Collective decision-making appears more egalitarian in populations where group fission costs are higher

Collective decision-making is predicted to be more egalitarian in conditions where the costs of group fission are higher. Here, we ask whether Trinidadian guppies (Poecilia reticulata) living in high or low predation environments, and thereby facing differential group fission costs, make collective decisions in line with this prediction. Using a classic decision-making scenario, we found that fish from high predation environments switched their positions within groups more frequently than fish from low predation environments. Because the relative positions individuals adopt in moving groups can influence their contribution towards group decisions, increased positional switching appears to support the prediction of more evenly distributed decision-making in populations where group fission costs are higher. In an agent-based model, we further identified that more frequent, asynchronous updating of individuals' positions could explain increased positional switching, as was observed in fish from high predation environments. Our results are consistent with theoretical predictions about the structure of collective decision-making and the adaptability of social decision-rules in the face of different environmental contexts

Geographic variation in sperm traits reflects predation risk and natural rates of multiple paternity in the guppy

Guppies (Poecilia reticulata) are models for understanding the interplay between natural and sexual selection. In particular, predation has been implicated as a major force affecting female sexual preferences, male mating tactics and the level of sperm competition. When predation is high, females typically reduce their preferences for showy males and engage more in antipredator behaviours, whereas males exploit these changes by switching from sexual displays to forced matings. These patterns are thought to account for the relatively high levels of multiple paternity in high-predation populations compared to low-predation populations. Here, we assess the possible evolutionary consequences of these patterns by asking whether variation in sperm traits reflect differences in predation intensity among four pairs of Trinidadian populations: four that experience relatively low levels of predation from a gape-limited predator and four that experience relatively high levels of predation from a variety of piscivores. We found that males in high-predation populations had faster swimming sperm with longer midpieces compared to males in low-predation populations. However, we found no differences among males in high- and low-predation populations with respect to sperm number, sperm head length, flagellum length and total sperm length

Experimental harvesting of fish populations drives genetically based shifts in body size and maturation

Size-selective harvesting in commercial fisheries can induce rapid changes in biological traits. While experimental and wild harvested populations often exhibit clear shifts in body size and maturation associated with fishing pressure, the relative contributions of genetic and environmental factors to these shifts remain uncertain and have been much debated. To date, observations of so-called fisheries-induced evolution (FIE) have been based solely on phenotypic measures, such as size data. Genetic data are hitherto lacking. Here, we quantify genetic versus environmental change in response to size-selective harvesting for small and large body size in guppies (Poecilia reticulata) across three generations of selection. We document for the first time significant changes at individual genetic loci, some of which have previously been associated with body size. In contrast, variation at neutral microsatellite markers was unaffected by selection, providing direct genetic evidence for rapid evolution induced by size-selective harvesting. These findings demonstrate FIE in an experimental system, with major implications for the sustainability of harvested populations, as well as impacts on size-structured communities and ecosystem processes. These findings highlight the need for scientists and managers to reconsider the capacity of harvested stocks to adapt to, and recover from, harvesting and predation. © 2013 The Ecological Society of America

The need for intra aortic balloon pump support following open heart surgery: risk analysis and outcome

