DOCSLIB.ORG

Modularity, Comparative Embryology and Evo-Devo: Developmental Dissection of Evolving Body Plans

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Modularity, Comparative Embryology and Evo-Devo: Developmental Dissection of Evolving Body Plans Developmental Biology 332 (2009) 61–69 Contents lists available at ScienceDirect Developmental Biology journal homepage: www.elsevier.com/developmentalbiology Review Modularity, comparative embryology and evo-devo: Developmental dissection of evolving body plans Shigeru Kuratani ⁎ Evolutionary Morphology Research Group, RIKEN Center for Developmental Biology, 2-2-3 Minatojima Minamimachi, Chuo-ku, Kobe 650-0047, Japan article info abstract Article history: Modules can be defined as quasi-autonomous units that are connected loosely with each other within a Received for publication 18 March 2009 system. A need for the concept of modularity has emerged as we deal with evolving organisms in Revised 18 May 2009 evolutionary developmental research, especially because it is unknown how genes are associated with Accepted 19 May 2009 anatomical patterns. One of the strategies to link genotypes with phenotypes could be to relate Available online 23 May 2009 developmental modules with morphological ones. To do this, it is fundamental to grasp the context in which certain anatomical units and developmental processes are associated with each other specifically. By Keywords: Evolution identifying morphological modularities as units recognized by some categories of general homology as Modularity established by comparative anatomy, it becomes possible to identify developmental modules whose genetic Evolutionary novelty components exhibit coextensive expressions. This permits us to distinguish the evolutionary modification in Morphological homology which the identical morphological module simply alters its shape for adaptation, without being decoupled Body plan from the functioning gene network (‘coupled modularities’), from the evolution of novelty that involves a Developmental constraints heterotopic shift between the anatomical and developmental modules. Using this formulation, it becomes possible, within the realm of Geoffroy's homologous networks, to reduce morphological homologies to developmental mechanistic terms by dissociating certain classes of modules that are often associated with actual shapes and functions. © 2009 Elsevier Inc. All rights reserved. The framework of bones being the same in the hand of a man, wing of as a possible link between the two. Modules are defined to represent a bat, fin of the porpoise and leg of the horse, - the same number of semiautonomous units or elements that are connected loosely with vertebrae forming the neck of the giraffe and of the elephant, - and others in a system (Raff, 1996; Carroll et al., 2001; Schlosser and innumerable other such facts, at once explain themselves on the Wagner, 2004; Klingenberg, 2008). There can be several different theory of descent with slow and slight successive modifications. modules defined in different contexts, such as those defined as The Origin of Species by Means of Natural Selection (Darwin, 1859) genetic, morphological, developmental and functional modules (for examples see Wagner et al. (2007), Klingenberg (2008)). Typically, …characters controlled by identical genes are not necessarily the animal body is made up of anatomical units that can often evolve homologous… The converse is no less instructive… homologous independently. For example, bats have obtained a wing based on the structures need to be controlled by identical genese and homology of forelimb module and gnathostomes have acquired jaws differentiated phenotypes does not imply similarity of genotypes. from the mandibular arch. Embryonic units such as these are also the de Beer (1971) sites at which regulatory genes are specifically expressed. Importantly, a discrete and specific regulation of genes is often Introduction associated with an anatomical unit. In the present review, the concept of modularities is considered in the context of development and Understanding the evolutionary changes involved in development evolution, as a possible conceptual tool to connect morphological and is not easy or simple. Changes can be seen at every hierarchical level of developmental units. The central issue is: how can we grasp the the developmental programs, anatomical patterns, or in the genes that interrelationships between different types of modules and how they function in morphogenetic development. To fill the gap between have changed through evolutionary processes? Because the hierarch- phenotypes and genes, the concept of modules has recently attracted ical organization of genes and any given anatomical structure do not the attention of researchers in evolutionary development (‘evo-devo’) correlate with each other, a conceptual framework has to be established