79 research outputs found

    Evolutionary ecology in-silico: Does mathematical modelling help in understanding the "generic" trends?

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    Motivated by the results of recent laboratory experiments (Yoshida et al. Nature, 424, 303-306 (2003)) as well as many earlier field observations that evolutionary changes can take place in ecosystems over relatively short ecological time scales, several ``unified'' mathematical models of evolutionary ecology have been developed over the last few years with the aim of describing the statistical properties of data related to the evolution of ecosystems. Moreover, because of the availability of sufficiently fast computers, it has become possible to carry out detailed computer simulations of these models. For the sake of completeness and to put these recent developments in the proper perspective, we begin with a brief summary of some older models of ecological phenomena and evolutionary processes. However, the main aim of this article is to review critically these ``unified'' models, particularly those published in the physics literature, in simple language that makes the new theories accessible to wider audience.Comment: 28 pages, LATEX, 4 eps figure

    Nonlinear effects of recombination on the evolutionary dynamics in Wright-Fisher type models and experiments

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    Fitness landscapes represent a mapping between genotypes and their fitness, which usually reflects their reproductive success. With this approach, evolution can be considered as a process in which populations move on a fitness landscape. The paths taken in this process depend crucially on their structure. Although the idea is quite old, it has gained renewed attention in recent years as advances in genetic sequencing have made it possible to capture the structure of fitness landscapes in greater detail. This in turn facilitates a more comprehensive and quantitative understanding of evolution. However, it is still unclear how these landscapes are structured on a large scale. This dissertation therefore considers theoretical as well as empirical fitness landscapes and investigates how populations are distributed across them. It is shown that not only the structure of the fitness landscape is crucial, but also which evolutionary forces are at work and how strong they are. In particular, the effect of recombination of genetic material is addressed and a possible advantage of recombination is described that has received comparatively little attention so far. This is the robustness against the effect of random mutations, which is greater in recombining populations

    Multi-locus interactions and the build-up of reproductive isolation

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    All genes interact with other genes, and their additive effects and epistatic interactions affect an organism's phenotype and fitness. Recent theoretical and empirical work has advanced our understanding of the role of multi-locus interactions in speciation. However, relating different models to one another and to empirical observations is challenging. This review focuses on multi-locus interactions that lead to reproductive isolation (RI) through reduced hybrid fitness. We first review theoretical approaches and show how recent work incorporating a mechanistic understanding of multi-locus interactions recapitulates earlier models, but also makes novel predictions concerning the build-up of RI. These include high variance in the build-up rate of RI among taxa, the emergence of strong incompatibilities producing localized barriers to introgression, and an effect of population size on the build-up of RI. We then review recent experimental approaches to detect multi-locus interactions underlying RI using genomic data. We argue that future studies would benefit from overlapping methods like ancestry disequilibrium scans, genome scans of differentiation and analyses of hybrid gene expression. Finally, we highlight a need for further overlap between theoretical and empirical work, and approaches that predict what kind of patterns multi-locus interactions resulting in incompatibilities will leave in genome-wide polymorphism data. This article is part of the theme issue 'Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'.Peer reviewe

    Isolation-by-Distance and Outbreeding Depression Are Sufficient to Drive Parapatric Speciation in the Absence of Environmental Influences

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    A commonly held view in evolutionary biology is that speciation (the emergence of genetically distinct and reproductively incompatible subpopulations) is driven by external environmental constraints, such as localized barriers to dispersal or habitat-based variation in selection pressures. We have developed a spatially explicit model of a biological population to study the emergence of spatial and temporal patterns of genetic diversity in the absence of predetermined subpopulation boundaries. We propose a 2-D cellular automata model showing that an initially homogeneous population might spontaneously subdivide into reproductively incompatible species through sheer isolation-by-distance when the viability of offspring decreases as the genomes of parental gametes become increasingly different. This simple implementation of the Dobzhansky-Muller model provides the basis for assessing the process and completion of speciation, which is deemed to occur when there is complete postzygotic isolation between two subpopulations. The model shows an inherent tendency toward spatial self-organization, as has been the case with other spatially explicit models of evolution. A well-mixed version of the model exhibits a relatively stable and unimodal distribution of genetic differences as has been shown with previous models. A much more interesting pattern of temporal waves, however, emerges when the dispersal of individuals is limited to short distances. Each wave represents a subset of comparisons between members of emergent subpopulations diverging from one another, and a subset of these divergences proceeds to the point of speciation. The long-term persistence of diverging subpopulations is the essence of speciation in biological populations, so the rhythmic diversity waves that we have observed suggest an inherent disposition for a population experiencing isolation-by-distance to generate new species

