Behavioural phenotype affects social interactions in an animal network

Animal social networks can be extremely complex and are characterized by highly non-random interactions between group members. However, very little is known about the underlying factors affecting interaction preferences, and hence network structure. One possibility is that behavioural differences between individuals, such as how bold or shy they are, can affect the frequency and distribution of their interactions within a network. We tested this using individually marked three-spined sticklebacks (Gasterosteus aculeatus), and found that bold individuals had fewer overall interactions than shy fish, but tended to distribute their interactions more evenly across all group members. Shy fish, on the other hand, tended to associate preferentially with a small number of other group members, leading to a highly skewed distribution of interactions. This was mediated by the reduced tendency of shy fish to move to a new location within the tank when they were interacting with another individual; bold fish showed no such tendency and were equally likely to move irrespective of whether they were interacting or not. The results show that animal social network structure can be affected by the behavioural composition of group members and have important implications for understanding the spread of information and disease in social groups.     

Bicyclic peptidomimetic tetrahydrofuro[3,2-b]pyrrol-3-one and hexahydrofuro[3,2-b]pyridine-3-one based scaffolds: synthesis and cysteinyl proteinase inhibition

A stereoselective synthesis of (3aS,6aR)-tetrahydrofuro[3,2-b]pyrrol-3-ones and (3aS,7aR)-hexahydrofuro[3,2-b]pyridine-3-ones has been developed through Fmoc protected scaffolds 12 and 13. A key design element within these novel bicyclic scaffolds, in particular the 5,5-fused system, was the inherent stability of the cis-fused geometry in comparison to that of the corresponding trans-fused. Since the bridgehead stereocentre situated beta to the ketone was of a fixed and stable configuration, the fact that cis ring fusion is both kinetically and thermodynamically stable with respect to trans ring fusion provides chiral stability to the bridgehead stereocentre that is situated alpha to the ketone. To exemplify this principle, building blocks 12 and 13 were designed, prepared and utilised in a solid phase combinatorial synthesis of peptidomimetic inhibitors 10, 45a-e, 11 and 46. Both series were chirally stable with 5,5-series 10 and 45a-e exhibiting potent in vitro activity against a range of CAC1 cysteinyl proteinases. Compound 10, a potent and selective inhibitor of cathepsin K, possessed good primary DMPK properties along with promising activity in an in vitro cell-based human osteoclast assay of bone resorption.     

Baseline susceptibility of Bemisia tabaci B biotype (Hemiptera: Aleyrodidae) populations from California and Arizona to spiromesifen

Susceptibility to spiromesifen, a tetronic acid derivative, was determined for three imidacloprid-resistant strains and 12 geographically discrete natural populations of Bemisia tabaci (Gennadius) (=Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) from California and Arizona by laboratory bioassays. Newly emerged first instars were sprayed with aqueous serial dilutions of spiromesifen and evaluated for toxicity to establish baseline susceptibility data. Interpopulation variability in susceptibility to spiromesifen was observed among the natural populations of whiteflies up to 29-fold; however, there was only 30-fold difference in susceptibility among natural and resistant populations tested. In general, spiromesifen was quite toxic to first instars across most of their geographic range, with LC50 values ranging from 0.210 to 6.08 microg (AI)/ml. The magnitude of variation was smaller among the three-resistant strains. These results suggest that the observed variability reflect natural variation in spiromesifen susceptibility among all the test populations, possibly due to previous exposure to insecticides at each location. The effectiveness of spiromesifen also was evaluated against all immature stages of whiteflies from three field and two resistant strains. Spiromesifen was significantly more active against early instars of whiteflies based on lower LC50 values recorded compared with the fourth instars. Spiromesifen was effective against the resistant strains including a Q-biotype of B. tabaci from Spain, which is highly resistant to neonicotinoids. Results of this study indicate absence of cross-resistance between spiromesifen and more commonly used neonicotinoids. Our findings suggest that spiromesifen should be considered an ideal candidate for whitefly resistance management programs in rotation with other effective chemistries.     

Excitable behavior can explain the "ping-pong" mode of communication between cells using the same chemoattractant

Here we elucidate a paradox: how a single chemoattractant-receptor system in two individuals is used for communication despite the seeming inevitability of self-excitation. In the filamentous fungus Neurospora crassa, genetically identical cells that produce the same chemoattractant fuse via the homing of individual cell protrusions toward each other. This is achieved via a recently described "ping-pong" pulsatile communication. Using a generic activator-inhibitor model of excitable behavior, we demonstrate that the pulse exchange can be fully understood in terms of two excitable systems locked into a stable oscillatory pattern of mutual excitation. The most puzzling properties of this communication are the sudden onset of oscillations with final amplitude, and the absence of seemingly inevitable self-excitation. We show that these properties result directly from both the excitability threshold and refractory period characteristic of excitable systems. Our model suggests possible molecular mechanisms for the ping-pong communication.     

Canopy interactions and physical stress gradients in subtidal communities

Species interactions are integral drivers of community structure and can change from competitive to facilitative with increasing environmental stress. In subtidal marine ecosystems, however, interactions along physical stress gradients have seldom been tested. We observed seaweed canopy interactions across depth and latitudinal gradients to test whether light and temperature stress structured interaction patterns. We also quantified interspecific and intraspecific interactions among nine subtidal canopy seaweed species across three continents to examine the general nature of interactions in subtidal systems under low consumer pressure. We reveal that positive and neutral interactions are widespread throughout global seaweed communities and the nature of interactions can change from competitive to facilitative with increasing light stress in shallow marine systems. These findings provide support for the stress gradient hypothesis within subtidal seaweed communities and highlight the importance of canopy interactions for the maintenance of subtidal marine habitats experiencing environmental stress.     

A solution approach for deriving alternative fuel station infrastructure requirements

When an alternative fuel is introduced, the infrastructure through which that fuel is made available to the market is often underdeveloped. Transportation service providers relying on such infrastructures are unlikely to adopt alternative fuel vehicles as it may impose long detours for refueling. In this paper, we design and apply a new solution approach to derive minimum infrastructure requirements, in terms of the number of alternative fuel stations. The effectiveness of our approach is demonstrated by applying it to the case of introducing liquefied natural gas (LNG) as a transportation fuel in The Netherlands. From this case, we learn that, depending on the driving range of the LNG trucks and the size of area on which those trucks operate, a minimum of 5–12 LNG fuel stations is necessary to render LNG trucks economically and environmentally beneficial.     

Mutational neighbourhood and mutation supply rate constrain adaptation in Pseudomonas aeruginosa

Understanding adaptation by natural selection requires understanding the genetic factors that determine which beneficial mutations are available for selection. Here, using experimental evolution of rifampicin-resistant Pseudomonas aeruginosa, we show that different genotypes vary in their capacity for adaptation to the cost of antibiotic resistance. We then use sequence data to show that the beneficial mutations associated with fitness recovery were specific to particular genetic backgrounds, suggesting that genotypes had access to different sets of beneficial mutations. When we manipulated the supply rate of beneficial mutations, by altering effective population size during evolution, we found that it constrained adaptation in some selection lines by restricting access to rare beneficial mutations, but that the effect varied among the genotypes in our experiment. These results suggest that mutational neighbourhood varies even among genotypes that differ by a single amino acid change, and this determines their capacity for adaptation as well as the influence of population biology processes that alter mutation supply rate.