to deal with the two variables simultaneously. To grasp ⁎ Fax: +81 78 306 3370. the modular structures in evo-devo biology from a top-down E-mail address: [email protected]. perspective, the discussion below focuses mainly on the relevance of 0012-1606/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.ydbio.2009.05.564 62 S. Kuratani / Developmental Biology 332 (2009) 61–69 comparative morphology to the field, including a consideration of how the body plan of animal phyla (von Baer, 1828; Raff, 1996; see below). developmental and morphological modules behave in the acquisition Thus, Geoffroy's rule can be applied primarily to animals that share of evolutionary novelties. thesamebasicbodyplanbasedonthesamemorphological modularity. What this implies is that the embryonic development Morphological modules: ideas from comparative embryology of various animals belonging to a taxon is under a certain developmental constraint to show limited changes in the connectiv- The concept of morphological homology is profoundly associated ities of organs (Fig. 1A; Maynard-Smith et al., 1985; for further with morphological modularity. Typically, animal bodies are con- elaboration see Müller and Wagner (1991), Hall (1994), Wagner and structed based on a body plan, which is made of comparable Müller (2002), Schwenk and Wagner (2003), Galis and Sinervo elements that we perceive as homologous modules to build up the (2003), Kuratani (2003); also see below). Modules and constraints plan. These include the various germ layers and their derivatives, are thus tightly linked with each other at various levels of segmental units, tissue and cell types. These units form even more morphogenesis and evolution. Morphological modularity is clear in complicated functional modules or organ systems as seen in highly organized animal groups such as arthropods and chordates. vertebrate limbs or nervous systems. Thus, the morphological modu- Comparative anatomists such as Richard Owen in 1848 and Carl larity itself can constitute a hierarchical system (Woodger, 1945; Gegenbaur in 1898 elaborated the concepts of homologies (morpho- reviewed by Hall (1998)). logical homologies) into systematized categories, which still help us Examples of homologous morphological modules relevant to evo- recognize the nature of morphological modularity. devo are best exemplified by the works of comparative morphology. First, morphological homology can be categorized into special and By the early nineteenth century, comparative anatomy had revealed general homologies. ‘Special homology’ refers to a relationship that the animal body is constructed from a set of morphologically between equivalent modules (or sets of modules) belonging to homologous units commonly found in a taxon, and that these units different animals, as we see between our arm and the bat wing are found in common connectivities. Geoffroy St. Hilaire (1818) called (Fig. 1B). This type of homology is divided further into complete and this the ‘principe des connexions’, which is still regarded as the incomplete types (Fig. 2). Of these, ‘complete homology’ means a simplest definition of morphological homology (Hall, 1998). This is perfect match of homologous modules, as seen in elements in the also a context in which archetypes have been postulated to represent forelimbs among amniote species, whereas ‘incomplete homology’ is a Fig. 1. Constraint and homology. (A) Various faces of different mammals share the same basic arrangement of organs, based on a common developmental program. Thus, morphological homology is conserved through the ancestral developmental constraint for the mammalian facial patterning program, which is hard to override through evolution. (B) Various hindlimbs seen in various tetrapods: 1 and 2, amphibians; 3–7, reptiles; 8, a bird; 9–16, mammals. Complete homologies can be established for many of the hindlimbs shown here. A is from Haeckel (1874), B is from Haeckel (1902). S. Kuratani / Developmental Biology 332 (2009) 61–69 63 derm, and induction of epibranchial placodes (Begbie et al., 1999; Holzschuh et al., 2005; see also Kuratani and Kirby (1991, 1992) for pharyngeal arch formation). In other words, somitomeric and branchiomeric modules in the vertebrate body are established under the influence of generative constraints (Wagner, 1994) derived from primary segmental modules in embryos, the somites and pharyngeal pouches, respectively (see Kuratani (2008) for generative constraint and serial homology). Links between morphological and developmental modules As mentioned above, there can be various types of modularities in developmental phenomena. Among these, the subdivisions of general homology (Homodynamie, Homotypie, Homonymie and Homonomie) are associated with specific functions of control genes that are often called ‘genetic toolkits’ (reviewed by Carroll et al. (2001) and by De Robertis (2008)).
