The asymmetric war of attrition

The paper, which has an informal discussion at the end, provides a game theoretical analysis of the asymmetric “war of attrition” with incomplete information. This is a contest where animals adopt different roles like “owner” and “intruder” in a territorial conflict, and where the winner is the individual prepared to persist longer. The term incomplete information refers to mistakes in the identification of roles. The idea by Parker & Rubenstein (1981) is mathematically worked out and confirmed that there exists only a single evolutionarily stable strategy (ESS) for the model with a continuum of possible levels of persistence and no discontinuities in the increase of cost during attrition. The ESS prescribes to settle the conflict according to “who has more to gain or less to pay for persistence”. The only evolutionarily stable convention is thus to give the player access to the resource who has the role which is favoured with respect to payoffs. By contrast, it was shown earlier (Hammerstein, 1981) for various asymmetric versions of the “Hawks-Doves” model that an ESS can exist which appears paradoxical with respect to payoffs. The nature of this contrast is further analyzed by introducing elements of discreteness in the asymmetric war of attrition. It turns out that some conditions must be satisfied in order to have the possibility of an alternative ESS which is not of the above simple commonsense type. First, a decision to persist (or escalate) further in a contest must typically commit a contestant to go on fighting for a full “round”, before he can give up without danger. Second, such a “discontinuity” must occur at a level of persistence where the contest is still cheap, and, finally, errors in the identification of roles must be rare.     

A benign approach to the preparation of freshwater bryozoan statoblasts for scanning electron microscopy (SEM) imaging

Abstract

Several different species of freshwater Bryozoa, belonging to the genera Plumatella, Rumarcanella and Fredericella, were detected within the Northern Mallee Pipeline (NMP) system in Victoria, Australia, that required definitive identification. These organisms produce asexual buds called statoblasts, with valves composed of sclerotised chitin that bear minute micro-ornamentations of considerable taxonomical significance. Imaging and analysis of these distinctive micro-ornamentations using scanning electron microscopy (SEM) is often employed for species identification. Meticulous preparation of statoblast samples is therefore required that necessitates the removal of adhering debris, dehydration and drying—whilst mitigating specimen damage and distortion. This technical note describes an approach whereby each of these three steps have been individually designed to be as benign as possible, using mild detergent/sonication to remove debris, a gradual and gentle dehydration procedure using ethanol, and critical point drying. For the overall process, these methods are chosen to optimise control and to minimise the use of harsh and hazardous chemicals.     

The use of adjunctive GPIIb/IIIa inhibitors in patients with unstable angina/non-Q-wave MI undergoing percutaneous coronary intervention

Glycoprotein IIb/IIIa receptor inhibitors represent a relatively new therapeutic approach in the field of antiplatelet therapy. Following the development of abciximab a number of small molecule GPIIb/IIIa inhibitors have been introduced such as tirofiban and eptifibatide. In this fast-moving field the interventional cardiologist needs a framework to guide decision-making for the individual patient. This review covers the efficacy and safety data from the clinical trials of GPIIb/IIIa inhibitors in the context of patients undergoing percutaneous coronary intervention for unstable angina/non-Q-wave myocardial infarction. There is an increasing body of evidence to support the efficacy of GPIIb/IIIa inhibitors in reducing the risk of adverse ischemic events in high and low risk patients undergoing percutaneous coronary intervention. A number of unresolved efficacy and safety issues remain, including the duration of treatment before and after intervention; whether a reduction in the heparin dose would further decrease the risk of hemorrhage without affecting the periprocedural thrombotic rate in patients undergoing PTCA with adjunctive GPIIb/IIIa inhibitors; and the cost-effectiveness of this therapy. When a thorough analysis of cost-effectiveness has been made, it will be easier to advocate the widespread use of these agents in all patients undergoing coronary intervention.     

Evolution of cooperation through indirect reciprocity

How can cooperation through indirect reciprocity evolve and what would it be like? This problem has previously been studied by simulating evolution in a small group of interacting individuals, assuming no gene flow between groups. In these simulations, certain ''image scoring'' strategies were found to be the most successful. However, analytical arguments show that it would not be in an individual''s interest to use these strategies. Starting with this puzzle, we investigate indirect reciprocity in simulations based on an island model. This has an advantage in that the role of genetic drift can be examined. Our results show that the image scoring strategies depend on very strong drift or a very small cost of giving help. As soon as these factors are absent, selection eliminates image scoring. We also consider other possibilities for the evolution of indirect reciprocity. In particular, we find that the strategy of aiming for ''good standing'' has superior properties. It can be an evolutionarily stable strategy and, even if not, it usually beats image scoring. Furthermore, by introducing quality variation among individuals into the model, we show that the standing strategy can be quality revealing, adding a new dimension to indirect reciprocity. Finally, we discuss general problems with currently popular modelling styles.     

