Dcc

Attraction Attractive response silenced Figure 8 Modulatorsofaxon navigation. Examples of ways in which responses of axons can be modulated during development (see text for description of each example) a, regulated gene expression b, post-transcriptional control c, local translation and d, receptor interaction. Modulation of axon guidance using such methods allows for the generation of diverse outcomes using a small suite of guidance cues. been identified in the initial axon segment (Steward...

References

Preferential representation of the fovea in the primary visual cortex. Nature 361, 719-721. Bishop, K. M., Goudreau, G., and O'Leary, D. D. 2000. Regulation of area identity in the mammalian neocortex by Emx2 and Pax6. Science 5464, 344-349. Bush, E. C., Simons, E. L., Dubowitz, D. J., and Allman, J. M. 2004. Endocranial volume and optic foramen size in parapithecus grangeri. In Anthropoid Origins New Visions (eds. C. Ross and R. Kay), pp. 603-614. Kluwer...

Stars and Stripes in the Cortex

Star-nosed moles have an exceptionally well-developed somatosensory system allowing them to identify and consume small prey items faster than any other mammal (Catania and Remple, 2005). This ability stems from the densely innervated mechanosensory star covered by tens of thousands of tactile Eimer's organs (Catania, 1995). As occurs for whiskers in rodents, the specialized glabrous Figure 1 Cortical barrels in the mouse as revealed by cytochrome oxidase histochemistry. In many rodents, the...

Vnc

otd Otx unpg Gbx2 _ Pax2 5 8 Hox1 orthologues Figure 6 Tripartite organization of the (a) Drosophila, (b) mouse, and (c) ascidian brain, based on expression patterns of orthologous genes. The expression of otd Otx2, unpg Gbx2, Pax2 5 8, and Hox1 gene orthologues in the developing CNS of (a) stage 13 14 Drosophila embryo, (b) stage E10 mouse embryo, and (c) neurula ascidian embryo. In all cases, a Pax2 5 8-expressing domain is located between an anterior otd Otx2 expressing region and a...

Conclusions

In this article I have discussed some of the evidence from star-nosed moles and rodents for how changes in the details of neocortical maps may be effected through alterations of sensory surfaces in the periphery. The title of this article was inspired by the conclusion that many of these peripheral influences on the organization of the brain may not require a change in the expression of patterning genes in the CNS during the course of evolution. Rather, relatively small changes in gene...

Conceptual Considerations

Evolutionary developmental biologists try to understand the mechanisms that produce homologous and homoplastic structures, and how variation and novelties originate during development and in evolution. Understanding these principles is essential for studying evolution of a complex biological structure, such as the brain. In this section, I provide a very brief analysis of the causes and principles of evolution, for then applying these ideas to the study of brain evolution in the following...

Relative Size versus Absolute Size

The most obvious difference between species is that they differ enormously in size. Because life began with tiny organisms, evolutionary increases in body size must have outnumbered or outpaced the decreases. This is true of organisms generally, but it also holds for several individual lineages, including mammals and, within mammals, primates (Stanley, 1973 Alroy, 1998). The most fascinating aspect of those changes in body size is that they involved much more than the isometric scaling up or...

Homology Similarity Due to Common Ancestry

All methods of ancestral character state reconstruction make explicit assumptions about the homology of the traits under study. In comparative biology the term 'homology' refers to similarity in form or function arising from common ancestry. In other words, homologous features among organisms can be traced to a single evolutionary origin. In the language of Garstang (1922), a homologous trait is a unique historical change in the developmental program of an evolving lineage. Homologous...

Character or Trait Data

Methods for estimating ancestral character states and analyzing phenotypic evolution may treat trait data either as continuous (quantitative) or discrete (qualitative) (Zelditch et al., 1995 Rohlf, 1998 Wiens, 2001). Continuously distributed trait values have no easily distinguished boundaries between phenotypes. Examples of continuous traits include the sizes of brains and brain regions (e.g., nuclei), the number of cells in a brain region, pigment intensity, amplitude or timing of...