Load more

Recommended publications
  • Modularity As a Concept Modern Ideas About Mental Modularity Typically Use Fodor (1983) As a Key Touchstone
    COGNITIVE PROCESSING International Quarterly of Cognitive Science Mental modularity, metaphors, and the marriage of evolutionary and cognitive sciences GARY L. BRASE University of Missouri – Columbia Abstract - As evolutionary approaches in the behavioral sciences become increasingly prominent, issues arising from the proposition that the mind is a collection of modular adaptations (the multi-modular mind thesis) become even more pressing. One purpose of this paper is to help clarify some valid issues raised by this thesis and clarify why other issues are not as critical. An aspect of the cognitive sciences that appears to both promote and impair progress on this issue (in different ways) is the use of metaphors for understand- ing the mind. Utilizing different metaphors can yield different perspectives and advancement in our understanding of the nature of the human mind. A second purpose of this paper is to outline the kindred natures of cognitive science and evolutionary psychology, both of which cut across traditional academic divisions and engage in functional analyses of problems. Key words: Evolutionary Theory, Cognitive Science, Modularity, Metaphors Evolutionary approaches in the behavioral sciences have begun to influence a wide range of fields, from cognitive neuroscience (e.g., Gazzaniga, 1998), to clini- cal psychology (e.g., Baron-Cohen, 1997; McGuire and Troisi, 1998), to literary theory (e.g., Carroll, 1999). At the same time, however, there are ongoing debates about the details of what exactly an evolutionary approach – often called evolu- tionary psychology— entails (Holcomb, 2001). Some of these debates are based on confusions of terminology, implicit arguments, or misunderstandings – things that can in principle be resolved by clarifying current ideas.
    [Show full text]
  • Transformations of Lamarckism Vienna Series in Theoretical Biology Gerd B
    Transformations of Lamarckism Vienna Series in Theoretical Biology Gerd B. M ü ller, G ü nter P. Wagner, and Werner Callebaut, editors The Evolution of Cognition , edited by Cecilia Heyes and Ludwig Huber, 2000 Origination of Organismal Form: Beyond the Gene in Development and Evolutionary Biology , edited by Gerd B. M ü ller and Stuart A. Newman, 2003 Environment, Development, and Evolution: Toward a Synthesis , edited by Brian K. Hall, Roy D. Pearson, and Gerd B. M ü ller, 2004 Evolution of Communication Systems: A Comparative Approach , edited by D. Kimbrough Oller and Ulrike Griebel, 2004 Modularity: Understanding the Development and Evolution of Natural Complex Systems , edited by Werner Callebaut and Diego Rasskin-Gutman, 2005 Compositional Evolution: The Impact of Sex, Symbiosis, and Modularity on the Gradualist Framework of Evolution , by Richard A. Watson, 2006 Biological Emergences: Evolution by Natural Experiment , by Robert G. B. Reid, 2007 Modeling Biology: Structure, Behaviors, Evolution , edited by Manfred D. Laubichler and Gerd B. M ü ller, 2007 Evolution of Communicative Flexibility: Complexity, Creativity, and Adaptability in Human and Animal Communication , edited by Kimbrough D. Oller and Ulrike Griebel, 2008 Functions in Biological and Artifi cial Worlds: Comparative Philosophical Perspectives , edited by Ulrich Krohs and Peter Kroes, 2009 Cognitive Biology: Evolutionary and Developmental Perspectives on Mind, Brain, and Behavior , edited by Luca Tommasi, Mary A. Peterson, and Lynn Nadel, 2009 Innovation in Cultural Systems: Contributions from Evolutionary Anthropology , edited by Michael J. O ’ Brien and Stephen J. Shennan, 2010 The Major Transitions in Evolution Revisited , edited by Brett Calcott and Kim Sterelny, 2011 Transformations of Lamarckism: From Subtle Fluids to Molecular Biology , edited by Snait B.
