The logic of divisively asymmetric contests - respect for ownership and the desperado effect

Abstract. It is current orthodoxy in biological game theory that in animal contests with easily recognized asymmetries between the contestants, an asymmetry will be used to settle the dispute. Here it is argued that, if the winning of contests plays a major part in gaining reproductive success, an individual will not be selected to respect an asymmetry which will place it always in the losing role. Asymmetries that create consistent losers of this sort are termed divisive asymmetries. Divisive asymmetries cannot be used to settle important contests in an evolutionarily stable way because the consistent losers will have no incentive to respect them

Natural Selection and the Maximization of Fitness

The notion that natural selection is a process of fitness maximization gets a bad press in population genetics, yet in other areas of biology the view that organisms behave as if attempting to maximize their fitness remains widespread. Here I critically appraise the prospects for reconciliation. I first distinguish four varieties of fitness maximization. I then examine two recent developments that may appear to vindicate at least one of these varieties. The first is the ‘new’ interpretation of Fisher's fundamental theorem of natural selection, on which the theorem is exactly true for any evolving population that satisfies some minimal assumptions. The second is the Formal Darwinism project, which forges links between gene frequency change and optimal strategy choice. In both cases, I argue that the results fail to establish a biologically significant maximization principle. I conclude that it may be a mistake to look for universal maximization principles justified by theory alone. A more promising approach may be to find maximization principles that apply conditionally and to show that the conditions were satisfied in the evolution of particular traits

ALTRUISM VIA KIN-SELECTION STRATEGIES THAT RELY ON ARBITRARY TAGS WITH WHICH THEY COEVOLVE

Hamilton's rule explains when natural selection will favor altruism between conspecifics, given their degree of relatedness. In practice, indicators of relatedness (such as scent) coevolve with strategies based on these indicators, a fact not included in previous theories of kin recognition. Using a combination of simulation modeling and mathematical extension of Hamilton's rule, we demonstrate how altruism can emerge and be sustained in a coevolutionary setting where relatedness depends on an individual's social environment and varies from one locus to another. The results support a very general expectation of widespread, and not necessarily weak, conditional altruism in nature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72180/1/j.0014-3820.2004.tb00465.x.pd

Evolutionarily Stable Strategies in Quantum Games

Evolutionarily Stable Strategy (ESS) in classical game theory is a refinement of Nash equilibrium concept. We investigate the consequences when a small group of mutants using quantum strategies try to invade a classical ESS in a population engaged in symmetric bimatrix game of Prisoner's Dilemma. Secondly we show that in an asymmetric quantum game between two players an ESS pair can be made to appear or disappear by resorting to entangled or unentangled initial states used to play the game even when the strategy pair remains a Nash equilibrium in both forms of the game.Comment: RevTex,contents extended to include asymmetric games,no figur

Management of acute small bowel obstruction from intestinal adhesions: indications for laparoscopic surgery in a community teaching hospital

Purpose: The aim of this study is to compare the results of laparoscopic management of acute small bowel obstruction (SBO) from abdominal adhesions to both exploratory laparotomy and secondary conversion to open surgery. Materials and methods: Ninety-three patients (mean age 61years) with adhesion-induced SBO were divided into successful laparoscopy (66 patients [71%]), secondary conversion (24 [26%]), and primary laparotomy (three patients). Results: Patients with successful laparoscopy had more simple adhesions (57%), fewer prior operations, and lower American Society of Anesthesiologists (ASA) class. Operative time was shortest in the laparoscopy group (74.3 ± 4.4min), as was the duration of both intensive care unit and hospital stay. Mortality was 6%, regardless of operative technique. Conclusions: A trial of laparoscopic adhesiolysis by a surgeon with advanced laparoscopic skills seems advisable in the majority of patients with acute adhesive SBO, whereas patients with more extensive adhesions, higher ASA class, and more than two prior abdominal operations often require laparotomy to achieve equally satisfactory outcom