Lam

Commissural axons in dorsal spinal cord extend axons toward netrin-1 expressing floorplate. Rig-1 represses responsiveness to Slits. Once past the floorplate, inhibition of Robos by Rig-1 is removed, and commissural axons are repelled from the midline After crossing, axons turn anteriorly and grow next to the floorplate, up an increasing gradient of Wnt4, a diffusible chemoattractant. Figure 7 Axon navigation in the ventral nerve cord of Drosophila and in the vertebrate spinal cord. a, The...

Phylogenetic Trees

Implicit in all phylogenetic methods for studying character evolution is a tree-shaped branching diagram, alternatively called a dendrogram, cladogram, phenogram, or tree, depending on the methods used to construct the diagram, and the information content it is intended to convey. It is important to note that each of the many alterative methods for building trees that are currently available was designed to communicate different kinds of information. The methods grouped formally as...

Jiy

Relative position of Relative position of centrosome, t 0 leading process, t 0 Figure 1 Steps in neuronal migration and the molecules involved. A prototypical migrating neuron contains distinct subcellular domains the leading process, the perinuclear domain, and the trailing process. Neuronal migration involves repeated cycles of (1) polarized extension of the leading process, followed by movement of the centrosome forward, (2) a highly coordinated movement of the nucleus closer to the...

Background and Introduction

1.07.1.1 Why Evolutionary Neuroethology The question of how nervous systems and behavior evolve is a core issue in both neurobiology and evolutionary biology. How can something as extraordinarily complex as the neuronal networks underlying behavior (neurobehavioral networks) tolerate change without compromising function The nervous systems, including the brains, of species within large taxonomic groups look remarkably similar while often producing strikingly different behaviors. Biologists, at...

Myelination

In the nervous system, developmental regulation of ion channels is not unique to neurons. Glial cells also display developmentally regulated properties of excitability (Sontheimer et al., 1992 Kressin et al., 1995 Bordey and Sontheimer, 1997 Maric et al., 1998 Bringmann et al., 2000 Pannicke et al., 2002 for review, see Waxman et al., 1993). The distribution of specific sodium and potassium channel isoforms in myelinated axons provides one of the most interesting examples of developmental...

Neuronal Migration

O Marin and G Lopez-Bendito, Consejo Superior de Investigaciones Cient ficas y Universidad Miguel Hern ndez, Sant Joan d'Alacant, Spain 2007 Elsevier Inc. All rights reserved. 1.11.2 Cellular Mechanisms in Neuronal Migration 170 1.11.2.1 Polarization of Migrating Neurons 170 1.11.3 Modes of Migration in the Developing Brain 173 1.11.3.1 Two Primary Modes of Migration in the Developing CNS 173 1.11.3.2 Evolutionary Advantages of Different Modes of Migration 175 1.11.4 Mechanisms of Radial...

Nonbilaterians Porifera Placozoa Ctenophora Cnidaria and Myxozoa

Porifera, Placozoa, Ctenophora, Cnidaria, and Myxozoa are the earliest diverging animal groups (Figures 1 and 2). Available evidence supports Porifera as the basal-most of these taxa. However, in contrast to traditional ideas, the sponges may not form a clade, and the interrelationships of the other basal metazoans are unclear at the present time (Rokas et al., 2003a Halanych, 2004). Three main groups of living sponges are recognized (1) Calcarea, or sponges with a skeleton of calcareous...

Deuterostomia

The three core phyla of the Deuterostomia are the echinoderms, the hemichordates (enteropneusts and pterobranchs), and the chordates (urochordates, cephalochordates, and craniates plus vertebrates Figure 3). In addition, recent molecular phyloge-netic research has added the enigmatic and rather simple worm X. bocki to the deuterostomes as well (Bourlat et al., 2003). Of the three main bilaterian clades, the high-level phylogeny of the deuteros-tomes is currently best understood. This section...

Info

Figure 8 The spiking (a, b) and nonspiking (c) telson-uropod stretch receptors compared. Left column, ventral views of dissected tailfans to show position of the ATU muscle and the receptors in a, M. quadrispina (Galatheidae) b, B. occidentalis (Albuneidae) and c, E. analoga (Hippidae). On the right side, the area of dorsal telson from which the ATU muscle fibers arise is shown compare to position of AT muscle in crayfish (Figure 5b). Arrows point to dorsal attachment of receptor strand on...