    [Show full text]
  • The Impact of Component Modularity on Design Evolution: Evidence from the Software Industry
    08-038 The Impact of Component Modularity on Design Evolution: Evidence from the Software Industry Alan MacCormack John Rusnak Carliss Baldwin Copyright © 2007 by Alan MacCormack, John Rusnak, and Carliss Baldwin. Working papers are in draft form. This working paper is distributed for purposes of comment and discussion only. It may not be reproduced without permission of the copyright holder. Copies of working papers are available from the author. Abstract Much academic work asserts a relationship between the design of a complex system and the manner in which this system evolves over time. In particular, designs which are modular in nature are argued to be more “evolvable,” in that these designs facilitate making future adaptations, the nature of which do not have to be specified in advance. In essence, modularity creates “option value” with respect to new and improved designs, which is particularly important when a system must meet uncertain future demands. Despite the conceptual appeal of this research, empirical work exploring the relationship between modularity and evolution has had limited success. Three major challenges persist: first, it is difficult to measure modularity in a robust and repeatable fashion; second, modularity is a property of individual components, not systems as a whole, hence we must examine these dynamics at the microstructure level; and third, evolution is a temporal phenomenon, in that the conditions at time t affect the nature of the design at time t+1, hence exploring this phenomenon requires longitudinal data. In this paper, we tackle these challenges by analyzing the evolution of a successful commercial software product over its entire lifetime, comprising six major “releases.” In particular, we develop measures of modularity at the component level, and use these to predict patterns of evolution between successive versions of the design.
    [Show full text]
  • Task-Dependent Evolution of Modularity in Neural Networks1
    Task-dependent evolution of modularity in neural networks1 Michael Husk¨ en, Christian Igel, and Marc Toussaint Institut fur¨ Neuroinformatik, Ruhr-Universit¨at Bochum, 44780 Bochum, Germany Telephone: +49 234 32 25558, Fax: +49 234 32 14209 fhuesken,igel,[email protected] Connection Science Vol 14, No 3, 2002, p. 219-229 Abstract. There exist many ideas and assumptions about the development and meaning of modu- larity in biological and technical neural systems. We empirically study the evolution of connectionist models in the context of modular problems. For this purpose, we define quantitative measures for the degree of modularity and monitor them during evolutionary processes under different constraints. It turns out that the modularity of the problem is reflected by the architecture of adapted systems, although learning can counterbalance some imperfection of the architecture. The demand for fast learning systems increases the selective pressure towards modularity. 1 Introduction The performance of biological as well as technical neural systems crucially depends on their ar- chitectures. In case of a feed-forward neural network (NN), architecture may be defined as the underlying graph constituting the number of neurons and the way these neurons are connected. Particularly one property of architectures, modularity, has raised a lot of interest among researchers dealing with biological and technical aspects of neural computation. It appears to be obvious to emphasise modularity in neural systems because the vertebrate brain is highly modular both in an anatomical and in a functional sense. It is important to stress that there are different concepts of modules. `When a neuroscientist uses the word \module", s/he is usually referring to the fact that brains are structured, with cells, columns, layers, and regions which divide up the labour of information processing in various ways' 1This paper is a revised and extended version of the GECCO 2001 Late-Breaking Paper by Husk¨ en, Igel, & Toussaint (2001).