A high-throughput cloning system for reverse genetics in <Emphasis Type="Italic">Trypanosoma cruzi</Emphasis>

Background  

The three trypanosomatids pathogenic to men, Trypanosoma cruzi, Trypanosoma brucei and Leishmania major, are etiological agents of Chagas disease, African sleeping sickness and cutaneous leishmaniasis, respectively. The complete sequencing of these trypanosomatid genomes represented a breakthrough in the understanding of these organisms. Genome sequencing is a step towards solving the parasite biology puzzle, as there are a high percentage of genes encoding proteins without functional annotation. Also, technical limitations in protein expression in heterologous systems reinforce the evident need for the development of a high-throughput reverse genetics platform. Ideally, such platform would lead to efficient cloning and compatibility with various approaches. Thus, we aimed to construct a highly efficient cloning platform compatible with plasmid vectors that are suitable for various approaches.     

Nonlinear time series analysis of food intake in the dab and the rainbow trout

Evidence suggests that dab and rainbow trout are able to quickly adjust their food intake to an appropriate level when offered novel diets. In addition day-to-day and meal-to-meal food intake varies greatly and meal timing is plastic. Why this is the case is not clear: Food intake in fish is influenced by many factors, however the hierarchy and mechanisms by which these interact is not yet fully understood. A model of food intake may be helpful to understand these phenomena; to determine model type it is necessary to understand the qualitative nature of food intake. Food intake can be regarded as an autoregressive (AR) time series, as the amount of food eaten at time t will be influenced by previous meals, and this allows food intake to be considered using time series analyses. Here, time series data were analysed using nonlinear techniques to obtain qualitative information from which evidence for the hierarchy of mechanisms controlling food intake may be drawn. Time series were obtained for a group of dab and individuals and a group of rainbow trout for analysis. Surrogate data sets were generated to test several null hypotheses describing linear processes and all proved significantly different to the real data, suggesting nonlinear dynamics. Examination of topography and recurrence diagrams suggested that all series were deterministic and non-stationary. The point correlation dimension (PD2i) suggested low-dimensional dynamics. Our findings suggest therefore that any model of appetite should create output that is deterministic, non-stationary, low-dimensional and having nonlinear dynamics.     

Bad guys turned nice? A critical assessment of Wolbachia mutualisms in arthropod hosts

Wolbachia are the most abundant bacterial endosymbionts among arthropods. Although maternally inherited, they do not conform to the widespread view that vertical transmission inevitably selects for beneficial symbionts. Instead, Wolbachia are notorious for their reproductive parasitism which, although lowering host fitness, ensures their spread. However, even for reproductive parasites it can pay to enhance host fitness. Indeed, there is a recent upsurge of reports on Wolbachia‐associated fitness benefits. Therefore, the question arises how such instances of mutualism are related to the phenotypes of reproductive parasitism. Here, we review the evidence of Wolbachia mutualisms in arthropods, including both facultative and obligate relationships, and critically assess their biological relevance. Although many studies report anti‐pathogenic effects of Wolbachia, few actually prove these effects to be relevant to field conditions. We further show that Wolbachia frequently have beneficial and detrimental effects at the same time, and that reproductive manipulations and obligate mutualisms may share common mechanisms. These findings undermine the idea of a clear‐cut distinction between Wolbachia mutualism and parasitism. In general, both facultative and obligate mutualisms can have a strong, and sometimes unforeseen, impact on the ecology and evolution of Wolbachia and their arthropod hosts. Acknowledging this mutualistic potential might be the key to a better understanding of some unresolved issues in the study of Wolbachia–host interactions.     

The strategy concept and John Maynard Smith’s influence on theoretical biology

Here we argue that the concept of strategies, as it was introduced into biology by John Maynard Smith, is a prime illustration of the four dimensions of theoretical biology in the post-genomic era. These four dimensions are: data analysis and management, mathematical and computational model building and simulation, concept formation and analysis, and theory integration. We argue that all four dimensions of theoretical biology are crucial to future interactions between theoretical and empirical biologists as well as with philosophers of biology.     

Strategic analysis in evolutionary genetics and the theory of games

This paper is written in memory of John Maynard Smith. In a brief survey it discusses essential aspects of how game theory in biology relates to its counterpart in economics, the major transition in game theory initiated by Maynard Smith, the discrepancies between genetic and phenotypic models in evolutionary biology, and a balanced way of reconciling these models. In addition, the paper discusses modern problems in understanding games at the genetic level using the examples of conflict between endosymbionts and their hosts, and the molecular interactions between parasites and the mammalian immune system.