristics may have limited success, and instead endorse pest risk analysis for proposed new imports coupled with rapid detection and early response for unintended and unwanted introductions.     

Variations among cell lines in the synthesis of sphingolipids in de novo and recycling pathways

There are several pathways for the incorporation of sugars into glycosphingolipids (GSL). Sugars can be added to ceramide that contains sphinganine (dihydrosphingosine) synthesized de novo (pathway 1), to ceramide synthesized from sphingoid bases produced by hydrolysis of sphingolipids (pathway 2), and into GSL recycling from the endosomal pathway through the Golgi (pathway 3). We reported previously the surprising observation that SW13 cells, a human adrenal carcinoma cell line, synthesize most of their GSL in pathway 2. We now present data on the synthesis of GSL in four additional cell lines. Approximately 90% of sugar incorporation took place in pathway 2, and 10% or less in pathway 1, in human foreskin fibroblasts and NB41A3 neuroblastoma cells. In contrast, approximately 50-90% of sugar incorporation took place in pathway 1 in C2C12 myoblasts. The C2C12 cells divide more rapidly and synthesize 10-14 times as much GSL as the other three cell lines. In C6 glioma cells, approximately 30% of sugar incorporation occurred in pathway 1 and 60% in pathway 2. There was no relation between the utilization of pathways for GSL and sphingomyelin synthesis in foreskin fibroblasts and C2C12 cells. In both cells pathways 1 and 2 each accounted for 50% of incorporation of choline into sphingomyelin. In five of the six cell lines that we have studied, most GSL synthesis takes place in pathway 2. We suggest that when the need for synthesis is relatively low, as in slowly dividing cells, GSL are synthesized predominantly from sphingoid bases salvaged from the hydrolytic pathway. When cells are dividing more rapidly, the need for increased synthesis is met by upregulating the de novo pathway.      

Nearest Neighbor Networks: clustering expression data based on gene neighborhoods

Background  

The availability of microarrays measuring thousands of genes simultaneously across hundreds of biological conditions represents an opportunity to understand both individual biological pathways and the integrated workings of the cell. However, translating this amount of data into biological insight remains a daunting task. An important initial step in the analysis of microarray data is clustering of genes with similar behavior. A number of classical techniques are commonly used to perform this task, particularly hierarchical and K-means clustering, and many novel approaches have been suggested recently. While these approaches are useful, they are not without drawbacks; these methods can find clusters in purely random data, and even clusters enriched for biological functions can be skewed towards a small number of processes (e.g. ribosomes).     

Surface Acidity and Solid-State Compatibility of Excipients with an Acid-Sensitive API: Case Study of Atorvastatin Calcium

The objectives of this study were to measure the apparent surface acidity of common excipients and to correlate the acidity with the chemical stability of an acid-sensitive active pharmaceutical ingredient (API) in binary API-excipient powder mixtures. The acidity of 26 solid excipients was determined by two methods, (i) by measuring the pH of their suspensions or solutions and (ii) the pH equivalent (pH_eq) measured via ionization of probe molecules deposited on the surface of the excipients. The chemical stability of an API, atorvastatin calcium (AC), in mixtures with the excipients was evaluated by monitoring the appearance of an acid-induced degradant, atorvastatin lactone, under accelerated storage conditions. The extent of lactone formation in AC-excipient mixtures was presented as a function of either solution/suspension pH or pH_eq. No lactone formation was observed in mixtures with excipients having pH_eq > 6, while the lactone levels were pronounced (> 0.6% after 6 weeks at 50°C/20% RH) with excipients exhibiting pH_eq < 3. The three pH_eq regions (> 6, 3–6, and < 3) were consistent with the reported solution pH-stability profile of AC. In contrast to the pH_eq scale, lactone formation did not show any clear trend when plotted as a function of the suspension/solution pH. Two mechanisms to explain the discrepancy between the suspension/solution pH and the chemical stability data were discussed. Acidic excipients, which are expected to be incompatible with an acid-sensitive API, were identified based on pH_eq measurements. The incompatibility prediction was confirmed in the chemical stability tests using AC as an example of an acid-sensitive API.

Electronic supplementary material

The online version of this article (doi:10.1208/s12249-014-0231-7) contains supplementary material, which is available to authorized users.KEY WORDS: acidity, atorvastatin, excipients, pH indicators, solid-state stability     

Design, synthesis and structure-activity relationship of N-substituted tropane muscarinic acetylcholine receptor antagonists

A novel series of N-substituted tropane derivatives was characterized as potent muscarinic acetylcholine receptor antagonists (mAChRs). Kinetic washout studies showed that the N-endosubstituted analog 24 displayed much slower reversibility at mAChRs than the methyl-substituted parent molecule darotropium. In addition, it was shown that this characteristic appeared to translate into enhanced which duration of action in a mouse model of bronchonstriction.     