    [Show full text]
  • Modularity in Animal Development and Evolution: Elements of a Conceptual Framework for Evodevo
    JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 285:307–325 (1999) Modularity in Animal Development and Evolution: Elements of a Conceptual Framework for EvoDevo GEORGE VON DASSOW*AND ED MUNRO Department of Zoology, University of Washington, Seattle, Washington 98195-1800 ABSTRACT For at least a century biologists have been talking, mostly in a black-box sense, about developmental mechanisms. Only recently have biologists succeeded broadly in fishing out the contents of these black boxes. Unfortunately the view from inside the black box is almost as obscure as that from without, and developmental biologists increasingly confront the need to synthesize known facts about developmental phenomena into mechanistic descriptions of com- plex systems. To evolutionary biologists, the emerging understanding of developmental mecha- nisms is an opportunity to understand the origins of variation not just in the selective milieu but also in the variability of the developmental process, the substrate for morphological change. Ultimately, evolutionary developmental biology (EvoDevo) expects to articulate how the diversity of organic form results from adaptive variation in development. This ambition demands a shift in the way biologists describe causality, and the central problem of EvoDevo is to understand how the architecture of development confers evolvability. We argue in this essay that it makes little sense to think of this question in terms of individual gene function or isolated morphometrics, but rather in terms of higher-order modules such as gene networks and homologous characters. We outline the conceptual challenges raised by this shift in perspective, then present a selection of case studies we believe to be paradigmatic for how biologists think about modularity in devel- opment and evolution.
    [Show full text]
  • The Emergence of Modularity in Biological Systems
    The Emergence of Modularity in Biological Systems Zhenyu Wang Dec. 2007 Abstract: Modularity is a ubiquitous phenomenon in various biological systems, both in genotype and in phenotype. Biological modules, which consist of components relatively independent in functions as well as in morphologies, have facilitated daily performance of biological systems and their long time evolution in history. How did modularity emerge? A mechanism with horizontal gene transfer and a biological version of spin-glass model is addressed here. When the spontaneous symmetry is broken in an evolving environment, here comes modularity. Further improvement is also discussed at the end. 1 Introduction Modularity is an important concept with broad applications in computer science, especially in programming. A module, usually composed of various components, is a relatively independent entity in its operation with respect to other entities in the whole system. For a programmer, the employment of a module will increase the efficiency of coding, decrease the potential of errors, enhance the stability of the operation and facilitate the further improvement of the program. Coincidently, the nature thinks the same in its programming life: various biological systems are also in a modular fashion! Let us take the model organism fruit fly Drosophila melanogaster as an example to sip the ubiquitous modularity in biological systems. In view of morphology, Drosophila is a typical modular insect, whose adult is composed of an anterior head, followed by three thoracic segments, and eight abdominal segments at posterior[1](Fig. 1). Such a kind of segmentation is induced by a cascade of transcription factors in the embryo. First, maternal effect genes which are expressed in the mother’s ovary cells distribute cytoplasmic determinants unevenly in fertilized eggs, which thus determines anterior-posterior and dorsal-ventral axis.
    [Show full text]
  • Evolution of Networks for Body Plan Patterning; Interplay of Modularity, Robustness and Evolvability
    Evolution of Networks for Body Plan Patterning; Interplay of Modularity, Robustness and Evolvability Kirsten H. ten Tusscher1,2*, Paulien Hogeweg1 1 Theoretical Biology and Bioinformatics Group, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands, 2 Scientific Computing, Simula Research Laboratory, Oslo, Norway Abstract A major goal of evolutionary developmental biology (evo-devo) is to understand how multicellular body plans of increasing complexity have evolved, and how the corresponding developmental programs are genetically encoded. It has been repeatedly argued that key to the evolution of increased body plan complexity is the modularity of the underlying developmental gene regulatory networks (GRNs). This modularity is considered essential for network robustness and evolvability. In our opinion, these ideas, appealing as they may sound, have not been sufficiently tested. Here we use computer simulations to study the evolution of GRNs’ underlying body plan patterning. We select for body plan segmentation and differentiation, as these are considered to be major innovations in metazoan evolution. To allow modular networks to evolve, we independently select for segmentation and differentiation. We study both the occurrence and relation of robustness, evolvability and modularity of evolved networks. Interestingly, we observed two distinct evolutionary strategies to evolve a segmented, differentiated body plan. In the first strategy, first segments and then differentiation domains evolve (SF strategy). In the second scenario segments and domains evolve simultaneously (SS strategy). We demonstrate that under indirect selection for robustness the SF strategy becomes dominant. In addition, as a byproduct of this larger robustness, the SF strategy is also more evolvable. Finally, using a combined functional and architectural approach, we determine network modularity.