<p>Abstract</p> <p>Background</p> <p>The early and intermediate outcome of patients requiring intraaortic balloon pump (IABP) was studied in a cohort of 2697 adult cardiac surgical patients.</p> <p>Methods</p> <p>136 patients requiring IABP (5.04%) support analysed over a 4 year period. Prospective data collection, obtained.</p> <p>Results</p> <p>The overall operative mortality was 35.3%. The "operation specific" mortality was higher on the Valve population.</p> <p>The mortality (%) as per time of balloon insertion was: Preoperative 18.2, Intraopeartive 33.3, postoperative 58.3 (p < 0.05).</p> <p>The incremental risk factors for death were: Female gender (Odds Ratio (OR) = 3.87 with Confidence Intervals (CI) = 1.3-11.6), Smoking (OR = 4.88, CI = 1.23- 19.37), Preoperative Creatinine>120 (OR = 3.3, CI = 1.14-9.7), Cross Clamp time>80 min (OR = 4.16, CI = 1.73-9.98) and IABP insertion postoperatively (OR = 19.19, CI = 3.16-116.47).</p> <p>The incremental risk factors for the development of complications were: Poor EF (OR = 3.16, CI = 0.87-11.52), Euroscore >7 (OR = 2.99, CI = 1.14-7.88), history of PVD (OR = 4.99, CI = 1.32-18.86).</p> <p>The 5 years survival was 79.2% for the CABG population and 71.5% for the valve group. (Hazard ratio = 1.78, CI = 0.92-3.46).</p> <p>Conclusions</p> <p>IABP represents a safe option of supporting the failing heart. The need for IABP especially in a high risk Valve population is associated with early unfavourable outcome, however the positive mid term results further justify its use.</p

Community assessment to advance computational prediction of cancer drug combinations in a pharmacogenomic screen

The effectiveness of most cancer targeted therapies is short-lived. Tumors often develop resistance that might be overcome with drug combinations. However, the number of possible combinations is vast, necessitating data-driven approaches to find optimal patient-specific treatments. Here we report AstraZeneca’s large drug combination dataset, consisting of 11,576 experiments from 910 combinations across 85 molecularly characterized cancer cell lines, and results of a DREAM Challenge to evaluate computational strategies for predicting synergistic drug pairs and biomarkers. 160 teams participated to provide a comprehensive methodological development and benchmarking. Winning methods incorporate prior knowledge of drug-target interactions. Synergy is predicted with an accuracy matching biological replicates for >60% of combinations. However, 20% of drug combinations are poorly predicted by all methods. Genomic rationale for synergy predictions are identified, including ADAM17 inhibitor antagonism when combined with PIK3CB/D inhibition contrasting to synergy when combined with other PI3K-pathway inhibitors in PIK3CA mutant cells.Peer reviewe

Social networks in changing environments

Social network analysis (SNA) has become a widespread tool for the study of animal social organisation. However despite this broad applicability, SNA is currently limited by both an overly strong focus on pattern analysis as well as a lack of dynamic interaction models. Here, we use a dynamic modelling approach that can capture the responses of social networks to changing environments. Using the guppy, Poecilia reticulata, we identified the general properties of the social dynamics underlying fish social networks and found that they are highly robust to differences in population density and habitat changes. Movement simulations showed that this robustness could buffer changes in transmission processes over a surprisingly large density range. These simulation results suggest that the ability of social systems to self-stabilise could have important implications for the spread of infectious diseases and information. In contrast to habitat manipulations, social manipulations (e.g. change of sex ratios) produced strong, but short-lived, changes in network dynamics. Lastly, we discuss how the evolution of the observed social dynamics might be linked to predator attack strategies. We argue that guppy social networks are an emergent property of social dynamics resulting from predator–prey co-evolution. Our study highlights the need to develop dynamic models of social networks in connection with an evolutionary framework

Learned mate recognition and reproductive isolation in guppies

Research on learned species discrimination has focused on the consequences of early experience. However, in species where parental care is limited or absent, including most fish, juveniles have fewer opportunities to learn from adult conspecifics. We examined male mate recognition in Trinidadian guppies, Poecilia reticulata, and in their sister species, the swamp guppy, P. picta. Choice tests revealed that males from localities where their species is the only poeciliid present initially mated. with conspecific and heterospecific females at random. In contrast, P. reticulata and P. picta found in sympatry preferred their own females. We then investigated the acquisition of mating discrimination by wild P. reticulata males from two allopatric populations. Males that were allowed to interact with females of both species learned within 4 days to distinguish conspecific partners, and within a week their species discrimination matched that of sympatric populations. This study confirms that learning is important in the acquisition of adult mating preferences and shows why learned mate preferences can be important in the last stages of speciation. (C) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All tights reserved.</p