Landscape composition influences patterns of native and exotic lady beetle abundance

Aim Coccinellid beetles are important predators that contribute to pest suppression in agricultural landscapes. Since the introduction of the exotic coccinellids Coccinella septempunctata L. and Harmonia axyridis Pallas into the USA, several studies have reported a decline of native Coccinellidae in agroecosystems. We aimed to investigate the influence of landscape composition on native and exotic coccinellid abundance within soybean fields. Location Iowa, Michigan, Minnesota and Wisconsin. Methods As part of a 2‐year study (2005–06) on the biological control of the soybean aphid, Aphis glycines Matsumura, we examined coccinellid communities in 33 soybean fields using yellow sticky card traps. Landscape heterogeneity and composition were measured at multiple spatial scales ranging 1–3.5 km from focal soybean fields where coccinellid sampling took place. Results Exotic species made up 90% of the total coccinellid community in Michigan soybean fields followed by Wisconsin (84%), Minnesota (66%) and Iowa (57%). Harmonia axyridis was the dominant exotic coccinellid in all states comprising 45–62% of the total coccinellid community, followed by C. septempunctata (13–30%). Two additional exotic species, Hippodamia variegata (Goeze) and Propylea quatuordecimpunctata (L.) were also found in the region. Overall, the most abundant native coccinellid was Hippodamia convergens Guerin‐Meneville; however, its abundance varied across the region, comprising 0% (Michigan) to 28% (Iowa) of the total coccinellid community. Landscape structure significantly influenced the composition of coccinellid communities in soybean agroecosystems. We found that native coccinellids were most abundant in low‐diversity landscapes with an abundance of grassland habitat while exotic coccinellids were associated with the abundance of forested habitats. Main conclusion We propose that grassland dominated landscapes with low structural diversity and low amounts of forested habitat may be resistant to exotic coccinellid build‐up, particularly H. axyridis and therefore represent landscape‐scale refuges for native coccinellid biodiversity.     

Non-native interactions play an effective role in protein folding dynamics

Systematic Monte Carlo simulations of simple lattice models show that the final stage of protein folding is an ordered process where native contacts get locked (i.e., the residues come into contact and remain in contact for the duration of the folding process) in a well‐defined order. The detailed study of the folding dynamics of protein‐like sequences designed as to exhibit different contact energy distributions, as well as different degrees of sequence optimization (i.e., participation of non‐native interactions in the folding process), reveals significant differences in the corresponding locking scenarios—the collection of native contacts and their average locking times, which are largely ascribable to the dynamics of non‐native contacts. Furthermore, strong evidence for a positive role played by non‐native contacts at an early folding stage was also found. Interestingly, for topologically simple target structures, a positive interplay between native and non‐native contacts is observed also toward the end of the folding process, suggesting that non‐native contacts may indeed affect the overall folding process. For target models exhibiting clear two‐state kinetics, the relation between the nucleation mechanism of folding and the locking scenario is investigated. Our results suggest that the stabilization of the folding transition state can be achieved through the establishment of a very small network of native contacts that are the first to lock during the folding process.     

Implications of Three Biofuel Crops for Beneficial Arthropods in Agricultural Landscapes

Production of biofuel feedstocks in agricultural landscapes will result in land use changes that may have major implications for arthropod-mediated ecosystem services such as pollination and pest suppression. By comparing the abundance and diversity of insect pollinators and generalist natural enemies in three model biofuel crops: corn, switchgrass, and mixed prairie, we tested the hypothesis that biofuel crops comprised of more diverse plant communities would support increased levels of beneficial insects. These three biofuel crops contained a diverse bee community comprised of 75 species. Overall, bees were three to four times more abundant in switchgrass and prairie than in corn, with members of the sweat bee (Halictidae) and small carpenter bee (Ceratina spp.) groups the most abundant. Switchgrass and prairie had significantly greater bee species richness than corn during the July sampling period. The natural enemy community at these sites was dominated by lady beetles (Coccinellidae), long-legged flies (Dolichopodidae), and hover flies (Syrphidae) which varied in their response to crop type. Coccinellids were generally most abundant in prairie and switchgrass, with the exception of the pollen feeding Coleomegilla maculata that was most abundant in corn. Several rare or declining coccinellid species were detected in prairie and switchgrass sites. Dolichopodidae were more abundant in prairie and switchgrass while Syrphidae showed no significant response to crop type. Our results indicate that beneficial insects generally responded positively to the increased vegetational diversity of prairie and switchgrass sites; however, when managed as a dedicated biofuel crop, plant and arthropod diversity in switchgrass may decrease. Our findings support the hypothesis that vegetationally diverse biofuel crops support higher abundance and diversity of beneficial insects. Future policy regarding the production of biofuel feedstocks should consider the ecosystem services that different biofuel crops may support in agricultural landscapes.