    [Show full text]
  • Modularity in Signaling Systems
    Modularity in Signaling Systems Domitilla Del Vecchio Department of Mechanical Engineering, Laboratory for Information and Decision Systems (LIDS), MIT, 77 Massachusetts Ave, Cambridge, MA 02139 E-mail: [email protected] Modularity in Signaling Systems 2 Abstract. Modularity is a property by which the behavior of a system does not change upon interconnection. It is crucial for understanding the behavior of a complex system from the behavior of the composing subsystems. Whether modularity holds in biology is an intriguing and largely debated question. In this paper, we discuss this question taking a control systems theory view and focusing on signaling systems. In particular, we argue that, despite signaling systems are constituted of structural modules, such as covalent modification cycles, modularity does not hold in general. As in any engineering system, impedance-like effects, called retroactivity, appear at interconnections and alter the behavior of connected modules. We further argue that while signaling systems have evolved sophisticated ways to counter-act retroactivity and enforce modularity, retroactivity may also be exploited to finely control the information processing of signaling pathways. Testable predictions and experimental evidence are discussed with their implications. 1. Introduction The idea that modularity is a general principle of biological organization and that signaling systems, in particular, are modularly assembled has been considered and discussed by several researchers [1,10,21]. In particular, a modular systems approach to understanding information transfer in signaling networks has been proposed as a way to defeat the complexity of networks [4,20,24,25]. For example, signaling pathways involved in caspase activation have been studied through a modular approach to determine the key contributors in triggering apoptosis [9].
    [Show full text]
  • Varieties of Modules: Kinds, Levels, Origins, and Behaviors RASMUS G
    116JOURNAL OF EXPERIMENTAL R.G. WINTHER ZOOLOGY (MOL DEV EVOL) 291:116–129 (2001) Varieties of Modules: Kinds, Levels, Origins, and Behaviors RASMUS G. WINTHER* Department of History and Philosophy of Science, and Department of Biology, Indiana University, Bloomington, Indiana 47405 ABSTRACT This article began as a review of a conference, organized by Gerhard Schlosser, entitled “Modularity in Development and Evolution.” The conference was held at, and sponsored by, the Hanse Wissenschaftskolleg in Delmenhorst, Germany in May, 2000. The article subse- quently metamorphosed into a literature and concept review as well as an analysis of the differ- ences in current perspectives on modularity. Consequently, I refer to general aspects of the conference but do not review particular presentations. I divide modules into three kinds: struc- tural, developmental, and physiological. Every module fulfills none, one, or multiple functional roles. Two further orthogonal distinctions are important in this context: module-kinds versus mod- ule-variants-of-a-kind and reproducer versus nonreproducer modules. I review criteria for indi- viduation of modules and mechanisms for the phylogenetic origin of modularity. I discuss conceptual and methodological differences between developmental and evolutionary biologists, in particular the difference between integration and competition perspectives on individualization and modular behavior. The variety in views regarding modularity presents challenges that require resolution in order to attain a comprehensive,
    [Show full text]
  • The Body Plan Concept and Its Centrality in Evo-Devo
    Evo Edu Outreach (2012) 5:219–230 DOI 10.1007/s12052-012-0424-z EVO-DEVO The Body Plan Concept and Its Centrality in Evo-Devo Katherine E. Willmore Published online: 14 June 2012 # Springer Science+Business Media, LLC 2012 Abstract A body plan is a suite of characters shared by a by Joseph Henry Woodger in 1945, and means ground plan group of phylogenetically related animals at some point or structural plan (Hall 1999; Rieppel 2006; Woodger 1945). during their development. The concept of bauplane, or body Essentially, a body plan is a suite of characters shared by a plans, has played and continues to play a central role in the group of phylogenetically related animals at some point study of evolutionary developmental biology (evo-devo). during their development. However, long before the term Despite the importance of the body plan concept in evo- body plan was coined, its importance was demonstrated in devo, many researchers may not be familiar with the pro- research programs that presaged the field of evo-devo, per- gression of ideas that have led to our current understanding haps most famously (though erroneously) by Ernst Haeck- of body plans, and/or current research on the origin and el’s recapitulation theory. Since the rise of evo-devo as an maintenance of body plans. This lack of familiarity, as well independent field of study, the body plan concept has as former ties between the body plan concept and metaphys- formed the backbone upon which much of the current re- ical ideology is likely responsible for our underappreciation search is anchored.