Interpreting selection when individuals interact

A useful interpretation of quantitative genetic models of evolutionary change is that they (i) define a set of phenotypes that have a causal effect on fitness and on which selection acts, and (ii) define a set of breeding values that change as a correlated response to that selection because they covary with the phenotypes. When the expression of one trait causes variation in other traits then there are multiple paths by which a trait can cause fitness variation. Because of this, there are multiple ways in which selection can be defined, and still be consistent with a causal effect of traits on fitness. We use this result to show that genetical theories of natural/kin selection ignore causation and because of this we suggest they shed little light on the nature of selection. When traits expressed by an individual are affected by traits of their social partners (indirect genetic effects), we suggest a causal partitioning that allows selection to be cast in terms of Hamilton's costs and benefits. We show that previous attempts to understand Hamilton's rule in the context of indirect genetic effects either lack generality, or do not adequately describe all the ways in which an individual's actions constitute a cost to the individual or a benefit to its social partner(s). Our results allow us to explore Hamilton's rule in a multitrait setting. We show that evolution always increases inclusive fitness, and when the traits are measured in units of generalised genetic distance evolutionary change in the traits is in the direction in which inclusive fitness increases the fastest. However, we show that Hamilton's rule only holds in a multitrait context when the suite of traits are at equilibrium. When they are out of equilibrium, the conditions for altruism to evolve may be more or less stringent depending on genetic architecture and how costs and benefits are defined.</p

The evolution of gregariousness in parasitoid wasps

Data are assembled on the clutch-size strategies adopted by extant species of parasitoid wasp. These data are used to reconstruct the history of clutch-size evolution in the group using a series of plausible evolutionary assumptions. Extant families are either entirely solitary, both solitary and gregarious, or else clutch size is unknown. Parsimony analysis suggests that the ancestors of most families were solitary, a result which is robust to different phylogenetic relationships and likely data inadequacies. This implies that solitariness was ubiquitous throughout the initial radiation of the group, and that transitions to gregariousness have subsequently occurred a minimum of 43 times in several, but not all lineages. Current data suggest that species-rich and small-bodied lineages are more likely to have evolved gregariousness, and contain more species with small gregarious brood sizes. I discuss the implications of these data for clutch-size theory

Synaptic Remodeling in the Dentate Gyrus, CA3, CA1, Subiculum, and Entorhinal Cortex of Mice: Effects of Deprived Rearing and Voluntary Running

Hippocampal cell proliferation is strongly increased and synaptic turnover decreased after rearing under social and physical deprivation in gerbils (Meriones unguiculatus). We examined if a similar epigenetic effect of rearing environment on adult neuroplastic responses can be found in mice (Mus musculus). We examined synaptic turnover rates in the dentate gyrus, CA3, CA1, subiculum, and entorhinal cortex. No direct effects of deprived rearing on rates of synaptic turnover were found in any of the studied regions. However, adult wheel running had the effect of leveling layer-specific differences in synaptic remodeling in the dentate gyrus, CA3, and CA1, but not in the entorhinal cortex and subiculum of animals of both rearing treatments. Epigenetic effects during juvenile development affected adult neural plasticity in mice, but seemed to be less pronounced than in gerbils

Synapse Plasticity in Motor, Sensory, and Limbo-Prefrontal Cortex Areas as Measured by Degrading Axon Terminals in an Environment Model of Gerbils (Meriones unguiculatus)

Still little is known about naturally occurring synaptogenesis in the adult neocortex and related impacts of epigenetic influences. We therefore investigated (pre)synaptic plasticity in various cortices of adult rodents, visualized by secondary lysosome accumulations (LA) in remodeling axon terminals. Twenty-two male gerbils from either enriched (ER) or impoverished rearing (IR) were used for quantification of silver-stained LA. ER-animals showed rather low LA densities in most primary fields, whereas barrel and secondary/associative cortices exhibited higher densities and layer-specific differences. In IR-animals, these differences were evened out or even inverted. Basic plastic capacities might be linked with remodeling of local intrinsic circuits in the context of cortical map adaptation in both IR- and ER-animals. Frequently described disturbances due to IR in multiple corticocortical and extracortical afferent systems, including the mesocortical dopamine projection, might have led to maladaptations in the plastic capacities of prefronto-limbic areas, as indicated by different LA densities in IR- compared with ER-animals