An adaptive response to uncertainty can lead to weight gain during dieting attempts

This is the final version of the article. Available from the publisher via the DOI in this record.Background and objectives: Peoples’ attempts to lose weight by low calorie diets often result in weight gain because of over-compensatory overeating during lapses. Animals usually respond to a change in food availability by adjusting their foraging effort and altering how much energy reserves they store. But in many situations the long-term availability of food is uncertain, so animals may attempt to estimate it to decide the appropriate level of fat storage. Methodology: We report the results of a conceptual model of feeding in which the animal knows whether food is currently abundant or limited, but does not know the proportion of time, there will be an abundance in the long-term and has to learn it. Results: If the food supply is limited much of the time, such as during cycles of dieting attempts, the optimal response is to gain a lot of weight when food is abundant. Conclusions and implications: This implies that recurring attempts to diet, by signalling to the body that the food supply is often insufficient, will lead to a greater fat storage than if food was always abundant. Our results shed light on the widespread phenomenon of weight gain during weight cycling and indicate possible interventions that may reduce the incidence of obesityThis work was supported by the European Research Council (Advanced Grant 250209 to Alasdair Houston) and a Natural Environmental Research Council Independent Research Fellowship (NE/L011921/1) awarded to A.D.

When is it adaptive to be patient? A general framework for evaluating delayed rewards

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The tendency of animals to seek instant gratification instead of waiting for greater long-term benefits has been described as impatient, impulsive or lacking in self-control. How can we explain the evolution of such seemingly irrational behaviour? Here we analyse optimal behaviour in a variety of simple choice situations involving delayed rewards. We show that preferences for more immediate rewards should depend on a variety of factors, including whether the choice is a one-off or is likely to be repeated, the information the animal has about the continuing availability of the rewards and the opportunity to gain rewards through alternative activities. In contrast to the common assertion that rational animals should devalue delayed rewards exponentially, we find that this pattern of discounting is optimal only under restricted circumstances. We predict preference reversal whenever waiting for delayed rewards entails loss of opportunities elsewhere, but the direction of this reversal depends on whether the animal will face the same choice repeatedly. Finally, we question the ecological relevance of standard laboratory tests for impulsive behaviour, arguing that animals rarely face situations analogous to the self-control paradigm in their natural environment. To understand the evolution of impulsiveness, a more promising strategy would be to identify decision rules that are adaptive in a realistic ecological setting, and examine how these rules determine patterns of behaviour in simultaneous choice tests.We thank the European Research Council for financial support (Advanced Grant 250209 to A.I.H.)

Towards a behavioural ecology of obesity

This is the author accepted manuscript. The final version is available from Cambridge University Press via the DOI in this record.Addressing the obesity epidemic depends on a holistic understanding of the reasons that people become and maintain excessive fat. Theories about the causes of obesity usually focus proximately or evoke evolutionary mismatches, with minimal clinical value. There is potential for substantial progress by adapting strategic bodymass regulation models from evolutionary ecology to human obesity by assessing the role of information

Clarifying the relationship between prospect theory and risk-sensitive foraging theory

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.When given a choice between options with uncertain outcomes, people tend to be loss averse and risk averse regarding potential gains and risk prone regarding potential losses. These features of human decision making are captured by prospect theory (PT)-a hugely influential descriptive model of choice, but one which lacks any unifying principle that might explain why such preferences exist. Recently there have been several attempts to connect PT with risk-sensitive foraging theory (RSFT), a normative framework developed by evolutionary biologists to explain how animals should choose optimally when faced with uncertain foraging options. Although this seems a promising direction, here we show that current approaches are overly simplistic, and, despite their claims, they leave key features of PT unaccounted for. A common problem is the failure to appreciate the central concept of reproductive value in RSFT, which depends on the decision maker's current state and the particular situation it faces. Reproductive value provides a common currency in which decisions can be compared in a logical way. In contrast, existing models provide no rational justification for the reference state in PT. Evolutionary approaches to understanding PT preferences must confront this basic problem.This work was supported by the European Research Council (ERC Advanced Grant 250209 to AIH)

Detection vs selection: integration of genetic, epigenetic and environmental cues in fluctuating environments

ArticleThere are many inputs during development that influence an organism's fit to current or upcoming environments. These include genetic effects, transgenerational epigenetic influences, environmental cues and developmental noise, which are rarely investigated in the same formal framework. We study an analytically tractable evolutionary model, in which cues are integrated to determine mature phenotypes in fluctuating environments. Environmental cues received during development and by the mother as an adult act as detection-based (individually observed) cues. The mother's phenotype and a quantitative genetic effect act as selection-based cues (they correlate with environmental states after selection). We specify when such cues are complementary and tend to be used together, and when using the most informative cue will predominate. Thus, we extend recent analyses of the evolutionary implications of subsets of these effects by providing a general diagnosis of the conditions under which detection and selection-based influences on development are likely to evolve and coexist.This work was supported by a Leverhulme Trust International Network Grant to the four authors and by a grant from the Swedish Research Council (621-2010-5437) to O.L

Evolution of trust and trustworthiness: social awareness favours personality differences