    [Show full text]
  • Phenotypic Plasticity and Modularity Allow for the Production of Novel
    Londe et al. EvoDevo (2015) 6:36 DOI 10.1186/s13227-015-0031-5 EvoDevo RESEARCH Open Access Phenotypic plasticity and modularity allow for the production of novel mosaic phenotypes in ants Sylvain Londe1*, Thibaud Monnin1, Raphaël Cornette2, Vincent Debat2, Brian L. Fisher3 and Mathieu Molet1 Abstract Background: The origin of discrete novelties remains unclear. Some authors suggest that qualitative phenotypic changes may result from the reorganization of preexisting phenotypic traits during development (i.e., developmental recombination) following genetic or environmental changes. Because ants combine high modularity with extreme phenotypic plasticity (queen and worker castes), their diversified castes could have evolved by developmental recombination. We performed a quantitative morphometric study to investigate the developmental origins of novel phenotypes in the ant Mystrium rogeri, which occasionally produces anomalous ‘intercastes.’ Our analysis compared the variation of six morphological modules with body size using a large sample of intercastes. Results: We confirmed that intercastes are conspicuous mosaics that recombine queen and worker modules. In addition, we found that many other individuals traditionally classified as workers or queens also exhibit some level of mosaicism. The six modules had distinct profiles of variation suggesting that each module responds differentially to factors that control body size and polyphenism. Mosaicism appears to result from each module responding differently yet in an ordered and predictable manner to intermediate levels of inducing factors that control polyphenism. The order of module response determines which mosaic combinations are produced. Conclusions: Because the frequency of mosaics and their canalization around a particular phenotype may evolve by selection on standing genetic variation that affects the plastic response (i.e., genetic accommodation), develop- mental recombination is likely to play an important role in the evolution of novel castes in ants.
    [Show full text]
  • Dispositional Properties in Evo-Devo in L
    This is a pre-print version of Dispositional Properties in Evo-Devo in L. Nuño de la Rosa and G. Müller (eds.) Evolutionary Developmental Biology: A Reference Guide. The final publication is available at Springer via http://doi.org/10.1007/978-3-319-33038-9_64-1 Dispositional Properties in Evo-Devo Christopher J. Austin and Laura Nuño de la Rosa Abstract In identifying intrinsic molecular chance and extrinsic adaptive pressures as the only causally relevant factors in the process of evolution, the theoretical perspective of the Modern Synthesis had a major impact on the perceived tenability of an ontology of dispositional properties. However, since the late 1970s, an increasing number of evolutionary biologists have challenged the descriptive and explanatory adequacy of this ―chance alone, extrinsic only‖ understanding of evolutionary change. Because morphological studies of homology, convergence, and teratology have revealed a space of possible forms and phylogenetic trajectories that is considerably more restricted than expected, evo-devo has focused on the causal contribution of intrinsic developmental processes to the course of evolution. Evo-devo‘s investigation into the developmental structure of the modality of morphology – including both the possibility and impossibility of organismal form – has led to the utilisation of a number of dispositional concepts that emphasise the tendency of the evolutionary process to change along certain routes. In this sense, and in contrast to the perspective of the Modern Synthesis, evo-devo can be described as a ―science of dispositions.‖ This chapter discusses the recent philosophical literature on dispositional properties in evo-devo, exploring debates about both the metaphysical and epistemological aspects of the central dispositional concepts utilised in contemporary evo-devo (e.g., variability, modularity, robustness, plasticity, and evolvability) and addressing the epistemological question of how dispositional properties challenge existing explanatory models in evolutionary biology.
    [Show full text]