Neurobehavioral Mechanisms and Biomechanics are Inseparable

Tailfan skeleton musculature, tailflip behaviors, and MG and LG neurons are interrelated. Before plunging into the analysis of any central nervous system, the machinery that the particular nervous system operates must be considered. For example, cephalo-pod mollusks have excellent visual capabilities and manipulative skills, as do humans, but our brain in an octopus would be as helpless in controlling Figure 4 The mosaic ancestry of sand crab digging behaviors. Limb movements of hippids (a, c)...

Invertebrates

Encephalization has not been as well studied in invertebrates as in vertebrates. Some structures have, however, been thought to play equivalent roles to the ones that the forebrain plays in mammals and birds. Invertebrates often cited for their cognitive skills are the hymenoptera on the one hand and the octopus and cuttlefish on the other (see Cognition in Invertebrates). Hymenoptera have the most complex social behaviors of all insects. Octopus and cuttlefish are at the extremes of the...

Scala Naturae versus Phylogenetic Bush

The idea of evolution proceeding along some kind of scale from simple to complex also has pre-evolu-tionary roots. Aristotle, for example, ordered animals according to the degree of perfection of their eggs (see Gould, 1977). Later religious thinkers then described an elaborate scale of nature, or scala naturae, with inanimate materials on its bottom rung and archangels and God at the other extreme. The early evolutionists, such as Lamarck, transformed this static concept of a scala naturae...

Phylogenetic Character Reconstruction

J S Albert, University of Louisiana, Lafayette, LA, USA 2007 Elsevier Inc. All rights reserved. 1.03.1 Introduction to Character State Reconstruction and Evolution 42 1.03.2.1 Homology Similarity Due to Common Ancestry 43 1.03.2.2 Homoplasy Convergence, Parallelism, and Reversal 43 1.03.2.3 Character State Polarity 43 1.03.2.4 Character or Trait Data 44 1.03.2.6 Phylogenetic Trees 45 1.03.3.1 Parsimony Optimization of Discrete Traits 47 1.03.3.2 Binary and Multistate Characters 47 1.03.3.3...

Introduction to Metazoan Phylogeny

This article provides an outline of our current understanding of the phylogeny of the kingdom Metazoa, which comprises all multicellular animals (most authors equate Metazoa with Animalia, but a few apply the latter name to a more inclusive group of Metazoa plus Choanoflagellata, the most likely sister taxon of animals). Metazoan phylogenetics has a long pedigree. The first generation of evolutionary biologists in the period immediately following the publication of Charles Darwin's On the...

The Retinal Projection and the Midline Choice Point Model Systems to Study Axon Pathfinding

Rgc Axon Diencephalon

During the past decade, our understanding of axon-pathfinding mechanisms has been advanced through the use of invertebrate and vertebrate model systems. Two well-known model systems have provided many insights into the processes of axon pathfinding and we will confine our discussion to these examples the vertebrate retinal projection and the midline of the developing CNS. Importantly, many of the guidance cues described in the previous section play integral roles in mediating axon guidance...

The Growth Cone A Central Player in Axon Pathfinding

The growth cone structure was first characterized more than a century ago by the Spanish neuroana-tomist, Ramon y Cajal. He imagined the growth cone as a ''soft battering ram'' that extending axons used to force their way through the embryonic brain (Ramon y Cajal, 1890). Following this discovery, it was shown that axons of embryonic neural tube tissue are tipped with growth cones and are able to grow along a glass coverslip (Harrison, 1910). These very active structures have now been...

Tripartite Organization of the Insect and Chordate Brain

The conserved expression and function of otd Otx and Hox genes suggest that invertebrate and vertebrate brains are all characterized by a rostral region specified by genes of the otd Otx family and a caudal region specified by genes of the Hox family. However, in ascidians and vertebrates, a Pax2 5 8 expression domain is located between the anterior Otx and the posterior Hox expression regions of the embryonic brain Holland and Holland, 1999 Wada and Satoh, 2001 . In vertebrate brain...

Parsimony Optimization of Discrete Traits

The principle of parsimony i.e., Occam's razor is widely used in the natural sciences as a method for selecting from among numerous alternative hypotheses. The principle of parsimony underlies all scientific modeling and theory building. The basic idea is that one should not increase, beyond what is necessary, the number of entities required to explain anything. In this context, parsimony means that simpler hypotheses are preferable to more complicated ones. It is not generally meant to imply...