    Adaptive speciation theory: a conceptual review

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    Speciation—the origin of new species—is the source of the diversity of life. A theory of speciation is essential to link poorly understood macro-evolutionary processes, such as the origin of biodiversity and adaptive radiation, to well understood micro-evolutionary processes, such as allele frequency change due to natural or sexual selection. An important question is whether, and to what extent, the process of speciation is ‘adaptive’, i.e., driven by natural and/or sexual selection. Here, we discuss two main modelling approaches in adaptive speciation theory. Ecological models of speciation focus on the evolution of ecological differentiation through divergent natural selection. These models can explain the stable coexistence of the resulting daughter species in the face of interspecific competition, but they are often vague about the evolution of reproductive isolation. Most sexual selection models of speciation focus on the diversification of mating strategies through divergent sexual selection. These models can explain the evolution of prezygotic reproductive isolation, but they are typically vague on questions like ecological coexistence. By means of an integrated model, incorporating both ecological interactions and sexual selection, we demonstrate that disruptive selection on both ecological and mating strategies is necessary, but not sufficient, for speciation to occur. To achieve speciation, mating must at least partly reflect ecological characteristics. The interaction of natural and sexual selection is also pivotal in a model where sexual selection facilitates ecological speciation even in the absence of diverging female preferences. In view of these results, it is counterproductive to consider ecological and sexual selection models as contrasting and incompatible views on speciation, one being dominant over the other. Instead, an integrative perspective is needed to achieve a thorough and coherent understanding of adaptive speciation

    The Extended Evolutionary Synthesis: a metascientific view of evolutionary biology, and some directions to transcend its limits

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    To approach the issue of the recent proposal of an Extended Evolutionary Synthesis (EES) put forth by Massimo Pigliucci and Gerd Müller, I suggest to consider the EES as a metascientific view: a description of what’s new in how evolutionary biology is carried out, not only a description of recently learned aspects of evolution. Knowing ‘what is it to do research’ in evolutionary biology, today versus yesterday, can aid training, research and career choices, establishment of relationships and collaborations, decision of funding and research policies, in order to make the field advance for the better. After reviewing the concepts associated to the EES proposal (categorized for convenience as mechanisms, measures, fields, perspectives and applications), I show their transience, and sketch out ongoing disagreements about the EES. Then I examine the deep difficulties, i.e., the enormity and complexity of the covered field, affecting the achievement of trusted metascientific views; the insufficiency of conceptual analysis to capture the substance of scientific research; the entanglement between empirical and metascientific concepts, between multiple chronologies, and between descriptive and normative intentions; and the ineliminable stakeholding of any reviewer involved in the reviewed field. I propose that disciplines such as scientometrics, ethnography, sociology, economics and history, combined with conceptual analysis, inspire a more rigorous approach to the evolutionary biology scientific community, more grounded and shared, confirming or transforming claims for ‘synthesis’ while preserving their maintenance goals

    Evolvability signatures of generative encodings: beyond standard performance benchmarks

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    Evolutionary robotics is a promising approach to autonomously synthesize machines with abilities that resemble those of animals, but the field suffers from a lack of strong foundations. In particular, evolutionary systems are currently assessed solely by the fitness score their evolved artifacts can achieve for a specific task, whereas such fitness-based comparisons provide limited insights about how the same system would evaluate on different tasks, and its adaptive capabilities to respond to changes in fitness (e.g., from damages to the machine, or in new situations). To counter these limitations, we introduce the concept of "evolvability signatures", which picture the post-mutation statistical distribution of both behavior diversity (how different are the robot behaviors after a mutation?) and fitness values (how different is the fitness after a mutation?). We tested the relevance of this concept by evolving controllers for hexapod robot locomotion using five different genotype-to-phenotype mappings (direct encoding, generative encoding of open-loop and closed-loop central pattern generators, generative encoding of neural networks, and single-unit pattern generators (SUPG)). We observed a predictive relationship between the evolvability signature of each encoding and the number of generations required by hexapods to adapt from incurred damages. Our study also reveals that, across the five investigated encodings, the SUPG scheme achieved the best evolvability signature, and was always foremost in recovering an effective gait following robot damages. Overall, our evolvability signatures neatly complement existing task-performance benchmarks, and pave the way for stronger foundations for research in evolutionary robotics.Comment: 24 pages with 12 figures in the main text, and 4 supplementary figures. Accepted at Information Sciences journal (in press). Supplemental videos are available online at, see http://goo.gl/uyY1R

    The Decoupling Hypothesis: A new idea for the origin of hominid bipedalism

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    Theoretical adaptive landscapes and mathematical representations of key constraints of evolutionary and primate biology are used to propose a new hypothesis for the origin of hominid bipedalism. These constraints suggest that the selective pressure that produced this novel form of locomotion was the need for effective suspensory and terrestrial movement. This testable hypothesis, termed the Decoupling Hypothesis, posits that bipedalism is an adaptation that enables the shoulder to maintain a high degree of mobility, a feature important to suspensory behaviors, in the face of significant demands for a high degree of stability, a feature important for highly effective terrestrial quadrupedism. Activity budgets and locomotor and postural behaviors of 18 primate groups, derived from published literature, were used to test a prediction of the Decoupling Hypothesis that bipedalism is a predictable behavior in primates which is correlated with intense demands for shoulder mobility and stability. Time was used as a proxy for estimating conflicting demands for shoulder stability and mobility. Bipedalism, as a proportion of all above-substrate locomotion, was predicted using logistic regression including seven linear variables and four two-way interaction terms. All possible regressions, using R2 and Mallow’s Cp as criterion, and stepwise variable selection procedures were used to determine significant variables. The model with a relatively high R2 (0.86) and the lowest Mallow’s Cp (-1.62), contained the following predictor variables: shoulder-abduction locomotion (p \u3c 0.0001), shoulder-abduction posture (p = 0.0003), and an interaction terms, shoulder-abduction locomotion by above-substrate locomotion (p = 0.011). The significant interaction term, predicted by the Decoupling Hypothesis, supports the hypothesis and suggests that further consideration is warranted
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