This is the final version of the article. Available from the publisher via the DOI in this record.Interest in the evolution and maintenance of personality is burgeoning. Individuals of diverse animal species differ in their aggressiveness, fearfulness, sociability and activity. Strong trade-offs, mutation-selection balance, spatio-temporal fluctuations in selection, frequency dependence and good-genes mate choice are invoked to explain heritable personality variation, yet for continuous behavioural traits, it remains unclear which selective force is likely to maintain distinct polymorphisms. Using a model of trust and cooperation, we show how allowing individuals to monitor each other's cooperative tendencies, at a cost, can select for heritable polymorphisms in trustworthiness. This variation, in turn, favours costly 'social awareness' in some individuals. Feedback of this sort can explain the individual differences in trust and trustworthiness so often documented by economists in experimental public goods games across a range of cultures. Our work adds to growing evidence that evolutionary game theorists can no longer afford to ignore the importance of real world inter-individual variation in their models.P.A.S. was funded by NERC grant NER/A/S/2003/00616 to J.M.M. and A.I.H

The imprints of AGN feedback within a supermassive black hole's sphere of influence

We present a new 300 ks Chandra observation of M87 that limits pileup to only a few per cent of photon events and maps the hot gas properties closer to the nucleus than has previously been possible. Within the supermassive black hole's gravitational sphere of influence, the hot gas is multiphase and spans temperatures from 0.2 to 1 keV. The radiative cooling time of the lowest temperature gas drops to only 0.1-0.5 Myr, which is comparable to its free fall time. Whilst the temperature structure is remarkably symmetric about the nucleus, the density gradient is steep in sectors to the N and S, with $\rho{\propto}r^{-1.5\pm0.1}$, and significantly shallower along the jet axis to the E, where $\rho{\propto}r^{-0.93\pm0.07}$. The density structure within the Bondi radius is therefore consistent with steady inflows perpendicular to the jet axis and an outflow directed E along the jet axis. By putting limits on the radial flow speed, we rule out Bondi accretion on the scale resolved at the Bondi radius. We show that deprojected spectra extracted within the Bondi radius can be equivalently fit with only a single cooling flow model, where gas cools from 1.5 keV down below 0.1 keV at a rate of 0.03 M$_{\odot}$/yr. For the alternative multi-temperature spectral fits, the emission measures for each temperature component are also consistent with a cooling flow model. The lowest temperature and most rapidly cooling gas in M87 is therefore located at the smallest radii at ~100 pc and may form a mini cooling flow. If this cooling gas has some angular momentum, it will feed into the cold gas disk around the nucleus, which has a radius of ~80 pc and therefore lies just inside the observed transition in the hot gas structure

Ecological genetic conflict: Genetic architecture can shift the balance between local adaptation and plasticity

This is the author accepted manuscript. The final version is available from University of Chicago Press via the DOI in this record.Genetic polymorphism can contribute to local adaptation in heterogeneous habitats, for instance as a single locus with alleles adapted to different habitats. Phenotypic plasticity can also contribute to trait variation across habitats, through developmental responses to habitat-specific cues. We show that the genetic architecture of genetically polymorphic and plasticity loci may influence the balance between local adaptation and phenotypic plasticity. These effects of genetic architecture are instances of ecological genetic conflict. A reduced effective migration rate for genes tightly linked to a genetic polymorphism provides an explanation for the effects, and they can occur both for a single trait and for a syndrome of co-adapted traits. Using individualbased simulations and numerical analysis, we investigate how among-habitat genetic polymorphism and phenotypic plasticity depend on genetic architecture. We also study the evolution of genetic architecture itself, in the form of rates of recombination between genetically polymorphic loci and plasticity loci. Our main result is that for plasticity genes that are unlinked to loci with between-habitat genetic polymorphism, the slope of a reaction norm is steeper in comparison with the slope favored by plasticity genes that are tightly linked to genes for local adaptation.This work was supported by grants from the Carl Trygger Foundation (CTS 15292) to OL and by a Leverhulme Trust International Network Grant to SRXD, PH, OL, and JMM

Adaptive learning can result in a failure to profit from good conditions: implications for understanding depression.

Published onlineThis is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/emph/eov009BACKGROUND AND OBJECTIVES: Depression is a major medical problem diagnosed in an increasing proportion of people and for which commonly prescribed psychoactive drugs are frequently ineffective. Development of treatment options may be facilitated by an evolutionary perspective; several adaptive reasons for proneness to depression have been proposed. A common feature of many explanations is that depressive behaviour is a way to avoid costly effort where benefits are small and/or unlikely. However, this viewpoint fails to explain why low mood persists when the situation improves. We investigate whether a behavioural rule that is adapted to a stochastically changing world can cause inactivity which appears similar to the effect of depression, in that it persists after the situation has improved. METHODOLOGY: We develop an adaptive learning model in which an individual has repeated choices of whether to invest costly effort that may result in a net benefit. Investing effort also provides information about the current conditions and rates of change of the conditions. RESULTS: An individual following the optimal behavioural strategy may sometimes remain inactive when conditions are favourable (i.e. when it would be better to invest effort) when it is poorly informed about the current environmental state. Initially benign conditions can predispose an individual to inactivity after a relatively brief period of negative experiences. CONCLUSIONS AND IMPLICATIONS: Our approach suggests that the antecedent factors causing depressed behaviour could go much further back in an individual s history than is currently appreciated. The insights from our approach have implications for the ongoing debate about best treatment options for patients with depressive symptoms.This work was supported by the European Research Council (Evomech Advanced Grant 250 209 to A.I.H.)

Birth data accessibility via primary care health records to classify health status in a multi-ethnic population of children: an observational study

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