What Is Encephalized

As recently as the 1960s, some researchers had a logic based on uncorrected absolute size for their evolutionary and or ecological hypotheses on ence-phalization. Most researchers today although see Byrne and Corp, 2004, for discussion assume that encephalization should be studied after some kind of complete or partial control for allometry, often assessed by body size see Scaling the Brain and Its Connections, Encephalization Comparative Studies of Brain Size and Structure Volume in Mammals,...

Further Reading

Acampora, D., Gulisano, M., Broccoli, V., and Simeone, A. 2001. Otx genes in brain morphogenesis. Prog. Neurobiol. 64, 69-95. Adoutte, A., Balavoine, G., Lartillot, N., Lespinet, O., Prud'homme, B., and de Rosa, R. 2000. The new animal phylogeny Reliability and implications. Proc. Natl. Acad. Sci. USA 97, 4453-4456. Arendt, D. and Niibler-Jung, K. 1999. Comparison of early nerve cord development in insects and vertebrates. Development 126, 2309-2325. De Robertis, E. M. and Sasai, Y. 1996. A...

Modes of Migration in the Developing Brain

Tangential Versus Radial Migration Brain

1.11.3.1 Two Primary Modes of Migration in the Developing CNS As discussed in the previous section, the cellular mechanisms underlying the migration of neurons are likely to be similar to those in other cell types. Despite these molecular similarities, two different modes of migration are classically distinguished within the developing brain, radial and tangential migration. In a general sense, radial migration refers to neurons that migrate perpendicularly to the surface of the brain. In...

Evolution of the Action Potential

RH Pineda and AB Ribera, University of Colorado at Denver and Health Sciences Center, Aurora, CO, USA 2007 Elsevier Inc. All rights reserved. 1.13.2 What Are Action Potentials 212 1.13.2.1 APs are Neuronal Signatures 213 1.13.2.2 AP Waveform Properties 213 1.13.3 Molecular Determinants of APs 214 1.13.4 Roles in Information Coding 215 1.13.4.1 Prior to Synapse Formation 215 1.13.4.2 During Synapse Formation and Early Circuit Activity 215 1.13.4.3 Mature Nervous System 216 1.13.5 Regulation of...

Character State Polarity

A central task of ancestral character state reconstruction is determining the direction or polarity of evolutionary change between alternative states of a character. The ancestral state is referred to as plesiomorphic or primitive, and the descendent state is referred to as apomorphic or derived. Establishing the polarity of a character state transformation is critical to understanding the functional significance of that event. Phenotypes determined to be primitive simply mean they precede the...

Ecdysozoa

Monophyly of the clade Ecdysozoa was one of the major surprises of the molecular phylogenetics of the Metazoa because it implied that the segmented arthropods and annelids were merely distant relatives, with the former a member of Ecdysozoa, and the latter a member of Lophotrochozoa. Ecdysozoa unites the arthropods e.g., insects, crustaceans, myriapods, and chelicerates , onychophorans velvet worms , tardigrades water bears , nema-todes roundworms , nematomorphs horsehair worms , priapulids,...

Cellular Mechanisms in Neuronal Migration

Despite prominent differences in the distance covered by distinct neuronal types until their final settlement in the brain, or even fundamental discrepancies in the primary mode of migration used by different populations of neurons discussed in detail in the next section , migrating neurons appear to use a basic set of cellular mechanisms that is roughly similar to those used by other cell types during vertebrate morphogenesis. In that sense, neuronal migration can be considered a cyclic...

IiG Compensatory Innervation in Development and Evolution

S L Pallas, Georgia State University, Atlanta, GA, USA 2007 Elsevier Inc. All rights reserved. 1.10.2 Evolution Exploits Developmental Events 154 1.10.2.1 Brain Evolution Results from Minor Variations on a Basic Vertebrate Plan 154 1.10.2.2 Developmental Mechanisms can Accommodate New Neurons and Trigger Matching Changes 1.10.3 Target Specificity and Its Role in Development and Evolution 155 1.10.3.1 Population Matching in the Retinotectal System 155 1.10.3.2 Role of Sensory Deprivation in...

Squared Change and Linear Parsimony

There are two general types of MP widely used in tracing the evolution of continuous traits squared-change parsimony and linear parsimony. Squared-change algorithms Rogers, 1984 seek to minimize the amount of squared change along each branch across the entire tree simultaneously, using a formula in which the cost of a change from state x to y is x y 2. Squared-change parsimony assigns a single ancestral value to each internal node to minimize the sum of squares change over the tree Maddison,...

The CNS Midline Pattern Formation and Axonal Guidance

In the nervous systems of bilaterians, specialized cells located at the midline of the neuroectoderm play an essential role in organizing the development of the CNS Tessier-Lavigne and Goodman, 1996 Dickson, 2002 . In insects and vertebrates, cells of the CNS midline are known to represent inductive centers for the regional patterning of the neuroecto-derm. Moreover, the CNS midline represents an important intermediate target where growing axons either cross and project contralaterally or...

Lophotrochozoa

The clade Lophotrochozoa Figure 8 was originally proposed on the basis of SSU sequence data to designate the lophophorates brachiopods, phoronids, and ectoprocts , annelids, and mollusks. Further investigations have increased lophotrochozoan membership also to include the echiurans, sipuncu-lans, entoprocts, platyhelminths, nemerteans, gnathostomulids, rotifers, acanthocephalans, cycliophorans, micrognathozoans, and possibly gas-trotrichs and chaetognaths. Lophotrochozoan monophyly is...

Common Bauplan for Animal Development

In 1830, a series of eight public debates were held at the Academie Royale des Sciences in Paris. The two opponents, George Cuvier 1769-1832 and Ftienne Geoffroy Saint-Hilaire 1772-1844 , were prominent and internationally renowned scientists. Both had made major contributions in many areas of natural history, including comparative anatomy and paleontology. Cuvier divided the animal kingdom into four completely separate branches or embranchements vertebrates, articulates largely arthropods and...

Introduction

The diversity of nervous systems is enormous. In terms of structural and functional organization as well as in terms of levels of complexity, nervous systems range from the simple peripheral nerve nets found in some of the basal invertebrate taxa to the centralized nervous systems and highly complex brains that characterize vertebrates and cephalopods. Starting in the eighteenth century, numerous attempts were undertaken to reconstruct the evolutionary origin of the diverse nervous system types...

IGi A History of Ideas in Evolutionary Neuroscience

G F Striedter, University of California, Irvine, CA, USA 2007 Elsevier Inc. All rights reserved. 1.01.1 Common Plan versus Diversity 1 1.01.2 Scala Naturae versus Phylogenetic Bush 3 1.01.3 Relative Size versus Absolute Size 4 1.01.4 Natural Selection versus Developmental Constraints 7 1.01.5 One Law, Many Laws, or None 9 1.01.6 Conclusions and Prospects 10 The notion that changes in the size of an object e.g., the body or the brain entail predictable changes in the proportional sizes of its...

M

Figure 1 Morphogenesis of the ventral nerve cord in a prototype insect a and of the dorsal neural tube in a prototype vertebrate b . Arrows indicate ontogenetic sequences yellow-green, neurogenic ectoderm blue, epidermal ectoderm. Reproduced from Arendt, D. and Nubler-Jung, K. 1999. Comparison of early nerve cord development in insects and vertebrates. Development 126, 2309-2325, with permission from The Company of Biologists Ltd. However, starting in the 1980s, a number of key findings...

Binary and Multistate Characters

Discrete characters may be characterized as either binary coded into two mutually exclusive alternative states or as multistate a transformation series of three or more discrete states . The alternative states of a binary character are generally although not necessarily explicit hypotheses of the primitive and derived advanced states of a single evolutionary transformation event, such as the origin or loss of a novel feature. A multistate character is a more complex intellectual device with...

Methods

Echinoderm Hemichordate

All widely used phylogenetic methods have been used to reconstruct metazoan phylogeny, including distance methods, parsimony analysis, likelihood analysis, and, most recently, Bayesian analysis. Currently, molecular sequence data have been analyzed with all these methods, and morphological evidence has been studied with both parsimony and Bayesian analysis. 1.02.2 Overview of Major Metazoan Clades and Grades Comprehensive molecular and morphological phy-logenetic analyses have generated...